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LSU Historical Dissertations and Theses Graduate School

1955

Sedimentology and Ecology of Southeast CoastalLouisiana.Robert Cuthrell TreadwellLouisiana State University and Agricultural & Mechanical College

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Recommended CitationTreadwell, Robert Cuthrell, "Sedimentology and Ecology of Southeast Coastal Louisiana." (1955). LSU Historical Dissertations andTheses. 114.https://digitalcommons.lsu.edu/gradschool_disstheses/114

SEDIMENT OLOGY AND ECOLOGY OF SOUTHEAST COASTAL LOUISIANA

A Thesis

Submitted to the Graduate Faculty of the Louisiana State University and

Agricultural and Mechanical College in partial fulfillment of the

requirements far the degree of Doctor of Philosophy

inThe Department of Geology

hyRobert Cuthrell Treadwell M.S., Louisiana State University, 1951

June, 1955

EXAMINATION AND THESIS REPORT

Candidate: Robert C. Treadwell

Major Field: Geology

Title of Thesis: Sedimentology and Ecology of Southeast Coastal Louisiana

Approved:

Date of Examination:

May 7 f 19??

Major Professor and Chal

Djy«rtJf*tho Otadhato School

EXAMINING COMMITTEE:

*

fiKC IUtP(M

TABLE OF CONTENTSPago

I INTRODUCTION......... ............................... 1H PHYSIOGRAPHIC FEATURES OF THE MARSHLAND................ 6

Abandoned distributaries........................... 6

Physiography....................................... 6

Vegetation......................................... 9Sediments........................................ 11

Stratigraphy...................................... ^General appearance............................... Il+Channel fill................................... 16

Natural leveeB....... ......................... 7

Summary......................................... ^Beaches........... 20

Sand beaches................. 2®Origin and development........................

0*1Vegetation..................................... CASediments ............................... 22

OilPhy s lography...................................Offshore bars.................................. 33

Shell beaches .............................. 33Origin and development......................... 33Sediments...................................... 36Physiography......... 36

Summary ............................ 38

ii

Pagon PHYSIOGRAPHIC FEATURES OF THE MARSHLAND (CONT.)

Stranded beach ridges or chenlers...................... 38

Gulf chenlers....................................... 39Physiography......... 39Vegetation........................................ 39Sediments.............. ,.............. 39Stratigraphy............................ *........ **1

Lake chenlers....................................... MSummary ^

Marsh................................................ ^5Phy s 1 ogr aphy........................................ **5Vegetation.......................................... **5Sediments..................................... **8Stratigraphy and paleontology........................ ^9Summary••••••.♦•*••».•••••»••••»»•»»»*•«»•«•••••••••••• 5

Tidal streams................ ........................ 55Origin................ ..... ....... 55Relation of origin to surface form.................... 58Channel shape..................................... •. 81Longitudinal appearance........................... 8lTransverse appearance............................. 83

Meander patterns............ 86

Vertical movement................................... 71Depth stability.......... 73Summary................................. 7^

ill

PageII PHYSIOGRAPHIC FEATURES QF THE MARSHLANDS (CONT.)

Lakes, bays, and sounds................................ 75Lakes and bays....................... 75Width and depth ..................... 75Shapes............. .................. ................. 7 8Elongate lakes............................. .......... 76

Rounded lakes......................... 77Sounds............... 81Summary•••••••••»••••••••••••••••»•••••...... 81

III SEDIMENTATION................................................ 83

Area treated................ 83

Method of study.................... 84Sediment types............................................. 83

Grain size............................................... 87

Sand beaches ...................................... 87

Shell beaches....... 90Water bottoms......................................... 90

Sorting................. 91Beaches ............................................... 92Water bottoms............... 92

Percent shell...................... 94Organic content............................ 94Glauconite and pyrite content......... 98

Lake and sound history as determined from cares...... 98

Summary............. 99

iv

Page17 ECOLOGI OF FORAMINIFERA AND MOLLOSCA....................... 102

Water properties................. 102Method of study......................................... 105Description of environments............................. 106Environmental factors............................... 109Species distribution.................. 112Nearshore Gulf environment............................ 112Sound environment..................................... 115Lake environment. ............................. 117Marsh environment..................................... 118Other microfossils.................................... 118

Summary................................................. 119V GEOLOGICAL HISTORY........................................ 121

Introduction..................... 121Development of the easternmost Louisiana marshlands....... 122Summary........... 127

71 BIBLIOGRAPHY.............................................. 128711 APPENDIX.................................................. 131*

Beach profile data................... 135Sediment analyses..... .......................... . 1^0Annotated synonymies .............. 1^7

71II 7ITA...................................................... 176

v

LIST OF TABLESPago

I Elevations and Widths of Levees 8U Sand Beach Data (Onshore) 135III Sand Beach Data (Offshore Bars) 13717 Shell Beach Data 1397 Complete Data of Sediment Samples 1^071 Comparison of Tidal Stream Widths and Depths ,

1935-3952 73VII Grain, pize and Sorting, Chandeleur and

Breton Island Beaches 86

VIII Distribution of Mollusca in St. BernardParish, Louisiana 1 *5

IX Distribution of Foraminifera in St. BernardParish, Louisiana 1^6

vi

LIST OF FIGURESPose

Figure 1 Index Map of Eastern Coastal Louisiana 2

Figure 2 Former Distributary Pattern of the Eastern Louisiana Marshlands 7

Figure 3 Distributary Stratigraphy, Orleans and St. Bernard Parishes 10

Figure 1* Vegetation on Levee of Abandoned Distributary 12

Figure 5 Distributary Stratigraphy, Unknown Bayou 15Figure 6 Exhumed Mangrove Swamp, Gulf Side of

Chandeleur Islands 23Figure 7 Idealized Cross Section of the Chandeleur Islands 25Figure 8 Beach Characteristics, Breton, Cat and Chandeleur

Islands 27Figure 9 West Slope of Sand Dunes, East End of Cat Island 28

Figure 10 Marshy Swale Deposits Being Eroded Near Center of North Side of Cat Island 29

Figure 11 Beach at North Point of Chandeleur Islands 31Figure 12 Oyster Shell Beach, Door PointFigure 13 Clam Shell Beach, South Shore of Mississippi Sound 35Figure Ik Beach Characteristics, Isle au Pitre and Freemason

Island 37Figure 15 North Side of Sand Ridge 1*0

Figure 16 Chenler Stratigraphy, Jefferson-Orleans Parish Line 1*2

Figure 17 Chenier Stratigraphy, Sand Ridge 1*3Figure 18 Shoreline Changes of Isle au Pitre and Vicinity,

181*8-57 to 1952 1*6

Figure 33 Eroding Marsh, South Side of Mitchell Island U7vii

PageFigure 20 Gross Section of Gate Island 50Figure 21 Statistical Analysis of Foraminifera in Four

Samples from the Gate Island Area 52Figure 22 Characteristic Appearance of Tidal Streams and Lake a 57Figure 23 Depth-Wldth Relationship of Tidal Channels 60

Figure 24 Stream Profiles Shoving Effect of Unequal Tidal Flow, Eastern Bayou La Loutre 62

Figure 25 Tidal Stream Profiles 64Figure 2 6 Cutoff Meander, Bayou Llngeo 69Figure 27 Cutoff Meander, Bayou Llngeo 70Figure 28 Tidal Stream Stratigraphy 72Figure 29 Elongate Lake Fanned hy a Shell Beach Blocking a

Die tributary Controlled Tidal Stream, Door Point 78

Figure 30 Incipient Rounded Lakes, Gate Island 79Figure 31 Hydrographic Contours 82

Figure 32 Sediment types 86

Figure 33 Median Grain Size 89Figure 34 Log Quartile Deviation 93Figure 35 Percent Shell in Sediment 95Figure 36 Organic Content 97Figure 37 Glauconite Content 98Figure 38 Salinity Distribution 104Figure 39 Distribution of Foraminifera, St. Bernard Parish 107Figure 40 Distribution of Mollusca, St. Barnard Parish 108

Figure 4l Mollusc a on Beach, Western Spit of North Point, Chandeleur Islands 114

Figure 42 Development of the St. Bernard Subdelta 123

viii

LIST OF PLATES

Plate 1Page

Meandering of Tidal Streams,Bayou Llngeo 67

lx

ABSTRACTA deltaic-marine contact Is now forming In the coastal area of

southeastern Louisiana which can he compared vith many similar Tertiary contacts of the Gulf Coastal Plain. Most of this area 1b an abandoned subdelta of the Mississippi River and Is composed of alluvial ridges (natural levees, beaches and chenlers), marshland water bodies.

Ihe alluvial framework consists of a series of abandoned distribu­taries radiating and sloping eastward from a focal point at New Orleans.As these distributaries built seaward they deposited characteristic fine­grained sediments vhlch can be divided Into six groups based upon grain size, appearance^and attitude. These are: prodelta clays, bar sands,natural levee silts and clays, channel fill sands and peats, lnterdls- trlbutary silts and clays and marsh clays and peats.

Sand beaches are essentially confined to an arcuate chain of narrow, low is land b which exhibit black mangrove swamp on their soundward side. Indurated sandstone slabs, blocks of delta silt, Igneous and metamorphlc pebbles, and shells are scattered along the beaches. Sand gives way to oyster shell along the Inner margin of the sounds, and clam shell beaches predominate on marshland lake Bhores.

Stranded gulf beach ridges, or chenlers, of the area are composed of medium sand and were barrier Islands before deltaic sedimentation entered the area and Isolated them in marsh. Smaller, silty lake chenlers are present In places around the borders of lakes Borgne and Pont char train and were formed during periods of delta erosion.

Brackish and salt marshes comprise most land In eastern coastal

Louisiana and are a featureless plain rising only a foot or two above sea level. Marsh sediment is composed of organic clay or silly clay and contains thin widespread beds of peat.

In many cases examination of the surface pattern of marshland tidal streams reveals burled natural levees or beaches. These are aids In morphological field mapping. Depth of tidal streams and marshland lakes and bays generally Increases with width; however, In tidal streams especially, there are maiy modifying factors. Largest of the lakes Is Pontchar train, which averages sons 15 feet In depth; by far the largest tidal stream Is the Blgolets which reaches a maximum depth of almost 100 feet.

Sediments of beaches and water bottoms of St. Bernard Parish have been analyzed for grain size, sorting, shell content, organic content and glauconite and pyrlte content. Sediment of the area can be divided Into six -types: fine, well sorted sand of Chandeleur and Breton Islandbeaches, shell of the marshland beacheB, fairly well sorted silty sand and silty clay of the sound bottoms, poorly sorted clayey silt and silty clay of the marshland lakes and shell, silt and clay of reefs. Shell content Is generally under 2$ except on reefs and shell beaches. Organic content Is under 2$ In the sounds but rises to 5# in Lake Lery (the inner, most marshland lake). Glauconite Is present throughout the area but Is never abundant.

Foraminifera and Molluscs distribution has been examined in samples from beaches, marsh and water bottoms. Salinity appears to be the prlncl. pal factor In controlling the distribution of these farms, although many other factors certainly exert an Influence. Four environmental facies and one subfacles are present In the area and each has its characteristic faunal assemblage.

The late Recent developmental Bequence of southeastern coastalxi

Louisiana has boon reconstructed, and several stages of deltaic and marine advances are postulated. Oldest surface features are the gulf chenlers vblch date back possibly 5000 years, and the earliest delta in the area Is over 2000 years old. The St. Bernard subdelta vas certainly veil established during Marksvllle time (500-700 A.D.).Since Marksvllle, sedimentation and erosion have shifted positions several times with the culmination of delta building ocourring in Plaquemlne time (1200-1500 A.D.). Shortly after the Plaquemino period the Mississippi Elver shifted to Its present course and marine erosion Is now rapidly attacking the land.

xli

ACKNOWLEDGMENTThis investigation vas made possible by the Office of Naval Research

as part of a study of trafflcability and navigability of coastal Louisiana (Project Number N7 onr 35608, Task Order Number NR 388 002).

The writer is indebted to many people for guidance and assistance in this vork. Dr. James P. Morgan, Field Supervisor and Associate Pro­fessor of Geology, has given his time freely in revising and correcting the manuscript. Dr. R. J. Russell, Project Director and Dean of the Graduate School, has critically read the paper; and Ik. H. V. Andersen, Associate Professor of Geology, has made valuable suggestions concerning the ecology.

During most of the field vork the writer vas accompanied by Leon G. Hunt; however, at different times a number of people assisted in the field--Mark A. Dixon, William G. Mclntire, Edvard W. Orton, Gayle Y. Treadvell and Frank A. Welder,

Mr. R. T. Abbott, The Acadeny of Natural Sciences of Philadelphia, checked the identification of the mollusks and identified certain species. J. P. E. Morrison, U. S. National Museum, checked the pulmonate gastropods. Dr. Clair A. Brown, Professor of Botany, Bacteriology and Plant Pathology, provided the background for identification of marshland plants. Engi­neering Branch, Corps of Engineers, New Orleans, Louisiana, and Mr.Charles R. Kolb, Waterways Experiment Station, Vicksburg, Mississippi, have made various unpublished reports available. Dr. William G. Mclntire's Indian pottery investigations have been of inxnaasurable aid.

xlil

Special thanks are also due T. J. Poole, Roger T. Saucier, and Louis Selg who prepared the Illustrations of this report.

Finally, the writer gratefully acknowledges the efforts of his wife, Gayle Y. Treadwell) In typing and checking the several rough drafts of the manuscript.

xlv

UTOSOOTCTIONRecent deltaic and marginal marine beds of eastern coastal

Louisiana are idealy situated for study of marine encroachment on a deltaic mass. Contacts between deltaic and marine strata are common throughout the Tertiary section of the central Gulf Coastal Plain, and many have been objects of deposltional environment studies. However, relatively few data are available on similar Recent deltaic-marine con­tacts . This lack of information is one important reason far a wide divergence of opinion concerning the deposltional environment of certain Tertiary formations. Critical studies of the Gulf Coastal Plain Recent seem to offer the best possibilities for aiding paleo. environmental studies of the coastal plain Tertiary.

This paper is intended to give an insight into phases of the geology, ecology and physiography of a formerly active deltaic area now being attacked by the sea. The area treated Includes all of Orleans and St. Bernard parishes and parts of Jefferson, Plaquemines and St. Tammany parishes, Louisiana, and Hancock County, Mississippi. It is bounded on the north by latitude 30° 201 N (near Slidell, Louisiana), on the east by longitude 88* k91 V (Chandeleur Islands), on the south by latitude 29° 27* N (Breton Island) and on the vest along Bayou Terre aux Boeufs to longitude 90* 30' W and the Mississippi River (Fig. 1).

The western part of the area is typical brackish and salt marsh, characterized by many shallow lakes, bayous and occasional natural levee ridges. Principal high ground, other than New Orleans, is formed by the Bayou La Loutre ridge. Trees grow on the high land while lower land

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supports marsh vegetation consisting of various grasses, sedges and rushes. In the eastern part of the area are Chandeleur and Breton sounds, water bodies 10 to 15 miles vide, flanked on their seaward side by a low, dis­continuous lBland chain, the Ghandeleurs. Several small marsh and shell Islands are present In central Chandeleur Sound directly behind the Chan­deleur Island arc.

Most of the area studied Is an abandoned portion of the Mississippi River delta. Land Is retreating before attack of the sea aided by compac­tion of Recent unconsolidated sediments, eastward tilt of the area and regional subsidence of the Gulf Coast geoqyncllne (Russell, 1936, pp. 180-195). Diminution of land is more rapid In St. Bernard Parish than elsewhere, and the land area has Shrunk from. 721 square miles In I807 (Fortier, 1911*, PP. 1*07 Ji08) to 617 square miles in 1939 (Son- deregger, 1939, P. 82).

thirteen months were spent In field investigation between February, 1952, and August, 1953. Laboratory studies were carried on until May,195^. The work Involved: 1. mapping of the physiographic units, such aslevees, beaches, marsh and chenlers in the field 2. obtaining detailed cross sections of the above physiographic units 3. making restricted hydrographlo surveys of the tidal channels, lakes and sounds U. collect­ing data on water salinity, temperature and pH 5. making routine sedi­mentary analyses 6. deriving statistical analyses of the foramlnlferal and molluscal populations of the area and 7, sampling water bottom sediments.

Because of the isolated position of most of the area, operations were largely carried on from boats, A skiff powered with an outboard motor vas used far dally work, and a 30 foot shrlmpboat, which served as quarters far the field party, vas employed to move about the area.

Most of the area Investigated contains a naze of tidal channels, lakes and hays. Because of the difficulties In traversing such

an area, both aerial photographs and naps wore employed. In addition to being Invaluable for travel, aerial photographs are especially useful In locating many obscure physiographic features not revealed on the best available maps.

Aerial photographs of this area were taken by the U. S, Navy In conjunction with the Office of Naval Research coastal marsh project at Louisiana State University, IVo series were made. The first was taken In the spring of 1951 to a scale of 1:23,600. The second set was made In February, 2952, and Is to a scale of 1:^0,000, The project was most fortunate In obtaining advanced U. S. Geological Survey quadrangle sheets which were revised from the 1951 set of photographs mentioned above.U. S. G. S. quadrangles of the 1935 series were also used In the work.In addition, the latest series of U, S. Coast and Geodetic Survey charts were available for field use. Older sets of both U. S. G. S. and U. S. C.& G. S., as well as a variety of very old, but Inaccurate, maps, were available far comparison with one another In the laboratory.

Although all parts of this vork are Interrelated, presentation seems best accomplished by dividing the paper Into four sections. Each treats one phase of the geologic features associated with strata farming a deltaic-marine contaot. The four divisions are:

1. Description and Interpretation of marshland physiographic features. Data are presented on the llthology, cross sectional attitude and physio­graphic appearance of sedimentary units encountered In a deltaic area now cut off from active sedimentation.

2. Description of sedimentary properties of the present brackish and marginal marine water bottoms. Grain size, sorting, organic content,

percent shell and glauconite and pyrlte content of sediments of lakes, bays and nearshore Gulf are discussed In some detail. Information Is presented on the source of the sediments.

3. Presentation of the ecology of Foraminifera and Mollusca. Sta­tistical analyses of these forms have been made and their distributional patterns Interpreted vlth the aid of sediment and vater properly data.

H. Reconstruction of the developmental sequence of deltaic and marine features In the area. Late Recent geologic history is postulated by observation of the relations of various physiographic units, faunal and sediment analyses of bare holes and archeological data. Rather complex deltaic history Is revealed In the area.

PHYSIOGRAPHIC FEATURES OF THE MARSHLANDThe surface of the eastern Louisiana mar ah lands consists of ah out

75# water, 20# marsh and 5# alluvial ridges (natural levees, beaches, chenlers), Ihese latter landforma comprise the backbone of marshland physiography and, therefore will be discussed first.

Abandoned Distributaries

PhysiographyIn the Ctrleans-St, Bernard parishes area abandoned distributary

systems of the Mississippi River radiate in a branching pattern from a focal point at New Orleans. The pattern formed hy the natural levee ridges of these distributaries is shown on Figure 2. The most important stream was Bayou La Loutre, a former main course of the Mississippi.Other significant distributaries were bayous Live Oak, Sauvage, and Terre aux Boeufs.

Greatest levee heights and widths are found on upper Bayou La Loutre, (Fig, l). Heights and widths both decrease seaward from the upper end of any distributary. This is partly the result of stream branching or bi­furcation and consequent narrowing and partly due to the disappearance of levees beneath marsh as they dip seaward (Table 1).

6

FORMER DISTRIBUTARY PATTERN

OF THE EASTERN LOUISIANA MARSHLANDS

L E G E N D

ABANDONED DISTRIBUTARIESINFERRED ABANDONED

DISTRIBUTARIESCHENIERSPROFILE AND CROSS SECTION

LOCATIONS

S C A L E

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Figure 2

8

Stream Location Fig. 2

Maximum levee eleva­tion In feet

Levee width exposed above marsh in feet

Approximate total levee width in feet

Bayou La Loutre 25 10 6670 8000II 2 6 5 3330 1*000II 27 2 330 1*000Bayou Terre aux Boeufs 28 k 1300 2000It 29 2 830 1500II 30 -2 0 900II 31 . -U 0 800Bayou Sauvage-Lesarle 32 3 itoo 3000It 33 2 1270 2000II 3t 1.5 850 1500Live Oak Bayou 35 -3 0 1800II 36 -3.5 0 1600

Table 1All levees with the exception of some northward trending distribu­

taries of the double Islands area around Bay Boudreaux (Fig. 1) . now slope seaward at a greater angle than those of the present Mississippi Biver; however, levee slope differs in various portions of the area. Theincreased levee slope is related to several processes. Subsidence due tocompaction of soft Becent sediments beneath the levees and possibly some effect of Gulf Coast geosyncline downwarping has carried levees downward. Compaction is more pronounced toward the south and east varying with depth to consolidated Pleistocene strata. This has resulted In eastward tilt of the area and has caused the seaward end of natural levees to dip and become covered with marsh or water. Other somewhat less important factors influencing levee slope are: length of time of abandonment, size andthickness of levees and local structural anomalies beneath levees (such as salt domes or faulting). Long abandoned and/or large, thick levees tend to be more deeply subsided and slope mare steeply seaward thanrecently abandoned or small levees. Salt domes tend to retard subsidenceand faults can either Increase or decrease levee slope.

9

The Increased levee slope Is in most places on the order of three times the slope of the Mississippi Biver. Bussell (1936, p. 47) calcu­lated eastward slope in St. Bernard Parish to he on the order of 0.5 feet per mile, and several slopes computed in this work approximate that figure. A comparison of abandoned distributary slopes of the area studied with that of the present Mississippi Biver is given below.

ApproximateLocation Stream or Streams Slope in Ft./Mi.

New Orleans to Gulf Mississippi Biver 0.10Orleans Parish Bayou Sauvage-Lesarie 0.11St. Bernard Parish Double islands (trending north) 0.10-0.12

" Bayou Terre aux Boeufs 0.30" Bayou La Loutre 0.34" Double islands (trending east) 0.40

Plaquemines Parish Biviere aux Chenes 0.45Bayou Sauvage-Lesarie and double islands (trending north) reveal

slopes very similar to that of the Mississippi Biver. This apparently results from the presence of Pleistocene sediments about 100 feet below the surface near Isle au Pitre (Bichards, 1939, P. 305) and even shallower along most of Bayou Sauvage-Lesarie. In addition, part of Bayou Sauvage- Lesarie is underlain by thick chenier sand deposits, and the double islands area, by remnants of an older subdelta.

Transverse levee slopes likewise vary throughout the area. Narrower levees (No. 34, Fig. 3) usually slope more steeply away from the channel than do larger levees (Nos. 35 and 38, Fig. 3). Bussell (1936, p. 75) thinks this is due to the fact that small streams build levees of less width but with crests equal in height to the main channels from which they gain their discharge.

VegetationThe elevation of a levee with reBpeot to its permanent water table is

largely responsible for its vegetative covering. Higher levees contain

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DISTANCES 8. ELEVATIONS IN FEET VERTICAL EXAGGERATION X 10LOCATION OF CROSS SECTIONS SHOWN ON FIG. 2

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11

fresh ground vater and usually are not subject to prolonged flooding,!whereas lover levees and marsh are subject to frequent flooding. Only

a cursory examination of vegetation has been attempted, and a much more complete report of levee plants is given by Brown (1936, pp. 423-440). However, the following Is a list of cosmon plants found on levees which stand more than a foot or so above vater level (Fig. 4).

1. Baccharis hallmifolla (Groundsel Tree)2. Cbmodon dactylon (Bermuda Grass)3. Celtic laevigata (Hackberry)4. Iva frutescenB (Marsh Elder)5. TarthenoclasuB qulnquefolla (Virginia Creeper)6 . ftuercus vlrglnlana (live Oak)7 . Rhus rad loans Poison Ivy)8. SataTmlnar (Palmetto)9. Yuoca alolfolla (Yucca)

Common plants occurring on levees which are very near vater level are:1, Iva frutescens (Harsh Elder)2. Spartlna cynosuroldes (Big Cord Grass)

SedimentBAs the subdelta forming St. Bernard and Orleans parishes prograded

seaward, characteristic Bedlments were deposited by each distributary.The typical sedimentary sequence is divisible Into six groups.1. Fine clays which are carried In suspension by the distributary but discharged into and deposited in the Gulf. These are commonly called prodelta clays (Fisk, et a i r , 1954, p. 86) and form the base of distribu­tary deposition.2. Sandy and silty bar sediments are deposited as a broad fan overlapping the prodelta clays immediately seaward from each distributary mouth. The numerous distributaries in St. Bernard and Orleans parishes result In widespread, overlapping bar sediment units. As the distributary extends seaward, it cuts through and reworks Its earlier bar deposit.

12

Fig. k Looking south from loft levee of abandoned distributary Just west of Delacroix Island, St. Bernard Parish. Levee vegetation is live oak, palmetto, and marsh elder. Levee flank depression lake in background.(lat. 29*^6 '11", long. 89^7'50")

13

3. Between areas of coarser bar sediment (interdistributary areas) finer clays and silts are laid down concomitantly with bar deposition, lhese interdie tributary sediments grade laterally into bar deposits.4. Natural levees are farmed by deposition of sediment during flood stage. As a river floods, its Increased volume and vater turbulencecause:.' the suspended sediment load to increase. As flood vaters top thechannel and Bpread laterally, their velocity is reduced. This results in deposition of coarser suspended sediment near the crest of the levee and increasingly finer sediment toward the interd is tributary basin. Levee silts and silly clays rest on and partly grade into bar deposits. In cross section, levees assume the farm of a double wedge, thickest near the stream channel and lenslng out away from the channel into the inter- distributary basin. In plan view levees appear as ridges paralleling the stream channel. Because deposition occurs above the low river stage vater table, oxidation takes place in most levee sediments and serves to set them apart from other materials of the marshland,5. Deposits which fill abandoned distributary channels are of two types. One consists of sands or silts similar to bar sediment and the other of fine organic clays and vegetation. Iho first group fills the bottom, orin same cases all, of the channel. Separation of this material from barsediment is sometimes difficult. Fine, mare ar less organic channel fill is found in the upper portion of many distributary channels. The specific history of a distributary determines which of, the two types is present.6. Marsh sediment is composed of more or less organic clay, silly clay and peat. It is formed from decaying vegetation admixed with fine clays or silty clays which are deposited during tidal or distributary overflow.After cessation of distributary flow in an area, levees subside and in­creasingly organic marsh deposits encroach upon and eventually cover them.

Stratigraphy of Abandoned Distributaries

General AppearanceStratlgraphlc relationship of sedimentary units associated with an

abandoned distributary is shown in Figure 5, a geologic cross section of Unknown Bayou (Location No. 37, Fig. 2). Interpretation of sediment types and their environment of deposition was modified from Fisk (1947c,pp. rU 2l).

The basal unit of the cross section is oxidized Pleistocene clays, silty clays and silty sands. The lowest Recent strata (unit A) consist of 50 to 70 feet of alternating beds of clay, silty clay, silt and sand. This unit represents shallow vater bay bottom sediments in existence prior to the advent of deltaic deposition in the area. Unit B, overtying the bay-bottom sediment, is between 20 and 40 feet thick and varies inversely with the thickness of units C and D. It is considered to be prodelta material deposited seaward of an active delta. Unit C consists of masses of clay and silty sand and ranges in thickness from eight to 35 feet. Dlls unit appears to have been deposited in the shallow lakes of interdistributary areas of an active delta. The bar deposit of Unknown Bayou (unit D) is composed of sand and silty sand. It was deposited just seaward of the stream as it encroached into the area. Unit E is composed of organic clay and scattered strata of silty clay. Feat layers are common. Thickness of this layer varies between two and 20 feet. These strata originated in interdistributary marshes and shallow lakes; some were laid down while the stream was active (baoksvamp or interdistributary deposits), and others, after the stream ceased to flow and its levees began to subside. Silty clays and clays of unit F farm the levee sediment. These deposits are thickest at the stream channel and lense out into the

PROFILE UNKNOWN BAYOU

.'I

., l i i l l l i l l t ;In i ' i .II, ,1. , 1,1 l, UNIT C H ,l

M— L1*11' ■l l , u l i l i l i , l i r i i i i , ii i i i V i i h ' i

_________ 5$.UNIT:u n it :*

UNIT• • • • •

■I. I '| H l ' i ' l |' •!! i!«I! 1111111 !jhUNIT

UNIT

. i *' i*i*i 'tS' t'l'iS'i' i ) » i i i t i i i i i j i i j i j j i j j ): t » i i i i , i i

i t i i i i 1 i i i!( ii i t i

,','UNITl» I l»,vt ! I ! ' it i ' ti!t!» t i i i i!i!it j i ; ) t i i 1 i ; i ; i' i f t i t 1 i i ii 1t 1 I 1 I It!i ; i i ! i i : i ! i ; i i t1 i i t i t 1 i i!ti i » i i i i t i1 » » i i i 1 t i:»i i i j t i ! i ! i ! i ! il i t i t i i t t i

ELEVATIONS IN FEET FROM MEAN SEA LEVEL.DISTANCE IN MILES.

