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LOS ANGELES BASIN, CALIFORNIA
EARLY PLIOCENE SEDIMENTARY HISTORY OF THE
LOS ANGELES BASIN, CALIFORNIA
By Bert L. Conrey
Professor of Geology
California State College, Long Beach, California
SPECIAL REPORT 93
California Division of Mines and Geology
Ferry Building, San Francisco, 1967
STATE OF CALIFORNIARonald Reagan, Governor
THE RESOURCES AGENCYNorman B. Livermore, Jr., Administrator
DEPARTMENT OF CONSERVATIONJames G. Stearns, Director
DIVISION OF MINES AND GEOLOGYIan Campbell, Siafe Geologist
SPECIAL REPORT 93
PRICE $1.25
\ /
Manuscript submitted for publication 1961, modified from Doctor of
Philosophy Dissertation, "Sedimentary History of the Early Pliocene
in the Los Angeles Basin," University of Southern California, 1959.
Page CONTENTS5 Abstract
7 Introduction
9 Regional setting
9 Physiography
12 Geology
12 Stratigraphic nomenclature
12 Definition of lower Pliocene
12 Identification and subdivision of lower Pliocene
13 Nature and distribution of the lower Pliocene rocks
13 Method of study
13 Field study
14 Electrical well logs
14 Laboratory study
14 Conglomerate
15 Distribution and thickness
16 Textures
16 Sedimentary structures
17 Composition
18 Sandstone
18 Distribution and thickness
20 Grain size
20 Sorting
21 Roundness
22 Sedimentary structures
22 Composition
25 Siltstone and silty shale
26 Distribution and thickness
27 Grain size
28 Sorting
29 Fissility
29 Mottled structures
30 Composition
35 Limestone
35 Volcanic sediments
36 Depositional environment
36 Submarine topography
37 Depth
44 Specific features
50 Overlying water
51 Rate of sedimentation
51 Tectonic activity
55 Mode of transportation
55 Turbidity currents
55 Evidence of the active role of turbidity currents
56 Source and direction of movement of turbidity currents
56 Submarine slumps
56 Evidence of the active role of submarine slumps
57 Normal surface and near surface currents
57 Evidence of the active role of surface currents
57 Source areas
57 Detrital material in the sedimentary rocks
58 Santa Monica Mountains source
59 San Gabriel Mountains source
59 Puente Hills source
60 Perris Uplands source
60 Santa Ana Mountains source
60 San Joaquin Hills source
60 Palos Verdes Hills source
60 Subaerial erosion of source areas
61 Volcanic sediments
61 Source
62 References
Page
10 Figure 2.
11 Figure 3.
14 Figure 4.
15 Figure 5.
16 Figure 6.
17 Figure 7.
18 Figure 8.
19 Figure 9.
20 Figure 10.
21 Figure 11.
22 Figure 12.
23 Figure 13.
24 Figure 14.
26 Figure 16.
27 Figure 17.
28 Figure 18.
ILLUSTRATIONS
FIGURES
Figure 1. Map of the coastal area of southern California and the continental
borderland.
Index and physiographic map of the Los Angeles Basin area.
Generalized geologic map of Los Angeles Basin and borders.
Structure contour map of base of upper Pliocene in the Los Angeles
Basin.
Isopach map of lower Pliocene.
Isopach map of lower-lower Pliocene.
Figure 7. Isopach map of middle-lower Pliocene.
Isopach map of upper-lower Pliocene.
Location map showing lines of stratigraphic sections for plates 1, 2,
and 3.
Lithofacies map of lower Pliocene.
Lithofacies map of lower-lower Pliocene.
Lithofacies map of middle-lower Pliocene.
Lithofacies map of upper-lower Pliocene.
Photos of sedimentary structures in conglomerates at location 22,
southwestern end of the Puente Hills.
25 Figure 15. Photos of sedimentary structures in conglomerate at the western endof the Puente Hills.
Sandstone isopach map for lower Pliocene.
Areal variation in average grain-size class of sandstone.
Stratigraphic variation of grain size for standstone along the western
side of the basin.
29 Figure 19. Stratigraphic variation of grain size for sandstone in the north-
eastern part of the basin.
30 Figure 20. Histogram showing variation of sorting coefficients for sandstone.
31 Figure 21. Median diameter-sorting coefficient curve for sandstone.
32 Figure 22. Median diameter-sorting coefficient plot for sandstone from the
northeastern and southwestern sides of the basin.
33 Figure 23. Areal variation in roundness of granule-size fraction of sandstone.
34 Figure 24. Photos of sedimentary structures in sandstone.
35 Figure 25. Areal variation in quartz-feldspar ratios in sandstone.
37 Figure 26. Areal variation in heavy mineral suites of sandstone.
41 Figure 27. Petrology of pebble and granule fractions of sandstone.
42 Figure 28. Petrology of pebble and granule fractions of sandstone.
43 Figure 29. Siltstone-silty shale isopach map for lower Pliocene.
44 Figure 30. Areal variation in average grain-size class of siltstone and silty shale.
45 Figure 31. Textural classification of fine-grained rocks.
46 Figure 32. Stratigraphic variation of grain size for siltstone and silty shale.
47 Figure 33. Photos of pebbly siltstone and cobbles from siltstone strata.
48 Figure 34. Histogram showing variation of sorting coefficients for siltstone andsilty shale.
49 Figure 35. Median diameter-sorting coefficient curve for siltstone and silty shale.
50 Figure 36. Photos of sedimentary structures in siltstone and silty shale.
51 Figure 37. Stratigraphic variation of acid-soluble material in siltstone and silty
shale.
52 Figure 38. Areal variation in composition of microfossil assemblages from basal
lower Pliocene strata.
53 Figure 39. Paleophysiographic map of Los Angeles Basin during early Pliocene.
54 Figure 40. Stratigraphic cross sections displaying pinch-outs.
57 Figure 41. Photos of sandstone cores.
58 Figure 42. Photos of sedimentary breccia.
PLATES
In pocket 1. Stratigraphic section A to D.
In pocket 2. Stratigraphic section F to B.
In pocket 3. Stratigraphic section E to C.
In pocket 4. Correlation between electrical well logs and stratigraphic sections.
ABSTRACT
The lower Pliocene strata in the Los Angeles Basin have a range in thickness from
a knife edge to more than 5,000 feet. The strata consist principally of conglomerate,
sandstone, siltstone, and silty shale. In addition, minor amounts of limestone, bentonite,
chert, and volcanic ash occur among the dominant rock units. The clastic rocks display
distinct areal variations in thickness, texture, and composition that provide evidence as
to their depositional environments, source areas, and modes of transportation. Addi-
tional clues are provided by sedimentary structures and microfossil assemblages in the
clastic rocks.
Sedimentary and faunal data indicate that the Los Angeles Basin was a deep sub-
marine basin during early Pliocene. The broad floor of the basin was probably rela-
tively flat; however, belts of irregular topography along the margins of the basin floor
are indicated by concentrations of coarse-grained clastic rocks. Comparative studies of
modern offshore basins suggest that the irregular topography represented submarine
fans and slump aprons. The submarine margins of the basin are identified by (1) the
position of the submarine fans and slump aprons, (2) sedimentary pinch-outs, and (3)
angular unconformities. The pinch-outs and angular unconformities suggest marginal
slopes of 6-10° along the eastern side of the basin and possibly 20° at its northwestern
margin. A submarine sill apparently separated the deep portion of the Los Angeles
Basin from the open sea along its present coastal margin. Faunal data indicate that
the lowest part of the sill was at the southwestern margin of the basin. The minimum
depth of the sill probably was 6,000 feet at the beginning of the Pliocene. At the close
of early Pliocene it shoaled to a minimum of 4,000 feet subsea.
The fossil faunas and sediments also provide clues as to the nature and movement
of the marine waters during the early Pliocene. The following conditions are suggested:
(1) deficiency in the oxygen content of the water at the water-sediment interface on
the bottom of the basin; (2) subsill waters ranging in temperature from 2.5° C. at the
beginning of the Pliocene to 3.5° C. at the close of the early Pliocene; (3) abnormally
low salinity of the surface waters until late-early Pliocene; and (4) dominant westward
and southward motion of bottom waters from the northern and eastern margins of
the basin.
An average yearly depositional rate of 0.07 cm. is estimated for the lower Pliocene
strata. This rate approximates that occurring in the modern submarine basins off the
coast of southern California.
The tectonic instability of the basin floor is a contributing cause of the areal varia-
tion in thickness of strata. Moreover, localities that were undergoing active upwarping,
downwarping, or faulting during the early Pliocene are delineated by sedimentary
patterns.
Sediments were transported into the basin in three ways: (1) turbidity currents; (2)
submarine slumps; and (3) surface currents. Most of the turbidity currents and sub-
marine slumps originated along the northern and eastern margins of the basin. The
surface currents were distributed uniformly in the basin.
Seven source areas for detrital rock debris were identified in this study: (1) Santa
Monica Mountains, (2) San Gabriel Mountains, (3) Puente Hills, (4) Perris Uplands, (5)
Santa Ana Mountains, (6) San Joaquin Hills, and (7) Palos Verdes Hills. The principal
source areas were the San Gabriel Mountains and Puente Hills. There is evidence that
many of the source areas were undergoing subaerial erosion.
ARLY PLIOCENE SEDIMENTARY HISTORY OF THE
)S ANGELES BASIN, CALIFORNIA
- Bert L. Conrey
ofessor of Geology
jlifornia State College, Long Beach, California
INTRODUCTION
One of the principal goals of this study was to de-
iirmine the nature of the environment of the Los.ngeles Basin during the deposition of the lower Plio-
sne sediments.
In the infancy of geology as a science it was recog-
ized that the natural processes in operation todayanctioned throughout the geologic past; therefore, to
iterpret physical events recorded in ancient rocks it
; necessary to recognize at least the products of the
atural processes in action today. With the maturingf the geological sciences in the 20th century greater
nd greater emphases have been placed upon the un-lerstanding of sedimentary processes and environ-
nents of deposition; the ultimate goal is, of course, the
nterpretation of the physical events preserved in the
ncient sedimentary rocks.
Until the past two decades most of the studies of
environments and sedimentary processes were confinedo terrestrial sediments which make up only a fraction
)f the ancient sedimentary rocks; the reason for this is
die relative inaccessibility of the marine sediments*vhich often require expensive equipment and ocean-going vessels to examine them properly. As a result,
:he earlier work by geologists concerning the marineenvironments and processes interpreted from the an-
cient sedimentary rocks was highly speculative. Recentyears have witnessed enormous advances in the studyof the sea floor; the results prior to 1950 were effec-
tivelv summarized bv Shepard (1948) and bv Kuenen(1950).
Certain areas naturally received more attention than
others due to their proximity to oceanographic institu-
tions. In this regard, the submerged area between the
mainland of southern California and its continental
slope, "continental borderland" of Revelle and Shepard
(1939), has been under investigation several years bythe Allan Hancock Foundation for Scientific Research(University of Southern California) and Scripps In-
stitution of Oceanography (University of California).
Most of the investigations by Scripps Institution of
Oceanography were performed prior to 1940. The
submarine basins on the "continental borderland" re-
ceived increased attention in recent years because ofcertain resemblances between them and the coastal
land basins of Los Angeles and Ventura (figure 1).
This interest was stimulated by the prolific oil deposits
in the ancient marine deposits of Miocene and Pliocene
age in the Los Angeles and Ventura Basins.
Several papers were published in recent years point-
ing out the resemblance between the living Foraminif-
era of the offshore basins and their fossil counterparts
in the Los Angeles and Ventura Basins. These data
were used to evaluate the conditions in the Los An-geles and Ventura Basins in the geologic past. Forexample, in 1933 Natland pointed out the similarity of
the living Foraminifera in one of the submarine basins
to those in the Pliocene sediments of the VenturaBasin. In addition, his foraminiferal studies indicated
that the Ventura Basin was a deep submarine basin
that progressively was filled during the Pliocene. Addi-tional comparisons between the living foraminiferal
populations in the submarine basins and their fossil
counterparts in the coastal land basins were made byCrouch in 1952; however, this time the analogy was
made between the Los Angeles Basin and the offshore
submarine basins. As with the Ventura Basin, the LosAngeles Basin Mas depicted as a deep submarine basin
that progressively was filled during the Pliocene. Ayear later Bandy (1953), in assigning the habitat of
living foraminiferal populations to their fossil counter-
parts, demonstrated changing rates of subsidence of
the Ventura Basin during the Pliocene. Furthermore,
he proposed a similar history for the Los Angeles
Basin.