^ PLEISTOCENE UNIT A | | | U N IT B [|Tj] U N IT C [ | ] U N IT D § | ] UNIT E UNIT F ^ UN1T G

DISTRIBUTARY STRATIGRAPHYUNKNOWN BAYOU ~ ORLEANS-PLAQUEMINES PARISHES

MODIFIED FROM U.S. ARMY ENGINEERS DATA.

Figure 5

16

marsh. Clays, silty clays and sll'ty sands (unit G) fill the farmer channel.The sequence Just described is -typical of the composition and attitude

of sediments associated with distributaries of the area. However, unit D, bar material, is generally more widespread in eastern St. Bernard Parish than shown in this example. The latest streams to enter that region built into water apparently only half the depth of that encountered by Unknown Bayou, and, consequently, bar material became thinner and more widespread.

Channel FillThe proceeding section illustrated the broader and geologically more

important aspects of the sedimentary sequence associated with distributa­ries. However, features of natural levees and channel fill, which are the only surface expression of abandoned distributaries, must be considered in more detail. The cross sections of Figure 3 ere typical of the varying stages of development found in channels and levees of the area.Three classes of channel fill are considered:A. Channel fill affected by distributary branching. A cross section of an unnamed branch of Bayou La Loutre (Location 38, Fig. 2) is presented on Number 38, Figure 3 . This section shows the typical appearance of abandon­ed distributaries immediately downstream from a point of bifurcation. When a distributary fork originates, one branch usually becomes dominant over the other. The smaller fork sooner or later begins to lose its flow volume to the larger, and water entering the smaller stream must deposit soma of its sediment load Just downstream from the branch. With continued reduction of flow the upstream end of the smaller branch receives more and more deposits. Eventually this results in filling of the headward part of the channel to such an extent that only a faint scar marks the site of

the farmer charnel. Hie channel deposits are clays, silty clays and silts. Oxidation of these channel fill materials is common to a depth of five to eight feet, and traces of oxidation are recorded from ten to 12 feet in one bore hole. This oxidation occurs when the abandoned branch is almost completely filled and some of the channel fill sediments fall above the lew water level of the remaining large distributary branch.B. Channel fill in reaches. Cross section Number 35, Figure 3 is located at Number 35, Figure 2. This section across a reach of Live Oak Bayou is several miles from the nearest branching. In such a situa­tion small tidal channels frequently occupy a portion of farmerdistributary channels. The upper 12 feet of the channel is filled withsoft, organic, gray clay but below that depth compact silts and silly cleye form the channel fill.C. Tidal channel on a roach but removed from tidal flow. This cross section (No. 3^, Fig. 3) Is located on Bayou Lesarle (Location 34,Fig, 2) and shows essentially the same features as the previous cross section. However, because of its enclosed position In the marsh, tides have had little success In maintaining flow through the channel. One bore hole In the channel was drilled to a depth of 15 feet through soft,peaty clay. Hie remnant tidal channel is choked with grass and is rapidlyfilling with vegetation and highly organic clays. In a cross section of Bayou Sauvsge a few miles west of this location Fisk (1944, pi. 17) shows soft, organic channel fill to a depth of 25 feet and sandy channel fill to the base of the channel at 55 feet.

Natural LeveesNone of the profiles described above show the complete shape and

18

thickness of levee material. Bare holes have shown that some natural levees In St. Bernard Parish exceed 15 feet In thickness and one and one-quarter miles In width. The vedge shape exhibited by most levees Is shown In part on Number 35, Figure 3. The four holes most distant from the channel have penetrated through levee Into bar material. This material Is encountered at ever increasing depths toward the channel. The vedge shape Is developed as a result of heavier sedimentation on the Inner part of the levee which in turn causes greater compaction and subsidence.

Most natural levees are veil oxidized In their upper few feet with highly mottled, llmonltlc patches. In many places they contain hard lron- manganese (?) nodules. Oxidation disappears downward. Over 20 cross sections of levees have been made, and, in addition, many levees have been cored with one or two holes. Not one of these barings has encountered well mottled levee material thicker than eight feet; however, a few traces of mottling have been found to 12 feet. The mottled or oxidized zone becomes progressively thinner seaward until, In several profiles, it disappears completely. As the depth to which oxidation originally farms depends on the amount of levee exposed to air, the zone of oxidation thins downstream as the height of the levee decreases. Normal downstream levee slope accounts for some of the difference of oxidation depth but does not account for levees on which there is no oxidation at all. Evidence at a buried levee Just east of Lake Machias (Location No, 5I4, Fig. 2) suggests the reason far lack of oxidation on the seaward portion of levees. At this location an Indian midden rests on the levee, but the levee material beneath it and to Its flanks Is not oxidized. This indicates either that the levees were not built mare than a few inohes above water level and oxidation could not begin or that large levees were formed, oxidized, and

later chemically reduced upon burial due to subsidence. The fact that a

large Indian habitation site la located on the levees at this locality Is not conducive to the Idea that the levee never stood mare than a few Inches above water level. Therefore, It seems probable that oxidized levees become reduced upon burial beneath marsh.

SunmarySignificant points of the discussion of abandoned distributaries

are:1. Natural levees are higher and wider near their point of origin and become lower and narrower downstream.2 . Nearly all levees In the area now slope seaward at a greater angle than those of the present Mississippi Biver, This Is the result of sub­sidence and eastward tilt of the St. Bernard subdelta.3. Narrower levees, usually associated with smaller streams, slope more steeply away from the channel than those of large streams.U. Sediments associated with distributaries vary from clay to sand, depending upon their site of deposition.5. Levees have essentially a double wedge shape, separated by a channel. They are thickest near the channel and lense outward into interdistribu- tary basins. Compact silty clay, usually oxidized In the upper few feet, composes the bulk of all levee material.6 . Channels of abandoned distributaries Immediately downstream from bifurcations are completely filled with relatively coarse and compact sands, Remnant channels are usually not present.7. Sections of abandoned distributary channels not affected by bifurcations reveal two -types of sediment. The bottom portion of the channel is filled with sands and silts, and the upper portion contains soft, gray clays and vegetation. Tidal channels frequently occupy portions of the former

distributary channels

BeachesA second group of prominent physiographic features of eastern

coastal Louisiana are sand and shell beaches. Sand beaches are essentially restricted to an arcuate chain of narrow islands extending approximately north-south and comprising the Chandeleur and Breton Island groups (Fig, 1) Total length of these islands is 52 miles, but passes varying from a few yards to four miles in width interrupt their continuity, Cat Island, Mississippi, is included in this section. Its length is about five miles. Scattered shell beaches are found along shores of many marshland lakeB, but their greatest development occurs along the inner shores of the Chandeleur and Breton sounds and on Freemason and North islands. The greatest length of continuous shell beach, 3 .5 miles, is developed at Isle au Pitre, but the average beach seldom exceeds a few hundred yards in length.

Sand Beaches

Origin and Development The Chandeleur Islands are considered to have been formed by erosion

and sorting of coarse materials of the former St. Bernard subdelta (Bussell 1936, pp. 60-61 and 3A7). Since their conception, the islands have been retreating landward under attack of the sea. Comparison of U, S. Coast and Geodetic Survey charts, topography dated 1852-75 and 1917, reveals westward movement over various parts of the chain.

21

30* 03' 30"30* 00' 00"29* 55' 00"29* 50' 00"29* 1*5' 00"29* UO' 30"29* 35' 00"29° 30' 00"29* 27’ 38"

North Latitude Westward Movement in Feet0 900

330 810

P160 1560 1500 2^00 600

Breton Island differs from the Chandeleur Islands in having a back­bone of older beach ridges behind the present beach. The island appears to have grown hy extending itself south and west. Longshore currents sweep sediment south along the ChandeleurB and deposit it at the western end of Breton Island. This could account for the accretionary beach ridges composing the island; however , available information is inconclu­sive. There is also a possibility that Breton Island formed as part of a former chenier trend which was related to the distributary phase of Bayou La Loutre. A few borings penetrating the sand mass of the island could determine which, if either, of these hypotheses 1b correct.

Cat Island originated as part of a very old barrier island trend which has been traced westward to the vicinity of New Orleans. Subsequent reworking by wave action has caused the development of a north-south trending spit on the eastern end of the island. This feature is continuously increasing in size while the remainder of the island is being eroded.

VegetationVegetation on the island beaches is sparse. Sand flat and dime areas

behind the beaches support sand rush (Flmbrlstylis castanea), saltwort Batls maritime) and marsh elder (Iva frutescens). On the rear and wider portion of most of the Chandeleur Islands black mangrove (Avicennia nitida) thrives in extensive sandy swamps. As the beach retreats under wave

attack, sand gradually overwhelms and kills the mangrove swamp. With continued movement of the beach, patches of dead mangrove and related sediment are exhumed and exposed on the seavard side of the Islands (Fig. 6). The older beach ridges of Breton Island are overgrown with waxnyrtle (ifrrlca cerlfera), and those of Cat Island, with slash pine (Plnus carlbaea) and palmetto (Sabal minor).

SedimentsFine sand (median grain size 0.13-0.18 mm.) composes the sediment

of Chandeleur and Breton Islands, and medium sand (median 0.30 mm.) predominates on Cat Island. Results of sedimentary analysis of beach sands are presented on Table' ^ (in Appendix) and discussed in the section on sedimentation.

The Chandeleur Islands are littered with shells. Mollusca collected on the islands are classified In a subsequent part of the paper. On the surface of the beach shelly constituents form a banded pattern parallel to the shoreline. Abundant coarse shell Is found on the backslope of beaches, whereas the foreshore contains relatively little shell. Minor zones of shell on the foreshore are present at swash lines. The coarse shell material arrived at its position atop the beach an a result of storm waves, and normal high tides gave rise to the minor bands of shell at the swash. It has been shown, however, that abundant shell does not extend to depth In these beaches (Russell, 1936, p. 61*). Several shallow borings made on the islands during this project substantiate this conclu­sion.

Indurated sandstone slabs displaying cross-bedding, cracks, boring clams and shell and wood fragments are comnon on the beaches of central and northern Chandolours. Some of the slabs must be considered limestone, as

23

Fig. 6 Exhumed mangrove svamp, Qulf side of Chandeleur Islands, opposite Monkey Bayou (lat. 29 Vf'26", long. 88*50'35").Photo fcy James P. Morgan.

they are almost pure coquina. Their lateral dimensions range from a few inches to about tvo feet, and thickness varies from one-half to tvo Inches. Cementing material Is calcium carbonate and Iron oxide. These features form on the backslope of the present beach and are exposed and broken Into slabs as the beach moves landward. Their origin Is discussed by Morgan and Treadwell (1951*, PP. 71-75).

Igneous and metamorphlc pebbles are found on the beaches of central and northern Chandeleur Islands. Their average diameter Is reported to be one and one.half Inches (Dohm, 1936, p. 397). Because of their anomalous Inclusion in an area of fine sand, Dohm undertook to solve the problem of their origin, but concluded that they could have four likely sources (1936, p. kOZ):

1. ballast from a ahlp2 . river Ice, that is, material transported down river3. Introduction by Indians4. elevating action of salt domes

PhysiographyAn Idealized cross section of the Chandeleur Islands Is shown as

Figure 7. The low, sandy and swampy islands slope very gently into the surrounding vater. In many places this results in beach foreshore widths' varying two or three fold between high and low tides, despite a tidal difference averaging less than two feet. The method of dividing foreshore and backshare is similar to that used by Shepard (19^8, p. 62). On the Chandeleurs the backshare.foreshore dividing line is drawn at the crest of the highest berm. This separates the seaward sloping portion of the beach from the zone of windblown sand and coarse shell which slopes

SOUND MANGROVE SWAMP BEACHBACKSHORE FORE­

SAND-SHELL.FLAT DUNES

SHORE

o-oooo* 20-3300' 0-200* 00-350'

GULF

SWAMPWATER SAND

IDEALIZED CROSS SECTION OF THE

CHANDELEUR ISLANDS

Figure 7

away from the Gulf\ The uppermost herm Is also the line along vhich driftwood and debris accumulates during Btorms.

For discussion of physical characteristics the beaches of Breton, Chandeleur and Cat Islands have been divided into six sections. Each of these vlll be discussed separately starting vith the northernmost, Cat Island.

Active beach formation is chiefly confined to the eastern end of Cat Island. Longshore currents have truncated the eastern end of the old beach ridges vhich form the backbone of the Island and developed a pair of north.south trending spits. The old sand ridges of the island form a solid buttress against vhich the present beach and dunes accumu­late. Dune sands have piled up to an elevation of 30 feet or more In places at the center of the east end of the island. Spits north and south of the island's center have no such firm support behind them, have not developed dunes and average only four or five feet in elevation.

The typical appearance of the east.central portion of Cat Islandn2is shown on Profile 2, Figure 8 . The island displays a narrow beach

backed by broad, high dunes vhich override the older beach ridges. Some idea of the magnitude of the duneB can be obtained from Figure 9. Marsh deposits have developed in swales between the older beach ridges. In places these are now exposed near sea level (Figure 10),

The northern eight miles of the Chandeleur Islands (north point to

^The beach consists of all material deposited by the vaves above vater level. Foreshore, dunes and sandflats are portions of the beach. Width and height variations of different portions of the beach, and swamp be­hind the beach, are shown on Figure.7 .

2All profiles referred to in this section are not included on Figure 8, as the large number of profiles made this undesirable. Physical data of the remaining profiles are listed on Tables 2 and 3, and the profiles are located on Figure 2.

14- PROFILEBEARING ®;mSURVEYED 6-13-52

Jwmm,'',' ifn rtf*mrniM

PROTILE 5 BEARING NOe'C SURVEYED

Ui<

PROFILE 9 BEARING N 5(fw SURVEYED 6-I5-.52 MARSH

SANDm m m m!'v ‘ '* * □ WATER

IvAV.VV.V,*,*//?**

profile: 13BEARING N20W SURVEYED fl- 13 - 52

PROFILE 12 BEARING N 50 W SURVEYED 6-13-52

Mm ®800

PROFILEBEARING N 00 CSURVEYED I I W s

I.W'iii’.ii'.ii

BEACH CHARACTEBRETON, CAT AND Cl

ISLANDSLOCATION OF PROFILES SHOW

W ATER LE V E L CO R R EC TED TO M EAN LOW WATER

PROFILEBEARING * -v-'

27

PROFILE 3BEARING NI5*ESURVEYED ft -1 5 -5 2

14001000 1200PROFILE

\RSH ^ND \TER

4 0 0

800

N W4 -

- 4

1000

P R O F IL E 1 4 BEARING N Ift’w SURVEYED ft - 13

1200 1400

— 4

800

AR A C T E R IS T IC S AND CHANDELEUR

>LANDSFILES SHOWN ON FIG. 2

MilIBi

PROFILEN 5 5 * WBEARING

SURVEYEDm m m. v It , w 11.\ •* • ,• , '

1000

400D IS T A N C E S A N D E L E V A T IO N S IN F E E T

V E R T IC A L E X A G G E R ­A T IO N X 10

600

Figure 8

Fig. 9 West slope of sand dunes, east end of Cat Island facing south along the hack, slope of the dunes (lat. 30*13'36", long, 88*04'25")

Fig. 10 Marshy swale deposits being eroded near center of north side of Cat Island. Picture facing east. (ca. lat, 30*13'50" long. 88*0 8'25")

30

ca. 29* 5 5* N. lat.) consist of a lm o s t unbroken sand beaches vith broad black mangrove swamps developed on their landward side (Fig. 11). An exception occurs on about one and one-half miles of beach where broad, low sandflats extend the entire width of the Island. Such flats seldom rise two feet above mean low water and are frequently cut by small tidal channels, mazy of which operate only at high tide. One of these "washover fans” (Price, 19V7, p. 1653) Is shown on Profile 5, Figure 8. Most of the northern section Is backed by mangrove swamp which averages some 11*00 feet In width In contrast to the Bectlon composed of sandflats which averages slightly over a mile (53^0 ft.). Profile 3, Figure 8 is fairly typical of the northern section. The beach displays a broad fore­shore (205 ft.), a fairly broad dune area (180 ft.) backed by mangrove but lacking sand flats. The beach on Profile 3 attains an elevation of 9.5 feet and Is the highest measured point on the Islands. Most beach in this section has a maximum elevation of five to seven feet. The north point of the islands has not changed appreciably from the appearance described by Russell (1936, p. 6l).

The third zone,farther to the south (lat. 29° 55' - 29° ^5'), 1b about 19 miles long. It Is the most stable part of the islands and dis­plays continuous beach backed by broad mangrove swamps. There are no washed through zones or passes. Profiles 8 and 9, Figure 8 are typical of this area. At mazy places In this zone exhumed marsh is exposed at the seaward edge of the foreshore. The beach crests are quite uniform,

« 1

and measured elevatlozis vary only between If.5 and 5*5 feet. Island w id th s

in t h iB zone average 3200 feet.Adjoining this zone and extending for the next 12.5 Riles to the south

(lat. 29° ^51 - 29* JfO' 05") is a series of mazy small islands. Beaches are seldom four feet high and washover fans form broad flats throughout

Fig. 11 Beach at north point of Chandeleur Islands. Picture facing southeast, (lat. 30*0 3’ 15”, long. 88*5 2’1*8'')

the area. Only a p™"*1.1 portion is backed by mangrove swamp. The width of the islands approximates one mile. Profile 12, Figure 8, is illus­trative of conditions in this sector.

Errol-Gosier Island is separated by about 2.5 miles of water from the aforementioned area. On 1917 surveys made hy the U. S, C. & G. S. the island was shown as a shoal area containing small islands, but since that time it has developed into a continuous strip of land. Older charts indicate that the process of island construction and degradation has been repeated several times since the first survey. During severe storms the island is destroyed, but it is built again during periods of calm weather. It is now extending Itself both to the north and south.ErroL-Cosier is about five m^les long and is backed with black mangrove swamp at all but one place. The ends of the island have a small beach ridge facing the sound (Profile 13, Fig. 8). Where surveyed, the island varies between four and ten feet in height and averages 1200 feet in width. Except at the ends of the island, where dune sands pile up five feet or so above the remainder of the beach (Profile lU, Fig. 8), the island is very Blmllar to the stable central portion of the Chandeleurs (lat. 29° ^5’ - 29* 55').

The most southerly, division is that formed >y Breton Island. Its length is 5.5 miles and average width, 1300 feet. A narrow tidal pass divides the island near its eastern end. Little of the beach is backed with mangrove, as most land behind the beach is composed of older beach ridges. Maximum elevations recorded in profiles of Breton Island varied between three and 12 feet (Profile 17, Fig. 8). Parts of the Island not backed hy beach ridges (Profilesl5 and 18, Fig. 8) consist of narrow fore­shores and low dune-sandflat areas gradually sloping out to Breton Sound.

33

Offshore BarsThroughout the length of the Islands two or more offshore hers are

present although they vere not surveyed on all profiles. Between the share and the first bar water depths vary from two to five feet. Ihe bar oocurs at an average distance of 90 feet from the share, with a crest about one foot below mean sea level. Several hundred feet seaward bar crest water depths are at least four or five feet. No detailed sur­veys vere made, so distances and depths between outer bare is not known.The following statement by Shepard (19^8, P. 85) probably applies.

"Off some coasts, particularly those with gently sloping beaches, a series of offshore bars is found at increasing depths seaward. Presumably these are due at least in pert to occasional periods of large breakers, which produce the outer bars, and are followed by periods of small breakers during which the smaller bars are formed."Surveyed characteristics of offshore bars are compiled in Table 3 .

Additional physiographic information on the Chandeleur Islands can be found in Bussell (1936, pp. 59-69).

Shell Beaches

Origin and Development Two distinct types of shell beaches are discernible in the eastern

Louisiana marshland. One is composed predominately of oyster shell (Crassostrea virglnlca) and the other of clam shell (Bangla cuneata).Oyster shell beaches are most prominent along the inner margin of sounds (Fig. 12) and on several islands in the sounds, although a few occur on marshland lake shores, These beaches have accumulated through continued wave attack on surrounding water bottoms, concentrating shell material along shares. Clam shell beaches are restricted to marshland lake and bayou shores (Fig. 13). Although many such beaches have farmed in the same manner

Fig. 12 Oyster shell "beach, Door Point,facing vest. (lat. 30*03'U6",1 . _

Fig. 13 Clem shell beach south shore of Mississippi Sound, formed by destruction of an Indian midden, (ca. lat. 30°07'00" long. 88*15'20").

36

as those of oyster shell, -the majority have a rather unique origin. This latter group is formed hy destruction of Indian middens and reconcentra­tion of the clam shells as "beach deposits. Marshland middens are composed almost entirely of Bangla shell and are a prolific source of beach material.

SedimentsShell beaches ere composed of 25-9¥f° shell with the remainder being

sand and silt. Because of the size and quantity of shell, mechanical analyses of the material result in much larger median grain sizes than obtained for sand beaches. Only four shell beach samples have been analyzed, but their medians ranged from 0.23 ®m. to 1.28 mm. Shell beach grain sizes exhibit wide variation, depending upon the species and con­dition of the composing shell and the amount of sand admixed. Near water level most shell beaches contain some sand (silt in inland lakes), but berms are composed entirely of shell.

PhysiographyShell beaches were surveyed at Freemason Island, Isle au Pitre and

Herron Bay, Hancock County, Mississippi. They are typically narrow but relatively high when compared with sand beaches of the Chandeleur Islands. (Compare Figs. 8 and 14). Shell beaches vary from 45 to 223 foot in width and from. 1 ,5 to 6.1 feet in height. Portions of Isle au Pitre (Profile 20, Fig. 14) support the largest shell beach in the area (Table 4). All of the large shell beaches are invariably made of oyster shell and lie on the inner sound shores. Clam shell beaches of the lakes seldom exceed three feet in height and 50-75 feet in width.

37

PROFILE 20 BEARING N 43° W SURVEYED

6-13-wmfo.

m m i m .

a v A v / . - . v .SB®\'Y,

250 swSURVEYED

6-13-52PROFILE 24 BEARING N9(fE SURVEYED

8 - 1 6 - 5 2

PROFILE BEARING

N

V .W

PROFILE 21 LEGENDBEARING N59 W SURVEYED 6-12-52 MARSH

SHELLWATERSAND

WATER LEVEL CORRECTED TO MEAN LOW WATER.DISTANCES AND ELEVATIONS IN FEET. VERTICAL EXAGGERATION X 10

CHARACTERISTICSBEACHISLE AU PITRE & FREEMASON ISLAND

LOCATION OF PROFILES SHOWN ON FIG. 2

Figure ]A

38

Summary1. Sand "beaches are confined to Breton, Cat and Chandeleur Islands.Shell "beaches are found on islands in the sounds, along the inner margin of the sounds and on marshland lake shares.2. Nearly all beaches are presently being driven toward or encroaching on land. "Very little progradation of beach deposits is occurring.3. (brain site of sand beaches is rather uniform. Medians vary between 0.13 mm. and 0.30 an. Shell beaches have a much vidor median size range, and analyzed samples varied between 0.23 ma. and 1.28 an.4. Beach elevations rarely rise above 10 feet and average about half of that except at Cat Island where some beach dimes reach heights in excess of 30 feet.5 . Beach foreshores are relatively narrow (Table 2). Sand or shell flats and/or dunes lying behind the foreshore are commonly the widest part of the beach.6 . All sand beaches of the area exhibit a series of offshore bars seaward of the beach.

Stranded Beach Ridges or ChantersIn addition to active beaches, the easternmost Louisiana marshlands

contain several old beach trends in the marsh. Former beaches of thisnature are known as chenlers (Howe, Russell and McGuirt, 1935, P. 3).development and occurrence of chenlers In western coastal Louisiana iswidely known, but few similar studies of these features have been made

•aeast of the Mississippi River . Eastern Louisiana chenlers are separable

comprehensive treatment of chenlers of eastern Louisiana has been undertaken as a thesis problem at Louisiana State University by Leon G. Hunt; however, the work has not been completed at this time.

39

Into tvo groups. One represents a post-Pleistocene Gulf shore formed prior to deltaic sedimentation In the area; the other results from, lakeshare erosion.

Gulf Chenlers

PhysiographyThe gulf chenlers form a northeast trending hand recognizable from

the vicinity of Kenner, Louisiana, to Cat Island and possibly Ship Island, Mississippi. This Is a distance of slightly over 30 miles, if Ship Island Is not Included. These features are as much as two miles In vldth and reach maximum elevations of around 15 feet, but they are buried beneath marah throughout much of their extent. Topographically, the eastern portion of the gulf ohenlers appears as groups of closely spaced ridges and .swales c/hHlgned parallel to chenler strike (Fig. 15). In a few places younger ridges truncate older ridges at an angle, Indicating changes In shoreline trends. Westward, In OrleanB Parish, the chenlers protrude above the marsh In only a few places. This section shows less ridge r alignment than In Mississippi, and the chenler surface Is more hummocky.

VegetationVegetation of the eastern Louisiana gulf chenlers Is predominately

slash pine (Plnus carlbaea) and live oak (Quercus virglnlana). In most places a dense undergrowth of palmetto (Sabal minor) is found.

SedimentsComposition of gulf chenlers is strikingly m l form. Medium sand

(median grain size near 0.30 mm.) occurs throughout, and sorting Is excellent. Shelly material Is rare. Information on Cat Island beach sediments

Fig. 15 North side of Sand Ridge, Hancock County, Mississippi (let. 30*13*00", long, 88°27'28")

kl

(Ho b, 13L-I36)and Sand Bldge sediments (Hos, 137-138) is presented in Table 5«

StratigraphyIt has been noted that the western section of eastern Louisiana

gulf ohenlers is largely burled beneath marsh. The sediment sequence and attitude associated with this chenler trend is shown in Figure 16

(Location 39, Fig. 2).Pleistocene, unit A, sands and clays form the basal part of the

section. Posting on the Pleistocene is 50 to 80 feet of soft, gray clay, unit B, containing several zones of silt and sand. These silts and clays vere deposited In brackish to marglnaL.raarlno environments.The upper portion of unit B Is composed of prodelta materials of the Mississippi Elver. Confined within unit B are the chenler and Its offshore sands (unit C). Clean sand composes the body of the ohenler, but the associated offshore material contains varying amounts of olay admixed with Band. At the c to s b section location the chenler crest is burled beneath 10 feet of peaty marsh material (unit D), and Its base rests about 1*0 feet below mean gulf level.

The -typical appearance of gulf chenlers on the eastern part of the trend is shown on Figure 17 (Location 1*0, Fig. 2). Only one of several chenler ridges In the area Is shown. At this location the chenler Is only partially buried under grey, slightly silty, organic clay, and rows of parallel ridges still extend some five feet above marsh. No attempt was made to penetrate the ridge on Its southern side, but bore holes on the north found the base lying approximately 16 feet below mean gulf level and apparently dipping slightly toward the south. This suggests that the center of the chenler lies somewhat deeper than the northern edge, A

0

-20

-40

-00

-00

-100

LOCATION NO. 39 LAKE PONTCHARTRAIN

MISSISSIPPI RIVERMETAIRIE

RIDGE

;%;:;u n it ommm

UNITUNIT C

UNIT

>,N\V vN''\On"\\\' ■>' s W' \\\\

\.\i\\yt,\ ,.\N\ . .\\ ■> , \ a n^ ,vv\\\v\\ \ X .\\y\\ .t\ > \ , A \ \ w A ^ v\w\ \\ \s A \ \ \

ELEVATIONS IN FEET FROM MEAN SEA LEVEL.DISTANCE IN MILES.

□ s a n d □ SAND AND SANDY CLAY □ SAND

AND SILTPEAT AND ORGANIC CLAY

CLAY AND SILT WATER PLEISTOCENE

CHENIER STRATIGRAPHYJEFFERSON-ORLEANS PARISH LINE

—100

MODIFIED FROMU.S. ARMY ENGINEERSDATA.

Figure 16

-erto

700105

10—

LO C A T IO N NO. 4 0

CHEN1ER

MARSH

UQ PLEISTOCENE

| | SPOIL BANK

CHENIER STRATIGRAPHYSAND RIDGE, HANCOCK COUNTY, MISSISSIPPI

HORIZONTAL AND VERTICAL DISTANCES IN FEET VERTICAL EXAGGERATION -20 TIMES DATUM - MEAN SEA LEVEL

I I I I I I I1000 1200 1400 1600

Figure

strattou of light grey, fossiliferous, silly clay Is found under and north of the chenler. This might veil he marine Pleistocene vhicb Is known to occur In Prairie terrace a mile or two to the north.

Lake ChenlersLake chenlers are confined to several areas along the shores of

lakes Bargne and Pontohartrain (Fig. 2). Their maximum vidth approximates one mile, and maximum height, five feet. The surface expression of these chenlers Is quite similar to that of the gulf chenlers. They are a series of closely spaced, parallel ridges and swales whloh are partially hurled. Live oak (Querous Virginians) is the most common tree on the lake chenlers, and dense undergrowth is common. No sedimentary analyses have heen made of lake chenler material, hut the composing material Is a rather uniform, coarse silt. Insufficient drilling was carried out on lake chenlers to present a good cross section; however, the general appearance of most Is similar to Sand Bidge, Mississippi (Fig. 17), except that most lake chenler ridges are covered vlth clam shell (Bangla cuneata) Indicating extensive Indian occupancy.

SummaryThe following conclusions can he drawn concerning chenlers of eastern

Louisiana:1. Two types of chenlers are found in the area— those composing former gulf beaches and those formed around lake harders.2. Topographically, most chenlers appear as raws of closely spaced, para­llel ridges and swales. The ridge and swale r&lignment In most places parallels the strike of the chenler sand mass. This Is in contrast to chenlers of western Louisiana where pronounced coastline changes have re­sulted in truncation of older chenlers by younger ridges.

3. Sediment of the gulf chenlers consists of medium sand with a median grain size of approximately 0.30 mm. Lake chenlers are composed of rather uniform, coarse silt.U. Gulf chenlers are higher, broader, and apparently thicker than lake chenlers. The bases of gulf chenlers lie between 20 and Uo feet below mean gulf level and apparently overlie Pleistocene strata throughout much of their length,

Marsh

PhysiographyThe discussion of physiography thus far has referred only to positive

topographic features— ridges that stand out from their surroundings.There, is one physiographic unit, marsh, that is neither strongly positive nor negative but comprises most of the land of eastern coastal Louisiana.The marsh is a featureless plain, a few Inches to two feet above mean sea level, interrupted only by open water of lakes or streams, natural levees or beach ridges. Erosion by wave attack is enlarging water bodies at the expense of marBh. One of -the most rapidly changing areas is Isle au Pitre where the amount of land diminution between 181*8-57 and 1952 is shown on Figure 18. Land bordoring directly on the sound is in rapid retreat in contrast to inland areas which have undergone comparatively little change. The ragged appearance of a rapidly eroding marsh Island in Cbandeleur Sound is shown on Figure 19.

VegetationFresh water marsh is not present in the area. Even in inland Orleans

Parish, marsh waters are slightly brackish. Types of marsh vegetation indi. cate the degree of salinity of surrounding waters, although elevation and

146

0.5

M ILE S

SH O R ELINE CHANGES OF ISLE AU PITRE AND VICINITY

1848-57 T O 1952

Figure 18

Fig. 19 Eroding marsh, south side of Mitchell Island, looking east.(lat. 29*5 3*30", long. 89*13'27")

other factors influence species' distribution. Listed below are salinity indicator plants and the zones to which they belong (C. A. Brown, 1951, pars. com.).Ifreah to slightly brackish

Altemanthera phlloxeroides (Alligator weed)Soirpus vali3ua (Bulrush J Taxodium distichum (Cypress)Typha sps. (Cattail)Zltanlopsla mlllacea (Cutgrass)

Brackish to saltyBaooharls halimifolia (Marsh elder)Barrichia frutescens (Sea oxeye)Dlstlohlls spioata (Saltmarsh grass)Iva fruteSoens (Marsh elder)Marlscus jamalcensls (Sawgrasa)Phragmites communis (Roseau)Scirpus olneyi (Three-cornered rush)Solrpus robustus (Leafy three-cornered rush)Spartina cynosuroides (Big cord grass)Spartlna patens (Pouch grass)

Salt waterAvicennla nitlda (Black mangrove)Batfamar i'tima(Saltwort)I’imbristylis castanea (Sand rush)Juncua roomerianus (Black rush)PhiloxoruB vermicular is (Salt water alligator weed)Sallcornla sp. (Jointed saltwort)Spartlna’~alternlflora (Oyster grass)

SedimentsMarsh sediment has fairly uniform composition throughout Orleans and

St. Bernard parishes. The chief variable is silt content. Inland, vege­tation and clay are the dominant constituents but nearer the pulf silt, deposited b7 storm waves, comprises a significant portion of the marsh. Marsh sediment is colored various shades of brown and dark gray, depending on the quantity of organic material present. Beds of compact, brown peat are widespread but average only a few feet in thickness. The typical

marsh sequence developed over most of Orleans and St. Bernard parishes is

presented "below (also see Fig. 20)Units Thickness (feet)

1 Vegetation, admixed with more or less silty olay...... . 12 Clay and olay, silty, organic, soft, dark gray to

"brown (frequently emits HgS odor when cored)............. . 5-303 Peat, "brown, compact. Layers occur within the

above unit at a depth of five to ten feet. (In Orleans Parish peat has been found to a depth of 15 feet and in strata up to five feet thick.)Peat, while widespread, is more lenticular thanthe other units.......................................... 0 .5 -1

it Clay, silty, and silt lenses, light gray, fairlycompact. In places contains oyster shells.Ihie unit is usually transitional with unitthree through a one-foot zone ............. 12-19

5 Silt and/or sand very fine and fine, light gray to white. The total thickness of this unit has not been ascertained. In general, the silt overlies the sand and where. penetrated is two to four feet thick. However, the silt is sometimes absent.While contacts between individual strata are sharp, unit five grades into unit four. Silt lenses in unit four represent the uppermost tracesof unit five material...................................... Unknown

Of course, local thickening and thinning of Individual units occur, and in places one or mare of the units may be absent. Only unit one occurs in marsh which has encroached on subsiding levees or chenlers. Other changes in the marsh sequence are related to the proximity of distributaries or lakes at the time the section was deposited. A distinct llthologic break oocurs between beds three and four. Ihe upper portion consists of highly organic marsh material mostly deposited at or above sea level in contrast to the lover strata (units four and five) which represent brackish water, bay or lake deposits.

Stratigraphy and Paleontology For discussion of marsh stratigraphy a lino of borings from eastern St.

Bernard Parish has been selected (Fig. 20; Location 53, Fig. 2). Comparison

LEVEL0-1

5 - - 5

10- -10

-15

-20

25 2 51000

VERTICAL SCALE & HORIZONTAL SCALE IN FEET Q SURFACE VECCTATON, ROOTS, ETC

Q BROWN ORGANIC CLAY, MANY ROOTS, H ,S 0 0 OR

■ peat£51 •SHELL

H CRAY SE.TY CLAY

HD CRAT MEDIUM S tT

g ] FINE WHITE SAND

CROSS SECTION OF GATE ISLANDBEARING OF SECTION N35*I5'E

SECTION LOCATION - NUMBER 53, FIGURE 2

Figure 20 V71o

51

of fauna from bore holes In this area with farms now living on water bottoms of Plaquemines and St. Bernard parishes (see ecology section) has made It possible to Interpret the developmental sequence of the marsh. Ten samples were collected from eight holes. Four were analysed statistically and the results are shown on Figure 21, In this figure hole depth has been plotted against the percentage of various genera and species.

It Is noted from the faramlnlferal analyses that the white, very fine and fine sands bottoming many holes contain an Incongruous assem­blage. Most of the genera shown on Figure 21 as "other calcareous farms" Inhabit strongly brackish to marine waters (above 20 o/oo salinity).This group Includes:

Bollvlna lawman1 Sanzawala strattonlBollvlna strlatula Lagona sp.Bollvlna sp. Konionella sp. of. aurlsBullmlna"sp. Qulnquelooullna sp.Dentallria sp. Slnhonlna sp.Mscorbfa sp. Robulus sp.flloblgerTna sp. tfrigerlna sp.fldmbellna sp. Virgulina pontonl

Various species of Blphldlum are found from slightly brackish to salty environments. The vldth of the Blphldlum band, Figure 21, remains Marly constant, because some species, especially Blphldlum llmosum, predominate in slightly brackish water, end others, such as Blphldlum gunteri, predomi­nate in strongly brackish water. "Botalla" beooarli parklnsonlana and "Botalla" beooarli teplda are most common In the 10 to 20 o/oo salinity range, but they occur from weakly brackish to marine environments. Blphldlum and "Botalla" are plotted separately on Figure 21. The"other arenaceous farms" group Includes:

52

— CM <0

Id Id Id Id-J -1 J -1CL OL Q_ CL2 2 2 2< < < <CO CO CO CO

100AMMOTIUM SALSUM

90-ARENACEOUS

80-

70-

60-

50-

30-

20-

10-

20 19 1518 17 16 14 1322 21DEPTH IN FEET

S T A T IS T IC A L ANALYSIS OF FORAMINIFERA IN FOUR

S A M P L E S FROM THE GATE IS LA N D AREA

Figure 21

53

Ammoaatuta salsa Arenoparrella mexicana EaplophragnioIdBa manilaensls haplophragmoldes wllbertl Mlllammlna fusca Toxiularla sp.Trochaamlna comprlmata ^ocbm m ina inflaia““ troofaamaiTnn maorescens

These speoles abound In weakly to moderately brackish habitats. A few tolerate salinities of 20 o/oo but roach their zenith in waters less than half of that figure.

Anmotlum salsum is counted in a separate part of the figure because it is both common and a good lndloatar of "intermediately brackish" environment. In present water bottoms of this area it is most abundant in waters of five to 15 o/oo salinity and occasionally reaches the 20 o/oo zone, but no higher.

The sand samples contain two distinct faunal groups which reflect contrasting ecological conditions. One group inhabits waters with a maximum salinity of 15 to 20 o/oo and generally less, and the other in­habits marine and Btrongly brackish waters (20-35 o/oo). It is concluded that the former of these conflicting classes must have been transported and re-deposited after death. Such a condition would exist on water bottoms in the vicinity of active distributary mouths. That the sand horizon represents the widespread bar deposits of the St. Bernard subdelta is further substantiated by the fact that both the depths to and thick­nesses of marsh unite throe, four and five are dependent on their relation to distributaries of the area. Near old stream courses the sand unit is higher than elsewhere and silt lenses in unit four increase in both number and thickness.

The second conclusion reached by this faraminiferal study is that silts and clays overlying the fine white sand horizon Indicate increasingly

freshor environment. Gradual extinction of "other calcareous farms", tremendous Increase of "Botalla" and moderate Increase of Anmotlum Indicate bottom conditions of decreasing salinity (probably around ten to 15 0 /0 0 at the 17-foot level). In the uppermost sample Anmotlum assumes the dominant role, and Ammoastuta, Arenoparrella, and Mlllammlna are almost as prominent. This indicates the presence of salinities of not mare than five to ten 0 /0 0 at the time of deposition. Such a con­dition la found In Bhallow bays or lakes In lnter-levee areas formed after distributary mouths have extended farther seaward. Three feet above the 13-foot sample these clays pass Into marsh deposits. Such deposits were laid down above water level. From the foregoing information it is postulated that the sequence of events In lnter-levee areas la as follows:1. The presence of open embayed area of the Gulf of Mexico with near normal salinities.2. Influx of sediment In advance of the mouths of distributaries and mixing and reworking of these sandB and silts with bay-bottom sediments3. Deposition of silts and clays of the interdistributary areas In depressions between natural levee ridgesb. Cessation of stream sediment deposition and resulting dominance of plant remains as organic debris5 . Sinking of marsh by compaction and regional subsidence and resulting dissection by wave action

Summary1. At least 80$ of easternmost coastal Louisiana land Is marsh. At the present time nearly all of it is being eroded.2. Marsh vegetation Is a good Indicator of the salinity of surrounding waters.

3. Marsh sediments are composed of fairly uniform clays and organic material. The chief variant Is silt, which Is common In marshes near the Gulf.4. Marsh stratigraphy Is rather uniform In easternmost coastal Louisiana. It Is separable Into upper arganlo marsh deposits and lower, less organic bay and lake deposits,5 . The developmental soquence of the marsh strata Is clearly discernible by fcramlniferal analysis, the results of which have been summarized.

Tidal StreamsExamination of all previous physiographic features has been concerned

with various land farms; however, In a marsh area such as easternmost coastal Louisiana, water bodies are no less Interesting. In addition to the countless numbers of lakes and bays, thousands of tidal channels wind their way through the marshes. Locally these streams are known as bayous; however, when they are short and deep and connect two larger water bodies, the term "pasB" Is applied.

OriginThe beginning of many tidal channels Is contemporaneous with the

formation of distributary mudflats and ponds of the delta. Original tidal drainage of the interdistributary area becomes concentrated along certain lines, and continued sedimentation and marsh growth Is conditioned by the developing tidal channels. In time the tidal streams became entrenched In their paths but slowly continue to modify their courses. As the active delta shifts Its deposltlonal area, tidal waters are allowed to ocoupy rem­nant distributary channels, farming a seoond type of tidal channel. A third type appears to have formed after active delta formation had ceased and marsh development approached Its present condition. These streams

5 6

originate during sever© storms which occasionally pile vater over the marsh to depths as great as ten feet (U. S. Arny, 1951, P. *0* As this vater drains from the marsh, It attempts to take the shortest route to open vater and occasionally succeeds In scouring a channel. However, this last process Is metre Important In causing alterations In existing channels than In opening nev ones.

Relation of Origin to Surface FarmSurface or near surface structural trends existing at the time of

tidal stream formation exert strong control over the resulting surface pattern (Fig. 22). Hence, analysis of stream patterns frequently reveals tlie controlling structural features, even vhen they are hurled under as much as five or ten feet of marsh. Common structures controlling marsh tidal stream patterns In this region are: natural levees, beaches,chenlers, terrace and faults.

Tidal channels develop between natural levees by adopting remnant distributary ohannels. Resistant levee materials confine the channel and give rise to a tidal stream vhoBe pattern closely resembles the latter phases of the distributary channel. The surface form produced Is one of rather straight, frequently long channels (Fig. 22). Even after levee sub. sldence, the pattern persists. Meanders sometimes develop between levees of former distributaries vhen tidal flow Is small, and -the channel becomes partly filled with marsh. Even then, the overall straight appearance Is preserved. Levees subside more rapidly than surrounding marsh, because they are more dense. As a result, vater bodies farm In levee flank depressions of the former distributaries (Russell, 1936, p. *f5). In many cases these flank depressions farm Irregular lagoons which often have adjoining tidal channels. Because of their ragged pattern and position just marshvard of

CHENIER

LEVEE

PARTIALLY CHENIER C O N T R O L L E D <

STREAM ^

CHENIERCONTROLLED

STREAM

r c v LEVEE * DISTRIBUTARY

CONTROLLED • STREAM

CHANNEL SCAR LAKES

LEVEE FLAN K DEPRESSION r " — S STREAM

OPEN* MARSH STREAM'LEVEE FLANK DEPRESSION

LAKE

.EVEE FLANK DEPRESSION

STREAMCOMPLEX ROUNDED L LAKE '

INCIPIENT ROUNDED LAKES

'OPEN* MARSH, STREAM S

o o.

PROBABLE DISTRIBUTARY CONTROLLED STREAM

MODIFIED FROM U&Q& SHELL BEACH QUADRANGLE, 1941 EDITION

Figure 22

58

fanner distributaries, they are easily distinguished from channels originating between levees.

Beaches block normal marsh drainage and tend to divert it parallel to the share. Even where prominent beach deposits are lacking, waves break over the share and deposit minor concentrations of silt and sand on the marsh surface. These build and strengthen coastwise marsh and,In mary cases, deflect stream courses parallel to the coast. Even when tidal streams are diverted by beaches, they continue to meander.

Chenlers Influence drainage In much the same manner as beaches (Fig. 22). Control over stream pattern is stronger, however, as chenlers of this area are both broader and higher than local beaches. Even burled chenlers tend to confine stream courses within troughs of their undulat­ing surface, although streams commonly cross from one trough to another. Where a tidal stream alternately follows and crosses buried chenier ridges and troughs, a zig-zag pattern of right angle bends develops.

Many faults occur throughout the marsh and, theoretically, should exert some control on marsh drainage. However, In no part of the area, even where faults are known to exist, could evidence of fault control of tidal streams be proved.

Streams that originate in marsh unaffected ty levees, beaches or chenlers develop meander patterns In inverse proportion to the volume of flow they receive. In other wards, a stream with small flow volume is likely to meander more than a stream with large flow volume. A stream draining a fairly "solid'' marsh into a protected lake is likely to exhibit more meandering than a stream connecting two large water bodies. It Is also apparent that the width of a stream's meander belt is directly proportional to the width of the stream. Wider streams possess wider

meander belts (Russell, 1936, p. 126).

59

If sufficient flow is forced through a tidal channel, the stream will seek the shortest path between its drainage areas regardless of underlying structures. This situation is usually achieved in short passes which more than likely develop as a result of Btarms. Storm vaters rise to depths of several feet over the marsh as a result of easterly or southerly winds.When this volume of water returns to the sea, it has tremendous scouring power and is capable of cutting deep channels.

The overwhelming majority of tidal streams exist in "open" or unob­structed marsh. Far less numerous, but second in abundance, are tidal streams originating between levees. The depth-wldth relationships between open marsh and levee-controlled tidal channels, as constructed from 85 stream profiles, is shown on Figure 23. The chart is divided into three bands. The uppermost represents depth-wldth relationships of tidal streams originating between levees, the central band represents depth-wldth relationships of tidal streams forming in "open" marsh, and the lower band shows that bends of "open" marsh tidal streams, like bends of gravity motivated streams, are deeper than the reaches. Thus it is shown that tidal streams flowing in "open" marsh are deeper for a given width than those existing between natural levees. The few chenier controlled streams plotted fall within the range of "open" marsh streams. This is because unconsolidated sand is easily eroded.

Extreme widths and depths occur in constrioted channels separating large bodies of water. The widest and deepest well defined tidal channel is the Flgolets, separating Lake Pontchartrain and Mississippi Sound, It has a width of Just under one mile and a maximum depth of 93 feet (U. S. C.& G. S. chart No. 878, 19^9). Tidal stream widths commonly vary from severalhundred yards in major passes to a foot or two in rills draining inner-marsh areas. Depths commonly vary from 25 feet to a few inches.

6o

CHANNEL WIDTH IN FEET O________________ 50 100t 1----- 1----- 1----- 1----- 1----- 1----- 1----- 1----- 1----- 1----- r 150_______________200

1---1---1---1---1---1 i l I I

LJLULu

X t- Q. . U 5 a

UJ2Z<Xo

10

15

20

AAA A

00

LEGEND0 -T>PEN' MARSH CHANNELS • - CHANNEL BENDS IN ‘OPEN* MARSH A - DISTRIBUTARY CONTROLLED CHANNELS □ - CHENIER CONTROLLED CHANNELS

DEPTH-W IDTH RELATIONSHIP OF TIDALCHANNELS

Figure 23

61

Many factors control the distribution of widths and depths of tidal streams. Of major importance are size and nature of drainage basins, bank and bottom constituents and amount of land area blocking free current exchange between basins. A few general statements can be made about several of these controlling factors and their effect on channel development.1. Exposure to the direction of open water and sudden Inflow and outflow of storm tides result in greater volume of tidal channel flow and, hence, larger channels than occur In more sheltered areas.2. Tidal streams connecting large water bodies tend to have larger flow volumes than those separating smaller bodies or those draining more or less "solid" marsh.3* Streams traversing large land areas that act as barriers to normal tidal flow have larger channels than those occurring In small areas of land.

Channel Shape

Longitudinal Appearance Longitudinal and transverse profiles of the seaward portion of Bayou

La Loutre are presented on Figure 24. The figure shows considerable inequality of cross sectional area along the different sections of the stream. Of course, where the cross sectional area Is large, the flow volume Is also correspondingly large. When certain portions of streams serve as tidal current connections between the surrounding bays, the flow volume and, consequently, the depth of these portions are increased. La Loutre is generally less than ten feet deep and 170 feet wide as far seaward as Bayou Petre (Profile A, Fig. 24). At that point it encounters a strong

tidal current path which sweeps through Bayou Petre, down Bayou La Loutre,

PROFILE A

PROFILE B

PROFILE C

PROFILE D

PROFILE E

PROFILE F

PROFILE GPROFILE

TRANSVERSE PROFILES

L

MAIN TIDAL CURRENT PATHS

SCALE MILES

LONGITUDINAL PROFILE

STREAM PROFILESSHOWING

EFFECT OF UNEQUAL TIDAL FLOW EASTERN BAYOU LA LOUTRE

PROFILES CORRECTED TO MEAN WATER LEVEL VERTICAL EXAGGERATION X 2SCALE IN FEET

Figure 2k

63

and enters the sound through Bayou Elol. In the portion of La Loutre lying between bayous Petre and Eloi (Zone I) the channel becomes both wider and deeper, reaching a depth of 12 feet and a width of 180 to 210

feet (Profiles C and D, Fig. 24). Just east of the Bayou Eloi-La Loutre Junction the stream narrows to 140 feet and the maximum depth 1b six feet. Between this point and the outlet to Morgan Harbor the stream Is rapidly filling with soft, organic clay containing living oysters (Zone II, Profile F, Fig. 2k), Between the pass Into Morgan Harbor and the present mouth of the bayou the stream handles considerable tidal flow, widens to approximately 600 feet and reaches a depth of 16 feet (Zone HI, Profile 0, Fig. 2k), Just east of this a one mile stretch of Bayou La Loutre has been separated from the remainder of the stream by erosion of the northern Bay Elol shoreline Into La Loutre (Zone IF, Fig. 24). Since the time lakeshare erosion tapped Bayou La Loutre, the Isolated eastern segment has received virtually no tidal flow (Zone V, Fig. 24). At the western end of this segment the bayou has become completely filled with sediment, but tides still keep the eastern end open to a maximum depth of six feet. Such tidal channel adjustment to changing conditions Is common throughout the marsh.

Transverse Appearance The distribution of depths acrosB a tidal stream Is ordinarily similar

to that of a normal gravity stream. Profiles In Figure 25 illustrate the transverse shape of tidal stream bottoms under varied conditions. Profile 42 Is a section of Deadman's Bayou (Location 42, Fig. 2). The appearance of this stream Is typical of that of mazy deep tidal channels of the area. The side slopes are fairly steep; the bottom Is flat. The rise at the channel center is found frequently and is composed of silt and oyster

SENW

20 20

NO. 4240 40

20 40 <0 ao 100 120 140 ISO 240

W°-FZ10 NO. 35 I20 —I—

40

20 2020 40 eo60 100 120 140 160

20 20NQ 45

120100 MO40 600 20 ao

NW SE

NO20 2020 40 60 60

20 2020 60

l ':: l MARSH CLAY

□ CHANNEL FILL

TIDAL STREAM PROFILESST. BERNARD PARISH. LOUISIANA

PROFILE LOCATIONS ON FIG. 2 DATUM-MEAN SEA LEVEL

Figure 25

65

shells. Deadman*b Bayou occupies a farmer distributary channel. Tho long Island on which it Is found Is ; aligned at right angles to the direction of tidal flew, and Deadman's Bayou Is the only path tidal waters can take between the adjoining bays without being forced around the Island. As a result, great volumes of Water are forced through this opening. Regardless of the fact that the stream Is bounded by compact levee material, It has attained great depth.

Profile 35, Figure 25 is located on Live Oak Bayou (Location 35,Fig. 2). This profile is typical of the majority of remnant distributary channels. The stream is very narrow, shoal and slopes very gently toward the center from both sides. It is bottomed with soft, organic clays In places containing mazy oysters. Live Oak Bayou Is on the same abandoned distributary as Deadman's Bayou. Their contrasting size Is due entirely to the great difference of tidal flow through them.

Profile h3 is located at Location 1*3, Figure 2. This stream, which is fairly deep for the area, Is beginning to shoal. Soft, dark, organic mud is covering the former bottom, and the eastern side of the stream has begun to assume a gentle slope. About 30 or 1*0 years ago this stream was removed from the major tidal currents by wave erosion which opened another bayou fourther east. The stream no longer carries its former flow and, consequently, is decreasing In size.

Profile 1*1* (Location 1*1*, Fig. 2) is a section of Bayou Llzigeo. At the profile location this stream Is deepening by rapidly cutting' into fairly compact marsh clays. Slopes of the sides are steep, and the bottom is flat. A cutoff meander has occurred at this location within the last twenty years and is resulting in rapid alteration of the channel shape. This stream Is discussed more completely In the section on tidal stream meandering.

Profile 45 (Location 45, Fig. 2) extends across a bend of a fairly deepl.tidal stream. The "talweg"^ and steepest slope occur on the outside on

what Is normally referred to as the "out-bank" side. The Inside of the tend, or "point bar", is filled with fine, organic mud and slopes gently toward the talweg. This is the situation which prevails in a normal gravity stream.

A seemingly abnormal situation found on the bends of a moderate number of tidal channels in the marsh is represented by Profile 46 (Lo­cation 46, Fig. 2). Instead of lying on the outside of the bend as visual, the talweg is nearer the inside. At all places where this has been observed, the angle of bend in the stream has been over 90*. It is not possible at present to give an explanation of this apparent reversal of normal conditions. However, it may be associated with tidal action during storms or changes in the course of a stream.

Meander PatternsA portion of Bayou Llngeo was surveyed with transit and profiled in

July, 1952, and again in January, 1953* Soundings were taken every five feet across 21 profile lines (FI. 1). The section studied is actively meandering and has developed a cutoff meander. In 1932 (U. S. C. & G. S.T-sheet 5316) the meander cutoff had not occurred and must have developed within the last 19 years. Adjustment of the channel to the new conditions is not completed, and rapid out and fill is taking place.

A contour map of the stream bottom is presented on Plate 1. Prominent features of the stream bottom are:

hTalweg, cut-bank, and point-bar are terms normally used for non-tidal streams but apply equally well to tidal streams.

AREJUS OF DEPOSITION AND EROSION

AREA OF DEPOSITION

AREA OF EROSION

ISOPACH MAP OF RECENT CHANNEL FILL

HYDROGRAPHIC CONTOURS

6T

A' D O'o4 7=r8

12

30010050

TRANSVERSE PROFILESVERTICAL EXAGGERATION X 2

SCALE IN FEET

MEANDERING OF TIDAL STREAMSBAYOU LINGEO, ST BERNARD PARISH

LOCATION NO. 4 4 , FIG. 2 SURVEYED 7/10/52 TO 7/13/52

WATER LEVEL CORRECTED TO BANK-FULL STAGE SCALE: I" 50'

ll& M l SHELL AND SILTY CLAY

MARSH CLAY

r - . r SOFT CLAY FILL

P la te 1

1. Two deep channels In the stream bottom separated by a ridge which is between one-half foot and two feet high. Oyster shell is concentrated in this ridge (Profile A-A' and C-C')<

2. Talvegs are at the outside of some bends (normal) (Profile B-B') and on the inside of others (abnormal) (Profile CLC')>

3. Six to nine feet of soft, organic clay fills the oxbow (Profile D-D1 & isopach map, Fig. 2U). Stream depths in the oxbow at bankfull stage vary from one foot near the active channel to eight feet at the far end of the oxbow.

k. A sill or ridge rises one to three feet above normal channel bot­tom at the neck cutoff of the oxbow (Profile E-E').

Three -types of sediment are associated with the stream:1. Light gray, sll*ty marBh clay occurs in areas being actively

eroded. The clay forms part of the typical sequence found beneath St. Bernard Parish marshes (Median, 0.02U; Sorting coefficient (So), 8,68; Log^So, 0,938)*

2. Admixed silty clay and oyster shell occupy most of the stream bed excluding the oxbow.

3. Soft, very dark gray clay capped at its surface with a lightbrown gel a few millimeters thick fills the cutoff meander (Average ofthree samples: median. 0 .03U; So. 6.7 8, Log So. 0 .831). This is

10typical material found in areas of stream fill, A strong north wind in January, 1952, resulted in abnormally low water which made possible photographing the channel fill (Figs. 26 and 27).

A comparison of two surveys made six months apart reveals no major changes in general configuration of either banks or bottom. Minor changes noted were:

Pig. 26 Cutoff meander, Bayou Lingeo, duringnorther (Jan. 2, 1953) Bayou Lingeo on right, cutoff meander- left and center. Water level le levered about three feet belcv m.s.l. Looking from near point E tovard point A. (lat. 29#1*3'16", long. 88*39'50”)

Fig, 27 Cutoff meander, Bayou Lingeo, during norther (Jan, 2, 1953) View Is of southeast bend of the cutoff, looking from Island toward point Q.(lat, 29*43'l6", long. 89*39'50")

71

1. Increase In water depth of nearly one foot across the sill atithe neck cutoff

2 . Seduction of depth In portions of the oxbow of about one foot3. Slight lateral shift of some contours on the stream bottomThe distribution of deposltlonal and eroalonal areas on the stream

bottom (FI, 1) shows that the meander cutoff has given the stream impetus to straighten its course in this section. Farmer talweg areas (outside of bends) are filling with sediment and reverse talwegs have developed, TldeB are given an opportunity to sweep almost straight through this portion of the stream and have resulted in cutting and lateral shifting of the inside of bends and virtual abandonment of the outside of bends.The meander cutoff has started a chain reaction which is resulting in shift of much of the channel length.