Sedimentary studies have also pointed out the re-
semblance between submarine basins on the "con-
tinental borderland" and the Los Angeles and Ventura
Basins. For example, in 1941 Shepard and Emery sug-
gested that the Pliocene sediments in the Los Angeles
and Ventura Basins were deposited in environments
similar to those of submarine basins. Analogies between
the mode of deposition in submarine basins and the
lower Pliocene marine deposits in the Ventura Basin
[7]
California Division of Minis and Geology SR '
118° 117°
121°
Q 10 20 30 40 50
,.•""""1"-—•**",.« -*«\. Statute Miles
ptuTdi Ml& ix *»a^_ntours in Fathoms -
-
-33
-32'
Figure 1. Map of the coastal area of southern California and the "continental borderland."
967 Early Pliocene History, Los Angeles Basin—Conri.y
vere pointed out by Natland and Kuenen (1951) andihepard (1951) in the "Symposium of Turbidity Cur-ents." In 1952, Emery and Rittenberg described the
ubmarine basins as incompletely filled counterparts of
he land basins of Ventura and Los Angeles. In their
)aper, they demonstrated a similarity between the
.ediments of the submarine basins and samples of the
ate Tertiary and Quaternary marine sediments ob-
:ained from the Dominguez oil field in the Los AngelesBasin. In subsequent studies of cores from Santa
Monica and San Pedro submarine basins, Emery recog-
nized the important role of turbidity currents in
transporting sands throughout the basins. Later, underthe sponsorship of Emery, Gorsline accepted a grant
for an extensive sedimentary study of these sands
(Gorsline, 1958). Additional cores and surface sedi-
ments were collected from Santa Monica and SanPedro Basins and evaluated in terms of sedimentaryfacies, depositional agents, and sedimentary source
areas. In this work, resemblances between the sub-
marine basin sediments and the Pliocene marine sedi-
ments of the Ventura and Los Angeles Basins werenoted. In addition, the previous concept of the sub-
marine basins as unfilled counterparts of the Los An-geles and Ventura Basins was again emphasized.
The abbreviated resume of the growth in the recog-nition of the resemblance between the existing sub-
marine basins on the "continental borderland" and the
ancient marine basins that once occupied the present
land sites of the Los Angeles and Ventura Basins waspresented to illustrate an ideal situation for the studyof sedimentary rocks from a submarine basin that
existed in the geologic past. In the matter of selecting
the best site for the present study, Los Angeles Basinwas selected rather than Ventura Basin for two prin-
cipal reasons: (1) far more data are available concern-ing the preponderance of the deposits whichunfortunately are blanketed by younger terrestrial
rocks, and (2) Los Angeles Basin is less deformed thanVentura Basin. The rocks of the lower Pliocene wereselected for this study because, in the first place, theyrepresent the most recent of the ancient submarinebasin deposits on which adequate subsurface data are
available; and secondly, the majority of the early com-parisons between the present offshore basin sedimentsand their ancient counterparts were made using these
lower Pliocene sedimentary rocks.
The method of attack of this problem involved first
and foremost an intensive study of the lower Pliocene
rocks throughout the basin. They were studied in
terms of distribution, thickness, textures, sedimentary
structures, and composition. This study ranged from
visual estimates to detailed laboratory analyses of sedi-
mentary samples. In addition, indirect lithologic data
were compiled from electric logs and where necessary
from drillers' logs. The fossil faunas contained in the
sediments, from the top and bottom of the lower Plio-
cene at several locations, were examined for ecologic
data. The sedimentary and faunal data were then eval-
uated using comparative information from the sub-
marine basins located in the adjacent "continental bor-
derland."
Acknowledgments. The writer is indebted to Dr.K. O. Emery, of the Department of Geology, Univer-sity of Southern California, who suggested the problemand gave advice and guidance during the course of thisstudy. Drs. Orvillc L. Bandy, Thomas Clements, Wil-liam H. Easton, and C. M. Bccson of the University ofSouthern California; and Dr. Hubert G. Schcnck ofStanford University who read the original manuscript(Conrey, 1959) and offered much helpful criticism.
Financial aid was provided by the Richfield OilCompany as a grant-in-aid through Dr. K. O. Emervfor the summer of 1954. The Allan Hancock Founda-tion, at the University of Southern California, providedoffice and laboratory facilities for analyses and storageof samples.
The writer gratefully acknowledges the fine cooper-ation of the many oil companies that provided data forthis study. In particular, the Standard Oil Companyof California was especially cooperative in supplvingcritical data and aiding the writer in reproduction ex-penses, and the Union Oil Company furnished most ofthe well cores and foraminiferal samples described in
this paper.
Regional setting
A brief discussion of the physiography and geologvof the Los Angeles Basin and adjoining region is pre-sented to acquaint the reader with the major landforms and their geologic make-up so that he can betterevaluate the writer's conclusions regarding deposi-tional environments and source areas. More detailed
discussions of the physiography and geology can beobtained from Reed and Hollister (1936), Larsen(1948), California Division of Mines Bulletin 170
(1954), and Poland and Piper (1956).
Physiography
The Los Angeles Basin is a structural depression nowso filled by sediments that its surface is a plain gentlysloping towards the sea. It has a northwest trend, 50miles long and about 20 miles wide. The basin is
bounded on the north by the Santa Monica Mountainsand Puente Hills, on the east by the Santa Ana Moun-tains and San Joaquin Hills, and on the west and south
by the Palos Verdes Hills and Pacific Ocean (figure 2).
North of the Santa Monica Mountains and PuenteHills are three structural depressions similar to the LosAngeles Basin but smaller in size; they are the SanFernando, San Gabriel, and San Bernardino Valleys.
A major mountain range, the San Gabriel Mountains,
forms the northern border of these valleys. East of the
Santa Ana Mountains is a series of hills and valleys of
subdued relief called the Perris Uplands.
The ocean floor to the south and west of the coastal
margin of the Los Angeles Basin grades from an in-
sular shelf to a succession of deep basins and submarine
banks and ridges, several of which arc capped by is-
lands (figure 1). The size, arrangement, and trend of
these submarine features strongly resemble the topo-
graphic features of the adjacent land (Shcpard and
Emery, 1941). The two submarine basins located in
closest proximitv to the Los Angeles Basin are the San
Pedro and Santa Monica Basins.
10California Division of Mines and Geoloov SR 9»
967 Early Pliocene History, Los Angeles Basin—Conrey 11
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12 California Division of Mines and Geology SR 93
Geology
A generalized picture of the geology of the Los
Angeles Basin and adjoining areas is presented in
figure 3. A brief summary of the geology is presented
in the following paragraphs.
Stratigraphy. The Los Angeles Basin is a structural
depression with its central floor buried beneath at
least 20,000 feet of Miocene and later deposits, princi-
pally sedimentary. In the southwestern part of the
basin its floor consists of crystalline schist (Franciscan
[?] schist or Catalina schist) of questionable Jurassic
age. This schist was penetrated by oil wells at 14,000
feet subsea in the vicinity of location 57 (Long Beach
field) and crops out 1,000 feet above sea level in the
Palos Verdes Hills. Little is known about the floor of
the remainder of the basin; however, Woodford and
others (1954) suggested that the similarity of Mesozoic
rock types forming the cores of the Santa Monica
Mountains to the northwest and the Santa Ana Moun-tains to the east indicates similar rocks composing the
central floor. They also suggested that along the north-
eastern margin of the basin the floor may be composedof crystalline rocks similar to those encountered in
the subsurface in the adjacent Puente Hills and those
cropping out to the north in the San Gabriel Moun-tains.
The Miocene and later rocks that fill the Los An-geles Basin crop out on the flanks of the Santa Monicaand Santa Ana Mountains. These Miocene rocks blan-
ket the Puente and San Joaquin Hills. In the SanFernando, San Gabriel, and San Bernardino Valleysthe Tertiary to Quaternary sequence of the Los An-geles Basin is repeated in an abbreviated manner. ThePerris Uplands, which lie to the east of the Santa AnaMountains, are composed principally of Mesozoic plu-
tortic and metamorphic rocks (Larsen, 1948).
Structure. The Los Angeles Basin is divided struc-
turally into fairly well defined blocks, mostly by major
faults or fault zones. A southwestern block is bounded
by a fault along the northeastern side of the Palos
Verdes Hills and by the Newport-Inglewood fault
zone, extending from Newport at the southeastern end
of the basin to the Beverly Hills field at its north-
western margin. The central block lies between the
Newport-Inglewood trend and the Anaheim fault zonethat extends northwestward into the basin from the
northeastern end of the Santa Ana Mountains. Thenortheastern block is bounded by the Anaheim fault
zone and the Whittier fault which can be traced alongthe southern margin of the Puente Hills. Within the
individual fault blocks, the most notable structural
features are anticlines.
The highlands bordering the basin consist of positive
blocks delineated, at least in part, by faults. The SanFernando, San Gabriel, and San Bernardino Valleysrepresent structural depressions between the positiveblocks.
STRATIGRAPHIC NOMENCLATURE
Definition of lower Pliocene
The lower Pliocene strata in the Los Angeles Basin
generally are referred to as the Repetto Formation, a
practice that unfortunately is well entrenched in litera-
ture. Repetto originally was proposed as a formational
name for the lower Pliocene siltstones cropping out
along Atlantic Boulevard in the eastern part of the
Repetto Hills (Reed, 1936). However, its usage im-
mediately was expanded far beyond the formational
concept and was applied instead to all lower Pliocene
rocks, irrespective of lithology (pis. 1-4), containing
characteristic foraminiferal assemblages similar to those
in the type area of the Repetto Formation.
In recent years, stage names have been assigned to
these lower Pliocene strata. In 1938, Kleinpcll pro-
posed the "Lower Pliocene" Stage, tentatively correlat-
ing this stage with the Pontian of Europe. In 1952,
Natland proposed the Repettian Stage for these lower
Pliocene strata. The type area of the Repetto Forma-tion was designated as the type locality of the Repet-
tian Stage.
In this report the lower Pliocene strata will be called
"lower Pliocene." This terminology is used in lieu of
the Repettian Stage since the biostratigraphic correla-
tions in this report were provided by paleontologists
who, at the time of this study, had not adopted the
Repettian, Venturian, Wheelerian sequence of stages
for the Pliocene that were proposed by Natland
(1952).
Identification and subdivision of lower Pliocene
The lower Pliocene strata are identified by the oc-
currence in the strata of foraminiferal markers diag-
nostic of Wissler's foraminiferal zones for the Repetto(1941). The lower Pliocene is subdivided into lower,
middle, and upper divisions on the basis of the three-
fold subdivision of the Repetto made by Wissler
(1941); this is displayed in Table I. The identification
and subdivision of the lower Pliocene strata at the
various locations were made by paleontologists fromseveral oil companies.
An extended discussion of the foraminiferal zones is
beyond the scope of this work; how ever, brief mentionof the species characterizing the upper, middle, andlower parts of this stage is pertinent. The top of upper-lower Pliocene is selected on the basis of the first
abundant occurrence of Cibicides mckannai Gallowayand Wissler (small form), and its base is placed at the
first occurrence of Karreriella viilleri Natland; Plecto-
frondicidaria catifornica Cushman and Stewart also
characterizes this interval. The top of middle-lowerPliocene begins with Karreriella viilleri Natland, andits base is placed at the first appearance of Liebusella
pliocenica (Natland). The lower-lower Pliocene be-
gins with the latter species, and its base is placed at
approximately the upward limit of Rotalia garveyensis
Natland; this also marks the beginning of continuousoccurrence of Karreriella milleri Natland and Hop-kinsina nodosa Natland. Typical lower Pliocene forami-
niferal assemblages are described by Martin (1952)
1967 Early Pliocene History, Los Angeles Basin—Conki.y 13
and White (1956). Typical foraminiferal assemblages
from the top and the base of the lower Pliocene are
described (Tables IV and V).
Table I. Stratigraphic correlation chart.1
Age
UpperPliocene
LowerPliocene
UpperMiocene
Stage
Venturian
(?)
Repettian
(?)