Vertical Movement of Tidal ChannelsTidal channel deposits become emplaced in the marsh sequence by-

subsidence and consequent upward growth of marsh and by depletion of a stream's flow volume which results in channel filling. Through careful examination of cares, tideil stream deposits can be differentiated from the normal marsh sequence. The cross sectional appearance of two tidal channels is presented on Figure 28.

The sequence of marsh deposits flanking these tidal streams is:Units Thickness (feet)

1. Clay, brown, highly organic.. k2. Feat, brown, compact........................ 1-1.53. Clay, and clay silty, light gray............ ?

Channel materials consist of soft, dark gray clay often containing Brachldontes, Crassostrea, and in places, Bangla. It is very similar to the light gray clays (Unit 3) of the marsh sequence but is usually less

LOCATION NO. 55

0 100 200 3001 I I I

HIGHLY S B ORGANIC CLAY

BR -BROWN MAR-MARINE SHELLCLM -CLA M SHELL MSN-MARSH SNAIL

SILTY CLAY COM-COMPACT MY - MYTILUS SHELL

| PEAT DK - DARK M - MEDIUM

8 2 CLAYGR-GRAY OYS-OYSTER SHELL

L T -L IG H T SFT - SOFT

LOCATION NO. 560 ICO 200 300 4001 I I I I

TIDAL STREAM STRATIGRAPHYLOCATIONS SHOWN ON FIG. 2 DATUM - MEAN SEA LEVEL

Figure 28

compact, darker, and In many places contains more shell. Channel deposits lense laterally Into the normal marsh sequence. In Number 55, Figure 28 the peat of the marsh section Is apparently cut out by the channel fill. Channel fill has been traced to a 15 foot depth In Number 5$, Figure 28, but In many oases It Is difficult to follow the fill at all.

Depth StabilityA comparison of stream widths and depths measured In 1935 (BusboH,

i

1936, pp. 51-55) vith those In 1952 generally show no great changes. A table listing stream depths and widths both In 1935 and 1952 Is given below. Part of the difference In the figures results from the impossibi­lity in re-occupylng the exact stations used by Bussell. Nevertheless, the few changes that have occurred are obvious.

Location 1935Width Depth

*

1952width Depth

Location Number on Figure 2

Liveoak Bayou 67 2.9 55 3.1 35’Deadman's Bayou 248 2 6 .6 240 36.5 42Bend Just east of Scow Pass h * 175 18.7 145 19.5 47

1/4 mile veBt of Scow Pass,Martlnbox Bayou 405 19.2 395 21 48

Blind dlstrib. by MartInbox Bayou 77.5 2 .0 78 2 .1 49

Between old and new en­trances to Drum Bayou 428 10.5 480 8 50

Martlnbox Bayou Just vest of VeBt Drum Bay entrance 198 7.6 200 17.3 51

Mouth of Bayou La Loutre 600 13 600 16 52

Table 6

The Boat obvious changes are: (l) the stream between the old and newentrances to Drum Bay from Martlnbox Bayou Is no longer in a major tidal path and is shoaling, (2) inroediately vest of the old (vest) entrance to Drum Bey, Martlnbox Bayou is deepening as a result of isolation of the shoaling section above, and (3) Deadman's Bayou was opened between 1917 and 1939 and is apparently still in the process of deepening.

Suxraaxy1. Tidal streams appear to originate in three ways:

a. growth of incipient inter distributary tidal drainage of an active delta

b. occupation of abandoned and partially abandoned distributaries as active river flow shifts to other areas

c. marsh erosion during storms2. The surface form of tidal streams reflects their mode of origin. Thepattern of many streams is controlled by physiographic units such aslevees, beaches, and chenlers. However, those developed in "open" marsh lacking control structures meander at will,3. Tidal channels of this area range from rills a foot or so wide and afew inches deep to troughs 100 feet deep and more than a mile wide.k. Major factors controlling width and depth of tidal channels are the size and nature of drainage basins and character of bank and bottom constituents.5 . Abrupt and large depth and width changes along a tidal stream can be caused by varying tidal current connections.6. The distribution of depths across a tidal ohaimel is generally Blmllar to that of a gravity stream.7 . Tidal streams meander in much the same manner as gravity streams.

75

8, Tidal stream fill deposits can be traced in the subsurface. These deposits become emplaced as a result of subsidence, upward growth of the marsh and channel fill sediments and/or by reduction of tidal stream flew and subsequent channel filling.

Lakes, Bays and Sounds Lakes, bays and sounds comprise approximately 75$ of the area of

southeastern Louisiana and constitute the final type of physiographic unit. Names applied to these water bodies depend largely on the degree of their enclosure. Lakes are completely or largely enclosed, but sounds are separated from the Gulf only by narrow barrier islands. The term bay is applied to waters which are intermediate between lakes and sounds, but its use is not consistent.

Lakes and Bays

Width and DepthMarshland lakes range in size from ponds of a few feet in diameter to

a length of UO miles and a width of 25 miles, as Lake Pont char train (Fig. 1). Depths of the largest lakes, Borgne and Font char train, average about 10 and 15 feet respectively. Other fairly large lakes or bayB, such as Boudreaux, Drum, Fcrtuna and Bob in, are in most places between four and six feet deep. Smaller lakes are almost invariably Iobs than three feet deep. Water of greater depth is confined to tidal channels or passes between lakes where currents are more rapid and have greater cuttingpower. A positive correlation exists between lake or bay size and depth_larger water bodies have greater depths. This is a result of two factors. First, the fetch of the wind is greater on large lakes resulting in larger waves and more effective bottom scour. Second, larger lakes or bays have

7 6

greater vater volumes to be transported by tides and, consequently, their bottoms are subjected to acre tidal scouring than occurs in small lakes.

Lake and Bay ShapesThere is wide variation in the shape of marshland lakes; however,

two prominent "types are discernible. One group shews a predominately elongate form, and the other group tends to be rounded. Transitions, gradations, and combinations of the types ocour, but it is usually pos­sible to unravel their sequence of development.

Elongate LakesElongate lakes are controlled by physiographic features— natural

levees, beaches or chenlers. MoBt conmon of the linear forms are levee flank depression lakes (Bussell, 1936, p. k$). These originate because natural levees are more dense than the surrounding marsh and compact sediments beneath them to a greater degree. This causes the levee to subside faster than the marsh. As a result, more or less elongate lakes form parallel to and Just marshvard of the crest of the controlling levee. Hopedale Lagoon (Figs. 1 and 22) is the typical levee flank depression lake. The shores of this lake are highly irregular but do not detract from the overall elongate appearance. Levee flank depression lakes exist even after the controlling levees have subsided beneath several feet of marsh. In an advanced stage, widening end ultimate Joining of levee flank depression lakes with those of inter distributary basins result; in the finger-like features such as Fishing Smack Bay (Fig. 1). Many buried natural levees have first been located by determining this type of lake pattern on aerial photographs.

Lakes resulting from other causes can also have a more or less elongate or linear outline. Several types of elongate lakes are: lakes between

accretion ridges of abandoned dietributaries, lakes between chenier ridges and tidal streams which hare become truncated and isolated by beach ridges (Fig. 39). All three of these types ere of limited oc­currence and are rather easily differentiated from levee flank depression lakes. These three types are outlined by fairly sharp boundaries and contrast sharply with the Irregular shores of flank depression lakeB. In addition they are, in most cases, of less areal extent.

Bounded LakesLakes with oval or rounded forms comprise the second type. These

develop in open marsh and are not restrained by levees or beaches. Even though land is subsiding, the origin of most of these lakeB can be attri­buted to either storms, marsh fires or animal "eat outs" (Bussell, 1936, pp. 117, 120, 121). In their initial stage this type of lake is of variable shape. Over most of the area the marsh is fairly firm. In suoh marsh initial ponds tend to be rounded or oval (Figs. 22 and 30). In areas of low, soft marsh, such as that between Lake Bob in and Bayou Terre aux Boeufs (Fig. 1), small ponds have Irregular outlines. Begardless of the initial lake form, continued erosion of lakeshares tends to round their outlines. Bussell (1936, pp. 120-121) states that erosion of lake­shares takes place largely during hurricanes, and that VWhen a hurricane is in progress, a point in the marshes not only may experience its most violent winds from any quarter but also will, in all probability, feel heavy winds from all." In this manner, he accounts for the round lake form. Undoubtedly, a great deal of erosion takes place during the hurri­canes, but another possible explanation lies in the wind direction distri­bution throughout a year. Monthly wind rosettes drawn from data of the New Orleans weather station (U. S. C. & G. S., I9U9 , P. **80) reveal that

78

Fig. 29 Elongate lake farmed by a shell beach blocking a distributary controlled tidal stream. Door Point.(lat. 30*03 W , long. 89*1 0'06")

Fig. 30 Incipient rounded lakes, Gate Island, facing vest along south share.(lat. 29*M*2V , long. 09*21,iK>") Photo hy Janes P. Morgan

80

no overwhelming prevailing wind direction exists in eastern coastal Louisiana, Southeasterly winds prevail in Bprlng, northeasterly, in winter, and southwesterly, in sunnier. While agreeing that much (and possibly most) marsh erosion occurs during hurricanes or other storms carrying high velocity winds, it is suggested that the erosion occurring during average years also tends to develop rounded lakes because of the lack of a prevailing wind direction.

Size of small lakes must increase slowly at first, but then more rapidly as wind fetch increases. Connection of the small lakes with other water bodies through tidal channels hastens bank erosion (Bussell, 1936, p. 119). If a rounded lake in "open" marsh continues to enlarge, it will eventually merge with another round lake. After the merger of several of various sizes, the resulting lake will have an Irregular out. line and the shares will be scalloped or arcuate, the pattern depending on the size and location of the composing lakes (as the larger lakes between bayous La Loutre and Terre aux Boeufs, Fig. l). Still further lake enlargement results in smoothing of the shoreline and partial removal of the arcuate shores (lakes Borgne and Pont char train, Fig, l). Probably the best example of the advanced stage in rounded lake development is Lake Borgne. An unknown number of lakes have merged to form this water body, and at its western end the outline of two large, rounded lakes is readily apparent. This lake has undoubtedly engulfed many elongate, mostly levee flank, lakes in its growth. Once a lake has reached the size of Borgne, levee materials are no longer able to check its expansion.

Of course, mergers of rounded and elongated lakes ocour at many places and produce an almost endlesB variety of forms. Nevertheless, lakes and bays are valuable clues in explaining marsh history and in addition indi­cate the consistency or firmness of marsh in which they occur.

81

SoundsChandeleur and Breton sounds are connecting todies of water totaling

some 50 miles In length and ten to 20 miles In width. Depths In the sounds vary from around five to 23 feet. Water depth Is less than 12 feet In most of the sounds, hut two relatively deep channels traverse the area from north to south (Fig. 31). In both oases these deeps are the paths of strong tidal currents.

The area occupied by the sounds was once land of the St. Bernard subdelta, but subsidence, eastward tilt of the area, and marine erosion have oombined to remove nearly all land from the sound. Old maps of the area show numerous Islands dotting the sounds, but today Freemason, North, and New Harbor Islands are the only ones remaining well out in the sound.

Summary1. Large water bodies have greater depths than small ones.2. Marshland lakes are divisible Into two types distinguished by their shape— elongate and rounded. The origin of each of these -types is distinctive.3. Subsidence, eastward tilt of the area and marine erosion are combining to Increase the size of all water bodies in the area.

.122it 21

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EXPLANATIONi SAMPLE LOCATIONS

DEPTHS IN FEET AT MEAN LOW WATER

DATA rnOM U S COAST AND CCODCTIC SURVEY CHARTS 1200, 1*70 1272, 1947 ISSUE.

Figure 31

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SEDIMENTATIONThe previous section has been devoted to describing the appearance

and distribution of the various positive and negative physiographic features within easternmost Louisiana marshlands. An evaluation of sediments and sedimentary processes affecting these features is ncrw in order. No attempt has been made to analyze sediments of natural levees, chenlers, ctr marsh in more detail than heretofore discussed. Laboratory or field studies of Mississippi Elver distributary sediments have not been oarrled out in the St. Bernard area; however, extensive information is available on Mississippi Elver materials in other parts of the alluvial valley (Fisk, 19**?+, PP. 18-20; 19^7 b, p. 56; and 1952, pp. 76-77). Analysis of chenier sediment has been carried out by L. G-. Hunt, in a thesis in progress at Louisiana State University. Studies of brackish marsh sediments are needed and would undoubtedly yield a great deal of information. However, a lack of time for adequate sampling and analysis precluded marsh sediment studies. It was decided to concentrate the investigation on beaches and water bottoms rather than obtain limited information on all sedimentary environments. In addition to furthering the ecological studies undertaken on this project, water bottom and beach sediment analyses correlate with other similar work in the Mississippi delta area (Krumbein, 1937, PP. 3-17; ana Steinmayer, 1939, PP. 1-23).

Sedimentary investigations of beaches and water bottoms were made of a triangular section of St. Barnard Parish with its base parallel to and sea­ward of the Ghandeleur Islands and its apex at the western end of Lake Lery. Extreme limits lie within latitudes 29*271 N and 30*0l* 1 N and longitudes

83

81*

88*1*8' W and 89*52 'W.

Method of StudySurface teach samples vere obtained at speclflo points along profiles

surveyed normal to the strand line. Samples vere collected at the bar, water level, first berm, second berm (if present), dunes (if present), and rear of beach. Samples were preserved in sealed glass Jars until analyzed. Water bottom samples vere collected with a small coring tube and a clam- shell snapper manufactured according to U. S, Arty Engineers' specifica­tions. Nearly all water bottom samples vere taken with the clam-shell greb sampler, but cores, not exceeding three feet in length, supplemented grab samples in the lakes. The top two or three tenths of a foot of sedi­ment was removed from the sampler and stored in glass Jars. Sedimentary analyses were obtained far a total of 12U samples (Fig. 31 and Table 5).

Samples were taken at specific Intervals on traverses across the lakes and sounds. Locations ware obtained by running the boat at a fixed velocity between two predetermined points. Tidal currents and wind created insignificant errors in a few sample looations. Water temperature, specific gravity, and depth vere noted at each station.

The writer analyzed kO of the samples collected, 67 vere analyzed by the laboratory established far the project, and analyses of 21 samples in Chandoleur Sound and the Gulf were obtained from B. Dana Bussell, U. S,Navy Electronics Laboratory, San Diego, California. The source of each analysis is indicated in the last column of Table 5*

Coarse fractions of all samples vere analyzed by sieving. Fine frac­tions prepared by the project sedimentation laboratory vere analyzed by the hydrometer method; the others vere analyzed by pipette. Besults indi­cate fairly good agreement between the two methods.

85

Cumulative curves vere prepared from the analyses from vhlch the median (M) , first quartlie (Ql) and third quartlle (Q3) vere obtained (Bruiribeln and Fettijchn, 1938, pp. 229-233). From this Information the geometric quartlle deviation (So) and log quartlle deviation (log^So) vere computed. A summary of these figures is given in Table 5*

Percent shell vas determined by estimation of the amount in each size grade as the samples vere velghed during analysis. The sum of the shell percentage In all size grades Is used as total percent shell. This method Introduces errors to be sure; however, because most of the shell is present in fragments larger than silt, and even very fine sand, the discrepancy Is very small. The percentage shell of each sample is also presented in Table 5.

Twenty-two samples vere used for determining organic content of the sediments. Each of the samples vas velghed, then boiled one hour In ten percent hydrogen peroxide, and rewelghed. The difference in weight before and after boiling is used as the amount of organic matter, other than shell, present. Data on organic content is likewise indicated on Table 5.

The glauconite and pyrite content of samples vas estimated. As each sample vas examined for Foramlnifera, the relative abundance of glauconite vas recorded. A slide of Moodys Branch greensand from Montgomery landing, Louisiana, considered of high glauconite content, vas used as a standard for "abundant glauconite", and each sample vas graded accordingly. Relative abundance of pyrite vas not recorded, as it Is always rare when present.

Sediment TypesSediments of beaohes and vater bodies are divisible into six types

(A through F) as shown on Figure 32. These groups overlap and grade into

Figure 32

.001.0039.250 .1252j0100100

-9090-

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-4040-

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2020-

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PEBBLE CRANULeICOARSE COARSE MEDIUM FINE I I SAND I SANO I SAND I SAND

.002.250 .125VERYFINESAND

SILT CLAY

SEDIMENT MEDIAN LOG 10 PERCENT PERCENT PERCENT PERCENTTYPE SIZE So SHELL SAND SILT CLAY

A .I30-J85 .018-084 0-10 99-100 0-1 0B .073 -J28 .054-197 0-10 7 0 - 95 5 -3 0 0 -5C .056-076 J35-595 0 -2 4 0 -8 0 15-55 5 -2 5D .006-037 .431 -3 4 2 0 -5 5 -3 5 25 -75 2 0 -4 0E .230-L28 .152-649 25-95 5 -7 5 0 • 0F J62-230 .469-315 4 5 -7 0 15-45 5 -3 5 5-10

00cr*

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one another in most cases; nevertheless, curves of each class are distinct. She classes vere established by plotting all analyses together and then separating the groups. The table belov Fig. 32 sumnarlzes the sediment types shown on that figure.

• Grain Size

Sand BeachesSand beaches are essentially confined to Ghandeleur and Breton Islands.

All samples on them fall into the fine sand group (A); however, several trends are noticeable. Sorting by vave current aotlon results in an in­crease of about one-third in median size from the nearshore Gulf samples to those on the Ghandeleur Island beaches. On the islands themselves there appears to be a slight Increase in median size toward the ends of the Island chain. Ihere is also some indication that portions of the islands which are frequently avash during storms contain slightly finer material than higher portions of the islands (contrast Profile 13 and Profile iJj, Table 7 ). There is also a great difference in median size between the Chandeleur Islands and Cat Island. Medians reach a maximum of 0 .1 8 mm. on the Ghandeleurs but average about 0 .3 mm. (medium sand) on Cat Island (Nos. 131-136, Table 5)•

Grain size data of beach profiles are listed on Figure 33 and Table 7 . Ihere is no consistent size variation between water level and first berm samples; however, size Increases between the first and second berms.Where dunes are present behind the berms, no consistent size difference between the two is apparent. At the rear of the beach, where it overrides the mangrove swamp, only four samples vere analyzed. Each is slightly coarser than other samples in its profile, but there are not enough samples to be conclusive. Considering the length of the islands, the number of

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.151 .151 .171 .052 .038 .043.150.047

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.155.050.151 .150 .152 .059 .068 .057

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Water Level .170.054

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Upper figures of each sample - Lower figures of each sample -

Median grain size Log^ quartlle deviation

Beach Sediment Analyses - Breton and Ghandeleur IslandsTahle 7

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profiles is so few, and else differences between portions of the beach are so small, that this comparison offers only a suggestion of grain size distribution on Breton and Chandeleur Islands,

Shell BeachesBeaches composed predominately of oyster shell fall Into the category

of type E sediment. Such beaches are restricted to mainland marsh islands, notably Isle au Pitre, Door Point, Mitchell Keys, Gardner Island, and Pass Feraandea, and Freemason and North Islands In Chandeleur Sound.

Small beaches, composed predominately of Bangla cuneata. occur atmany placeB In the lakes, but no samples from them have been analyzed.

Only four samples vere analyzed from oyster shell beaches. The vide variation In percent shell (2k to 9*1%) results In similar vide varia­tion In grain size. Summary of these analyses Is found In Table 5.

S Water BottomsThe most widely distributed sediment types In the area are B and C

which bottom Chandeleur and Breton Sounds. The nearshore Gulf samples obtained from P. Dana Bussell also fall Into type B. Sediment of type B is prominent In the northern and central two-thirds of the sounds and type C, in the southern and vestern third. A narrow zone of type C andone sample of type D is found in the deep channel of northeastern BretonSound (Fig. 3l<), Median grain size of the sediment at each sample loca­tion is shown on Fig. 33.

Limits of types B and C are veil demarked ty the 0.05 median grain size contour. This line approximates the Inner edge of the sounds north to Bayou La Loutre and then extends In a northwesterly direction across lkrum Bay. The 0.05 median grain size contour, also enoloses type C sedi­ment In northeastern Breton Sound. As contours on Figure 33 Indicate,

91

slightly coarser sediments are found In northern Chandeleur Sound than In southern Chandeleur and Breton sounds.

Type D sediment bottoms the marshland lakes and Innermost sound areas south of Bayou La Loutre. One Isolated sample has been found In the deep channel of northeast Breton Sound. Nearly all water bottom sediments Inland of the 0.05 contour, with the exception of shell reef samples, belong to -type D.

Shell reefs form a distinct sediment class, type F. The reefs sre composed chiefly of Crassostrea vlrglnlca In a matrix of silt and clay.The variations In grain size result from both size and abundance of oysters In the samples. Oyster reefs are present In many marshland lakes, but most notably at Christmas Camp, Calebasse, Fortune, and Coqullle lakes (Fig. 1). One large reef area has been discovered In central Chandeleur Sound and Is shown on the hydrographic contour map (Fig. 31) by the closed six-foot contour Just east of Comfort Island (Fig. l). The other areas of Isolated six-foot contours along the inner margin of Chandeleur Sound are probably reefs also, but have not been sampled.

SortingUsing geometric quartlle deviations (So), Trask established a set of

values for different degrees of sorting (Krumbein and Pettijohn, 1938, p. 232). In thiB paper log quartlle deviations will be used Instead of geometric quartlle deviations, because the former compose an arithmetic series and have valueB which are directly comparable to each other. Trask's geometric quartlle deviation values and equlvllent log quartlle deviation values are given below.

92

geometric quartlle deviation log quartlle deviationVeil sorted.... Normally sorted Poorly sorted..

less than 2 .5 about 3 .0 greater than k .5

Iosb than O.39B about 0.1*77 greater than 0.653

On Figure 3 the log quartlle deviation is plotted for eaoh sample loca­tion, - The entire area Is contoured to show the sorting variation. Very good to very poor sorting occiirs and it Is apparent that the sediment types are dependent on sorting as veil as on grain size for their differentiation.

The most perfectly sorted sediments in the area (type A) occur on the sand beaches. The log quartlle deviation of samples from beach profiles is presented on Figure 31* and Table 7 . Longitudinally, sorting is quite uniform and no trends are noticeable. There are,however, some differences in samples taken along profiles across the beaches. In most cases sorting values decrease from water level to the first berm and again from thefirst berm to the second. Sorting values of dunes vary a great deal. The best sorting of all is found In several dtane samples, but others show little difference from berm or water level samples, Because of lnsufflolent data, samples from the rear of the beach are difficult to evaluate but appear as well or better sorted than berms or most dunes. At least, the

v few samples taken are definitely better sorted than water level samples.It has been noticed that frosting of sand grains Is not particularly

conmon on the beaches. Furthermore, frosting of dune sands Is not noticea­bly greater than froBting of other beach sands.

Beaches

Water BottomsBest sorting of vater bottom sediments occurs In a narrow zone of

south Ghandeleur and north Breton sounds and In the northern Gulf samples.

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CATEISLAND

.59

LO G Q U A R T I L E DEVIATION

S T BERNARD PARISH, LOUISIANA

EXPLA NATIO N£ SAMPLE LOCATIONS

• LOG QUARTILE DEVIATION 117 OF SAMPLE

S 4 3 2 I O * 10

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* - > u j j ! / / 1

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y y y

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Figure 34

This type B sediment has log quartlle deviation values below 0.1. In northern Chandeleur Sound samples and southern Gulf samples values rise slightly above 0.1 accompanying a slight general rise In median grain size (compare Fig. 33 and Fig. 3*0. The most poorly sorted -type B sediments are those which have five to ten percent shell mixed with the other constituents.

Type C sediment Is more clearly demarked from type B by sorting than by grain size. This "normal" sorting Is well displayed in the deeper partb of northeastern Breton Sound.

"Normal" to "poor" sorting occurs In type D sediment. In the marsh, land lakes this type occurs west of the 0.5 contour (Fig. 3*0, sad In the sound -type D Is confined within the same contour.

Percent ShellShell has tremendous effect on both size and sorting of a sample.

This Is clearly displayed by the cumulative curves of sediment types E and F (Fig. 32) in which shell content is high.

In most samples shell constitutes less than two percent of the total. In marshland lake reefs, shell was found to form 55$ to 69$ of the sediment and In the central Chandeleur Sound reef shell constitutes 23$ to 51$.Shell beaches contain from 24$ to 94$ shell. Other areas of higher than normal shell concentration lie close to the upper Blopes of the two deep topographic depressions traversing Chandeleur and Breton sounds (Fig. 31 and Fig. 35).

Organic ContentGenerally speaking, organic content Increases as grain size decreases.

The reason lies in the fact that most fine material Is found In lakes, and coarser sediments In the sounds. This relation Is only incidental to grain

I

IWOCX MAP

ATOMLAKC CHARLCS

flAYOU

QUILLC LAKE ATHANASIO

LOUIS

LAKCCALCBAS

v LeDCj*55’ 54.4

.GARDNERIS LA N D40

3.97

P E R C E N T S H E L L IN S E D IM E N T

ST BERNARD PARISH, LOUISIANA

EXPLANATION| SAMPLE LOCATIONS• SHELL CONTENT, PERCENT

a51 OF SAMPLE

a 4 3 2 I 0 5 10

>tn•<?

ztfso*

W f \ \ \v\^ \ N> v \ v

1.47

+

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116-20

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£<Cy 2.51 30*0.30

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Figure 35

VfKf

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size, as fine materials found In Breton Sound have lov organic content values similar to other sediments of the sound. Relatively high organic content of the lakes is a result of their proximity to the marsh.

Organic content composes nearly one percent of the sound sediment. This rises to two percent near the marshland border and then gradually Increases to five percent In Lake Lery (Fig. 36). All samples analyzed came from fairly large lakes. If samples from small enclosed ponds or the marsh Itself had been examined, much higher arganlo content values would certainly have been obtained.

The only two reef samples examined displayed slightly lower organic content than nearby sediments. Two samples offer a suggestion that this may be the case In other reef sediments.

Glauconite and Pyrite Content Glauconite Is present In sediments from marshland lakes, Chandeleur

and Breton sounds, and a few beaches. It is not abundant anywhere in the area. Figure 37, showing the distribution of glauconite, indicates that it Is more consistently present and more abundant in northern Chandeleur Sound than anywhere else In the area, lhis section, In general, corres­ponds to the area of coarsest bottom sediments other than shell reefs.Pyrite has been observed only In four samples. Two occurrences are in lakes (Nos, 2 and 13, Fig. 31) and two, In the innermost sound south of Bayou La Loutre (Nos. 14 and 40, Fig. 31). Other Information concerning these samples is found In Table 5.

Lake and Sound History as Determined from Cares Fourteen cores have been taken in lakes Athanasio, Calebasse, Lery,

Robin and Hope dale Lagoon. From these cores several facts concerning the sedimentary history of these lakes can be ascertained. Same of the cores

S H f tm r o n r

INDEX MAP

ATOMa LAKC C H A A LtS

t b o u o r e a u k

K:* ; P ,,S

• "S H C LL ISLANO % f \ LAK E9

/ z

t£io- _ | _

^ 4.81

d "

H.AKC \ ICOQUILLC 77W CAN LOUIS

A f f l RODIN3.23

iir^

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zsz

aAiias« LAKC

LAKC * ATHANASIO '

s e?CATE

ISLAN D

/14

^ SARONER

=y c— ^

ORGANIC C O N T E N T

ST BERNARD PARISH, LOUISIANA

EXPLANATION• SAMPLE LOCATIONS •

• ORGANIC MATTER, PERCENT115 OF SAMPLE

S 4 3 2 I O

«. •<* •-,tH

ISLAND 402.69

■E T

471.06

4 •

N

48

iii°* | +

All PITRE

110-20

)U 0 R tA U X1 1 4 -1 0 #

54 ^ *

CO-13

S H C L L IS L A N D L A K C

%

FREEMASON SLA NOUOBGAH

'Sa-WJif<iy 1.79

G A T EISLANO

0.45

0.49

5 8 - 7

SO-2

Figure 36

INOCX M A P

IATOM

iL A fte CMAALCJ

^ BOU0«tAUX

^ t P '£

SHELL ISLAND/\ LA** J

ISLAN DCDQUILLC / LAKE ^ ATHANASIO

\JT, L A K EMANIAS—L 10 —4V R« LAKE

C A LE8A 3S C

VR

40G L A U C O N I T E C O N T E N T

47

. 4- -

ST BERNARD PARISH, LOUISIANA 48

EXPLANATION. SAMPLE LOCATIONS • APPROXIMATE GLAUCONITE R CONTENT OF SAMPLE C-COMMON, R-RARE, VR-VERY RARE

O-ABSENTU lL tS

ISLEA U P IT R E

ne-20

^tST K*RAKO BAr 114-10

^ t F > <

C O -13

s h e l l isl

I A “ *c0 y / . a

FR E E M A S O N IS L A N DVOROA«*

fo-W4/3 8 V R

C A T C IS L A N D

5 8 -7

Figure 37

In Lake Lery show' silts hurled heneath present lake bottom sediments. These silts are remnants of farmer distributaries which trend from north to south across the lake (Fig. 2). Second, In Lake Calebaase at 1.5 feet below the present bottom and In Hopedale Lagoon at 2.5 feet below the present bottom definite marsh deposits have been encountered In two of the cares. Lake bottoms have built up as a result of erosion, subsidence and reworking of the marsh deposits buried below the lake bottom as the area subsided.Third, three cores taken in Lake Robin revealed a lack of shell at the bottom, a zone of little shell, and an upper zone of abundant shell. Most of the Bhell Is Mullnla lateralis. This sequence occurs In the upper 1.5 feet of sediment and apparently indicates a gradual Increase of salinity In the lake.