Delmonttan
Mohnian
Faunaldivision
Lowe
Upper
Middle
Lower
Guide fossils
Bulimina subacuminata Cushmanand Stewart
Cibicides mckannai Galloway andWissler
Plectofrondicularia californica Cush-man and Stewart
Karreriella milleri Natland
Liebusella pliocenica (Natland)
Rotalia garveyensis Natland
Bulimina sp. (large, crushed)— rare occurrence —
Bulimina sp. (large, crushed)— abundant occurrence -
Gyroidina rotundimargo
R. E. & K. C. Stewart
Bolivina hughes! CushmanCassidulinella ren u Una form i:
(Natland)
Bulimina uvigerinaformis Cushmanand Kleinpell
Baggina californica Cushman
Foram-iniferal
zone
' Chart modified from Wissler (1941) and Natland and Rothwel! (1954).
NATURE AND DISTRIBUTION OF THELOWER PLIOCENE ROCKS
The lower Pliocene in the Los Angeles Basin is rep-
resented primarily by a group of sedimentary rock
units consisting of varying proportions of siltstones
and siltv shales, sandstones, and conglomerates. Minorquantities of volcanic ash, bentonite, chert, and lime-
stone appear among the dominant rock units.
The lower Pliocene rocks appear at the surface atonly a few scattered localities along the periphery ofthe Los Angeles Basin where they terminate againstMiocene rocks. Basinward, they plunge beneath a thickblanket of younger sedimentary rocks to an estimateddepth of more than 10,000 feet below sea level in thestructural center of the basin (refer to the structurecontour map, figure 4).
There is a general thickening of the lower Pliocenetowards the structural center of the basin; however,the maximum recorded thickness occurs north of theMontebello oil field where more than 5,000 feet ofsection (corrected for dip) has been penetrated by oil
wells. Isopach maps are presented for the followingunits: the entire lower Pliocene (figure 5), the lower-lower Pliocene (figure 6), the middle-lower Pliocene(figure 7), and the upper-lower Pliocene (figure 8).
These maps show rather distinctive patterns; their sig-
nificance will be discussed in later sections. Thick-
tongues of lower Pliocene rocks appear to radiate fromMontebello to the west (4,000-foot section at Potrerooil field) and to the south, where the section is in
excess of 4,500 feet at La Mirada. Secondary patterns
also extend westward towards the center of the basin
from the vicinity of Brea-Olinda and Yorba Linda oil
fields, as well as from Burruel Ridge.
Method of study
The surface exposures of the lower Pliocene weredescribed in various degrees of detail by several ear-
lier authors whose contributions will be discussed later
in this paper. As a result, the writer concentrated his
efforts upon the main body of the lower Pliocene
which lies buried beneath the younger rocks in the
basin. The major source of data was the subsurface
cores obtained from oil wells at 27 locations in the
basin. The core data had to be supplemented by elec-
trical well log data, drillers' logs, or merely thickness
data (based upon faunal studies) in critical areas wherecores were either entirely lacking or poorly repre-
sented. The locations identified in this report are dis-
played in figure 9.
Field study
Well cores from 27 locations were examined and
described using the standard subsurface litho-logging
method for cuttings, described by LeRoy and Crain
(1949). The textures, colors, general composition, and
sedimentary structures were recorded on a strip log
at the appropriate subsurface depth. The only addi-
tional equipment used not described by the previ-
ously cited authors was a geological sand-measuring
magnifier. This is a commercially produced pocket
magnifier containing a special reticle which has sand
grain sizes etched as circles around its periphery and
in its center has a one millimeter grid with one of its
squares subdivided into 0.2 mm squares. In the de-
scription of sedimentary rock units, comparative ref-
erences were made, whenever possible, to coarse- and
fine-grained constituents of the cores that were col-
lected for more detailed laboratory analyses. Unfor-
tunately, it was not possible to construct a complete
subsurface section at any one locality, owing to lack
of completely cored sections ami less than 5 percent
recovcrv of manv of the cores.
California Division of Mines and Geologi SR 93
.--•', * K
i
/
t\ \\\Vv ——
—
500o «^ V —i N.
•
1 *T~^ -J v^pTURNBUU
\ \ \Vv\\I\ \W^ —->T\ •
EXPLANATION
WALNU.T yy
C« / WL.
<^y> OUTCROPS OF ROCKS *Ps.
OLDER THAN PLIOCENE \ VOUTCROPS OF LOWER
PLIOCENE ROCKS
CONTOUR INTERVAL1000 FEET
j^ "'FAULT
• LOCATION
DATUM - BASE OF UPPERPLIOCENE
ZEROCONTOUR • SEA LEVEL
t
if
, —-
Figure 4. Structure contour map of base of upper Pliocene in the Los Angeles Basin.
Surface exposures of the lower Pliocene rocks wereexamined and described using the same parameters for
the well cores. However, since most of the surface
exposures had been described previously by otherauthors, the writer devoted most of his efforts to col-
lecting representative samples for laboratory analyses.
Electrical well logs
The lack of cored sections at critical points in thebasin, in addition to the incompleteness of the coresamples at many of the locations, necessitated the useof indirect lithologic data, which were interpretedfrom electrical logs run at oil well drilling sites. Themethod of interpretation of the lithologic data fromthe electrical well logs is described by Doll (1948),and by LeRoy and Crain (1949). Three lithologic"types" were identified on the electric logs: (1) "con-glomerate;" (2) sandstone; and (3) "shale." Sporadiccore data from the "conglomerate" demonstrate thatit is generally a compound unit composed of inter-bedded sandstones and conglomerate. Similar charac-teristics also appear in a few extremelv coarse-grainedsandstone units. The "shale" represents either siltstoneor silty shale; the writer was unable to differentiatebetween the two on the basis of electrical log charac-
teristics. The characteristics used to identify the three
lithologic parameters were established from typical
self-potential (SP) and resistivity curves recorded op-
posite cored intervals.
Laboratory study
Representative surface and subsurface (well core)
samples were analyzed in the laboratory for texture
(siz.c, sorting, and roundness). In addition, selected
samples were examined for organic carbon, insoluble
residue, mineralogy, petrology, and foraminiferal
popualtions. For the convenience of the reader, the
method and results will be discussed together in later
sections.
Conglomerate
The conglomerate beds cropping out along the
margins of the basin have received a great deal of at-
tention in the past by several investigators. One of the
earliest studies encompassing the basin was carried out
by Edwards (1934). Subsequently, more detailed
studies were made by Bellemin (1938) and Kundert(1952) in the western portion of the Puente Hills, and
by Olmsted (1948) in the Little Puente Hills. Otherworks, referring to the conglomerate beds, were by
967 Early Pliocene History, Los Angeles Basin—Conrev
\\\V
ii\\< hS<\
£
—
—
_
Figure 5. Isopach map of lower Pliocene.
Woodford and Daviess (1949), Stark (1949), Rich-mond (1950), Colburn (1953), and Price (1953).
Very little has been published about conglomeratein the subsurface sections of the lower Pliocene. Thesubsurface data consist of very generalized strati-
jraphic columns for a few oil fields in publications of
the State of California; in particular, the California
Division of Mines Bulletin 118 (1943). Also, pebbleswere reported in lower Pliocene cores in the WestCoyote Hills (vicinity of location 43 of this paper)by Edwards (1934). Conglomerate was indicated in
the subsurface section of the Standard Oil Company-Murphv Whittier 62 well site (location 23 of this
paper) by Kundert (1952). As a result of the paucityof investigations into the nature and distribution of the
conglomerates in the subsurface section, the writer
concentrated his efforts in this direction.
The conglomerate bodies described in this paper
generally are interbeds of sandstone and conglomerate
rather than entirely conglomeratic. They, however,
differ sufficiently from the adjacent rock bodies to be
considered a distinct entity. Entirely conglomeratic
bodies occasionally occur in the lower Pliocene sec-
tion. As a result, the writer used two sets of symbols
for conglomerates(plate 1).
in the stratigraphic sections
Distribution and thickness
The areal distribution of the conglomerate is best
depicted in the lithofacies maps (figures 10-13); how-ever, it should be stressed in using these maps that
there is meager control in the central portion of the
basin.
In the first place, the conglomerate bodies are lim-
ited to the landward side of the basin, being particu-
larly thick and widespread in northcentral and north-
eastern portions and relatively thin and scattered along
the northwestern margins of the basin. Secondly, the
most conglomeratic section is probably near the west-
ern end of the Pucntc Hills, in the subsurface. This
assumption is based primarily upon the work of
Kundert (1951). He described a westward increase in
the quantity of conglomerates in a distance of less
than 2 miles from approximately 1 00-foot thickness
at location 2 3 to a thickness in excess of 900 feet in an
incompletely exposed section located half a mile west
of location 22 (refer to plate 1).
16California Division of Mines and Geology SR 93
t0$ ,- •'\ / HE?ET\
•**t
• -A - ^ fo*r
IX « -. > • - J'• # \ V-"" '-,-;, TJ«M1ULL L
Figure 6. Isopach map of lower-lower Pliocene.
The thickness of the individual conglomerate bodiesis best displayed in the stratigraphic cross section
ABCD (plate 1). As would be expected, the thickest
conglomerate bodies occur in the area of the greatest
concentration of conglomerates. In the basin, thethickest surface exposure (300 feet ±) is in the Whit-tier Hills at location 22, and the thickest subsurfacebody (500 feet ±) appears in the Montebello field
at location 14. In sharp contrast to the thick con-glomerate bodies are the conglomerates cropping outalong the southern flank of the Santa Monica Moun-tains at locations 3 and 88. These units are relativelythin, normally ranging in thickness from a few inchesto 3 feet.
Textures
Less than 1 percent recovery of cores taken fromthe subsurface conglomerate bodies deterred any com-prehensive textural study of geographic or strati-
graphic significance. As a result, texture was givenlittle consideration beyond a few notes on grain sizeand roundness. In regard to grain size, the largestclasts were encountered in the conglomerate beds crop-ping out in the Whittier Hills (vicinity of location 22)where they range up to a foot in diameter.
In the over-all analysis of the size distribution of
the conglomerate strata, boulder-size clasts appearalong the northwestern and northcentral margins of
the basin (locations 3, 22, and 88); conglomerate con-taining cobbles extends into the basin in the northcen-
tral area at locations 14 and 17 and north of the Ana-heim nose at locations 61 and 64. The conglomerate at
the remaining locations contains pebble-size clasts. Onefinal note: it is conceivable that boulder-size clasts dooccur in the conglomerate cored at location 14 since
the largest, which measured 3 inches across, is merelyan end fragment of a clast.
The only other textural parameter that could bedescribed with some sense of confidence is the round-ness of the clasts. Almost all of the clasts with theexception of those at locations 3, 76, 86, 88, and a fewbodies at 22 show good roundness, ranging from roundto subround; the exceptions (sedimentary breccia) are
primarily angular to subangular.
Sedimentary structures
Sedimentary structures that proved of value in de-
termining the manner in which conglomerate clasts
were transported and the direction of their transpor-
96" Early Pliocene History, Los Angeles Basin—Con hi ->
17
M
' «f;. t /<
W4LNUT V ) //
Figure 7. Isopach map of middle-lower Pliocene.
ration were recognized in the conglomerate bodies
cropping out along the western end of the Puente
Hills. These diagnostic structures are described as
follows:
1. Graded bedding is represented by a progressive
decrease in the size of the clasts from the bot-
tom to the top of the conglomerate bed. Anextreme case of this is displayed in figure 14,
which shows a succession of conglomeratebodies individually grading from cobbles at the
base to sand at the top.
2. Sharp contacts can be recognized at the base of
many of the conglomerates (figure 14).
3. Imbrication of clasts is displayed in several con-glomerates at location 22. The clasts are imbri-
cated so that their c-axis dips in a northwarddirection from the Puente Hills; however,their c-axis would dip southward if the strata
were reoriented to a horizontal position (fig-
ure 15).
4. Pinch-outs were recognized as a typical wedgeform and in the nature of a cut out of the
lower portion of the conglomerate (figure 15).
The pinch-out direction is south at the south-
western end of the Puente Hills.
5. Preferred orientation of the elongated clasts
was recognized in several conglomerates crop-
ping out in the vicinity of location 22. Thelong axis of the clasts was oriented in a north
to north-northw est direction.