Bottoms of the lakes are oxidized in the upper few millimeters. A light brown film of ferric compounds forms the oxidized zone, and dark gray ferrous compounds abound below. Both lake and sound sediments seldom show any trace of bedding. Deposition In this area Is rather slow and sediments contain many polychaetes and mollusks which continually destroy any bedding that is developed.

Logs have been examined of three borings in Chandeleur Sound made by the U. S. Amy Engineers. They show an upper seven foot zone of gray, silty clay and silty sand underlain by gray clay or silty day to a depth of UO feet where the borings end. This upper seven foot zone apparently represents reworked material resting on sediments of the former St. Bernard subdelta. Subsidence has allowed the reworked zone to accumulate to this thickness.

SummarySix sediment types have been established according to their cumulative

100

curve characteristics. Median diameters vary between extremes of 0.006 and 1.28 millimeters (clayey silts to very coarse sand, Wentworth grades). However, samples with median diameters larger than fine sand contain a high percentage of shell and crwe their size to this factor. Sorting ranges from excellent (log quartlle deviation less than 0 .1) on the Chandeleur Island beaches, in the Gulf Just seaward of the Islands, and In part of Chandeleur and Breton sounds, to poor (log quartlle deviation greater than O.653) In marshland lakes.

The finer and more poorly sorted sediments generally occur In the lakes, while coarser and better sorted material Is found In the Innermost Gulf and beaches. Exceptions occur In shell reef and shell beach deposits where sediment Is coarse and generally poorly sorted.

Finest and most poorly sorted of sound samples are found In north, eastern Breton and southeastern Chandeleur sounds. All type D and most -type C sediment In the sounds Is concentrated In that area. This fine material results from Influx of sediment-laden Mississippi Elver waters from the eastern passes of the Elver. The material Is carried north between Breton Island and the mainland by Incoming tides and dropped as the tidal current fans out and meets a similar current which sweeps down from northern Chandeleur Sound. Little new material Is added to the sediments of northern Chandeleur Sound and tidal scour Is allowed to winnow out the fines. This accounts for the relatively coarse sediments found In that area.

Little variation occurs In either size or sorting over the Chandeleur Island beaches. However, grain size Increases about one.third between the shallow Gulf samples Just seaward of the islands and the beach Itself.

Grain size analyses of Cat Island and Sand Eidge, Mississippi, chenier sands reveals their sediments to be approximately twice as coarse as

101

Chandeleur Island sediment. Furthermore, the heavy mineral suite of Cat Island closely resembles that of beaches farther east along the Gulf Coast, and that of the Chandeleur Islands resembles the Mississippi River suite (Dobm, 1936, pp. 381, 382). These facts alone show that Cat Island Is of a different origin than the Chandeleurs and Is not the result of wave attack on deposits of the former St, Bernard subdelta which formed the Chandeleurs. Cat Island Is part of a series of cbenterspresent long before the advent of deltaic deposition in this area.

Shell normally makes up less than two percent of the sediments In this area; however, in shell reefs the percentage rises to a high of 69

and reaches In one shell beach sample.Organic content Is very low throughout the sounds. It reaches a

value of two percent at the marsh land, sound border and gradually rises to a high of five percent in Lake Lory. Higher values are undoubtedly present in small ponds and in the marsh, but samples from these have not been analyzed.

Glauconite is concentrated in north Chandeleur Sound, an area of relatively coarse, well sorted sedimentB, but occurs in lake and soundsamples throughout the area. It is never abundant.

ECOLOGY OF FORAMINIFERA AND MOLLUSCA Biogenetic components form a significant part of the deltaic and

marginal^ marine sediments of southern Louisiana. Of the potential fossil forming animals, Foraminifera and Mollusc a are two of the most widely used in atratigraphic and environmental studies. Quantitative and qualitative analyses of the ahove forms served as a foundation for interpretation of the deltaic sequence from bore hole data (see marsh section).

"Water PropertiesInterpretation of statistical analyses of Foraminifera and MolluBca

requires physical information concerning their habitat. Water bottom sediments have been discussed and data on the water follows.

Only limited data on salinity, temperature, and pH of waters of the area are available. Most were obtained while samples were being collected and, consequently, do not show seasonal fluctuations in these properties.

Salinity ranges obtained during sampling in March, June, and August,1953, and another set obtained during January, 195k, are listed below.

Salinity in Parts per Thousand March, June, August, 1953 January, 1954

Inner lakes (sample nos. 1-8) 11.5-16.5 6.3-10.5Outer lakes (sample nos. 9-16) 17.9-22.U 10.5-12.3Inner sound (sample noa. lU, 17, 21,

22 , 26, !*0, 1»6) 21.1*_2l4.6Central sound (sample nos. 18, 19, 23, 2k, 27-29, M-^3, U7-U9) 2k.1-27 .6

Outer sound (sample nos. 20, 25, 30, H , 1*5, 50) 2k.6.28,k

102

103

The salinity distribution pattern recorded from July 31, 1953, to August 2, 1953, is shown on Figure 38. The paths of tidal invasion into the sounds are demarked by salients of high salinity penetrating from the north and south.

Salinity during spring months is usually lower than during the rest of the year. High spring discharge from both the Mississippi and Pearl rivers is carried into the area. In addition, rainfall is normally high during spring and early summer and diminishes in the winter months. The effeot of fTesh water discharge Into Mississippi Sound Just north of the project area is shown by Owen and Waters (1950, pp. 333, 33*0 and Butler (1952, pp. 18, 19) and Gunter (1953, PP. 37, ^0, 1*2, 63-71), In summary, it is found that approximate salinity limits can be set for the various water bodies:

Surface water temperatures, compiled from observations during sampling and from published reports (Butler, 1952, pp. 18, 19 and Gunter, 1953, PP. 63-71), show variations between 13* and 31° C. Readinga taken during sampling show little difference between lake and sound temperatures.

Data on pH were collected during one trip to the area on January 27, 195^, and also taken from Butler (1952, pp. 18, 19) and Gunter (1953,PP. 63-71), Headings are available only in the lakes and the innermost sound. The extreme variation is from 7.1*2 to 8.15. A traverse from inner lakes to the inner sound was rim, and no trend in values was noti­ceable. However, Butler (1952, p. 9) reports that in Mississippi Sound, "High readings usually paralleled high salinity levels and low pH values accompanied low salinity levels, 11

Lakes........Sounds...... ,'Nearshore gulf

5 - 2 0 0 / 0 0 15-30 0 / 0 0 25-35 0 / 0 0

SMRCVtfOAT

IATON

iCAKC CHARLES

^ 5OUORE.AUK

SHELL ISLAND f\ LAKE i

16.511.5

c d q u i l l c ISLAND'

22720,4 ’Lo

23.724.1

S A L I N I T Y D I S T R I B U T I O NSURFACE WATERS ANALYZED

7/31/5 3 TO 8 / 2 / 5 3 ST BERNARD PARISH, LOUISIANA

4624.6

26- <r

EXPLANATIONSAMPLE LOCATIONS

# SALIN ITY OF SAMPLE IN 2&3PARTS PER THOUSAND

M ILES

loh

ISLEAU PITRE

26.1< r* HOUOREAUXB A* yrt*T KiRA«o bay.

f t * *> ;27.5

25 .502

23. B'

S H C LL ISLA N O[\ l-AKt i

2027.6

24

27.623

26.022

23.4

20.9

0039It r e c m a s o nISLAND27

23.510;

. / VHy 25.627.3

32 9433ISLANO* 34 SO3730

2 2 7* ISLAND ^023.7 42

24.624.1 '43

25.4

9044

27.5

25

60-726

24.

V77-J

V . _____ >.a

Method of StudySediment samples collected from St. Bernard Parish vere examined

for Foraminifera In order to establish faunal distribution patterns and determine environmental factors responsible far these patterns. While examining the samples it became apparent that a considerable number of Mollusc a were present, and their study seemed warranted even though the samples were rather small.

During field wart approximately one pint of sediment was collected at 47 of the sampling stations shown on Figure 31. Field samples were flrBt screened through sieves with openings of 1.0 millimeters. The finer fraction was reserved for faraminiferal analysis and the coarser, for molluscal. From the coarse fraction of each sample, the total number of Mollusca was ■ counted. The number of specimens in each sample was then assigned a value as follows:

Mollusca are reported in this manner because of the relatively small number of Individuals in each sample, the somewhat unequal size of the samples, and the random collection of some samples along beaches. Dis­tribution of the Mollusca is shown on Table 8.

The fraction to be examined for Foraminifera was washed through a screen having 0.074 mm. openings. Each sample was then reduced to examination size by being passed through a microsplit. Following this, the sample was again divided into coarse and fine fractions by being passed through a sieve with openings of 0.147 Samples were then placed under the microscope and generally 300 to 400 specimens were counted. All material observed was then weighed, and total population figures were calculated to give the number of specimens per gram of

1-3 specimens .4-10 specimens Mare than 10..

BareCommonAbundant

106

washed sediment. Total populations of "both coarse and fine fractions are presented In Table 9. Bis percentage of each species within a a ample was computed separately far the coarse and fine fractions and Is shown In Table 9. Distribution of the mare common Foraminifera and Mollusca Is shown on Figures 39 and 1*0.

Deducing total population figures to the number of specimens per gram of sediment has one disadvantage. A greater volume of original sample of fine marsh and lake sediment is required to make a gram of weighed sample than of the relatively coarse sound and beach sediment. Benefits of this method over the more standard procedures are speed of analysis and derivation of a constant against which the total population of samples can be compared. If used again, the method would be altered to make use of equal volume of original sample rather than equal weight of washed sample. Nevertheless, the method preserves the overall rela­tions of population distribution.

Examples of species reported are on deposit in the Louisiana State University Geology Museum.

Description of EnvironmentsFour environmental facies and one subfacies are recognized in this

area. The nearshore open gulf facies is found seaward of the Chandeleur Islands. Salinity in this fades is between 25 o/oo and 35 o/oo, water is In excess of 20 feet in depth, and the nearshore gulf floor Is composed of fairly clean sands In most places. Many nearshore open gulf species are washed onto the Chandeleur Islands, and the assemblage there Is considered a beach subfaoles. The sound facies includes Breton and Chandeleur sounds where salinities range from 15 o/oo to 30 o/oo, average water depths are ten to 20 feet, and the bottom sediments range from

107

!i

I

iiI

LOCATION INNER LAKES OUTER LAKES SOUND

STATION I t A S • TlS sisPELOSPHAERA ? SP

•VALVULINERIA*” SP

AMMOTIUM PSEUDOCASSIS

US

3>C l

TROCHAMMINA COMPRIMATA

TROCHAMMINA INFLATA

ARENOPARRELLA MEXICANA 0 X 1TROCHAMMINA MACRESCENS

HAPLOPHRAGMOIDES WILBERTI

AM MOASTUTA SALSA T>HAPLOPHRAGMOIDES MANILAENSIS

MILIAMMINA FUSCA

AMMOTIUM SALSUM

ELPHIDIUM MATAGORDANUM

ELPHIDIUM GUNTERI

ELPHIDIUM LIMOSUM

AMMOBACULITES SP I

•ROTALIA* BECCARII TEPOA

•R O TA LIA * BECCARII FWRKINSONIANA

AMMOBACULITES DILATATUS

ELIPHIDIUM POEYANUM

MILIOLIDAE

EPONIDELLA GARDENISLANDENSIS

NONIONELLA SP CF N. AURIS

BULIMINELLA ELEGANTISSIMA

AMMOBACULITES EXIGUUS

AMMOSCALARIA PSEUDOSPIRALIS

BOLIVINA STRIATULA

ELPHIDIUM INCERTUM MEXICANUM

HANZAWAIA STRATTONI

TROCHAMMINA LOBATA

* m u d x i m a n

~ I~ T

J_L3X ~i— r

<D=■ i

m rrn=axpx rr tr r i>i i_i_i_] i i>i —1~ t~

i— LJ= aXE

<x

< = G Z

<n

O 0-10% < > 1 0 -3 0 % ^ ABOVE 30% OF SAM PLE

Figure 39

OUTCH LAKtlLOCATION MMCII IA M U

STATION

PELECYPODA

VOLSELLA 0EMI33A CRAN0SI331MA

RAN CIA CUNEATA

TELLINA VERSICOLOR

MULINIA LATERALIS CORBULOIDES

BRACHIDONTES RECURVUS

CiQZ IXKC I>3ZE=cxiCRASSOSTREA VIRONICA

ABRA AEQUALIS

CRASSINELLA LUNULATACORBULA SP

OOSINIA DISCUS

MACOMA TACELtFORMIS

TRACHTCARDNJM MURICATUM

TACELUS DIVISUS

LUCINA SP

ANADARA TRANSVERSA

NUCULANA CONCENTRICA

LUCINA MULTILINEATA

TELLINA ALTERNATA

DONAX TUMIDA

ANADARA BRASILIANA

ATRINA SERRATA

MERCENARIA MERCENARIA

DINOCARDIUM ROBUSTUM

BARNEA COSTATA

ANADARA 0VALI3AEQUtPECTEN IRRADIANSCONCENTRICUS___________

CASTROPODA

<03LITTORINA IRRORATAMELAMPUS BIDENTATU3 BOENTATUS____________LITTORIDINA SP

ACTEOCINA CANALICULATA

CREPDULA PLANA

ANACHIS OBESA

CERITHIUM SP

TURBONILLA SP

POLINICE3 DUPLICATU3

MITRELLA LUNATA OUCLOSIANA

OLIVELLA MUTICA

CERITHIUM MUSCARUM

ausycoN co n tr a r iu m

BUSYCON SPIRATUM

CREPIDULA FORNICATA

THAIS HAEMASTOMA HAYSAE

PHALIUM CRANULATUM

STROMBUS PUCILIS ALATUS

MUREX FULVE3CEN3 ?

OLIVA SAYANA

3CAPHOPODA

DENTALIUM TEXASIANUM

< I > — 0 - 3 3PECMEN3 ^ ^ - 3 - 1 0 SPECIMENS

< D > > 10 SPECIMENS

109

clean BandB to clayey silts. The lake facies Includes the countless marshland lakes. Salinities vary between 9 o/oo and 20 o/oo, water depths In most places are less than ten feet, and the sediments are silty clay and clayey silt. The marsh facleB occurs throughout most land In the area. Salinity variations are comparable with those of the lakes, and the sediments are organic clays and clayey silts.

Environmental Factors The distribution of Foraminifera and Mollusca is controlled by many

factors (Van Andel & Postma , 1954, P. 131 & Phleger, 1954, p. 603). The environmental factors considered are-.water temperature, hydrogen Ion concentration, sediment organic content, sediment grain size and water salinity. These properties were examined In order to determine the influence of each.

Water temperature. Seasonal temperature differences in this region are no more than 20* C., and variation between lake and sound surface temperatures Is negligible. In this shallow nearshore area It appears that water temperature exerts no control over local biofacies.

Hydrogen Ion concentration. Data on pH are available only In lakes and the Innermost Bound. Headings vary between 7.42 and 8.15, Butler (1952, p. 9) states that pH values rise with salinity, in which case pH might have some bearing on the change of fauna occurring as the sound is approached from the lakes. The rise of pH with salinity was not noticeable in -the line of readings taken between Hopedale Lagoon and Bay Eloi. Con­sidering the narrow limitB of pH change and the inconsistent change with salinity rise in the project area samples, pH Is probably not a great factor in limitation of these environments.

Organic content. Sediments of the sounds contain less than 2$

110

organic material, whereas marshland lake bottoms, which are continually supplied with vegetation, display values up to 5$ of organic content.In other words, organic matter Increases as salinity decreases, and it is therefore very difficult to differentiate the effects of these two environmental factors. However, the organic content is relatively low in water bottom sediments of the area and probably has only slight influence on Mollusca and Foraminifera distribution. Marsh species occur in sediment containing a great deal of vegetation, but whether or not organic content is the deciding factor in marsh species distribution has not been determined.

Grain size. Within the sounds both relatively coarse and fine sediments occur in zones of similar salinity. In fact, the finest sediments of the sound approximate the size of lake materials. Comparison of the distribution of diagnostic Foraminifera in lake and sound sediments with similar grain sizes reveals that great change occurs in both frequency of a species and presence of different species between the two areas. However, comparison of fine and coarse bottom sediments from the same salinity zone of the sound reveals very little change in foraminiferal distribution. Therefore, grain size does not control the foraminiferal distribution. Mollusca are not abundant enough to be treated as the Foraminifera above; however, dominant occurrence of a ttolluscan species within either the fine, "muddy" materials or the coarse, "clean" sands of the sound is strongly suggestive of at least partial distributional control by bottom sediments. Shells of the following molluscan species were found to be concentrated according to bottom sediment type.

Ill

"Clean" Sands "Muddy" Sands and "Muddy" SiltsAequlpecten irradlans concentricus Crassostrea virginicaAnadara transversa Macoma iageliformisAtrina serrata TTuculana sp.Busy con contrarium Tagelus“dlvisusBusy con spiraium Tellina versicolorBonax 'bumida Luclna sp.Mercenarla mercenaria Huculana acuta Oliva sayana Olivella mutica Tollnices" dupllcatus

No control of bottom sediment is apparent in the distribution pattern of other molluscan species. However, in the Gulf seaward of the Chandeleurs salinity is more uniform, therefore, bottom sediment grain size is undoubtedly a major factor in controlling the distribution of Mollusca as well as Foraminifera in the Gulf.

Distribution of most Mollusca and Foraminifera of this area does not seem to be principally controlled hy any factors thus far discussed. Fairly sharp environmental breaks ocour at borders of lakes, sound, and qulf with salinity boundaries of 5-20 o/oo in lakes, 15-30 o/oo in sounds, 25-35 o/oo in the nearshore Gulf. In addition it has been stated that fine and coarse bottom sediments from the same salinity zone in the sounds show little change in the distribution of most species. It seems that the gradual change of fauna from the lakes to the Gulf, concomitant­ly with the gradual change of salinity in that same zone, Indicates that salinity is the major factor controlling the distribution of Foraminifera and Mollusca in this area. Within their salinity range certain species, especially among the Mollusca, have a preference of bottom sediment type.

Great differences occur in total foraminiferal populations of the samples. Maximum population per gram of sediment between the sizes of 1 .0 mm. and 0 .1 ran. is about 2^,000 Individuals, and the mln-fming is one. Large populations ocour in the marsh and lakes and low populations are

112

found in the sound and on 'beaches. It might appear that total population decreases vlth increasing grain size; however, fine materials in sounds possess the same small populations that ocour in surrounding coarse sediments. Therefore, grain size is not the deciding factor vlth re- latlon to size of foraminiferal population.

In contrast to Foraminifera, molluscal population differences between lakes and sound are small, and total populations are low in both areas. Reefs, whether in lakes or sounds, are the only zones of high molluscal population, density in water bottoms. In most places, popu­lations are even higher in the marsh than on reefs.

Due to the large foraminiferal and molluscal populations in marshes and in places in lakes, it appears that local food supply is greater in those places, but from available data it is not possible to determine just what factors control this supply.

Species Distribution The four environmental facies of the area are: nearshore gulf,

sound, lakes, and marsh. Beaches are considered a subfacies of near­shore gulf. Beefs are not considered a separate facies because they have no effect on the foraminiferal fauna and although certain species of Mollusca are concentrated on reefs, none has been found entirely con­fined to reefs. Distinction can usually be drawn between species indi­genous to an environment and those which have invaded it. This is Indicated by alterations in species frequency as environmental boundaries are transgressed.

Nearshore Gulf Environment This facies occurs just seaward of the Chandeleur Islands. Publi­

cations, treating areas from Florida to Texas, were used to check the

113

occurrence of species indicative of this zone (Abbott, 195^ J Bandy, 19 Cary, 1906} Dali, 1809} Ladd, 1951} Maury, 1920, 1922; Morris, 195U Barker, Phleger, and Pierson, 1953} Perry, 1950} Phleger, 3951, 1951*} Phleger and Parker, 1951} and Pulley, 3952).

To some extent gulf Foraminifera are carried into the sounds by currents entering around the ends of Chandeleur and Breton Islands.Widely scattered gulf farms occur in lakes and lagoons and serve as evi­dence of current transport. However, the widespread, lew frequency occurrence of gulf foraminiferal and ttolluscal species in the sounds indicates that they have adjusted themselves to physical conditions there. As samples from the Gulf bottom were lacking, nothing can be said about the possible extension of brackish forms into the Gulf. Available literature seems to Indicate that what invasion does occur is limited to nearshore areas.

Foraminifera and Mollusca of beach samples consist mainly of gulf forms, although a few marsh and lake species are found. Presence of the latter results from retreat of the Chandeleur Islands over buried rem­nants of the St. Bernard subdelta and exposure of the delta material to marine erosion. Relatively high percentages of very few foraminiferal species are found on the beaches. This most likely results from destruc­tion of fragile farms by waves and concentration of strong tests along shore. To a lesser extent there is concentration of certain species of Mollusca shells (Fig. 4l).

Species listed below occur in the sampled area but are indicative of the nearshore gulf environment.

114

Fig. 4l Mollusca on boach, western spitof North Point Chandeleur Islands, (lat. 30*03'13 , long. 88*52 W )

115

Foraminifera MolluscaBollvlna lowmanl Bucoella cf. frigidaBuliminella of. paaaendor: ___________ ilegantisslma

Anadara transverse Architectonics nobilis Dlnocardlum robuatum Donax tumid a Lablosa plicate11a

lassendarfenslsElphldlum dlacoldale Eanzavaia strationim a n n m --------Nonionella cf. aurisyirgullria"pontonl

Another group of essentially gulf Mollusca occurs both seaward and land­ward of the Chandeleurs hut does not extend landward of the sand belt flanking the Islands.

Aequipecten lryadlans concentricus^ Atrlna serrata-]3usycon contrarium 5 Susy con splratum "Cerlthium muse arum'Mercenaria mercenaria^Oliva seyansQ

The following Foraminifera reach optimum frequency in beach samples:

Species abundant on beaches but also abundant In water bottom samples aze:

A few species are restricted to Chandeleur and Breton sounds. Many others are present but appear to have Invaded from either the Gulf or In­land lakes. The sounds, therefore, are essentially a mixing area. Pre­dominantly gulf Foraminifera which are present in low frequency In the sounds are:

Elphidlum gunter1 Elphldlum incertum mexloanum

El-phldlum ■poevanumllRotalla~ becoarll parklnsonlana

Sound Environment

5Living specimens found

116

Bollvlna lowmanl Bollvlna strlatula Buliminella cf. baBsendorfensis Buliminella elegantlaslma Djeoarbla flarldana Sanzawala strattonl Nonlonella of. aurla Pyrgo ap.Qulnquelocullna ape.Vlrgullna nontonl

Mollusca occurring In both sound and beach samples and reported from thenearshore Qulf are listed below. In many cases It is not known whetherthey reach their zenith in the Ctulf or sounds.

Abra aecualls Anaohls obesa Anadara transverse Cantharus canceller la’Corbula sp.Craaslnella lunulata Dental lum texaslanum Do sinla disous Luolna multlllneata Mltrella lunata ducloslana Perlnloraa inequale Poltnlcea dunllcatus Tellina alternate Turbonllla sp.

SpeoleB which best distinguish the sound environment are listed below.They are almost exclusively confined to the sound In the sampled area andhave not been reported In other papers as prominent In the Gulf.

Foraminifera MolluscaAmmobaoulltea dllatatus Bittlum varlumAmaosoalarla ■pseudosplraliB Maccma tagellformlsEponldella gardenislandensls Nuoulana acutaTrochanmlna lobata Tagelus dlvlsus

Extension of gulf Foraminifera Into the sound Is matched by a similarInvasion of the sound by Foraminifera from the marsh and lakes. Mostare restricted to the Inner and central portions of the sounds. For ami-nlfera listed below are marsh and lake spoolss found in the sounds:

117

Ammot-tim salsum Elphldium matagcrdanum Haplophragmoldes vllbertl Mlllammlna fusca

Lake EnvironmentThe lake environment le restricted In speoles but abundant In indi­

viduals . Only one foraminiferal species, Amnobaoulltes sp. 1, and no Mollusca are entirely confined to lakes, nevertheless, Ammotlum sals urn, Elphldlum llmoBum, and Rangla cuneata are most abundant In the lakes and are probably Indigenous to them. Elphldlum llmosum and Kang la cuneata do extend Into the sound, and Ammotium salsum occurs rarely In the Gulf.The lake environment Is best Identified by the lack of distinctive gulf, marsh, or sound species. The following speoles ocour most cosmonly In the lakes:

Foraminifera MolluscaAmaobaculltes sp. 1 Aoteoolna canaliculateAmmotium salsum Brachldontes recurvusElphldlum llmosum Crassostrea vlrginlcaElphldlum matagordanum Crepldula planaHaplophragmoldes manllaensls Llttarldlna sp.Haplophragmoldes vllbertl Mullnla lateralis cprbuloldes

Rangla cuneata Tellina versicolor

Some marsh Foraminifera have invaded the lakes, but they form only a small percentage of the lake fauna and, In many oases, Individuals are smaller than In their marsh habitat. Slnoe nearly all marsh molluscal species are pulmonate, there is no such Invasion by Mollusca, but occasional­ly vashed shells of marsh speoles are found In lakes. Foraminifera vhich have invaded the lakes from marsh are:

Ammoastuta salsa Arenoparrella mexloana Millammlna fusea Trocfaammlna comprlmata frochammlna inflata TTochaamina macrescens

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Marsh EnvironmentMarsh facies seem to he the only group not invaded by fauna from

adjacent environments. All hut three forms reported from marsh are foundin lakes and a fev as far seaward as central Chandeleur Sound. However,the abundance of individuals nearly always decreases sharply as theoriginal marsh environment is left, and in many oases individuals aresmaller than in their marsh habitat. Only one species native to lakes,Amaotlum salsum. occurs in marsh and that, at low frequencies. Thereis little crossing of facies boundaries except movement of empty testsby waves and currents. The species confined to marsh are:

Foraminifera MolluscaAmmotlum nseudocasslB Llttorlna lrrorataPolosphaera ? sp. Melampus bldentatua hldentatus'^Valvullnerla11 sp, Volsella demises granoslsslma

In addition the following Foraminifera reach their maximum abundance inmarsh and are considered lndlgeneous to it:

Ammo astuta salsa Arenoparrella mexloana Mlllanmlna fusca Trochammlna comprlmata Trochammlna inf lata Trochammlna macrescens

Other MiorofossilsForaminiferal specleB which have been encountered very rarely in the

area and did not seem particularly important are not Included in Table 9.These species are:

Caflsiflullna sp.Clblcides sp.Globlgerlna sp.Qttnbellna sp.Hanzawaia sp.Lagena spp.Masaillna sp.Mlllolinella sp.Planullna sp.Pseudoclavullna sp.

119

Foraminifera are not the only common mlcrofosslls In the area. In addition there are (in order of abundance): Ostracoda, Dlatomaceae,Eadlolarla, and Characeae. Each of these farms occurs from the marsh through the sounds, but Radlolarla and Dlatomaceae are more common In the sounds, and most Characeae are found In the lakes. The Ostracoda are found In almost equal numbers in marsh, lakes and sound. None of these types approaches the abundance of Foraminifera. Annotated synony­mies of each speclea of Foraminifera and Mollusca are found in the appendix.

SummaryGeneral characteristics of each environment are listed below.