Composition
Prior to this report, Edwards (1934), Bcllemin
(1938), Olmsted (1948), and Kundert (1952) studied
the composition of the conglomerate cropping out
around the periphery of the basin in varying degrees
of detail in order to evaluate source areas. In this study
the writer concentrated his efforts on the evaluation
of the subsurface conglomerate beds. Unfortunately,
the inadequacy of the cores from the subsurface con-
glomerate bodies did not permit quantitative studies ol
their composition. Nevertheless, the recognized rock
types were an aid in evaluating the potential source
areas; their significance will be discussed in a later
section covering potential source areas.
18California Division of Mines and Geology sr n
• $ +\_ + •* y i
r' ( V'^^r*«o »*.•.
f-— MULT
• LOCATION
'son
^#1 <"P,d '°^
J/\"X
/.
*©ei
**lFigure 8. Isopach map of upper-lower Pliocene.
Sandstone
The lithologic characteristics of the sandstone re-ceived little attention by previous investigators beyondthe usual field description of the sandstone beds crop-ping out around the periphery of the basin. General-ized data covering the existence of sandstones in thesubsurface are presented in the following technicalpapers and maps: California Division of Mines, Bulle-tins 118 and 170; U. S. Geological Survey, Oil and GasInvestigation, A4aps 83 and 117; and American Associ-ation of Petroleum Geologists, special publications(1958, Guidebook of oil fields—Los Angeles and Ven-tura regions; and 1952, "Cenozoic correlation sectionsacross the Los Angeles Basin").
Distribution and thickness
Sandstone occurs in the lower Pliocene strata atmost of the locations in the basin. Distinct patterns inthe distribution and thickness of the sandstones wererecognized. These are displayed geographically in thelithofacies map (figure 10) and in the sandstone iso-pach map (figure 16). Points of particular interestare the thick lobe of sandstone extending into the basinfrom its northcentral margin and the general concen-
tration of the sandstone in the central portion of the
basin. The thickest sandstone (400 feet plus) was meas-ured at location 22 (plate 1). However, this thickness
is exceptional since at other locations the maximumthickness of the sandstones approximates 100 feet.
A direct relationship exists between the thickness
of individual sandstone bodies and the quantity of
coarse clastic rocks (sandstone and conglomerate) in
the stratigraphic section. For example, sandstones av-
eraging 100 feet in thickness appear at all locations
where the coarse clastic rocks make up more than
50 percent of the stratigraphic section, whereas nosandstones of 100-foot thickness appear at locations
containing less than 25 percent coarse clastic rocks.
Lhis quantity and thickness relationship is demon-strated by comparing the stratigraphic and electrical
well logs with the sand percentages displayed on the
lithofacies map (figure 10). For example, stratigraphic
sections (plate 1) display a distinct thinning of thesandstone bodies from location 11, which contains 47percent coarse elastics, to location 10, which contains28 percent coarse elastics.
The writer was unable to recognize a basin-widetrend of either increasing or decreasing amounts of
196" Early Pliocem- History, Los Angeles Basin—Conrey 19
Rll w
^A*V- 3 &-•
Figure 9. Location map showing lines of stratigraphic sections for plates 1, 2, and 3.
sandstone from the top to the bottom of the lowerPliocene. For example, the locations in the Playa del
Rev, Inglewood, and Dominguez fields (10, 11, and31 respectively) display a general increase of sand-stone towards the top of the lower Pliocene. How-ever, in the Santa Fe Springs, West Coyote, EastCoyote, and Brea Olinda fields (33, 43, 44, and 46)the maximum accumulation of sandstone is in the lowerportion of the lower Pliocene; and in the Montebello,Rosecrans, and Long Beach fields (14, 30, and 56) themaximum accumulation of sandstone occurs near thecenter of the lower Pliocene.
Throughout the previous discussion, the term "sand-
stone body" was used to describe a stratigraphic in-
terval of sandstone that includes several individual
beds. The compound nature of the sandstone bodies
can be detected readily in surface exposures but not in
the subsurface. For surface examples, at location 22
the thickest sandstone body (400 feet plus) is com-posed of a series of interbedded brown and whitesandstones, the thickest not exceeding 10 feet. At loca-
tion 64 (Burruel Ridge) the 100 foot sandstone body
consists principally of 54- to l/2 -inch-thick interbedded
layers of sandstone.
Frequently, the writer only could detect the com-pound nature of the sandstone bodies in the subsurface
by variations in grain sizes and electrical log charac-
teristics. For example, in the Long Beach field, at loca-
tion 56, no uniformity appears in the median diameters
of samples that were taken at stratigraphic intervals of
5 to 15 feet in several 100-foot thick sandstone bodies.
If these sandstone bodies were single beds, one wouldexpect uniformity, either as a consistent median diam-eter or more likely as a progressive change in mediandiameters. The compound nature of the sandstone
bodies at location 56 is further substantiated by the
electrical log characteristics from a well located a
quarter of a mile east (plate 4). The electrical log in-
dicates changes in the sandstone bodies by the fluctu-
ations of the self-potential and resistivity curves at
intervals not greater than 10 feet. These fluctuations
represent a sedimentary change that may be bedding
since the electric responses generally indicate a change
in permeability or clay content. Similar compound
characteristics are displayed in the Inglewood field,
at location 11, in the grain size studies and the elec-
trical log characteristics.
20 California Division of Mines and Geology SR 93
Figure 10. Lithofacies map of lower Pliocene. The percentage of conglomerate is calculated in terms of coarse-grained elastics rather than of the
entire sedimentary section.
Thin beds of sandstone were recognized both in out-
crops and the subsurface. The thinnest beds were iden-
tified in subsurface cores from the Playa del Rey,Dominguez, East Coyote, and Santa Fe Springs fields
(locations 10, 31, 33, and 44 respectively). At these
subsurface locations, laminations of less than 2 mm.thickness sporadically appear in the sandstones; thevare particularly well represented at location 33. Theselaminations appear as either alternating layers of sandand biotite, or sand and carbonaceous matter.
Grain size
Visual estimates of the grain size of the sandstonewere made with a geological sand-measuring magni-fier during the field lithologging of the surface out-crops and subsurface cores. In this study, the sandstonecould be classified only in Wentworth's broad sand-size classes (very fine, fine, medium, etc.). In addi-tion to the field estimate, 300 samples were collectedfrom different locations and analyzed, using the con-ventional screening method with the Ro-Tap auto-matic shaking machine. Whenever possible, the sampleswere collected at the individual locations at strati-graphic intervals of 100 feet or less.
A very generalized grain-size distribution map of the
basin (figure 17) uses Wentworth's sand-size classes of
very fine, fine, and medium. This map is based uponcombined data from the visual estimate and the me-chanical analysis (Ro-Tap). Note, there is a certain
parallelism between the distribution pattern shown onthis map and the pattern of the conglomerates on the
lithofacies map, figure 10.
The stratigraphic variations in the median diameters
of the sandstones are displayed on figures 18 and 19.
The values represent the coarsest sandstones at each
noted interval and were obtained by the previouslymentioned conventional screening method. These data
are presented to demonstrate that there is no consistent
basin-wide increase or decrease in grain size of the
sandstones from the top to the bottom of the lowerPliocene.
Sorting
Trask's sorting coefficients * for 300 sandstone
samples, analyzed by using the conventional screen-
* The Trask sorting coefficient is So - -J coarse quartile 0225%:
fine quartile (Q75%)
!96" Early Pliocene History, Los Angeles Basin—Conki^— ——
;
-^-^ T^
—
v / ,--—5 — ——
EXPLANATI0N ^V^^V \ / 1—r •*-•«_ ^^••"^*eJOUTCROPS OF ROCKS V- ^ ~~ ~ — ^ «k\ 1 '\ J^ * ' -'-.«, / •OLDER THAN PLIOCENE C ~^*" — —
' V :
:
: \ / \ S • ""*-^i. I^-"^-^ * \\ f +\ •• / •
^^*^ yOUTCROPS OF LOWER \~L-~^5T —'— ^'- • \ \VJ; \ f
• . ~v>PLIOCENE ROCKS hjTLZn\^^_-\i : :
': \ vlj \ I"
•>„ „_ __. __ 5^ __— —* \, » \ \ *>. \ •Eiitftho^*
LIMITS OF LITHOFACIES E^T^^£?\ —"V_"V : :; :: : : :
:
\f . 1 \ ^
UNITS £^~^TZ^ticr~-±.^i :::::: \ \ l\ • x -^ '
LIMITS OF CONGLOMERAfj ^^H^S |\ V \# J I T\ *PERCENTAGE DITISIOjg' ^M >~ -*=~ ~ -\ :::::::i|:::^ N \ / I P3k /
• LOCATION ,..- ^**x ^/ X
-,& \ f •V_-t-_A
^^^-S q> Pedro \:\j.; — :; .:. F~= £!____TV, •' eubsurface Mrgln of^a\_/ WV : r~— 'V
- \ ^w Lower Pliocene rocks
2 16 6MILES *~ r^/* J? 4^
SCALE ^'tSs & *
Figure 11. Lithofacies map of lower-lower Pliocene.
ing method, range from 1.21 to 6.25. As shown in
figure 20, the distribution is such that 83.5 percent ofthe samples have a sorting coefficient smaller than 2.5,
which according to Trask's limits would he consideredwell sorted. In addition, figure 20 shows a modal sort-
ing coefficient of 1.90 to 2.00; this plots out to a meanof 1.99 on a percentage cumulative curve. Possibly,if additional samples had been analyzed, the modemight have differed slightly; however, one can predictwith a fair degree of confidence that the preponder-ance of the samples still would be well sorted. Thisassumption is substantiated in the plot of median diam-eters versus sorting coefficients of the sandstonesamples (figure 21). Even though the sandstone showsprogressively poorer sorting with an increase in grainsize, the medium sandstones are still well sorted. Me-dium sand is the coarsest of the average sand-sizeclasses at some 20 locations in the basin.
Figure 21 also demonstrates that a few sandstonebeds display far poorer sorting than others of the samegrain size. All of these anomalous samples came fromthe northeastern side of the basin, and most are fromstrata adjacent to or interbedded with conglomerates.A further comparison of median diameters and sort-
ing coefficients was made between samples from loca-
tions in the northeastern and the southwestern portions
of the basin (figure 22). Note that the sandstone bedsfrom the northeastern locations consistently display
poorer sorting than do their southwestern counter-parts. Furthermore, the relationship between mediandiameter and sorting is very indistinct in the north-
eastern locations.
Roundness
The sand grains show little sign of roundness andwould be described as angular to very angular, ac-
cording to Krumbein's classification. The angularity
continues from the very fine into the coarse (500 to
1000 microns) sand fractions. Distinct roundness of
sand grains can be recognized in grain sizes larger than
1000 microns; of these, only the pebble-size grains
show a consistently high degree of roundness, rangingfrom subround to round.
The very coarse and granule sized fractions do pre-
sent a rather interesting picture in their different de-
grees of roundness, at several locations throughout the
basin. The pattern of their distribution is presented in
figure 23. Although this pattern is in accordance with
the depositional trends, which will be discussed later,
the writer docs not want to call these findings con-
California Division of Mines and Geology SR 93
Figure 12. Lithofacies map of middle-lower Pliocene.
elusive because they are based upon limited data: sonic
locations are represented by only one sample.
Sedimentary structures
Sedimentary structures that proved of value in de-termining the mode of transportation of sandstoneswere recognized in or associated with the sandstonebeds. These structures are as follows:
1. Graded bedding is represented by a progressivedecrease in the size of the sand grains from thebottom to the top of the bed. This is exempli-fied in sandstones cropping out at the southwest-ern end of the Puente Hills. An example is dis-played on figure 24-A.
2. Sharp basal contacts appear in many of the sand-stones. Surface and subsurface examples are dis-played on figure 24-B.
3. interstratification of medium- to coarse-grainedsandstone beds with siltstone deposits occurs atlocation 22 (figure 24-C). Similar structures un-doubtedly exist in the subsurface strata but werenot identified by the writer due to the poorquality of the cores.
4. Laminations were recognized in the sandstones
at several locations.
Composition
The primary purpose of this sedimentary study wasto identify stratigraphic or areal differences in the
composition of the sandstone. As a result, only the
prominent minerals and rocks in the sandstones wererecorded. The coarse fraction of samples, selected at
intervals throughout the lower Pliocene from different
locations, was examined first with a binocular micro-scope for variations in composition, thus identifyingprominent minerals by their physical characteristics.
The resulting data demonstrate that the coarse frac-
tion consists principally of feldspar, quartz, biotite,
and rock (primarily of silicic composition). Secondaryamounts of carbonaceous matter and shell fragmentsappear sporadically.
There is considerable variation in the relative
amounts of the minerals, particularly in an areal sense.
This is demonstrated by the quartz-feldspar ratios,
based upon visual study, as displayed on the isopleth
map (figure 25). Note that the trend of high quartz-
feldspar ratio areas, at the northwestern margin and
967 Early Pliocene History, Los Angeles Basin—Conrey• " " —... . ..... .j^
23
y '% (
•y '/....
".
\&&^ ootcro?s 0? lower,
pliocene hocks
uhiti of lithofaciespvits.
f^-- FiOLT
• LOCATION
*-
^ '
Figure 13. Lithofacies map of upper-lower Pliocene.
the northeastern portion of the basin, is in contrast
to the relatively low quartz-feldspar ratios at otherlocations, particularly in the northcentral portion ofthe basin. The quantity of quartz measured by this
method appears to be too low because of the reactionof several rock fragments to stains. As pointed out in
an earlier section, most of the rock fragments are
quartzofeldspathic and Mould give a positive feldspar
reaction, increasing the percentage of feldspar at theexpense of the quartz.
The types of feldspars (potash or plagioclase) andquartz were identified in the medium size fractions ofsamples at several locations by means of stains, as de-
scribed by Twenhofel and Tyler (1941). This studyproduced several interesting points; in particular: the
plagioclase feldspars are more abundant than the potashfeldspars, and there is a measurable variation in therelative amounts of potash and plagioclase feldspars in
the basin (figure 25).
Biotite is an important constituent in many of the
sandstones, 61 percent of a very fine sandstone sample
at location 50; in others, it appears in negligible quan-tities. This variation is primarily a reflection of the
sandstone's grain size; that is, the finer sandstones con-tain more biotite than the coarser. However, this is
not the entire answer. There are a few examples of
more biotite in the coarser sandstones and slight areal
fluctuations in the quantity of biotite in sandstone
samples of comparable grain size.
Sandstone is generally classified in terms of either
environment, texture, or mineralogy. In terms of en-
vironment, these sandstone bodies would be classified
as marine; texturally, they range from very fine sand-
stone to very coarse sandstone, and mineralogically
they would be classified as arkose.*
The heavy minerals from composite samples, repre-
senting the lower, the middle, and the upper-lowerPliocene throughout the basin, were examined to de-
termine if distinct variations in composition could be
detected. In addition, samples from Recent stream
channels in potential source areas were analyzed. Theheavy minerals were separated from the samples 1>\
using a heavy liquid, acetylene tetrabromide (specific
gravity 2.96), and a simple filtering funnel. This pro-
cedure was outlined by Krumbcin and Pcttijohn
(1938). Next, the prominent minerals were identified
'Pcttijohn (1957) defines an arkose as a sandstone in which (1) the
detrital matrix is absent or scanty (under IS percent), andfraction is characterized by 25 percent or more labile constituents
(feldspar and rock frasments) of which feldspar forms half or more.
24 California Division of Minis \\i> Geology SR 93
i
#\
%\w**^
.. te ."***
Figure 14. Sedimentary structures in conglomerate at location 22,
southwestern end of the Puente Hills. A (top). Graded bedding. Succes-
sion of conglomeratic bodies individually grading from cobbles to sand.
8 (bottom,). Sharp basal contact between conglomerate and sandstone.
in each sample as follows: the non-opaque mineralsby the oil immersion method described bv Larsen andBerman (1934), and by Krumbein and Pettijohn(1938); and the opaque ones, which consisted of blackmetallic grains, by their attraction to a magnet. Afteridentification, the percentage of each mineral in theheavy fraction was estimated in a count of 300 min-eral grains, using a binocular microscope.
The heavy-mineral suites from the individual samplesare not diagnostic of specific source rocks; this is
demonstrated in a very generalized manner in TableII. Nevertheless, a plutonic source dominated by rocksof granodiorite to quartz-diorite is indicated whenthe composition of the light minerals also is taken intoaccount. There is a measurable variation in the amountsand, in some cases, in the types of characteristic heavyminerals occurring at the different locations. This vari-ation is portrayed in figure 26; its significance will bediscussed in later sections.
Table II. Source o\ heavy minerals.
Heavy minerals Typical source rocks '
Biotite Widespread in rocks of all kinds.
Chlorite Commonly low-grade regional mctamorphic,
also alteration product (commonly hydro-
thermal) particularly in rocks containing
micas and ferromagnesian minerals.
Epidote .Commonly low-grade regional mctamorphic,
also alteration product (commonly hydro-
thermal) of rocks containing feldspars ;ind
ferromagnesian minerals.
Garnet In plutonic and common in mctamorphic.
Hornblende Widespread in rocks of all kinds.
Ilmcnite Widespread in rocks of all kinds. In igneous
rocks, particularly common in ultrabasic and
sparse in silicic plutonic.
Magnetite Widespread in rocks of all kinds.
Sphene Widespread in rocks of all kinds, particu-
larly common in silicic and intermediate
plutonic.
Zircon Widespread in locks of all kinds, cuhcdral
forms particularly common in silicic plu-
tonic.
A pctrologic study w as made of the granule to
pebble sized fractions of man) sandstones throughout
the basin. The areal distribution of the major rock
classes represented by the granules and pebbles is dis-
played on the map, figure 27. In addition, the rock
t\ pes characterizing the assemblages are presented in
figure 28. The accuracy of this study was limited bythe smallness of the grains and their method of identi-
fication, which was visual analysis using a binocular
microscope. In particular, the texture was often verydifficult to identify; as a result, genetically different
rocks of similar mineralogy could not be distinguished
from one another. This method might have created the
following inaccuracies: ( 1 ) the plutonic rocks of this
study could contain a certain proportion of gneiss andpossibly mica-quartz schists; (2) feldspar porphyries,
which were distinguished from quartz-feldspar por-
phyries by the absence of quartz, might be incorrectly
identified at times due to the smallness of the fragmentscontrolling the appearance of quartz, and (3) the frag-
ments designated as slate could be indurated black
shale.
In figure 28, rock types are listed that aided in
evaluating potential source areas. Three of these rock
types, which were named ambiguously "weatheredquartzofcldspathic," "orange quartzofeldspathic," and
quartz-feldspar porphyry, were examined in thin sec-
tions for a more positive identification. Nine granules
of "weathered quartzofeldspathics," from different lo-
cations in the basin, displayed similar mineral charac-
teristics in the thin section; as follows: 80 percent
quartz, 15 percent feldspars, nearly 5 percent plagio-
clase (oligoclase to andesine), 1 percent biotite (pale
brown with bronze luster), and less than 1 percentgreen amphibole and zircon. Taking into considera-
tion the megascopic character, subangular to subroundfragments with yellowish color (iron oxide), along
1 References: Henrich (1956); Kraus, Hunt, and Ramsdell (1951); Krum-bein and Pettijohn (1938), and Milner (1940).
1967 Early Pliocene History, Los Angeles Basin—Con
Figure 15. Sedimentary structures in conglomerate at the westernend of the Puente Hills. A (top). Imbrication of clasts at location 22.B (middle). Pinch-out at location 21. C (bottom,). Pinch-out at location22. Conglomeratic body outlined by dots.
-— ^ ..
1~ V ^
Dip South
. .. r » ....... *-v »*.-«• * ••**
...»-••••
^ A ' tf
-
S %S
REY 25
with the mineralogy the writer concludes that the"weathered quartzofeldspathics" probably are weath-ered residuals of silicic plutonics of granite compo-sition, or possibly quartz monzonite.
Clues to the identity of the "orange quartzofeld-spathic" granules were obtained from (1) a thin sec-tion of a large pebble of orange-colored plutonic rock-associated with granules in a conglomerate at location87 and (2) a spectrochemical test of the pebble andseveral granules from location 33. The thin sectionshowed a composition of alkali granite; as follows: 30percent quartz, 40 percent plagioclase (principallyalbite), 26 percent potash feldspar (orange orthoclaseand microcline), 2 percent white mica, and 2 percentmyrmekite. In regards to texture, the thin-sectionspecimen was medium-grained xenomorphic and dis-played both granulation and rccrvstallization. \
chemical composition comparable to that of granitewas determined for the pebble by a spectrochemicalanalysis, which measured 6.4 percent potassium oxide,0.88 percent calcium oxide, and 2.5 percent sodiumoxide.
The rocks identified as quartz-feldspar porphyryin this petrologic study range in color from light-
brown gray to light-green gray. They consist ofphenocrysts of anhedral quartz, euhedral to subhcdralfeldspar, and subhedral mica (principally biotitc, oc-casionally chlorite) set in a fine-grained groundmass.In a thin section of a pebble from a sandstone at loca-tion 44 the feldspar was identified as zoned plagioclase(oligoclase to andesine). This pebble compares favor-ably in texture and composition with dacite-porphyrvclasts contained in conglomerates at the southwesternend of the Puente Hills and dacite-porphyrv bedrockcropping out at the northeastern end of the San JoseHills and central San Gabriel Mountains.
Siltstone and silty shale
The siltstone and silty shale beds rank second in
abundance to the sandstone beds. As a group, theyconsist of light greenish gray to dark gray, poorlyconsolidated to indurated sedimentary rocks; theyrange in texture from sandy silt to clayey silt and in
structure from massive to fissile and locally laminated
rocks. For numerous reasons, the writer did not at-
tempt to separate the massive from the fissile rocks in
the usual classic sense, such as siltstone or shale. First,
there are insufficient data at most locations to permitstratigraphic subdivision on this basis because the cores
commonly were too small to establish fissilitv. Second,
this subdivision appears to be artificial at many loca-
tions because lithologicallv similar rocks differ only in
fissilitv. In addition, this fissilitv fluctuates in a homo-geneous section, and in many instances its diastrophic
derivation can be recognized. Third, the criteria used
to distinguish between shales and their massive equiva-
lents are not agreed upon by sedimcntologists. This
will be discussed in the later section on sedimentary
structures. In the final analysis, the writer found a
textural subdivision of these rocks more realistic for
this study than a structural subdivision. Generally,
these rocks were identified as either clay siltstone or
siltstones.
California Division of Mines and Geologi
v ' v. \
SR 93
V\\{ %
— — * V-^ ^ \\_ TllBMftLlI 1 ...
V
C 5*'
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'i*ii two **''
EXPLANATION
rm»a mk.ls
X
>SSSSS>'OUTCROPS OF ROCKS
OLDER THAN PLIOCENE
OOTCM)PS OF LOWER
PLIOCENE ROCKS
ISOPACH INTERVAL
500 FEET
p- FAtTLT
LOCATION
• •
*>\ v \\\ 7/ //J - £&&-
a .. \ \ \:_^ \ I \.y<
i
~V\ • \ \ wH^a \ \ *\ \ »jb«»rt»c« mofjin of
•\ **— J \ \ \ *^ Lomi Plioe«n« rocU
X
*>
Figure 16. Sandstone isopach map for lower Pliocene.
The lithology of these rocks has received as little
attention by previous writers as did the sandstonesand conglomerates. These references were cited pre-
viously in the general discussions of the sandstonesand conglomerates.
Distribution and thickness
The siltstone and (or) silty shale strata were identi-
fied in the lower Pliocene at all locations in the LosAngeles Basin. Their areal distribution and thickness
are displayed best in the isopach map (figure 29) andin the lower Pliocene lithofacies map (figure 10). Adistinct contrast between the distribution of theserocks and the previously discussed sandstones is recog-nized readily by comparing isopach maps, figures 16and 29. Briefly, thick accumulations of siltstones andshales are localized in three areas: northeast, northcen-tral, and the northwestern edge of the basin. In con-trast, the sandstone strata are distributed with moreuniformity; distribution is confined principally to thecentral portion of the basin.
_The stratigraphic distribution and thickness of these
fine-grained rocks are displayed on the lithofaciesmaps of the lower, middle, and upper-lower Pliocene,
in the stratigraphic sections, and in the electrical well
logs. A brief study of these illustrations reveals that
the sections consisting almost entirely of fine-grained
rocks occur along the margins of the basin; in par-
ticular: in the Repetto Hills, around the Palos VerdesHills, and to the southeast in the vicinity of Newport.
The thick bodies of these fine-grained rocks are
composites of many individual beds. The fissility in
many of these bodies made identification of beddingdifficult, even on surface exposures. In the subsurface,
subdivision of the large bodies was made even moredifficult due to the incompleteness of core samples.