Facies Foraminifera MolluscaNearshoreOpen Gulf Facies Many distinctive species Many distinctive species

Moderate number of In­dividualsLittle invasion of brackish farms

.Moderate to abundant indivi­dualsLittle Invasion of brackish forms

Open Gulf Facies A few Gulf species are Beach subfacles dominant

Very few individuals Most fragile tests broken or destroyed

A few Gulf species are dominant Mazy individuals Most fragile tests bro­ken or destroyed

Sound Facies Few distinctive species Moderate number of indi­viduals

Few distinctive apeciBS Moderate number of in­dividuals

Essentially a mixing en­vironment between lakes and Gulf

Essentially a mixing en­vironment between lakes and Gulf*

Lake Facies Very few distinctive speciesAbundant individuals Lake environment invaded to some degree by marsh, sound, and even Gulf species

Very few distinctive speciesModerate number of indivi­duals, abundant In reefs Invasion by species from adjacent environments is limited

Facies Faraminifera MolluscaMarsh Facies Few distinctive species

Abundant individuals A few species traverse the boundary between lakes and marsh

Few distinctive species Abundant individuals Ho invasion of water bottom farms

GEOLOGICAL H38TQRT

IntroductionDuring the past several thousand years Orleans and St, Bernard

parishes have been the site of active Mississippi River sedimentation. Complex deltaic development has occurred, but the area is no longer re­ceiving sediment, and the processes of subsidence and marine erosion predominate.

Reconstruction of the deposltional history of the area vas accom­plished chiefly by study of the Interrelationship of various physio­graphic units. The age differences of many streams must be determined by using overlap, truncation, and superposition of distributary patterns. Faunal and sediment analyses of borings have helped develop the deltaic sequence, but the number of adequately deep holes Is Insufficient.

Combined with physical evidence, aroheological data (principally olasslficati'on of Indian potsherds) has been a most Important aid In deciphering the succession of subdeltas (Melntlre, 1954). When the Mississippi River vas flowing through this area, Indian habitation vas concentrated on levees, as they farmed the principal high ground. On these levees refuse sites (middens) are found vhloh often contain potsherds capable of being classified and dated. The established chronology of archeological cultures as developed in the lower Mississippi River Valley (Phillips, Ford, Griffin, 1951, p. 454) Is:

121

122

Culture DateHistoric 1700-dateNatchez 1500-1700Flaquemlne 1200-1500Coles Creek 850-1200Troyville 018

Marksvllle? 500- 700Tchefuncte 0- 500Archaic B.C.- ?

Where physical evidence Is insufficient, the minimum age of naturallevees can he established through classification of potsherds found on

cIndian oooupation sites situated on those levees.

Development of the Easternmost Louisiana Marshlands The probable sequence of events In the area investigated as pre­

sented on Figure k2 Is discussed below.1. Prior to the first deposition of Recent Mississippi River sedi­

ment this region vas an open embayment of the Gulf of Mexico. Land, other than Pleistocene terrace, vas confined to a series of barrier Islands or chenlers. The chenler trend Is distinguishable today from Ship Island, Mississippi, to a point a fev miles vest of Nov Orleans. Natural levees of Bayou Sauvage-Lesarle, one of the older streams of the area, cross and rest on these chenlers. In addition, Tchefuncte and possibly Archaic sites are present on the chenlers, but these stranded beaches probably predate Indian occupation more than a millennium (possibly 3000-1*000 years).

2. Some former lake beaches bordering parts of lakes Borgne and Pontchartrain are the next oldest exposed features of the area. In the

HFiek (19^, PP. ^3-M) has developed a stream chronology In Orleans and St. Bernard parishes. Some of the sequence does not agree vith evidence obtained In the present field vork; hence, Fisk's datings vlll not be used.

ea'oo'

TCHEFUNCTE PERIOD MARKSVILLE PER

ea'oo

COLES CREEK PERIOD PLAQUEMINE PER

123

AO 00\RKSVILLE PERIOD

8000LAQUEMINE p e r io d

TROYVILLE PERIOD

DEVELOPMENT OF THE ST. BERNARD SUBDELTA

[IH ACTIVELY GROWING DELTAIC AREA DURING PERIOD

B DELTAIC LAND DEVELOPED DURING PREVIOUS PERIOD

PRE-DELTAIC CHENIER DEPOSITS

LAKE CHENIER - INDICATING EXISTENCE OF PRE-TCHEFUNCTE DELTA MASS

SCALE10 0 10 20

STATUTE MILES

Figure k2

12k

vicinity of New Orleans these silty fanner lake beaches overlie the gulf chenlers. Several Indian sites In Orleans Parish and one site In St. Bernard Parish have yielded Tchefuncte potsherds from these lake chenlers, which Indicate that the chenlers are at least 1500 years old. The forma­tion of lake beaches has apparently been repeated several times in the past. Younger ridges nearer Lake Pontchartrain contain Coles Creek pottery, and older ridges, farther from the lake, contain Tchefuncte.On the north shore of Lake Bargne a farmer lake beach (Fig. 2) truncates levees, which necessarily implies an older age far the levees. However, no pottery has been recovered from either the chenler or leveeB so that their dates are unoartain. If this Is a Tchefuncte lake chenler, the abandoned distributary represents the oldest stream pattern preserved at the surface In the area. There was necessarily a very old delta present before the formation of lake chenlers could occur; however, no streams at the surface today have been proved to belong to this delta.

3 . Following, and possibly partly contemporaneous with, this subdelta was another dated ty its prevailing Marksville pottery. The oldest definitely datable levees belong to this period. The delta must have been of great areal extent, as Marksville artifacts are found from the Bayou Biloxi area to the Chandeleur Islands. At or Just before Marksville time the natural levee ridges radiating eastward from New Orleans began to occupy their present position and possibly formed the buried east-west leveeB of the northern Bayou Biloxi district. About this same time Bayou La Loutre extended its course at least as far east as the Great Bend, as is evidenced by Marksville sites In this area. La Loutre distributaries now extend north from the nartfaweBt comer of the Great Bend and pasB beneath marBh level. The fact that these levees abruptly branched east and west suggests that the Bayou Biloxi area levees

125

tentatively assigned to Sauvage are older and caused deflection of Marksville Bayou La Loutre distributaries (Fig. 2).

A Marksville Bite on the anastomosing pattern of streams found between the present Mississippi River and Bayou Terre aux Boeufs indi­cates that the river began foaming the network of channels associated with Blvlere aux Chenes at that time.

4. The anastomosing pattern of the Blvlere aux Chenes area,Initiated during Marksville, continued to grow during the Troyville period. This stream net covered the area from Bayou Terre aux Boeufs as far Bouth as Point a La Hache. At the same time distributaries originating from the southwest corner of the Great Bend of Bayou La Loutre occupied the area now covered by lakes Bobln, Coqullle, Cale- bass e, Machias, Fortune and the adjacent part of Chandeleur Sound.Today all levees In this area are beneath marBh but are still traceable.The fate of distributaries of the Bayou Biloxi area during this period is uncertain, but they were apparently largely abandoned. Contrasting physiographic expression separates the enclosed area of Bayou Biloxi marsh from the embayed double islands area to the east, and It appears that marine agencies eroded the Bayou Biloxi marsh westward to approxi­mately longitude 89* 28' Vest during Troyville. Indian pottery reveals a similar contrast In the two areas. In the Bayou Biloxi marsh Marks­ville pottery Is common, but the double islands area contains only Coles Creek and Plaquemlne sherds. If Bayou Biloxi marBh were being eroded during Troyville time, one would expect to find scattered shell beacheB such as those found along the inner border of Chandeleur Sound today. However, there has been about seven feet of subsidence of levees in the Bayou Biloxi area and such beaches, if present, are burled. As a result, none have been found. A good possibility exists that part of the Chandeleur

126

Islands originally formed from erosion of the Marksville delta at this time.

5. During Coles Creek time Bayou La Loutre distributaries extended eastward veil Into the area of Chandeleur and Breton sounds. Bayou La Loutre vas still the trunk stream and can still he traced as a submerged ridge some ten miles south Into Breton Sound (Fig, 31), Activity In southern St, Bernard Parish gradually declined during Coles Creek. Mean­while, the network of channels In northern Plaquemines Parish continued to receive Increasing flcrv.

Bayou Terre aux Boeufs originated during the Coles Creek Period.It branched southward from Bayou La Loutre, but encountered streams of the Blver aux Chenes net which were rapidly declining. ThiB caused deflection of Terre aux Boeufs both east and vest. The short segment to the vest extended Into the Lake Lery depression. The branch eastward first paralleled and then occupied one of the older Blvlere aux Chenes network of streams. This junction is shown on Figure 2.

6. Plaquemlne delta building vas simply an extension of ColesCreek patterns. Maximum extent of St. Bernard deltaic deposition apparently vas reached during this period. Plaquemlne distributaries continued to build over remnants of the Marksville subdelta In many places and needed only a small volume of sediment to occupy a large area. The delta extended east of the Chandeleur Islands, possibly north to the Mississippi Coast, and south an unknown distance beyond Breton Island. Meanwhile, the lover Mississippi Blver continued to extend, enlarge and stabilize Itself, so that by the close of Plaquemlne time the present river had become the dominant outlet. Discharge to the east waned and finally ceased with Bayou Terre aux Boeufs being the last active distributary. The St, Bernard

127

subdelta vas thus deprived of active sedimentation, and marine erosion ■became the dominant process. In the past U00 or so years the deltaic area In St. Bernard Parish has been reduced at least to one-third of lte maximum size.

The net result of Recent sedimentation In the easternmost Louisiana marshlands has been formation of a series of Interfingering lenses of deltaic and marginal-marine clays, silts and sands, the thickness and areal distribution of which changer rapidly. Biogenetlo components of the sediments also change rapidly with the altering environments. Transgressions and regressions of sediment types, blofacles and physio­graphic features extend up and down dip (east and west), while more uniformity of facies exists at any horizon along the generally north- south strike. The present marginal-marine sediments of eastern Louisiana are underlain by several gradational lenses of deltaic and inner-nerltic marine strata and appear to have formed under circumstances similar to certain deltaic-marine contacts of the Gulf Coast Tertiary.

SELECTED BIBLIOGRAPHYAbbott, R. T., 195b, American Seashells, Van Nostrand Co., New York, 5 *1 pp.Andol, T., van and Fostma, H., 19^, Recent Sediments of the Gulf of Faria,

Vol. 1, Ver. Eon. Nederlandse Akad. Vet., afd. Nat. Eerste Reeks,Deel 20, No. 5, 21*5 pp.

Bandy 0. L., 1951*, "Distribution of Some 8h allov-vater Faraminifera in the Gulf of Mexico", U. S. Geol. Surv. Frof. Pap. 25U-F, pp. 225-11*!.

Barnstein, Helmut, 1938, "Foraminiferen der meerlschen und brackiscben Bezirke des Jade-Gebietes", Senkenbergiana, B. 20, s. 386-U12.

Barton, D. C., 1926, "Meandering in Tidal Streams", Jour. Geol., Vol. 36,No. 7, pp. 615-629.

Brown, Clair A., 1936, "The Vegetation of the Indian Mounds, Middens, andMarshes in Plaquemines and St. Bernard Parishes", in "Lower Mississippi River Delta", Dept, of Conservation Louisiana Geol. Survey Bull. 8, pp. 1423-1*1*0.

_________ , 19l*5, Louisiana Trees and Shnubef, Louisiana Forestry Comm.,Bull. 1, 262 pp.

Brady, H. B., 1881*, Ohe Voyage of H. M. S, Challenger, Zoology, Vol. 9, pp. 13^-135 and 21*9-251, pl. 1, figs. 9-16.

Binney, V. G., editor, 1858, The Complete Writings of Thomas Say on the Conchology of the United States, H. Bailliere, New York, p. 2l*2,

_________ , 1863-1861*, Bibliography of North American Conchology, Smith­sonian Inst., Washington, Ft. 1, 650 pp., Ft. 2, 298 pp.

Butler, Philip A., 1952, Effect of Floodwaters on Oysters in Mississippi Sound in 1950", Research Report 31, Fish and Wildlife Service, U. S. Dept, of Interior, 20 pp.

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Cary, L. R., 1906, "A Contribution to the Fauna of the Coast of Louisiana", Gulf Biol, Sta., Louisiana State Board of Agriculture and Immigration, Bull. 6, pp. 50-59.

. and Spaulding, H. M., I909?, "Further Contributions to the Marine Fauna of the Louisiana Coast", Gulf Biol. Sta., Louisiana Bull., Bull. 11, pp. 13-21.

128

Cushman, J. A., 1944, "Foraminifera from the Shallow Water of the New England Coast", Cushman Lab. Faram. Bee., Spl. Put. 12, 37 PP*

_________ , and Bronnimann, P., 1948, "Some New Genera and Species ofHlrrrwwiir>4-p«r>ft from Brackish Water of Trinidad", Contr. Cushman Lab. Foram. Bes., Vol. 24, pt. 1, pp. 15-21.

, and Bronnimann, P., 1948, "Additional New Species of Arenaceous Faramlnlfera from Shallow Waters of Trinidad", Contr. Cushman Lab, Fooram. Res., Vol. 24, pt. 2, pp. 37-42.

Ball, W. H., 1885, "List of Mollusca Comprising the Quaternary Fossils and Recent Forms", U. S. Geol. Survey Bull. 24, 336 pp.

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, 1890-1903, "Contributions to the Tertiary Fauna of Florida", Trans. Wagner Inst. Sol. Phila., Vol. 3, pts. 1-6, 1654 pp.

Dapples, E, C., 1942, "The Effect of Macro-Organisms upon Near-Shore Marine Sediments", Jour. Sed. Petrology, Vol. 12, No. 3,pp. 118-126.

I>yke, Ray A., 1941, "Climate of Louisiana", in Climate and Man, U, S. Dept, of Agriculture, pp. 894-903.

Ellison, S. P., Jr., 1951, "Microfossils as Environment Indicators In Marine Shales", Jour. Sed. Petrology, Vol. 21, No. 4, pp. 214-225.

Fisk, H. N., 1944, Geological Investigation of the Alluvial Valley of the Lower Mississippi River, Mississippi River Commission, Vicksburg, Miss., 78 pp.

1947a, Geological Investigation of the Veterans Administra- tion Hospital Site, New Orleans, Louisiana, Unpublished Report,U. S. Arny Engineers, 39 pp.

, 1947b, Fine-Grained Alluvial Deposits and Their Effects on Mississippi River Activity, Waterways Experiment Station, Vicksburg, Miss., Vole, 1, 2, 82 pp.

, 19470, Geological Investigation of the Proposed Algiers Lookslte and Intracoastal Waterways Canal, Unpublished Report,U. S. Amy Engineers, 26 pp.

, 1952, Geological Investigation of the Atchafalaya Basin and the Problem of Mississippi River Diversion, Waterways Experi­ment Station, Vicksburg, Miss., Vols. 1, 2, 145 PP.

, Mo Farlan, E., Jr., Kolb, C. R., Wilbert, L. J.. Jr., 1954,"Sedimentary Framework of the Modern Mississippi Delta , Jour.Sed. Petrology, Vol. 24, No. 2, pp. 76-99.

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Fortier, Alcee, 19lh, Louisiana, Century Historical Assoc., Vol. 2, pp. h07-h08.Coyer, R. A., 1950, "The Occurrence of Pronounced Salinity Variations in

Coastal Louisiana Waters*1, Jour. Mar. Res., Vol. 9, PP. 100-110.Glaser, 0. C., 190*1, "An Incomplete List of the Fauna of Cameron, Louisiana",

Gulf Biol. Sta., Louisiana Bull., Vol. 2, pp. hl-h2.Goldstein, August, Jr., 19h2 ''Sedimentary Petrologic Provinces of the Northern

Gulf of Mexico", Jour. Sed. Petrology, Vol. 12, No. 2, pp. 77“8h,Gunter, Gordon, 1953, "The Relationship of the Bonnet-Carre Spillway to Oyster

Beds in Mississippi Sound and the 'Louisiana Marsh111 with a report on the 1950 Opening, Publ. Inst. Mar, Sci., Vol. 3, no. 1, pp. 17-71.

Hadley, Wade H., Jr., 1936, "Some Notes on the Recent Mollusca from Plaquemines and St, Bernard Parishes" in "Lower Mississippi River Delta", Dept, of Conservation, Louisiana Geol. Surv, Bull. 8, pp. h03-h06.

Harry, Harold W., 19h2, "List of Mollusca of Grand Isle, Louisiana, Recorded from The Louisiana State University Marine Laboratory 1929-19^1", Occa­sional Papers Marine Lab., Louisiana State University, 13 pp.

Hilgard, E. W., I87O, Record of the Examination of Specimens of Borings from the New Orleans Artesian Well, House Document 1, hist Cong., 3rd sees.,Pt. 2, Appendix L 2, pp. 352-361.

_________ , and Hopkins, F. W., 1878, Report upon the Specimens Obtained fromBorings Made in 187b Between the Mississippi River and Lake Borgne, at the Site Proposed for an Outlet for Flood Waters, House Document 1, h5th Cong., 3rd Sess., Pt. 2, Vol. 2, pt. 2, Appendix W 2, pp. 855-890.

_________ , l88h, "Physico-Geographical and Agricultural Features of the Stateof Louisiana", Tenth Census of the United States, Vol. 6, pp. 109-193.

Howe, H, V., Russell, R. J. and McGulrt, 1935, "Reports on the Geology ofCameron and Vermillion Parishes, Dept, of Conservation, Louisiana Geol. Surv., Bull. 6, 2h2 pp.

Johnson, Charles W., 193h, "List of Marine Mollusca of the Atlantic Coast from Labrador to Texas", Proo. Boston Soo. Nat. Hist., Vol. hO, No. 1, 20h pp.

Korafeld, M. M., 1931, "Recent Littoral Foraminifera from Texas and Louisiana", Contr. Dept. Geol. Stanford University, Vol. 1, No. 3, pp. 77-101.

Krumbein, W, C. and Petti John, F. J., 1938, Manual of Sedimentary Petrography, Appelton-Century-Crofts, Inc., New York, 5h9 PP.

_________ , and Aberdeen, Esther, 1937, "The SedimentB of Bar atari a Bay",Jour. Sed. Petrology, Vol. 7, No. 1, pp. 3-17.

Ladd, H. S., 1951, "Brackish-Water and Marine Assemblages of the Texas Coast, with Special Referenoe to Moilusks", Publ. Inst. Mar. Sci., Vol. 2,No. 1, pp. 125-163.

Loeblich, A. R,, Jr., and Tappan, Hollen, 1953, "Studies of Arctic Foraminifera", Smithsonian Miscellaneous Collections, Vol. 121,No. 7, pp. 9, 33.

Lowman, S, W., 19**9, "Sedimentary Facies in Gulf Coast", Bull. Amer. Assoc. Petrol. Geol., Vol. 33, No. 12, pp. 1939-1997,

_________ , 1951, "The Relationship of the Biotic and Lithlc Facies inRecent Gulf Coast Sedimentation", Jour. Sed. Petrology, Vol. 21,No. 1*, pp. 233-237.

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_________ , 1922, "Recent Mollusca of the Gulf of Mexico and Pleistoceneand Pliocene Species from the Gulf States", Pt. 2, Soaphopoda, Gastropoda, Amphineura, Cephalopoda", Bull, Amer. Paleo., Vol. 9,No. 38, 11*2 pp.

Mclntire, William G., 195**, Correlation of Prehistoric Settlements and Delta Development, Unpublished Dissertation, Louisiana State University.

Miller, N. D., Jr., 1953, "Ecological Study of the Foraminifera of Mason Inlet, North Carolina", Contr. Cushman Found. For am. Res.,Vol. 1*, pt. 2, pp. 1*1-63.

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_________ , Phleger, F. B., and Pierson, J. F., 1953, "Ecology of Forami­nifera from San Antonio Bay and Environs, Southwest Texas", Cushman Found. Foram. Res., Spl. Pub. 2, 75 pp.

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Fhleger, F, B., 1951, "Ecology of Foraminifera, Northwest Gulf ofMexico", Pt. 1, Foraminifera Distribution, Geol. Soc. America Mem.U6, 88 pp.

, 193k, "Ecology of Foraminifera and Associated Micro- Organisms from Mississippi Sound and Environs", Bull. Amer. Assoc. Petrol. Geol., Vol. 30, No. 4, pp. 504-647.

, and Parker, F. L., 1951, "Ecology of Foraminifera, Narth- vest Gulf of Mexico", Pt. 2, Foraminifera Species, Geol. Soc.America Mem. k6, 64 pp.

, and Walton, W. P., 1950, "Ecology of Marsh and Bay Forami-nifera", Amer. Jour. Soi., Vol. 248, No. 4, pp. 274-294.

»

Phillips, P., Ford, J. A., and Griffdn, J. B., 1951, "Archaeological Survey in the Lower Mississippi Alluvial Valley, 1940-1947",Papers Peabody Mus. Amer. Arohaeol. and Ethnol., Harvard Univ.,Vol. 25, -p. 454.

Post, Rita J., 1951, ''Foraminifera of the South Texas Coast", Inst.Mar. Sci., Vol. 2, No. 1, pp. I65-I76,

Price, W. A., 1947, "Equilibrium of Form and Forces in Tidal Basins of Coast of Texas and Louisiana", Bull. Amer. Assoc. Petrol. Geol.,Vol. 31, No. 9, PP. 1619-1663.

Pulley, T. E.. 1952, "An Illustrated Check List of the Marine Moilusks of Texas", Texas Jour. Soi., Vol. 4, No. 2, pp. 167-199.

Richards, H. G., 1939, "Marine Pleistocene of the Gulf Coastal Plain, Alabama, Mississippi and Louisiana", Bull. Geol. Soc. America,Vol. 50, pp. 297-316.

Russell, R. J., 1939, "Louisiana Stream Patterns", Bull. Amer. Assoc. Petrol. Geol., Vol. 23, No. 8, pp. 1399-1227.

, 1940, "Quaternary History of Louisiana", Bull. Geol. Soc. Smerlca, Vol. 51, No. 8, pp. 1199-1234.

Russell, R. J, et al, 1936, "Lower Mississippi River Delta", Dept, of Conservation, Louisiana Geol. Survey Bull. 8, 454 pp.

Shepard, F. P., 1948, Submarine Geology, Harper Co., New York, 348 pp. , 1952, "Revised Nomenclature for Deposltlonal Coastal Features"

Amer. Assoc. Petrol. Geol., Vol. 36, No. 10, pp. 1902-1912.Steinmayer, R. A., 1939, "Bottom Sediments of Lake Pontchartrain,

Louisiana", Amer. Assoc. Petrol. Geol., Vol. 23, No. 1, pp. 1-23.

Sonderegger, V. H., 1939, Classification and Uses of Agricultural and Forest Lands In the State of Louisiana and the Parishes, Louisiana Dept, of Conservation, Division of Forestry, Bull. 24, Vol. 8,p. 82.

U. S. Amy, Carps of Engineers, 1951, The Intracoastal Water]Vay, pt. 2, Gulf Section, p. 4.

U. S. Coast and Geodetic Survey, 1949, United States Coast Pilot, Gulf Coast, 3rd ed., p. 480.

_________ , 1951, Surface Water Temperatures at Tide Stations, AtlanticCoast, North and South Amsrioa, Spl, Publ. 278, p. 35.

_________ , 1953, Density of Sea Water at Tide Stations, Atlantic Coast,North and South America, Spl. Publ. 279, PP. 41-42.

Zerbe, W, B., and Taylor, C. B., 1953, "SeaWater Temperature andDensity Seduction Tables", Spl. Publ. 298, U. S. Dept. Commerce, Coast and Geodetic Survey, 21 pp.

APPENDIX

135

•Height of Bear Marsh Above Water LevelSwash Line Height

Number of Berms on Foreshore

Thickness of Beach

Composition of Shoreline

Height of Dunes Above Beach

Maximum Beach Height

Backshare Width (Flat)

Backshare Width (Dunes)

Foreshore Width

Total Beach Width

Location

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Table

2

136

Height of Bear Marsh Above Water LevelSwash Line Height

Number of Berms on Foreshore

Thickness of Beach

Composition of Shoreline

Height of Dunes Above Beach

Maximum Beach Height

Backshare Width (Flat)

Backshore Width (Dunes)

Foreshore Width

Total Beach Width

Location

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Table

2

137

Tide HeightWhen Surveyed

Number of Bars Observed

Distance from Share to First Bar

Maximum Water Depth Inside Bar

Minimum Depth of Bar

Batio a/b

Minimum Height of Bar (b)

Bar Width (a)

Location

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Number of Bars Observed

Distance from Shore to First Bar

Maximum Water Depth Inside Bar

Minimum Depth of Bar

Batio a/b

Minimum Height of Bar (b)

Bar Width (a)

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number of Berms on Foreshore

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Notch Height

Swash Line Height

Total Height

Width of Backehore

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Total Beach Width

Location

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Samp. Latitude Longitude Depth $Shell Organicno. 0 ' " • ' " feet content_______ m.s.l.

1 29 48 00 89 49 212 29 49 30 89 39 013 29 44 27 89 41 234 29 41 54 89 37 365 29 44 26 89 38 316 29 43 42 89 36 217 29 44 40 89 35 328 29 44 01 89 30 589 29 41 25 89 32 3610 29 42 06 89 30 1611 29 44 51 89273712 29 46 00 89 25 4613 29 39 36 89290714 29 42 30 89 23 0015 29 49 23 89 24 2916 29 54 09 89 15 5717 29 58 18 8908 1818 30 00 00 89 02 4319 30 01 09 88 58 3020 30 02 45 88 52 5721 29 51 32 8915 2422 29 53 12 89 08 4223 29 53 34 89 02 0624 29 54 27 88 58 1025 29 55 00 8853 0626 29 48 31 89 14 0027 29 48 00 89 08 4828 29 47 28 89 04 1229 29 47 12 88 59 1830 29 46 36 88560031 29 45 24 89 16 06

. .a a a a 4,812.5 a a a a —

aa m

3.0 *a«

5.8 0.59 3.7716.5 65.424.0 a a a . . .

3.0 1.02 3.235.0 44.755.5 3.66 . . .

5.0 4.95 2.526.0 0.35 a a a

6.0 54.40 1.309.0 I.23 . a a

4.5 69.13 . . .

6.0 0.95 0.656.0 6.15 1.3011,0 0,12 0.1616,0 1,28 . . .

10.0 0.44 0.114.5 0.08 . . .

10.0 1.10 . . .

15.0 5.15 1.9717.0 1.3813.0 9.06 1.283.5 0.11 2,018.5 50.64 1.4610.5 2.51 1.796.0 I.07 . . .

13.0 0.30 0.89

Glauconite fyrite Medianmm.

01 Q3 So Log 10 So

Sed.type Source

B 0 0.019 0.0039 0.042 3.28 0.516 D 30 B . a a ... ... . . . . . . D. . . ... 0.017 0.0038 0.034 2.98 0.474 D 3VB 0 0.037 0.0080 0.059 2.72 0.435 C-D 3VB 0 0.0139 0.0029 0.053 4.27 0.631 D 20B

00

1,60 0.185 4.40 2.94 o.4& F 0taA0

V

0 0.0103a a a

0.0021. a a

0.047 4.71«a*.