It is possible that stratification is portrayed by the
fluctuations in the electrical log characteristics
throughout the intervals representing these rocks.
These fluctuations also might represent different de-
grees of fissility.
Thin beds of these rocks were recognized in the
outcrops and in the subsurface. The thinnest beds took
the form of laminations that appeared occasionally in
the cores at most of the locations and probably wouldhave been recognized at all locations if more core
data were available. Most of the laminations occur as
alternating layers of coarse and fine particles, com-
1967 Early Pliocene History, Los Angeles Basin—Conrf.y 27
* V.H^'N. \ \. WALNUT . J
MEDIUM SANDSTONE^
|f----j FAULT
• LOCATION
,^v * :-
• I
V ^--subsurface margin ofV s* \<msr Pliocene rocks
\ *
r"'->.
**V
>^
Figure' 17. Areal variation in average grain-size class of sandstone.
posed of either silt and sand or clay and silt; how-ever, one sample at location 10 was composed of alter-
nating layers of carbonaceous matter and silt.
Grain size
In the field examination of the cores and outcrops,
the fine-grained rocks were subdivided into grain-size
classes of either siltstone, mudstone, or claystone. Theinadequacy of this type of identification was recog-nized. Nevertheless, the studv enabled the writer to
group rocks of similar grain sizes and to identify broadstratigraphic fluctuations in grain sizes. This visual esti-
mate was coordinated with a more accurate pipette
grain-size analysis of numerous samples that previously
were identified visually. The samples analyzed by the
pipette method were selected from several stratigraphic
levels at each location. These samples represent the
finest grained (visual estimate) sample at each level.
The results of these studies were plotted on strati-
graphic sections and the grain-size distribution map(figure 30). A change was made in terminology; the
term "clay siltstone" was substituted for mudstone.
Only minute quantities of claystone were found in
the lower Pliocene, which were, on further analysis,
determined to be of volcanic origin (bentonite); they
are discussed in the section devoted to volcanic rocks.
Clay siltstone is the finest grained rock that appears
in significant quantities, as was concluded by compar-ing the sand, silt, and clay percentages of the finest
grained rock samples at each location with the param-
eters for clay siltstone, siltstone, and coarser grained
rocks (displayed on the triangular diagram in fig-
ure 31).
There is a distinctive grain-size distribution pattern.
Siltstone prevails in the northcentral and northeastern
part of the basin, whereas clay siltstone prevails else-
where. Also, the average grain size of these rocks de-
creases across the basin from its landward to its coastal
margins. These patterns are illustrated best in the grain-
size distribution map (figure 30).
As was the case for the sandstone, there does not
appear to be a consistent basin-wide increase or de-
crease in the grain size of these siltstone rocks from
the top to the bottom of the lower Pliocene. This is
illustrated in the stratigraphic median-diameter plot
in figure 32.
Pebble-size clasts were in the cores of siltstones at
locations 14 and 38. At location 14, in the Montebello
28California Division of Minis wi> Geology SR 93
0)
, cU 0)
d) oft o
P Hft,
iglewood Rosecrans Long Beach
13 Mi. SE
119 Mi. SE ^ 13 Mi t
SE »
Grain Size(Microns)
Grain Size(Microns)
Grain Size(Microns)
Figure 18. Stratigrophic variation of grain size for sandstone along the western side of the basin.
field, 5-10 mm. clasts were imbedded in a red (iron
oxide stained) siltstone cored 975 feet below the topof the lower Pliocene, and 10-12 mm. clasts wereimbedded in a gray siltstone cored 2,010 feet belowthe top of the lower Pliocene. At location 38, Heath,clasts up to 20 mm. across were in a gray siltstone
cored 435 feet below the top of the lower Pliocene.Smaller granule-size clasts were in a core of gray silt-
stone 1,410 feet below the top of the lower Plioceneat location 56, in the Long Beach field. The clasts
were distinctly foreign to the environment repre-sented by the siltstone. They were commonly of plu-tonic origin and were visibly worn, ranging from sub-round to round. Examples of pebbly siltstone arepictured in figure 33.
Cobble-size clasts appear in the siltstone strata crop-ping out at locations 52 and 88 (Malaga Cove and
Potrcro Canyon). The clasts collected at location 52
were subangular and attained a maximum size of ap-
proximately 5 inches. A few displayed cavities similar
to pholad borings (figure 33-A). Their composition
(silicified tuff and claystonc) is similar to the older
rocks cropping out in the adjoining Palos Verdes Hills.
At location 88 the clasts consist of subangular to angu-
lar chips and blocks of sandstone, limestone, and slate
that appear as bedrock in the adjacent Santa Monica(Mountains. The largest block measured was 8 inches
across. A few of the sandstone clasts displayed borings
(figure 33-B).
Sorting
Sorting coefficients, measured by the conventional
pipette method, range from 1.74 to 4.80. As shownin figure 34, the samples are distributed so 29.5 percent
96" Early Pliocene History, Los Angeles Basin—Conker 29
500 1000
n Size (Microns)
500
Grain Size (Microns
1000
Figure 19. Stratigraphic variation of grain size for sandstone in the
northeastern part of the basin.
have a sorting coefficient smaller than 2.5, which ac-
cording to Trask's limits would be considered wellsorted. The sorting-coefficient modal (2.60-2.70) ofthese samples falls between the well sorted (2.5) andthe normally sorted (3.0) values of Trask.The relationship between grain size and sorting co-
efficient displayed by sandstone also appears in these
rocks; however, it is not clearly defined (figure 35).
[n contrast to the sandstone, the fine-grained rocksshow progressively poorer sorting with a decrease in
grain size.
An improvement in sorting from the landward to
the coastal margins, which was displayed in the sand-
stone, does not appear in the fine-grained rocks. Fur-thermore, the poorest sorting is in the southern part
of the basin, at locations 77 and 82, where the rocksdisplay far poorer sorting than indicated by their
median diameters. Poor sorting is also in evidence in
several samples from locations 46 and 61. The sand-stone beds at location 61 also arc poorly sorted.
Fissility
The full range of the following fissility scale(McKee and Weir, 1953) is represented in the fine-grained sedimentary rocks.
Fissility Description
Massive Partings greater than 120 cm.Blocky Partings between 120 cm. and 60 cm.Slabby Partings between 60 cm. and 5 cm.Flaggy Partings between 5 cm. and 1 cm.Shaly Partings between 1 cm. and 2 mm.Papery Partings less than 2 mm.
The papery fissility is limited to one sample of ben-tonitic clay from location 44, in the East Coyote field.
If the writer were to select the grade of fissility thatappeared most frequently in the fine-grained rocks,he would select flaggy. This does not mean that thefine-grained rocks at any one location are entirclvflaggy. On the contrary, several grades of fissility arerepresented at the individual locations.
The exact cause of fissility is an interesting problemthat, unfortunately, the writer did not find time to
investigate in detail. Previous authors have suggestedthat fissility was related to the following: the abund-ance of platy minerals, such as clay and mica; the
degree of cementation; the amount of weathering;
and the amount of tectonic activity. It is assumedthat fissility increases with increases in clay or micacontent, weathering, and tectonic activity. It dimin-
ishes with an increase in cementation. At least three
of these factors appear in surface exposures at loca-
tion 7 where rocks with the highest clay content arc
flaggy to slabby, but the massive rocks generally con-tain little clay. In addition, fissility is often perpen-dicular to bedding; this suggests its tectonic origin.
Finally, the role of weathering is demonstrated bygreater fissility appearing in the weathered rocks than
in those freshly exposed.
Mottled structures
Mottled structures appear in the cores. They con-
sist of irregularly shaped lumps, lenses, pockets, tubes,
or pods of sedimentary rock randomly enclosed in a
medium of contrasting texture. The texture of the
irregular bodies is generally coarser than the matrix,
such as silts in clay and sands in silts. In some cases,
the mottles have clear-cut boundaries; and in other
cases their boundaries are very indistinct, appearing as
mere clusters of sand or silt grains. The smallness of
the cores makes impossible an orientation analysis of
the mottles. Examples of these are illustrated in fig-
ure 36.
Mottled structures appear in the cores from most
of the locations and probably would be recognized
at all of the locations if more core data were available.
They are most profuse at locations 33 and 56, in the
Santa Fe Springs and Long Beach fields respectively.
The other locations are marked by only sporadic oc-
currence of the mottles.
Mottles of similar appearance were found in shallow-
water sediments of the Gulf of Mexico by Moore and
30 California Division of Mines and Geology SR 93
Figure 20. Histogram showing variation of sorting coefficients for sandstone.
Scruton (1957). They also were found in sedimentsof the Santa Monica and San Pedro Basins, off the
coast of southern California, by Gorsline (1958). Theflow casts in sedimentary rocks, described by Shrock(1948), may represent the mottled structures of this
paper. However, the horizontal alignment of these
flow casts does not agree with the random arrange-ment of many mottles from the Los Angeles Basin.
Composition
The sand-size fractions of the fine-grained rockshave nearly the same composition as the sandstone,differing principally in proportions of the components.In this regard, they differ from the sandstone by anincrease in the relative amounts of mica, carbonaceousmatter, organic hard-parts, heavy minerals, and occa-sionally glauconite and by a decrease in the relativeamounts of feldspar, quartz, and rock (generally ab-sent). With the exception of glauconite, the variationsof these minerals and rock undoubtedly reflect theirdependence on grain size. For example, the median-grain size of the heavy minerals and mica is a veryfine sand; this generally represents the greatest pro-portion of the sand-size fraction of these fine-grainedrocks. As a result, the heavy minerals and mica appearin their greatest abundance in the sand-size fraction ofthe fine-grained rocks. On the other hand, the median-gram size of the quartz and feldspar falls in a coarsersize class (fine sand in one study by Rittenhouse,1943); therefore, they appear in lesser amounts in thesand-size fraction of the fine-grained rocks. The de-pendence of minerals on grain size was pointed out
?,^USiy-
b-v
,
several authors; in particular: Russell(1936), Rittenhouse (1943), Emery and others (1952)and Pettijohn (1957).
The occurrence of greater amounts of carbonaceousmatter and organic hard-parts in the sand-size fractions01 the fine-grained rocks than in the sandstones is alsoan example of the interdependence of composition andgrain size; however, it is on an entirely different basis
than the minerals. That is, it is probably due to the
depositional environment. To elaborate, the carbona-ceous matter and organic hard-parts appear in greater
relative amounts in the fine-grained sedimentary rocks
because they represent marine deposits formed in sites
less favorable for receiving foreign detrital material
than sandstone. The increase in the amount of carbo-
naceous matter and organic hard-parts with a corre-
sponding decrease in grain size of marine sediments
was demonstrated in the work of Emery and Ritten-
bcrg (1952) on the California basin sediments.
Also, there are distinct variations in the composition
of the fine-grained rocks. In some samples, these varia-
tions represent median-grain size; for example, the
abundance of clay in the very fine-grained rocks. In
other samples, they represent environment. This en-
vironmental control is exemplified best by comparingrocks of similar grain sizes from different locations.
For example, the sand-size fraction of samples with a
14 micron median diameter at location 33, in the Santa
Fe Springs field, is composed primarily of quartz, feld-
spar, and mica; there are negligible quantities of or-
ganic hard-parts and carbonaceous matter. On the
other hand, the sand-size fraction from samples of the
same median diameter from location 53, in the vicinity
of the Palos Verdes Hills, contains appreciable amountsof organic hard-parts (mostly foraminiferal tests), car-
bonaceous matter, heavy minerals, and glauconite (10percent); these are mixed with large quantities of
quartz, feldspar, and mica. Other samples of similar
median diameter (10-12 microns) at location 53 also
contain comparable proportions of these constituents.
Three of the constituents that appear to be of environ-
mental significance; namely: glauconite, organic mat-ter, and calcium carbonate will be discussed in follow-
ing paragraphs.
Measurable quantities of glauconite occur at onlythree locations. Two of these locations (52 and 53)are adjacent to the Palos Verdes Hills, and the third
location (85) is at the southern margin of the basin
in the Newport field. The thickest sequence of glau-
196" Early Pliocene History, Los Angeles Basin—Con KM31
5.0
U.5
"i
—
i—
i
—i1 r Tar—in
—
qtt T—
1
1—
I
•u»
'UL
li.O
3.5
iMOE§3.o|-O
a
2.5
2.0-
.5-
l.d
•61•Ik
•li.