0.673a a a

D22

B 0 0.162 0.052 1,16 4,72 0,674 F 2VB • 0 0.0196 0.005 0.053 3.25 0.512 D 2VB 0 0,021 0,0023 0.080 5.89 0.770 D 20 0 0.0062 0,0014 0.032 4.78 0,679 D 2B B 0.355 0.037 2.50 8.22 0.915 F 2a B 0,0181 0.0033 . 0.0422 3.71 0.569 B 2B 0 2.30 0.160 lo.oe 3.79 0.579 V 2a 0 0.076 0.025 0.104 2.04 0.310 C 2B 0 0.103 0,085 0.126 1,22 0.086 B 2c 0 0.089 0.068 0.118 1.32 0.120 B 2c 0 0,102 0.075 0.145 1.40 0.146 B 2B 0 0.160 0.132 0.196 1,22 0.085 A-3 2B 0 0.070 0.0125 0.101 2.83 0.452 C 20 0 0.075 0.051 0.095 1.36 0.135 C 2B 0 0.094 0.073 0.121 1,29 0.110 B 2B 0 0.101 0.072 0.145 1.42 0.152 B 2C 0 0.101 0.068 0.166 1.56 0.192 B 2C 0 0.056 0.0145 0.086 2.44 0.387 C 2B 0 0.255 0.045 2.70 7.74 0.889 F 2B 0 0.108 0.081 0.145 1.39 0.127 B 2VB 0 0.080 0.064 0.100 1.25 0.097 B 2VB 0 0.035 0,0116 0.073 2.51 0,400 C.D 2... — 0.0156 0.003 0.047 3.96 0.597 D 1Sediment Analyses

Beaches and Water Bottoms Table 5

Samp. Latitude Depth #Shell ^Organic Glauconite PyrJno. • i « « t •< feet

m.s.l.content

32 29 1*1* 53 8913 u . . . . . . . . .33 29 1*1* 22 89 11 30 . . . . . .3*1 29 1*1* 00 89 09 20 . . . 23.53 . . .35 29 1*3 50 89 07 07 . . . --- . . .36 29 1*3 35 09 05 3l* . . . —37 29 1*3 1*8 89 00 1*2 . . . --- . . .38 29 1*6 20 885622 . . . . . . . . .39 29 1*8 30 88 53 10 6.91 . . .1*0 291*0 36 89 22 52 8.5 3.97 2.69 TO1*1 291*0 09 69 18 12 8.5 0,30 . . . 01*2 29 391*5 89 ll* 15 11.0 0.29 0.1*5 TO1*3 29 39 18 89 091*8 12.5 0.1*3 . . . 01*1* 29 38 1*6 89 01* 1*7 15.0 ■ 0.21* 0.1*9 01*5 29 38 30 89 00 18 13.0 1.66 1.53 B1*6 29 36 1*2 89 27 5!* 7.0 1*5.90 . . . 01*7 29 35 30 89 23 20 11.0 1.1*7 1.06 01*8 29 3l* 21 89 185!* 11.0 0.1*9 . . . B1*9 29 32 18 8911* 00 16.0 1 .6 1.51 TO50 29 30 23 89 10 23 17.5 1.19 . . . C51 29 32 21* 89 09 03 21.0 0.02 .*—1 . . .52 29 25 36 885!* 31 . . . . . . . . . . . .53 29 25 36 8851* 31 . . . . . . . . . . . .5** 29 30 00 88 52 59 . . . . . . . . .55 29 30 00 8852 59 . . . --- . . . —56 29 35 06 885OOO . . . . . . . . .57 29 35 06 8850 00 . . . 0.77 —58 29 39 52 881*8 51 . . . 0.15 — —59 29 1*1* 03 881*71*6 . . . . . . . . . —60 29 1*8 57 881*7 05 . . . . . . . . . . . .6l 29 5l* 1*6 881*5 1*2 . . . . . . . . . . . .62 29 58 56 88 1*7 53 . . . . . . . . . . . .63 30 0!* 16 8850 00 . . . . . .61* 30 (A 16 8850 00 . . . . . . . . . . . .65 30101*1* 88 53 56 . . . . . . . . . . . .66 3010 1*1* 8853 56 . . . . . . . . . . . .

H0000000000

Table 5

Medianan.

01 03 So Log 10 So

Spa;Hype

Source

0.079 0.069 0.091 1.15 0.060 B 10.001* 0.070 0.101 1.20 0.079 B 10.081* 0.073 0.125 1.31 0.117 B 1O.O83 0.071 0.105 1.22 0.085 B 10.105 0.081* 0.117 1.18 0.072 B 10.101 0.080 0.122 1.23 0.090 B 10,057 0.011* 0.068 2.20 0.31*5 C 10,121 0.096 o.i6i» 1.31 0.U7 B 10,0182 0.0055 0.01*0 2.70 0.1*31 D ... 20.079 0.066 0.096 1,20 0.081 B 20.078 0.062 0.098 1.26 0.099 B 20,083 0.068 0.101 1,22 0.0&7 B 20.0135 ca.00l6 0.077 6.95 0.81*2 D 20,089 0.072 0.118 1,28 0.107 B 20.179 0.058 2.750 6.88 0,81*0 F 20,068 0.023 0.113 2.21* 0.351 C 20.071* 0.061 0.089 1.20 0.079 B-C 20.058 0.0062 0.096 3.91* 0.595 C 20,102 0.057 0.1l*2 1.57 0.197 B 2o.oid* 0.021*5 0.073 1.73 0,237 B-C 20.093 0.067 0.108 1.27 0.105 B 10.091* 0.071 0.111* 1.27 O.lOl* B 10,118 0.101 0.135 1.16 0.061* B 10.115 0.098 0.131 1,16 0.061* B 10.127 0.098 0.156 1.26 0.101 B 10.126 0.096 0.159 1.29 0.110 B 10,128 0.101 0,11*5 1.20 0.078 B 10.109 0.090 0.126 1.18 0.073 B 10.097 0,082 0.113 1.18 0.070 B 10,118 0.097 0.136 1.18 0.073 B 10.073 0.061* 0.083 1.11* 0.057 B 10.088 0.077 0.099 1,11* 0.055 B 1O.O85 0.075 0.096 1.13 0.051* B 10.062 0.01*0 0.081 1.1*2 0.152 *!*-• . 10.070 0.063 0.082 l.ll* 0.057 -

Samp.no.

latitude • 1 11

Longitude• t n $Shell Medianmm.

Q1

67 29 *7 *8 88 59 03 9*.3 1.280 0.72568 30 08 *2 89 1138 *5.8 0,*00 0.2*069 30 08 *3 89 1127 28.9 0.295 0.20870 30 09 03 89 u 0* 23.8 0.230 0.18571 29 27 *2 89 12 55 0 0.170 0.1*972 29 27 *2 89 12 55 — 0.175 0.15573 29 27 *2 89 12 55 0.175 0.1557* 29 27 39 89 12 00 — 0.185 0.16075 29 27 39 89 12 00 a i a a 0.170 0.15076 29 27 39 89 12 00 0.175 0.15577 29 29 *2 89 09 *8 — 0.170 0.15078 29 29 *2 89 09 *8 0.170 0.15279 29 29 *2 89 09 *8 — 0.173 0.15580 29 28 28 89 10 16 — 0.150 0.13081 29 28 28 8910 16 — 0.155 0.13582 29 28 28 89 10 16 m mm 0.165 0.1*063 29 30 5* 89 05 *5 0.155 0.1256* 29 30 5* 89 05 *5 --------- 0.170 0.15065 29 30 5* 89 05 *5 --------- 0.170 0.15086 29 36 07 89 00 02 --------- 0.1*9 0.12787 29 36 07 89 00 02 M a «a 0.130 0.12088 29 36 07 89 00 02 0.163 0,1*789 29 36 07 89 00 02 mmm 0.160 0.15590 29 39 *7 89 56 00 5.5 0.153 0.13091 29 39 *7 89 56 00 *.5 0.130 0.11092 29 39 *7 89 56 00 — - 0.151 0.13093 29 39 *7 89 56 00 a a a 0.151 0.1309* 29 *5 03 88 51 *5 ;*;5 0.150 0.12595 29 *5 03 88 51 *5 — 0.151 0.1*796 29 *6 02 88 51 I3 *.5 0.152 0.13097 29 *6 02 88 51 13 1.5 0.171 0.15598 29 *7 18 88 50 37 7.9 •0.1*9 0.12599 29 *7 18 88 50 37 1.2 0.160 0.135100 29 *7 18 88 50 37 3.6 0.150 0.135

Table 5

Q3 So Log 10 Sed. Source#_ _ _ _ _ _ _ _ _ _ _ _ _ _ So_ _ _ _ _ T y p r _ _ _ _ _ _ _ _ _2.250 1.77 0.2 7 E 3i»,800 *.*6 0.6*0 E 31,600 2.77 0.**2 E 30.375 l.*2 0.152 E 30.190 1.13 0.05*1 A 30.195 1.12 0.050 A 30.195 1.12 0.050 A 30.235 1.21 0.08U A 30.180 1.10 0.039 A 30.190 1,11 0,0*5 A 3O.197 1.15 0.059 A 3O.I85 1.11 0.0*13 A 30.190 1.11 0.0*5 A 30.165 1.13 0.052 A 30.170 1.12 0.050 A 30,180 l.l* 0.055 A 30.180 1,20 0.079 A 30.190 1.13 0.052 A 30.185 1.11 0.0*5 A 30.170 1.16 0.06* A 30.1*7 1.11 0.0*5 A 30.180 1.11 0,0*3 A 30.170 1.05 0,020 A 30.175 1.16 O.O65 A 30.151 1.17 0.068 A 30.170 1.15 0.059 A 3O.I65 1.13 0.052 A 30.170 1,17 0.068 A 30.175 1.09 0.038 A 30.169 1.1* 0.057 A: 30.190 1.11 0.0*3 A 30.160 1,13 0.05* A 30.176 1.1* 0.057 A 30.168 1.11 0.0*7 A 3

Salop, Latitude Longitude $Shell Median 01no, 0 t it 0 1 » no.

101 29 1*7 18 8850 37 0.170 0.152102 291*8 26 88 50 12 u 0.160 0.135103 29 1*8 26 88 50 12 0.5 0.168 0.11*8101* 29 1*8 26 88 50 12 0.162 0.152105 29 1*8 26 88 50 12 0.171 0.160106 29 1*9 26 88 1*9 52 11* .1 O.I58 0.135107 291*9 26 881*9 52 9.5 0.162 0.11*0108 29 1*9 26 881*9 52 0.160 0.11*9109 29 55 1*8 881*9 56 19.5 0.170 0.135110 29 55 W 881*9 56 0.6 0.173 0.150111 29 55 1*8 88 1*9 56 0.8 0,160 0.129112 29 55 to 88 1*9 58 0.5 0.168 0.158113 29 55 to 88 1*9 56 w H w111* 30 00 51 88 5027 o.£ 0.139 0.120115 30 51 06 88 50 30 0.1* 0.150 0.129116 30 51 06 88 50 30 mmm M a» _117 30 51 06 88 50 30 0.6 0.175 0.11*9118 30 03 ot* 88 52 08 ll*.8 0.175 0.151*119 30 03 d* 88 52 08 0.7 0.175 0.11*6120 30 03 01* 88 52 08 0.171* 0.11*6121 29 1*7 50 89 51 ’*8122 29 1*8 37 89 38 to123 29 1*9 27 89 25 53121* 291*3 to 89 25 31*125 29 1*0 00 89 3l* 3l»126 30 13 36 89 27 30127 29 !*i* li* 89 33 07128 29 50 16 89 ll* 22129 29 1*7 21 8853 11130 30 Ol* 19 8910 06

Table 5

Q3 So log 10 Sed, Source *_ _ _ _ _ _ _ _ _ _ _ _ _ So Ifype0.180 1,09 0.036 A 30.175 1.1* 0.05? A 30.180 1,11 0.0 3 A 30.170 1.06 0.025 A 30.189 1.09 O.O36 A 30.185 1.17 0.068 A 3.0.180 l.ll* 0.055 A 30,162 1.0*1 0,018 A 30.220 1.28 0.106 A 30.197 1.15 0.060 A 30.190 1.21 0.081* A 30.172 l.Ci* 0.018 A 3— — — A 30,162 1.16 0.065 A 30.170 1.15 0.060 A 3

0.208 1,18 0.073 A 30.211 1.17 0,068 A 30.210 1,20 0.079 A 30.208 I.19 0.076 A 3

Samp.no,

Latitude« i it

Longitudee t i>

piell Medianm .

01 03

131 30 13 30 89 (A IB 0.250 0.199 0.273132 30 13 30 89 <*18 - - - 0.295 0.255 0.326133 30 13 30 89 ol* 18 — 0.275 0.230 0.30013* 30 15 03 89 03 1*0 0.300 0.275 0.320135 30 15 03 89 031*0 0#29lt 0.250 0.302136 30 15 03 89 031(0 0.306 0,280 0.350137 30 13 56 89 25 oi* 0,21*0 0.225 0.260138 30 13 56 89 25 12 0.1*25 0.377 0,1*60

*L E. D. EuaboII 2- E. C, Treadwell 3- Project Sediment Laboratory

Table 5

So Log 10 Sed. Source*So IJrpe

1.17 0.0681.13 0,01*1* «...

l.ll* 0.057 . . .

1,08 0.0321.10 0,01*1 m m m

1.12 0.01*8 m m m

1.07 0.068 m m m

1.11 0,01*3 m m m

0i»5

MARSH INNER LAKES OUTERLAKES SOUND | BEACHES

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Table 8

Ik6

LOCATION Ft HINNER LAKES OU1EURIKE8 80UND8STATION IBmB«11 I4 111tIt11111it1111484114X21221)414127n 114142212411414121SOM41aanMMfclTOTAL POPULATION >o.i4smm. RS0S OPsM| s8

o30nw0o •■)g§sw8•>8 0 0om*N0N00 M00•M M0S 04045oMw4344•0**N00 •0♦0 ~ 5 2AMMOASTUTA SALSA 3 9.s t 3 “AMMOBACULITES OILATATUS .1 .8 3 It • s14 4 B2II7T 7AMMOBACULITES EXlCUUS II 2 II j84AMMOBACULITES St>. 1 37e9 4 8 39 3 2AMMOTIUM SALSUM e19iiSBSSI878456si18184C•C43841718 2112ItU 40 8 1813 14 « '9•7 19_ISazAMMOTIUM SR 1AMMOSCALARIA PSEUDOSPIRAL1S 4 t 9 * 18 £ »ARENOPARRELLA mexicana 33IS14 3 9 \4 23219A4 f8 f9 •BOLIVINA -OWMANI - - 4 jDISCORBIS FLORIDANA tELHH1DIUM DISCOIDALE 4ELPHIDIUM GUNTERI uELPHIDIUM GUNTERI GALVESTONENSE toelpMidIum KUGLERI 3elPHIdIUM INCEftTUM MGXICANJM'” 8 8 8 39 2 • 10ELPHIplUM LIMOSUM 8 | * 3 3 a % 3 4ELPHIOIUV maTaGORDANUM 7 4 A8 34Z 4t9 Z R19 f 1I 4 4 9 1ELPHIDIUM PoEVaNUM ■84 914 2 1 f4 2 41 11449 IIV Bsc21 9 33elPHidIUm vadescEns AEPoNidelLA OARDFNISUA'RBENSIS 3 3GAilbRYlNA EXILIS • 3HANZAWAIA , STRATTONl. . m 2 .8HAPlopHrAgMoides tM kiilaensis 4 .8 .2 A 3 A ?''HAPLOPHRAGMOIDES” WILBERTI ' T417 S.93■« 2 73a7 82 3 8 2 4MILIAMMINA FUSCA 1® 4*11I4z 8 2 11i3 I 1 £NONIONELLA CF. AURIS R1 -NUBECULARIA LU Cl FUG A 91 PEL.C • RA 9 CP 31 PSAt.MOSP IAeRA EliscA? 1 ITPSEUDOCLAVULINA GRACILIS «PYRGO SP *OUINQUELOCULINA CE LAMARCKIANA «QUINQUELOCULINA SABULOSA ' r •OUINQUELOCULINA SEMINUUIM a ■ 3 3QUINQUELOCULINA SEMINULUM JUGOSA “ ■SuInoUeloculina sps. i & z 3 • 6 3 M 9s 3c•s 4 4 00"ROTALIA" BECCARII PARKINSONIANA 3sel2474188134ss3toeIS344C38ISIS4C612731175C331433414192237332181341 100 21 23"ROTALIA" BECCARII TEPIOA 70 i.1tIt■4 a 0S4 a s IS13s 7 tcta633 818931IS7IIt2367 8 \TRQCHAMMII-A COMPRIMATA t\19,S ZTROCHAMMlK A iNFLATA 2 4 ,9 ■ * s 4TROCHAMMINA LOBATA • J 8TROCHAMMINA MACRESCENS ,1 0 3 0-9 4 "3 9“VALVULINERIA* SR .5 1VIRGULINA PONTONI __ _ _ _ ___ _ _ _ _ _ _ _ ■_ _ _ _ _ _ _ _ _ _ _

LOCATION ImarET sh IlNNER LAKES (OUTERLAKES SOUND8 BEACFC8STATION IBIE34121124%i)iIS110ii12nII4440142121&174741277)11au»2411II nto4441 ait10H10)TOTAL POPULATION <o.i49->ox>T4 N*N1N 0No0000 s sace0S0o0N §8Zo00o0NaM00802oM?00000 g 0 000o 0 00« KCl 0M71Moo OAmmoasti/ta salsa 87 " j 7 •AMMOBACULITES EXIGUUS j 91733 2 13AMMOTIUM PSEUDOCASSIS .7AMMfi+ruM lJUVENIPu 3433so298382M32824681ST6«29rBIT83K 28«»If331 4 T 8 esi13 19tcARENOPARRELLA MEXICANA IQ1017 a “9 2 4 3 4BOLIVINA STRIATIII A • r ♦ 8BUCCELLA CF FRIGIDA ■ 13BULI MIN ELLA CE GA55ENBDRFENST5 " ' ■ ■BULIMINELLA ELEGAKITiGSIma ■ - ■ “ I •DISCORBIS FLORIOANA •ELPHIDIUM (JUVENILE!EPONIOELLA GARDEN ISLANDENSIS Jjgaudryina fxilis i _l_ 2gUmbelina SP THAPLOPHRAGMOIDES MANILAENSIS Zj”HAPLOPHRAGMOIDES WII.RFRTI tl710“■ ±i4. 1 ,7 it^ tCTammiWa fusca ..... u 2Cfl ii.4_2£T8_ 7J8_ 7739NONIONELLA CE AURIS i 4 7PSAMMOSPHAERA FUSCA 7 5 ""PSEUDOCLAVULINA GRACILIS T « 7PYRGO SP b B b 7 •QUINQUELOCULINA (JUVENILE) a(JUVENILE) toeaTT7917231217isu4_272824IB32aIS171 s» •0 27 80S7N X5 ss41 bTROCHAMMINA COMPRIMATA 2“ i S_ r— r"P” r"TROCHAMMINA INFLATA T 34 5 rT 7r L8 rL.■JROBHAJMB pra MACRE5C ER5 n 4 7 hr 7 L P b b■‘valvuliN-RIa’ 8R T r ui iZr L. r”VIRGULINa poNtoni rrL rrC t cL t L LLL T L r

• PRESENT SUT NOT FOUND IN FREQUENCY COUNT

Table 9

ANNOTATED SYNONYMIES

Foraminifera

Ammoastute salsa Cushman and Bronnlmann AnnnoaBtuta salsa CUSHMAN and BRONNIMANN, 19^8, Contr. Cushman Lab. Forem.

Bes., vol. pt. 1, p. 17, pi. 3, figs. 1^-16.This species is reported from marshy areas in Trinidad, northeastern

U. S. and off Panama and Ecuador. In St. Bernard Parish it 1b present in all maTBh samples from 1 to 5$ and in one sound and four lake samples in frequencies less than 1$.

Ammobaculites dilatatus Cushman and Bronnimann Ammobaculites dilatatus CUSHMAN and BRONNIMANN, 19^8, Contr. Cushman Lab.

Foram. Fes., vol. 2^, pt. 2, p. 39, pi. 7, figs. 10, 11.Itypical specimens ore found in many places in Chanda lour Sound but

always in lav frequencies. This form is reported from the Gulf of Peria, Trinidad, and the Gulf of Mexico.

Ammobaculites exiguus Cushman and Bronnimann Ammobaculites exiguus CUSHMAN and BRONNIMANN, 19^8, Contr. Cushman Lab.

Foram, Bes., vol. 2h, pt. 2, p. 38, pi. 7, figs. 7, 8.This form is reported from shallow water of the Gulf of Paria,

Trinidad, and the northwest Gulf of Mexico. Locally, it is common in Chandeleur Sound in low frequencies and is almost exclusively confined to the fine fraction of samples.

IU7

148

AmmobaculiteB sp. 1This species Is larger (length, 0,6-0.8 mm.) and has more Inflated

chambers than Ammotium sal sum. It is common in lakes of the area. Wherepresent, it constitutes a small percent of the fauna.

Ammotium pseudocassis (Cushman and Bronnimann)Ammobaculites pseudocassis CUSHMAN and BRONNIMANN, 1948, Contr. Cushman Lab.

Foram. Bes., vol. 24, pt. 2, p. 39, pi. 7, fig. 12.In the samples examined this form occurs in low frequency in two

marsh samples. It is reported from brackish muds of Trinidad.

Ammotium salsum (Cushman and Bronnimann)Ammobaculites salsus CUSHMAN and BRONNIMANN, 1948, Contr. Cushman Lab.

Foram. Bes., vol. 24, pt. 1, p. 16, pi. 3, figs. 7-9.Considerable variation occurs in forms assigned to tills species. It

occurs commonly throughout the area, and highest percentages are reached in the marshland lakes. It has been reported from brackish lake and bay areas of Trinidad and Texas.

Ammotium sp. 1This species Is very small (length, 0,24 mm., width, 0.11 mm.),

greatly compressed and finely arenaceous. It is present in one lake sample.

Ammoscalaria pseudospiralis (Williamson)Proteonlna pseudospirale WILLIAMSON, 1858, Bee. Foram. Great Britain, p. 2,

pi. 1, figs. 2, 3.Specimens of this form are fairly common in the sounds. In the

United States the species has been reported from the northwest Gulf of Mexico and coastal Texas.

Arenoparrella mexicana (Kornfeld)Irochammlna inflate (MONTAGU) var. mexicana KORNFELD, 1931, Contr.

Stanford Geol. Dept., vol. 1, p. 86, pi. 13, fig. 5.Epical specimens occur throughout the marshes and lakes in the area.

It is common in shallow brackish waters of coastal Louisiana.

Bolivina lowmani Phleger and Parker Bollvlna lowmani PHLEGER and PARKER, 1951, Mem. 46, Geol. Soc. America,

pt. 2, p. 13, pi. 6, figs. 20, 21.This species is common in the northern Gulf of Mexico. In the study

area a few individuals have been found in Chandeleur Sound.

Bolivina striatula Cushman Bolivina strlatula CUSHMAN, 1922, Publ. 311, Carnegie Instit,, Washington,

p. 27, pi. 3, fig. 10.In the area investigated specimens occur in low frequency in four

Chandeleur Sound stations. The species is found in shallow water of thenorthern Gulf of Mexico.

Buccella sp. cf. frigida (CuBhman)Pulvlnulina frigida CUSHMAN, 1922, Contr. Can. Biol. 1921, p. 12.

A few specimens are recorded from two stations in Chandeleur Sound. The species is reported from coastal Louisiana, HudsonB Bay, Canada, and Buzzards Bay, Massachusetts.

150

Buliminella sp. cf. bassendorfensis Cushman and Parker Buliminella bassendorfensis CUSHMAN and PARKER, 1937, Contr. Cushman Lah.

Foram. Res., vol. 13, pt. 1, p. 40, pi. 4, fig. 13.This form is reported to "be common above 100 m. in the northwest Gulf

of Mexico, It occurs at frequencies below 1$ in two sound samples in St, Bernard Parish.

Buliminella elegantissima (d'Orbigny)Bullmina elegantissima D'ORBIGNY, 1839, Toy. Amer. Merid,, vol. 5, pt. 5,

"Foraminiferes", p. 51, pi. 7, figs. 13, l1*.This species is reported to be fairly common above 80 m. in the north­

west Gulf of Mexico. It occurs at low frequencies in four sound stations in St, Bernard Parish.

Discorbis floridana Cushman Dlscorbis floridana CUSHMAN, 1922, Publ. 311, Carnegie Instit., Washington,

P. 39, pi. 5, figs. 11, 12.Specimens are present in frequencies less than 2$ at two stations in

Chandeleur Sound. The Bpecies is reported as characteristic of depths shallower than 60 m. in the northwest Gulf of Mexico.

Elphidium discoidale (d'Orbigny)Polystome11a discoldalis D'ORBIGNY, 1839, in de la Sagra, Hist. Phys, Pol.

Nat. Cuba, "Foraminiferes", p. 56, pi. 6, figs. 23, 2k.Questionable specimens have been found at one location in Breton

Sound. The species is reported from the West Indies and the Gulf of Mexico.

151

Elphidium gunteri Cole Elphidium gunteri COLE, 1931, Florida State Geol. Surv. Bull. 6, p. 3^,

pi. If, figs. 9, 10.This Is a very common, species in the northern Gulf of Mexico and

hrackish waters along the Gulf Coast. In St. Bernard Parish it is common in the sounds and on "beaches "but rare in marsh and inner lakes.

Elphidium gunteri galvestonense Kornfold Elphidium gunteri COLE var. galvestonensls KORNFELD, (part), 1931, Contr.

Dept. Geol. Stanford Univ., vol. 1, no. 3, p. 87, pi. 15, fig. 1 (not 2, 3).One Chandeleur Island semple contained a few good specimens of

Elphidium galvestonenBe. The species is fairly common in shallow water of the northern Gulf of Mexico.

Elphidium lcugleri (Cushman and Bronnimann)Crlhroelphldlum kugleri CUSHMAN and BRONNIMANN, 19^8, Contr. Cushman Lab.

Foram. Res., vol. 2k, pt. 1, p. 10, pi. 1», fig. 4.This species is described from brackish inshore muds of the west

coast of Trinidad. Epical specimens occur at one outer lake location at low frequency, In this area it appears that through gradation in thickness of test, number of chambers, and size this species overlaps Juvenile indi­viduals of Elphidium poeyanum.

Elphidium incertum mexicanum Kornfeld Elphidium incertum (WILLIAMSON) var. mexicana KORNFELD, 1931, Contr. Geol.

Dept. Stanford Univ., vol. 1, no. 3, p. 89, pi. 16, figs. 1, 2.In the area studied specimens are fairly common In central and outer

152

sound and "beach samples at frequencies mostly under 10$. This form is reported from the Gulf of Mexico to a depth of 100 m.

Elphidium limosum (Cushman and Bronnimann)Cribroelphidlum limosum CUSHMAN and BROUN IMAM, 19*4 8, Contr. Cushman Lah.

Foram. Res., vol. 2h, pt. 1, p. 19, pi. *4, fig. 7.No crihrate aperture is present on specimens from this area; other­

wise, they are typical. It is reported from inshore mud, "brackish water,'hmangrove swamp and west coast of Trinidad.

Elphidium matagordanum (Kornfeld)

Nonion depressula ('WALKER and JACOB) var, matagordana KORNFELD, 1931,Contr. Dept. Geol. Stanford Univ., vol. 1, no. 3, p. 87, pi. 13, fig. 2.In the area investigated this form is widespread in lakes end sounds,

"but frequencies are usually "below 5$. It is reported from the northwest Gulf of Mexico to a depth of 117 m.; however, it is usually found above 90 m.

Elphidium poeyanum (d'Orbigny)Polystomella poeyana D'ORBIGNY, 1839, in do la Sagra, Hist. Phys. Pol,

Nat. Cuba, "Faraminifores'1, p. 55, pi. 6, figs. 25, 26.This species is reported from shallow water in the Gulf of Mexico.

It is common in St. Bernard Parish, especially in Chandoleur Sound and beach samples.

Elphidium vadeBcens Cushman and BronnimannCribroelphidlum vadescens CUSHMAN and BRONNIMANN, 19*48, Contr. Cushman Lab.

153

Foram. Bes., vol. 2k, pt. p. 18, pi. k, fig. 5.A few specimens probably "belonging to this species are present at

one lake station in the area examined. Frequency is less than 1$, This species was described from brackish muds on the west coast of Trinidad.

Eponidella gardenislandensis Akers Eponidella gardenislandensls AKERS, 1952, Jour. Paleo., vol. 26, no. It,

p. 61+8, fig. 2.This form is reported from brackish water along the southeastern

Louisiana coast and is present at four stations in Chandeleur Sound. It composes Iobs than 1$ of the samples,

Gaudryina exilis Cushman and Bronnimann Gaudrylna exilis CUSHMAN and BRONNIMAUN, 191+8, Contr. Cushman Lab. Foram.

..Bes., vol. 2k, pt. 2, p. 1+0, pi. 7 , figs. 15, 16.In the samples examined, this species is present at two lake stations

and composes less than 1$ of the fauna in each case. Specimens are some­what smaller (length, 0.25 mm.) and apparently slightly coarser grained than those reported from the Gulf of Paria, Trinidad.

Henzawaia strattoni (Applin)Truncatullna americana CUSHMAN var. strattoni APPLIN, 1925, in Applin,

Ellisor, and Kinker, Bull. Amer. Assoc. Petrol. Geol., vol. 9, no. 1

P* 99) 3, fig* 3*This species is common in fairly shallow water of the Gulf of Mexico.

It forms less than 1$ of the Foraminifera in one lake and two sound samples in the area studied.

Haplophragmoides manilaensls Andersen HaplophragmoldeB manilaensls ANDERSEN, 1953, Contr. Cushman Found. Foram.

Res., vol. k, pt. 1, p. 22, pi. k, fig. 8.This species Is present in one sound, four lake, and two marsh

samples. Frequency is generally under 1$. The species was described from brackish water of coastal Louisiana.

Haplophragmoides vilberti Andersen Haplophragmoides vilberti ANDERSEN, 1953, Contr, Cushman Found. Foram.

Res., vol. *t, pt. 1, pp. 21, 22, pi. It, fig. 7 .This is a common species in marsh and lakes and is also present in

five sound samples. In one marsh sample it makes up 22$ of the assemblage, but at most stations it comprises less than 5$. It was described from brackish water of coastal Louisiana.

Miliemmina fusca (H. B, Brady)Quinquelocullna fusca H. B. BRADY, 1870, Ann. Mag. Nat, Hist., ser. k,

vol. 6, p. It7 (286), pi. 11, figB. 2, 3.In St. Bernard Parish this species is abundant in marsh, common in

lakes and rare in sounds. It is reported from brackish and marshy regions in many parts of the world.