•61
'61
is
X.
•17
\'V.
X- •
\
• v. '
t
Conpiled iron Location*?
10,11, li.,17,28,30,33,
38,U.,1|6,56,61,75
• • •
•• :\*
at • .
.^X\
?oW -I I ' I L1000
Figure 21. Median diameter— sorting coefficient curve for sandstone.
rotrJ I l u
conitic rocks occurs at location 53 where paleontolo-
gists of an oil company reported significant quantities
(90 percent in some samples) of glauconite in the
sand-size fraction (coarser than 104 microns) of all
the fine-grained rocks sampled, except those occurringin the basal' 50 to 75 feet of the lower Pliocene. Theextremely large amount of glauconite measured in
these rocks was undoubtedly due to the limited size
range of the samples examined. This was demonstratedwhen the writer examined the entire sand-size fraction(coarser than 62 microns) from cores of these fine-
grained rocks selected from the same intervals as thesamples described by paleontologists of the oil com-pany.
Oil Co. sample Writer's sample
Depth Median (courser than (coarser than
(feet) (microns) 104 microns) 62 microns
10 12 60% glauconite 2 glauconite
525 10 2o glauconite 2 glauconite
700 14 "i 1 glauconite 10 glauconite
900 10 >S% glauconite glauconite
1100 9.6 40 glauconite 5 glauconite
Considerable amounts of glauconite were recognized
at location 52 (.Malaga Cove). Again, the oil companyidentified larger quantities of glauconite, ranging from75 to 90 percent, in the coarser than 104 microns por-
tion of many samples. Comparative analyses, by the
writer, of three samples indicated that the 75 to 90
32California Division of Mines and Geolocs
S.Oi r
U.5
U.o-
3.5-CO
hZLU
OLi.
Li.
LU
o 3.q-o(D
DCOw .2.5"
2.0-
t—
r
-t rr -x x
—
tt—i—i—
r
*\
*X
X
•\
N . *x
1.5-
l.o*
X Location-NX side of basin
No* s Di,17,Wi,6l
• Location-* aid* of basin
Mo's 11 k 56
••• * V a *
ft
\•• •
2000J I I I L
1000
MEDIAN DIAMETERS IN MICRONST00~
J I L
Figure 22. Median diameter—sorting coefficient plot for sandstone from the northeastern and southwestern sides of the basin.
percent figure was far too high for the entire sand-size
fraction. Instead, 50 percent probably would be morerepresentative. In the Newport field, at location 85,
approximately 1 percent was identified in the sand-
size fraction (coarser than 104 microns) of two fine-
grained samples from the basal part of the lower Plio-
cene.
The glauconite appears to be foreign to the environ-
ment represented by the fine-grained rocks in which
it is found. For example, the glauconite, which is gen-
erally associated with an oxidizing environment, is
contained in sedimentary beds strongly indicative of a
reducing environment; such as those containing 6-12
percent organic matter and free iron sulfide minerals
967 Early Pliocene History, Los Angeles Basin—Conrei 33
^
TlB^^^py^v }
^gjlllilig^^ iL
V i!H
\h !!'ii"iiiiBEXPLANATION
kctcmps of BOCB \ I| |
1 1i
1.
1 , 1 . 1 . 1 . I .TxX-—
*
jOLCZB THAI FUOCHB \ '1 1 1 I . I |
'
|•
| ' | '|
I dC.J,i 1 1
11 1 lU!i=
f-'~- fAOLT
• LOCATIOI
107. - 1TJKBKBS BXLOV EOOIMESS STHBOL3R£F2R TIE KUMBK OF SAMPLES EXAHUOD
/
f-y-WALNUT , )
TURN8ULL \^
•hv
1
" <
•1
II•
1
ra/—
y~—
/
,- -PWITIF. <«>' KMd H .
'. •
1\\ v
* a.
v v '
''• v.T*"
•
•/
nbsorfac« margin oflover Pliocene rock*
/• IDn 1 i» SK 8 WE
COH>aET30i CHAST FOE TI3DAI. ESTaiTIDM Of mmm^ f Pnura. Kit
ys
Figure 23. Areal variation in roundness of granule-size fraction of sandstone.
in sand-size fractions. Furthermore, foraminiferal tests,
common containers of glauconite, contain iron sul-
fide minerals. A more likely source for glauconite is
a local submarine high that is actively supplying detri-
tus to these locations.
Sixty-eight samples of the darkest and finest grainedrocks were examined for organic matter. The sampleswere selected from 27 locations and, whenever avail-
able, at stratigraphic positions representative of lower,
middle, and upper lower Pliocene. The organic carbonwas measured first by the empirical method of oxida-
tion with potassium dichromate and then back titra-
tion with ferrous ammonium sulfate, as described byAllison (1935). These values were then converted to
total organic matter by multiplying by the factor of
1.7, which is generally accepted for soil humus. Abrief evaluation of the data follows:
1. The highest value of organic matter, 11 percent, was found for
a sample taken from a well core at location 75.
2. The lowest values of total organic matter were found for two
samples taken from surface exposures along the southwestern
end of the Puente Hills, at location 22. These values averaged0.5 percent.
3. An areal trend in the distribution of the organic matter is indi-
cated by this study. This is exemplified by a progressive increase
in the values of total organic matter from the northern (inland)
margin of the basin to its southern (coastal) margin, as follows:
North South
Montebello Santa FeSprings LongBeach Wilmington
(Loc. 14) (Loc. 33)
Average total
organic ma-
terial 1.4% 4.2%
Median grain
size 0.022 mm. 0.016 mm.
(Loc. 56) (Loc. 68)
5.6% 8.5%
0.013 mm. 0.009 mm.
The carbonate content of the fine-grained rocks
was tested both in the field and in the laboratory bytheir reaction to dilute hydrochloric acid. In the field
study, the rock fragments were immersed in cold acid,
and the rate of effervescence was observed. This test
proved particularly useful in demonstrating a strati-
graphic variation in carbonate at the individual loca-
tions. This variation was substantiated by laboratory
tests in which the percentage by dry weight of the
material soluble in dilute acid was determined for
many samples at several of the locations. In addition,
an areal trend in the distribution of carbonate was
demonstrated by the results of the laboratory analyses.
That is, the highest values of soluble materials were
found for samples collected at locations in the south-
34
'':c.-^f
California Division of .Minis and Geology
i
- - .«
-c r-^
Figure 24. Sedimentary structures in sandstone. A (upper left). Graded bedding of sand layer (60 mm. thick) cropping out at the southwestern end
of Puente Hills, showing sharp basal contact with the underlying siltstone. 8 (upper right). Sharp contact between very fine sandstone (white) and silty
shale in a core sample from location 28. C (lower left). Medium- to coarse-grained sandstone interbedded with siltstone. Sand layer of A appears at
this location. D (lower right). Laminations of fine- and very fine-grained sandstone in a core from location 44. The laminae of very fine sandstone
also contain carbonaceous matter (dark layers).
ern (coastal) part of the basin. The stratigraphic andareal fluctuations of soluble materials are demonstratedin figure 37.
The nature of the carbonate can be identified read-ily in the sand-size fractions of these rocks. It consists
principally of foraminiferal tests with secondaryamounts of broken fragments of pelccypod shells andother organic hard-parts. The nature of the carbonatesin the fine-grained fractions can only be surmised,because it was not investigated specifically by thewriter. However, it probably is composed primarilyof disseminated fragments of organic hard-parts,
rather than inorganically precipitated calcite. This as-
sumption is based upon the observation that onlv a
few of the samples were so cemented that they couldnot be decomposed, at least partially, by merely soak-ing in water.
The composition of the fine-grained rocks is re-
flected in their color. In view of this, the writer re-
corded their colors during the lithologging of subsur-face cores and surface sections. The color terms usedin this study were obtained from the "Color Chart"prepared by a committee of the National ResearchCouncil in 1948. The fine-grained rocks in the basindisplay colors ranging from light to dark values asfollows: light gray, light green-gray, light olive-gray,gray, gray-brown, olive-gray, dark gray, and dark
gray-brown. A stratigraphic trend in color values can
be identified throughout the basin. This consists of
decreasing color values from the top to the bottom of
the lower Pliocene. The consistency and amount of
change in color values vary, to some extent, w ith the
location. For example, in the southern (coastal) part
of the basin dark gray and dark gray-brow n prevail in
the lower portion of the stratigraphic section at all
locations, except 6H. At most of these locations, the
consistent occurrence of these low color values is lim-
ited to the lower-lower Pliocene. In addition, at manyof these locations, the low color values occur sporadi-
cally at higher stratigraphic levels, beginning in the
lower portion of the upper-lower Pliocene. In contrast
to this, the lowest color values identified at most of the
locations in the northern (inland) portion of the
basin range from gray to olive gray. Locations 33 and
49 (Santa Fe Springs and Richfield fields) were ex-
ceptions to this trend, displaying the dark grays and
dark grav-browns in their basal strata.
The source of the color in the fine-grained rocks
was not investigated. Nevertheless, certain color
sources are suggested which agree with the knownlithology of the rocks, as follows:
1. The low color values in many of the samples are caused by
either organic matter, biotite, or both.
'57 Early Pliocene History, Los Angeles Basin—Conrfy 35
Figure 25. Areal variation in quartz-feldspar ratios in sandstone.
2. The olive and brown colors represent organic matter. The
highest values of total organic matter were from either brown
or dark gray-brown samples.
3. The green color probably represents illite.
Limestone
Limestone nodules and lenses appear sporadically in
in the lower Pliocene at many locations. Their distri-
bution is displayed on the stratigraphic sections. In
regard to size, they are thin bodies, generally a fewinches thick. The thickest body measured 12 inches.
Characteristically, the limestone beds have the samesuperficial appearance as the other rock bodies withwhich they are in direct association. For example, the
limestone beds frequently appear as dense dark-grayrocks in a sequence of dark-grav siltstone and (or)
.. silty shale. Also, they commonly appear as light-gray
sandv bodies in a sequence of light-gray sandstonebeds. No organic structures were found in the lime-
stone by the writer.
The limestone probably is of secondary origin, rep-
resenting a concentration of inorganic calcitc in the
pre-existing sediments. This assumption is based uponthe combined strength of the following previous ob-servations: (1) lack of organic structures in the lime-
stone samples, (2) color and textural similarity be-
tween limestone and the adjacent rock bodies, (3) thin
lenticular to nodular shapes, and (4) sporadic distribu-
tion.
Volcanic sediments
Thin layers of bentonite, volcanic ash, and occasion-
ally intercalated layers of ash and chert were identified
in the cores at several locations in the basin. Their
stratigraphic position and areal distribution are pre-
sented in Table III.
Original core descriptions indicated that most of
these layers are only a few inches thick. Nevertheless,
a few layers of ash, 1 to 2 feet thick, were identified
at wells in the southwestern portion of the basin. In
the Dominguez field, a 2-foot-thick ash bed was
described in the original core description of a well, and
two 1 -foot-thick beds of ash and bentonite were cored
in several wells in the Plava del Rev field (YVissler,
1941).
Table III demonstrates that most of these rocks
occur in the upper-lower Pliocene. Moreover, in al-
most every case they were restricted to foraminiferal
zones (of'Wissler) 2. 3, and 5. A few ash and chert
beds were recognized in middle-lower Pliocene. The
36 California Division OF Minis and GEOLOGY SR 93
Tabic 111. Stratigraphic positioji of volcanic sediments.
Foram-iniferal
zones
Locations
St »ge 9 10 11 12 II 28 50 31 13 14 46 50 52 53 56 H 77
a
1
2
B
B
B
T'
13
T
T
B
B
B
B
P.
P.
C
B T
P,
B
P.
3
4
5
6
T
T7
wz
9
8
oo
a;
9
10
o11
12
13 1
C
TC
T
14
2
15
16
17
18
1 Described by other authors from wells in the vicinity.
T-Tuff B-Bcntonite C-Chert.
occurrence of ash and chert in foraminiferal zone (ofWissler) 13 of this stratigraphic interval may be ofareal significance.
The bentonite usually occurs as a light green-gray("Color Chart") claystone with a greasy luster andfeel. The rock reacts characteristically when immersedin water, swelling several times its original volume.Compositional studies of the bentonite beds includedX-ray diffractometer studies of three samples, whichwere interpreted by Dr. Ralph E. Grim of the Uni-versity of Illinois as follows:
Composition
Composed almost wholly of montmorillon-ite; also, small amounts of quartz.