Nonionella sp. cf. auris (d'Qrbigty)Valvullna auris D'ORBIGNY, 1839, Voyage dans l'Amerique Meridionals, vol. 5,

pt. 5, "Foraminiferes", p. ^7, pi. 2, figs. I5-I7 .This form is common on the west coast of South America and 1b reported

as a fossil in the southeastern United States Coastal Plain. It occurs at low frequencies in four samples in the sounds. This species has been

155

reported as Nonionella oplma in several publications on Gulf Coastal areas.

Nubecularia lucifuga DefTance Nubecularia lucifuga DEFRANCE, 1825} Mineralogie et Geologie in Diet.

Sci. Nat., vol. 35, p. 210.One specimen of this species was found in a sample from the Chande­

leur Islands. It is reported from tropical and temperate seas, most generality occurring in the‘'littoral and laminarian (2-10 fathom)*' zones.

Pelosphaera (?) sp.A few specimens apparently belonging to this genus have been recovered

from one marsh sample. The individuals in this sample averaged 0.9 ram. greatest diameter, This is much smaller than the type species, and, heretofore, the genus has been reported from open marine waters. There­fore, this is a questionable identification,

Psammosphaera fusca (?) Schulze PsammoBphaera fusca SCHULZE, 1875, I, Comm. Wus . Untersuchung Deutsch.

Meere, Jarosbor., p. 113, pi. 2, fig. 8.In the area investigated forms probably belonging to this species

have been found at one lake and one sound station. Specimens average 0.2-0.3 mm. in diameter*. This is much smaller than specimens originally described but falls within the size range given by Brady (188*1, p. 250).The species has a wide distribution in marine waters.

Pseudoclavulina gracilis Cushman and Bronnimann

Psoudoclavulina gracilis CUSHMAN and BRONNIMANN, 19^8, Contr. Cushman Lab,

Foram. Res., vol. 2k, pt. 2, p. *f0, pi. 7, figs, 17, 18.Specimens are smaller (maximum length, 0.35 mm., maximum width,

0.09 mm.) than typical. They form less than 1# of the samples atthree lake stations. This species was described from the Gulf of Paria,Trinidad.

Pyrgo sp.Three samples in Chandeleur Sound contain this small species. It

does not make up more than 2# of the fauna at ai r station,

Quinqueloculina sp. cf. lemarckiana d'Orbigny Quinqueloculina lamercklana D'ORBIGNY, 1839, in de la Sagra., Hist. Phys.

Pol. Nat. Cuba, "Foraminiferes", p. I89, pi. 11, figs. 1*J, 15.Individuals grouped under this species are thinner and in many cases

smaller than those found in the Gulf. Otherwise, they are similar. 1^1 a specieB is reported aB the most common Quinqueloculina of the northwest Gulf of Mexico and attains greatest frequency at depths shallower than 100 m.

.Quinqueloculina sabulosa Cushman Quinqueloculina sabulosa CUSHMAN, 19^7, Contr. Cushman Lab. Foram. Res.,

vol. 23, pt. lj, p. 87, pi. 18, fig. 22.A few specimens of this form have been found in Chandeleur Sound.

It is reported in the Atlantic from Capo Hatter os, North Carolina, to Florida.

Quinqueloculina seminulum (Linn^)Serpula somlnula LINNE, 1767, Syst, Nat., ed. 12, p. 126*1.

This species is present in low frequency at four stations in the sounds and is a widespread shallow water species.

Quinqueloculina seminulum Jugosa Cushman Quinqueloculina semlnulum (LINNE) var, Jugosa CUSHMAN, 19^, Cushman Lab.

A few specimens have been found at one station in Breton Sound. The»

species is widely distributed off the Atlantic coast south of Cape Cod, Massachusetts.

"Botalia" beccarii parkinsonians (d'Orbigny)Boaallna parkinsonians D'OEBIGNZ, 1839, in d® la Sagra, Hist. Phys. Pol.

Nat. Cuba, "Foraminiferes11, p. 99, pi. *», fig0* 25-27.This is a very common brackish to shallow marine species. In St.

Bernard Parish it occurs in samples from beaches, sounds and lakes, but it is most abundant in sounds.

Instit., Washington, p. 79, pi. 1.The species is reported from the Gulf of Mexico and the West Indies

from 2 m. to 9 m. depth. In St. Bernard Parish it was found on beaches and in sounds and lakes but is most common in the sounds. It is not, however, as abundant as "Botalia" parkinsonians.

Trochamnlna comprimata CUSHMAN and BRONNIMANN, 19^8, Contr. Cushman Lab.

Foram. Bes., spec, publ, no. 12, p. 13, pi. 2, fig. 15.

"Botalia" beccarii tepida CushmanINN^) var. tepida CUSHMAN, 1926, Publ. 3^, Carnegie

Trochammlna comprimata Cushman and Bronnimann

Foram. Res., vol. 2h, pt. 2, p. 1+1, pi. 8, figs. 1-3.In the area studied this form occurs at all three marsh and three

lake stations. Maximum frequency is attained In marsh where it reaches 17$. It composes less than 1$ of the lake fauna. The species was describ­ed from brackish muds of a mangrove swamp on the west coast of Trinidad.

Trochammina inflate (Montagu)Nautilus inflatus MONTAGU, 1808, Test. Brit., p. 8l, pi. 18, fig. 3.

This form is common along many marshy coasts. In the study area it occurs in all three marsh, one sound and six lake samples. Maximum frequency (6$) is reached In the marsh.

Trochammina lobata Cushman Trochammina lobata CUSHMAN, 19^, Cushman Lab. Foram. Res., spec. publ.

no. 12, p. 18, pi. 2, fig. 10.This species has been found In one beach and two outer sound samples

at low frequencies. It has been reported from shallow waters at many places along the New England coast.

Trochammina macrescens Brady Trochammina inflate (MONTAGU) var. macrescens BRADI, IB7O, Ann, Meg. Nat.

Hist., ser, k, vol. 6, p. 290, pl. 11, fig. 5*Tills form was found at two' marsh, five lake, and two inner sound

stations and is always low in frequency. It is reported from brackish waters and marshes of many coasts.

"Valvulineria" Bp.While quite similar to Valvulineria, this is actually a new genus. It

is restricted to marsh samples and in most places occurs in low frequency,

Virgulina pontoni Cushman Vlrgulina pontoni CUSBMAN, 1932, Contr. Cushman Lab. Foram. Bes., vol. 8,

pt. 1, p. 17, pi. 3, fig. 7.A few specimens were found at one sound location. The species occurs

in the Gulf of Mexico usually at depths shallower than 125

Mollusca

Pelecypoda

Abra aequalis (Soy)AmphldeBma aoquails SAT, 1822, Jour. Acad. Nat. Sci. Phila., 1st. Ser.,

vol. 2, p. 307.ThiB species was found at ten stations in Chandeleur and Breton

sounds. It is reported from North Carolina to Texas and the West Indies.

Aequipecten irradians concentricus (Soy)Peoten concentrlcus SAY, 1822, Jour. Acad, Nat. Sci. Phila., 1st Ser.,

vol. 2, p. 259.This form is quite common on the Chandeleur Island beaches. Numerous

living individuals have been found in shallow water directly behind the islands. In the sampled oreo the species is restricted to sandy bottoms. The range is from New Jersey (rare) to Georgia and from Louisiana to Tampa, Florida.

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Anadara brasiliana (Lamarck)? ^rca braziliana LAMARCK, 1819, Anim. sans Vert., vol. 6, p.

A fev specimens were found on 'beaches, but none were recovered from water bottoms. This species is distributed from North Carolina to Texas and the West Indies and is closely related to A. lncongrua Say.

Anadara ovalis (Bruguiere)Area ovalis BRUGUI^RE, 1792, Enc. Meth., p. 110.

This species has been reported from Cape Cod, Massachusetts, to the West Indies and the Gulf states. It is quite common in beach samples throughout the Louisiana coast and is commonly reported as Arming campechensls (Gmelin).

Anadara transversa (Say)Area transverse SAY. 1822, Jour. Acad. Nat. Sci. Phila., 1st Ser., vol. 2,

p. 269.The species is reported from Cape Cod, Massachusetts, to Florida and

Texas. Specimens have been found at one beach and four sound locations but always in low frequency.

Atrina serrata (Sowerby)Pinna serrata SCWERBY-, 1825, Tank. Cat. App., p. 5.

This form has been recovered from the Chandeleur Islands and has been taken alive from sands beneath four feet of water immediately west of the central Chandeleurs. It has been reported from North Carolina to the southern half of Florida and in the Caribbean Sea.

Barnea costata (Lirme)/Pholas costatua LINNE. 1758, Syst. Nat., ed. 10, p. 669.

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The range of this species is from Massachusetts to Florida and Texas, the West Indies and Brazil, It is fairly common on teaches in the area studied hut has not been recovered in bottom samples.

Brachidontes recurvus (Rafinesque)? Mytilus recurvus RAFINESQUE. 1820, Mon. Coq. Biv, Ohio, p. 55.

This form has been found in nine lake, one inner sound and three beach stations and is usually rare vhen present. It is found from.Cape Cod, Massachusetts, to the West Indies.

Chione (?) sp.Several specimens have been taken from two stations in central Chande­

leur Sound.

Corbula sp.This species is found at one beach and five sound stations. It is about

5 mm. long, 3.5 mm. wide and ornamented with numerous concentric ridges. Very fine beaded radial ridges occur in grooves between the concentric markings.

Crassinella lunulata (Conrad)Astarte lunulata CONRAD, 1837, Jour. Acad. Nat, Sci. Phila., 1st Ser., vol. 7 ,

P. 133.In St, Bernard Parish this species is found in sound and beach samples.

It is reported from seven stations and is most abundant on the reefs. It ranges from Cape Cod, Massachusetts, to the Gulf CoaBt and the Barbados.

Crassostrea virginica (Gmelin)Ostrea vlrglnlca GMELIN. 1792, Syst. Nat., p. 3336.

This is the most abundant mollusk in the area and is present from the

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inner lakes to the outer beaches. It has been reported from the Gulf of St.Lawrence to the Gulf of Mexico and the West Indies.

Dinocardium robustum (Solander)Cardium robustum SOLANDER, I786, Portland Cat., p. 58.

Shells of this species are fairly common on the Chandeleur Islands and are recorded from three beach stations. The species is found from Virginia and north Florida to Texas, Mexico and Brazil.

Donax tumida Philippi Donax tumlda PHILIPPI. 181*8, Zeitschr. Mai., p. 1U7 .

Living specimens range from rare to abundant in very shallow water Just below sea level on the Chandeleurs. The species has been recorded at three beach and two outermost sound locations and is restricted to sandy bottoms.It occurs from the east coast of Florida along the Gulf Coast to Mexico.

Dosinia discus (Reeve)Artemis discus HEEVE, 1850, Conch. Icon., vol. 6, pi. 2, fig. 9.

In the area investigated this form does not show a clear-cut preferencefor any Bediment type. It occurs in low frequencies at six sound and fourbeach locations and is reported from Virginia to Florida, the Gulf states and the Bahamas.

Ensis minor Dali Ensis minor PALL. 1899, Proc. U. S. Nat, Mus., vol. 22, p. 108,

ThiB species is reported from New Jersey, the east and west coasts ofFlorida and Texas. Several specimens were taken at one location in northern Chandeleur Sound.

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Labiosa plicatella Lamarck Labiosa plicatella LAMARCK, l8l8, Anlrn. sane Vert., vol. 5, P. ^70.

Individuals of this species are occasionally found on the Chandeleur Islands. The species haB often been reported as Anatlna canaliculate and is found from North Carolina to Florida, Texas and the West Indies.

Lioberus castaneus (Say)Modlola castanea SAY, 1822, Jour. Acad. Nat. Sci. Phila., 1st Sa**.,

vol. 2, p. 266.One individual is present in one Chandeleur Sound reef sample. The

species is found on the east and vest coasts of Florida and the West Indies.

Lucina multilineata Tuomey and Holmes Luclna multilineata TUOMEY and HOIMES, 1857, Pleioc. Fob. S. Car.,

p. 61, pi. 18, figs. 16, 17.Specimens sre reported from North Carolina to the Gulf Coast, along

the Gulf Coast and Cuba. In the area studied the species vas found at one beach and tvo sound stations.

Lucina sp.The length of this species is 2 , 5 - 3 nmn. Ib is ornamented vlth about

ten prominent radiating ribs with subordinate concentric ribs. It lias been found in one beach and six sound samples and mostly on sandy bottoms,

Macoma constricta (Bruguiere)Solen constrictus BRUGUESRE, 1799, Mem. Soc. Hist. Nat., vol. 1, p. 126,

no. 3.This form has been found in low frequency on the Chandeleur Island

l&t

and Door Point 'beaches. One individual is recorded from a Lake Calehasse sample. The species is reported from Nev Jersey to Florida to Texas, the West Indies and Brazil.

Macoma tageliformis Dali Macoma tageliformis DALL, 1900, Trans. Wagner. Instit. Sci., vol. 3,

Pt. 5, P. 1055.This species is recorded from Texas and Puerto Bico. In the investi­

gated area it was found at eight sound stations but was rare in every case.It prefers fairly muddy bottoms.

Mercenaria mercenaria (Linne)Venus mercenaria LINNE, 175^, Syst. Nat., ed. 10, p. 686.

Specimens are recorded from the Gulf of St, Lawrence to Florida and the Gulf of Mexico. The species was introduced to Humbolt Bay, California.In the area studied it is recorded from beaches and shallow water behind the Chandeleur Islands and is fairly common.

Mulinia lateralis corbuloides (Deshayes)Mactra corbuloldes DESHAIES, 185^, Pro'c. Zool. Soc, of London, p. 63.

This is one of the most abundant molluslcs in the area. It is found from the inner lakes to the beaches, but it seems to show slight preference for fairly low salinities and muddy bottoms. It occurs commonly along the Gulf Coast.

Nuculana acuta (Conrad)Nucula acuta CONRAD, I83I, Amer. Mar. Conch., p. 32, pi. 6, fig. 1.

The species is found from Ehode Island to the Antilles and from

California to Chile. Occurrence of the species in the area studied is confined to five outer sound samples. It is restricted to the cleaner send bottoms.

Nuculana sp.This form is larger than Nuculana concentrlca (length, 0.9 mm.,

width, 0.4 mm.) and has much finer concentric striations. It is found at three inner sound stations. Two of the three occurrences are on reefs and the other is in mud.

Ostrea frons (Linne) jfrtllus frons LINNE, 1758, Syst. Nat., ed. 10, p. 704.

Occurrences of this species are reported fl'om North Carolina, the east and west coasts of Florida, Louisiana and the West Indies. One specimen has been found on a Chandeleur Island beach.

Periploma ineguale C. B. Adams Perlploma inequale C. B. ADAMS, 1842, Amer. Jour. Sci. and Arts, vol. 43,

P. 1*5.One specimen of this species is recorded from Chandeleur Sound. It

is reported from South Carolina to Florida and Texas.

Eangia cuneata (Gray)Gnathodon cuneatua GRAY, I83I, in Sowerby, Gen. Shells, no. 36, figs. 1-3.

This form is found from the west coast of Florida to Mexico. In the area examined it is present in the lakes and inner sounds and on beaches. This species composes the majority of Indian middens in the Louisiana marsh­land. Its presence on Chandeleur Island beaches seems due to erosion of

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buried St. Bernard subdelta sediments seaward of the islands.

Rangia flexuoBa (Conrad)Gnathodon floxuosa CONRAD, 1839, Am. Jour, Sci., 1st. Ser., vol. 38,

p. 92, fig. 1839.Occurrences of this form are noted along the Gulf Coast from

Louisiana, Texas and Mexico. In the study area a few specimens have been found at the north point of the Chandeleur Islands.

Semele purpurascens (Gmelin)Tonus purpurascens GMELIN, 1792, Syst. Nat., vol. 6, p. 3288.

This species is recorded as "rare" f*om one station in inner Chandeleur Sound. It has been found from North Carolina to the southern half of Florida to the West Indies and Brazil and is fairly common in shal­low water.

Tagelus divisus (Spengler)Solen divisus SPENGLER, 1791*, Skrift. Nat. SelBk., vol. 3, p. $6,

This form is more common than Tagelus plebelus in the area investi­gated. It is recorded as "rare" from one beach and Bix sound samples. Specimens are largely confined to the portion of Breton Sound under the influence of the muddy Mississippi River sediments. The species is recorded from Cape Cod, Massachusetts, to south Florida, the Gulf States and the Caribbean.

Tagelus plebeius (Solander)Solen plebelus SOLANDER, 1786, Portland Cat., p. 42.

Collection of this species has been limited to one location in lakes

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and two on teaches. It is rare in all three samples. This form is found from Cape Cod, Massachusetts, to Florida and the Gulf Coast and has often been reported as Tagelus glbbus.

Tellidora cristata (Recluz)Lucina cristata RECLUZ, 181*2, R^rue Cuvier, p. 270.

There are two occurrences of this species in the sounds, and it is rare in both. Its range is from North Carolina to Mexico.

Tellina alternata Say Telllna alternata SAY, 1822, Jour. Acad. Nat. Sci. Phila., 1st. Ser.

vol. 2, p. 275.Two "rare" occurrences of this species are recorded from Chandeleur

and Breton sounds. It is reported-from North Carolina, Florida and the Gulf-States.

Tellina versicolor Cozzens Tellina versicolor COZZENS, 181*3, in Ds Ehy, Nat. Hist., New York, 5,

p. 209, pi. 26, fig. 172.This form is found at maiy stations in the lakes and sounds, but it

is always rare when present. Its distribution suggests that it has a preference for fairly muddy bottoms. It is found from New York to the southern half of Florida to the West Indies.

Trachycardlum muricatum (Linn^)Cardium muricatum LINNE, 1758, Syst. Nat., ed. 10, p. 680.

This species occurs in one beach and three sound Bamples. It is not present in outer sound or Chandeleur beach samples. It is found from North

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Carolina to Florida, Texas and the West Indies,

Volsella demlssa granosissima (Soverby]

Modlola demissa granosissima SOWERBT, 191, Proc, Mai*

P. 9.This is the only species of Pelecypoda found liv~±xB

Bernard marsh, and it is very abundant, It is found -si

vest coasts of Florida, the Gulf Coast and from the G-txI

S o c _

1 1 »L.

eas't and

to South Carolina. It has also been introduced to CaJL

Gastropoda

Acteocina canaliculata (Say)

Volvarla canallculata SAY, 1827, Jour. Acad, Nat, ScL. _____

vol. 5, pt. 2, p, 211.

In St. Bernard Parish this species has been fount<1 Jf.llttia

in the lakes and sounds and on beaches. It is report

Edvard Island, Canada, to Mexico and the West Indies*

p. 260) places this species under the genus Betusa,

_ _«* ls-fc.,Ser.,

i n H — '<r~rjw f r e q u e n c i e sP r i n c e

Abbo-fc-t. (195^,

Anachis obesa (C, B, Adams)

Bucclnum obesa C. B, ADAMS, 185, Pr08* B08* oc. Nat

Specimens have been recorded in lov frequencies f

from inner lakes to central sounds, and they shew no in

sediment type, It is found from Virginia to Florida

the West Indies,

=- _ E l iZ“ r-oxn 3^ n r e f e :

-fc2a©

. 2 y p, 2,;n s-fcations

siaJL bottom

S-tmates and

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Archltectonlca nobills Roding Archltectonlca nobllis BODING, 179$, Mus. Bolt., vol. 2, p. 78.

This species is often reported as Archltectonlca granulata (Lamarck) and ranges from North Carolina to Florida, Texas and the West Indies. It has been found on one beach of the Chandeleur Islands.

Bittium varium (Pfeiffer)Cerlthlum varium PFEIFFER, l&O, Arch, fur Naturg., p. 256, no. 139,

This form is reported common on grassy bottoms in shallow water of western Florida. It is present In one Chandeleur Sound sample adjacent to Freemason Island. Here the bottom Is clean sand covered with grass.The species is distributed from Maryland to Florida, the West Indies,Texas and Mexico.

Busycon contrarium (Conrad)Fulgur contrarlus CONRAD, 18^0, Am. Jour. Sci., 1st. Ser., vol. 39, P. 387.

The species is quite common on Chandeleur Island beaches, and living specimens have been recovered from the sandy water bottoms directly behind the islands. It has been found from South Carolina to Florida and the Gulf States.

Busycon spiratum (Lamarck)Pyrula spirata LAMARCK, 1816, Ency. Meth. (Vers.), pi. h33, Liste p. 8.

In this area Busycon spiratum has been found on Door Point, Freemason Island, and quite commonly on the Chandeleur Islands. The species Is dis­tributed from North Carolina to Florida and the Gulf States.

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Cantharus cancellaria (Conrad)Pollla cancellaria CONRAD, 181*6, Proc. Acad. Nat. Sci. f’hila., vol. 3,

p. 25, pi. 1, fig. 12.This species is distributed from Florida to Texas and Yucatan. A

few individuals have heen found in one Chandeleur Island sample and one Chandeleur Sound sample.

Ceritbium muse arum Say Cerlthlum muse arum SAY„ 1832, Amer. Conch. ,V, pi. 1*9, fig. 1,

In the area investigated this form has been found in low frequency on beaches of the Chandeleur Islands and in one sound sample. It occurs from the southern half of Florida to the Gulf Coast and the Vest Indies.

Cerithium sp.This common form has been found in one outer lake and eight sound

samples. It averages 7 mm. in length and has an elongate spire and seven to eight whorls. The crossing of its axial and spiral ribs results in eight double rows of nodes to a whorl on the spire and five rows of nodes on the body whorl. Spiral ridges are light brown, and the overall color is light buff. Aperature is oval; inside of outer lip crenulate; thickened varix behind lip; anterior canal short, oblique; posterior canal almost lacking.

Crepidula fornicata (Linne)Patella fornlcata LINNE, 1767, Syst. Nat., ed. 12, p. 1257.

Specimens were found at the north point of the Chandeleur Islands and Isle au Pitre, The species occurs from Nova Scotia to Florida and the Gulf of Mexico and Colombia.

Crepidula plana Say Crepldula plana SAY, 1822, Jour. Acad. Nat. Scl. Phila., lot, Ser,,

vol. 2, p. 226.The species is found from Florida to the Gulf States and rarely in

the West Indies. It has been recorded from 11 stations from the lakes, sounds and beaches of St. Bernard Parish and is found attached to other shells.

Epitonium sp.One specimen of this small gastropod has been found in central

Chandeleur Sound.

Littoridina sp.In St. Bernard Parish this species has been found in four lake, one

sound and two Chandeleur Island samples. The shell is small and is sue- ceptable to transport by currents; however, its concentration in lakes suggests a habitat of under 20 0/00 salinity. No living specimens were noted, This species may bo Littoridina sphinotostoma Abbott and Ladd, which was described from brackish waters of coastal Texas,

Littorina irrorata (Say)Turbo irroratus SAY, 1822, Jour. Acad. Nat. Sci, Phila., 1st. Ser.,

vol. 2, p. 239.This is the most abundant gastropod in the more saline marsh areas.

It has not been noted in weakly brackish portions. The species is reported from Massachusetts to north Florida, Texas and Jamaica.

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Melampus bidentatus bidentatue Say Melsmpus bldentatus SAY, 1822, Jour. Acad. Nat. Sci. Phila., 1st. Ser.,

vol. 2, p. 21*5.The distribution of this species is Nova Scotia to Texas. It is

abundant in the marsh of southwestern coastal Mississippi but has not been found in the marsh of St. Bernard PariBh.

Mitrella lunata duclosiana (d'Qrbigny)Columbella ducloslana D'ORBIGNY, 1&6, Moll. Cuba, ii, p. 136, pi. 21,

figs. 31-33.The species was noted in two sound and two beach samples, and

living specimens were taken from the reef at station 27, Chandeleur Sound, It has been reported from Cape Cod, Massachusetts, to Florida, Texas and the West Indies.

Mur ex fulvescens (?) Sowerby Murex fulveacens SOWERBT, 183^, Conch. Illust., Murex, fig. 30.

One individual, questionably referable to this species, has been found on the beach at the north point of the Chandeleur Islands. The species is reported from North Carolina to Florida and Texas.

Nasaarius acutus (?) (Soy)Nassa acuta SAY, 1822, Jour, Acad. Nat. Sci. Phila., 1st. Ser., vol. 2,

P. 231*.Only one occurrence of this species has been noted in soft, silty

clay of inner Chandeleur Sound. The specimen is broken and not definitely identifiable. The species is found from the west coast of Florida to Texas.

Neritina reclivata (Soy)Theodoxua recllTatua SAT, 1822, Jour. Acad. Nat. SCI. Phila., lat Ser.,

vol. 2, p. 257.Fragmenta of this species vere found in one Chandeleur Island sample,

hut complete individuals have heen found in sediment filling swales of buried beach ridges in Hancock County, Mississippi. The specimens on the Chandeleurs were most likely dorived from the St. Bernard subdelta sediments being eroded Just seaward of the islands. The species has been reported from Florida to Texas and the West Indies,

Odostomia impressa (?) (Say)Turritella impressa SAY, 1822, Jour. Acad. Nat. Sci. Phila., 1st. Ser.,

vol. 2, p.One questionable specimen has been recovered from one sample in

Chandeleur Sound. The species is common in shallow water off Florida end the Gulf Coast.

Oliva say ana Ravenel Oliva sayana RAVENEL, 183 , Cat. Roc. and Fos, Sh. in the cabinet of

Edmund Ravenel, M.D., Charleston, S. C., p. 19.Specimens were found in low frequency on the Chandeleur Island

beaches; however, large numbers of this species have been observed on the sand flats behind the north end of Errol Island at low tide (August, 1952). The species ranges from North Carolina to Florida and the Gulf States.

Olive 11a mutica (Say)

Oliva mutica SAY, 1822, Jour. Acad. Nat. Sci. Phila., 1st. Ser.,

171*

vol. 2, p. 228.

Distribution of this species is apparently controlled "by "both salinity and "bottom, sediment. It is present in three sound samples of sediment type two at low frequencies and in no others. The species is found from North Carolina to the Gulf Coast and the West Indies.

Phalium granulatum (Born)Caasis granulatum BORN, 1778, Index Mus. Caes. Vind., p. 239.

This species has been recorded from two samples on the Chandeleur Islands and is fairly rare. Distribution is from North Carolina to the Gulf of Mexico and the West Indies.

Polinices duplicatus (Say)Natlca dupllcata SAY, 1822, Jour. Acad. Nat. Sci. Phila., 1st.Ser., vol. 2,

P. 2kj.Specimens have been reported from Cape Cod, Massachusetts, to

Florida and the Gulf States. In St. Bernard Parish it occurs commonly on the beaches and has been found in one inner sound sample. The two specimens from the inner sound had their periostracum intact, but the body whorls were occupied by Crepidula plana, therefore, these shells may have been transported,

Pyramidella sp.Only one specimen referable to this genus has been noted. It was

found on a Chandeleur Island beach.

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Strombus pugilis alatus Gmalln 3trombus alatus CMELIN, 1792, SyBt. Nat., vol. 6, p. 3513 •

Specimens vary from nearly spineless forma through those with spines on the last row to thoBe with two rcrws of prominent spines, A few forms approach Strombus pugllls in the prominent second spine row, but they lack the usual orange color. In the area studied this species is found only on the northern Chandeleur Islands. It has been reported from South Carolina to the east and west coasts of Florida and Texas.

Thais haemastoma haysae (Clench)Ihals floridana haysae CHINCH, 1927, The Nautilus, vol. 1*1, pp. 6-8.

This oyster drill is common along the Gulf Coast and is reported from northwest Florida to Texas, Strangely enough, it has not been recovered from any of the oyster reefs in the sampled area, but it is common in placeB on the beaches.

Turbonilla spa.These two species occur in one beach and seven sound locations. The

smaller (length, 1* mm.) species has distinctive ornamentation of generally 23 vertical ribs crossed with spiral grooves broken at each rib.

Scaphopoda

Dontalium texasienum Philippi Dentalium texasiana PHILIPPI, 181*8, Zeitschr. Malak. p. ll*l*.

One individual has been taken from each of two locations in central Chandeleur Sound. The species has been reported from North Carolina and

the Gulf ,StateB.

VITARobert C. Treadwell was barn in Galveston, Texas on October 28,

1928. He attended grammar and high school in Houston, Texas, and graduated from Stephen F. Austin High School in June, 19^5* From 19^5 to 19^9 he attended the University of Texas, receiving his B.S. in Geology from that institution in August, 19^9. His graduate studies were initiated at Louisiana State University in the fall of 19^9, and he received an M.S. in June, 1951. Since that time he has been affiliated with the Office of Naval Research and the Coastal Studies Institute at Louisiana'State University, Si September, 1951,he married Gayle R. Young of Lalce Charles, Louisiana.

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