Composed of montmorillonite.
Composed largely of montmorillonite, ap-preciable amounts of feldspar, and smallamounts of mica.
In addition, thin sections were made from the samplesat locations 10 and 31. Both thin sections display shardsof glass dispersed in an oriented-shred structure. Thisstructure has been explained bv others (Heinrich,1956) as probably a result of pressure-packine.
Foraminiferal
zoneLocal
i
y (of Wissler)
10 5
31 3
44 5
Commonly, the volcanic ash is partially decomposedinto clay; as a result, no distinct pumice shards wereidentified in the samples. Nevertheless, distinct glass
shards were recognized.
DEPOSITIONAL ENVIRONMENTOne of the principal goals of this study was to
determine the nature of the environment of the LosAngeles Basin during the deposition of the lower
Pliocene sediments. This involved several factors; such
as submarine topography, overlying water, rate of
deposition of sediments, and tectonic activity.
The evaluation of the environment was carried out
primarily bv comparing sedimentary and faunal data
from the lower Pliocene rocks w ith similar information
from submarine basins located in the adjacent offshore
area. Sedimentary data were presented in previous sec-
tions and reference will be made to these sections
throughout the following discussions.
Submarine topography
The Los Angeles Basin has been described byWoodring, Crouch, Natland and Rothwell and by sev-
eral other writers as a deep marine basin during early
'67 Early Pliocene History, Los Angeles Basin—Conrey 37
Figure 26. Areal variation in heavy mineral suites of sandstone.
'Pliocene. This conclusion was based primarily upon'the similarity between the fossil foraminiferal assem-blages contained in the lower Pliocene rocks and the
modern assemblages sampled in the deep submarinebasins off the coast of southern California. Many of
these writers also pointed to foraminiferal evidence of
distinct changes in depth of water in the Los Angeles' Basin during the deposition of the lower Pliocene sedi-
ments.
To evaluate the depth conclusions of previous au-
thors, in addition to seeking evidence of submarinetopography in the basin during lower Pliocene, the
writer examined and described 45 foraminiferal as-
semblages sampled from the top and the base of the
lower Pliocene strata at seven locations. The results
arc listed in Tables IV and V. In addition, foraminif--eral assemblages from five locations, which had beenselected at stratigraphic intervals of approximately 200feet, were scanned briefly for the relative abundance ofarenaceous, hyaline, bcnthonic and planktonic foram-inifera.
Depth
References were made by authors mentioned aboveconcerning the depth of water in the Los Angeles
Basin during early Pliocene. These references rangedfrom a minimum figure of 2,000 feet to a maximum of
nearly 8,000 feet. For example, Woodring (1938)estimated a depth range of 2,000 to 4,000 feet on the
basis of modern representatives of the fossil echinoids
and mollusks contained in the lower Pliocene strata.
At the other extreme. Crouch ( 1952) proposed a depthrange from 3,650 to 7,650 feet. This was based upon a
comparison of modern Foraminifera, occurring in off-
shore submarine basins, with their fossil counterparts
in the lower Pliocene strata. A moderate view of
depth, also based upon foraminiferal studies, was ex-
pressed by Natland and Rothwell (1954) and by Nat-land (1957). They proposed that the depth of water
ranged from approximately 3,000 feet at the beginning
of Pliocene to 4,500 feet in the latter part of early
Pliocene. They concluded that the depth of water wasreduced to approximately 4,000 feet at the close of
early Pliocene.
Beginning of Pliocene. The conclusions of this
writer are not in complete accordance with any of the
previous authors. The fossil foraminiferal assemblages
from basal lower Pliocene beds (Table IV) compare
the most favorably with modern assemblages living in
38 California Division of .Minis and Geology SR 9
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K.- Early Pliocene History, Los Angeles Basin—Conri 'i 41
&S 1
Figure 27. Petrology of pebble and granule fractions of sandstone. Map shows areal variation of rock classes.
California Division of Mines and Geology SR 9
Figure 28. Petrology of pebble and granule fractions of sandstone. Map shows areal variation of rock types.
the abyssal biofacies * biozone (6,000 feet deep orgreater). This conclusion is based upon the joint oc-currence in the fossil assemblages of many Buliminarostrata, Uvigerhia hispida, Nonion barleeanus, Uvige-rina proboscidea, and varieties of Uvigerina senticosa;
in addition to scattered occurrences of a few Gyroi-dina soldanii, Hoghtndina elegans, and Fullenia bul-loides. The biofacies of the living representatives ofthese Foraminifera are outlined in Table VI.
A comparison of the faunal patterns in the basal
Pliocene beds and the sedimentary patterns in the en-tire lower Pliocene (refer to figure 5) indicates thatthe proposed minimum depth of 6,000 feet is probablythe sill depth t of a submarine basin. The basin floorconceivably could be 2,000 feet below sill depth, asin the case of two modern submarine basins: SantaCruz and San Nicolas (figure 1).
The faunal pattern indicates the existence of a sub-marine basin by areal variations in the compositionof the foraminifera! assemblages. The differences inthese assemblages are not in the nature of species sinceeither the same species or other species characteristic
ll?,1?11?' arK'/" r flor ol assemblage characteristic of a specific environment.
t Sill depth is the greatest depth at which there is free horizontal communication between basins (Sverdrup, Johnson, and Fleming, 1949).
of the same biofacies were recognized at most of the
locations. This is typical of modern faunal assemblages!
living below sill depth in the submarine basins on the
"continental borderland" (Crouch, 1952 and Resig,
1958) because the bulk of the water trapped in the
basins retains approximately the same temperature,
salinity, and oxygen content that occurs at sill depth
(Emery, 1952 and 1956). The significant areal changein the foraminifera] assemblages is in the number of
dwarfed Foraminifera, + arenaceous Foraminifera, andto a lesser extent planktonic Foraminifera. For ex-
ample, the microfossil assemblages at location 85
(Newport), which occupy a peripheral position in
the Los Angeles Basin now and probably did at the
beginning of the Pliocene, contain less than 1 percentdwarfed hyaline Foraminifera, less than 1 percentarenaceous Foraminifera, and nearly 15 percent plank-
tonic Foraminifera. On the other hand, the assemblagesfrom locations 10, 12, 14, 31, and 44, which occupydistinct basin locations now and probably did at the
beginning of the Pliocene, contain a high proportionof dwarfed hyaline Foraminifera, arenaceous Forami-
J "Dwarfed" Foraminifera are relatively small mature forms of the species;commonly, the "dwarfed" forms are less than half the size of thelarger individuals.
Early Pliocene History, Los Angeles Basin—Conrey
/ „)VV /
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^////U- OUTCROPS OF LOWER^^ PLIOCENE ROCKo
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-M^\ \\ \
X x • V X *A \ ^-subsurfoce margin of
• f
—
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ower Pliocene rocke
v x- X
/. j£ vi v !
Figure 29. Siltstone-silty shale isopach map for lower Pliocene.
"rifera, and little or no planktonic Foraminifera. Theseareal variations are depicted in figure 38.
The change in the composition of the foraminiferalassemblages may represent an areal change from an'open sea environment, possibly at or near sill depth,to an environment at the water-sediment interface onthe floor of a submarine basin where the waters arelow in oxygen. The high percentage of arenaceousForaminifera and dwarfed hyaline Foraminifera is pre-sumed to indicate a deficiency of oxygen on the basis
of ecologic studies of modern foraminiferal assem-blages. For example, Lowman (1949) pointed out thedominance of arenaceous Foraminifera in (1) micro-faunal assemblages from foul brackish-water marshes,lays, and lakes and (2) benthonic microfaunal assem-blages from deep-marine deposits in the Gulf of Mex-'ico where plant and mineral components suggest a lowoxygen content. Two of the dominant arenaceousgenera, Cyclammina and Haplophrngmoides, that Low-man identified in the deep-marine deposits, representa major portion of the arenaceous Foraminifera in thebasal Pliocene assemblages in the Los Angeles Basin(Table IV). Haplophragmoides also was found byLowman in the foul brackish-water marshes, bays, andlakes. The dwarfed hvaline Foraminifera were re-
ported as characterizing the oxygen-poor environmentof the floor of Santa Cruz Basin, off the coast of south-
ern California (Crouch, 1952). Abnormal forms of
hyaline Foraminifera also were recognized locally in
the oxygen-poor waters of Plava del Rey lagoon
(Easom, 1954) and the Salton Sea (Arnal, 1957).
The low oxygen content of the waters at the water-
sediment interface on the bottom of the Los AngelesBasin during early Pliocene is suggested by sedimen-tary data. Iron sulfide minerals occurred both in a free
state and in microfossil tests in many of the basal
Pliocene samples. In addition, the fine-grained strata
at many of the locations contained relatively large
amounts of organic carbon (6.6 percent at location
Close of early Pliocene. The foraminiferal assem-
blages from the top of the lower Pliocene (Table V)suggest a shallowing of water over the sill to a mini-
mum depth of 4,000 feet at the close of early Pliocene.
This depth was selected on the basis of the occurrence
of many Cassidulina translucens and Uvigerina hispido-
costata; and scattered occurrences of Eponides umbo-natus, Nonion pompilioides, and Pullenia bitlloides in
the foraminiferal assemblages. This joint association
of Foraminifera is characteristic of modern assem-
44 California Division <>i Mines and Geolo(.\ SR dj
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Figure 30. Areal variation in average grain-sized class of siltstone and silty shale
bkges living in the lower bathyal biofacies (Table VI)As in the basal Pliocene evaluation, the faunal and
sedimentary patterns portray a submarine basin at theclose of the early Pliocene. A transition from normalto abnormal assemblages containing a high percentageof dwarfed Forammifera again marks the change fromlocations on or near sill depth to locations on the floorof the submarine basin.
Specific features
The paucity of horizontal control in the centralportion of the basin and inadequate faunal data (neg-ligible zonation below sill depth) leave little to workwith in evaluating the nature and amount of sub-marine topography in the Los Angeles Basin durin-the deposition of lower Pliocene sediments. Never-theless, certain inferences can be made from recentstudies of modern submarine basins off the coast ofsouthern California.
In 1952 Emery and Rittenberg related the flatnessof basin floors to the width and depth of fill of thebasin. Thar study revealed a general tendency to-wards wider, flatter, and thus more deeply filled basinsnearer shore than further out; 7,000 to 10,000 feet ofnil occur in the wide relatively flat-floored Catalina
Basin and San Diego trough. They reasoned that theflatness of the floor was roughly proportional to thedepth of fill, reasonably assuming that the originaltectonic floor was more irregular than the surface ofsediments atop it.
In applying these observations to the lower PlioceneLos Angeles Basin, it is plausible that the floor of thebasin was relatively flat. This observation is based,first, on the size of the basin (approximately 20 miles'across), which is equaled in size only by the relativelyflat-floored Santa .Monica Basin located immediatelyoffshore. Secondly, there was considerable filling of theLos Angeles Basin prior to the beginning of the Plio-cene; at least 8,000 feet of deep-marine .Miocene sedi-mentary strata occur in the basin.
Belts of irregular topography along the margins ofthe Los Angeles Basin floor during early Pliocene areindicated by concentrations of coarse-grained elastics(figures 10-13). This possibility is substantiated byrecent studies of the Santa Monica and San PedroBasins by Gorsline (1958) in which he identified slumpaprons and submarine fans. His observations are sum-marized as follows:
1. The lower part of the coastal slopes of the basins is fronted byslump aprons with hummocky surfaces that cover the basal slopes
Early Pliocene History, Los Angeles Basin—Conrey 45
Clay
Sand Silt
Figure 31. Textural classification of fine-grained rocks (from Shepard, 1954).
and merge with the flat basin floor. The slump origin of these
features was recognized from a study of the sediments' texture.
The diagnostic features were contorted bedding, micro-breccias,
pebbly silts, "mixed structures" (interspersed pockets of sand
Iand mud), and massive silty-sand muds with no apparent bed-
ding.
2. Submarine fans appear at the mouths of active submarine can-
yons that extend down the coastal side of the basins. These
fans are characteristically semicircular areas of sediments ex-
hibiting moderate relief. For example, the surface of the Dumefan rises 300 to 450 feet above the general level of the floor
of the Santa Monica Basin at the mouth of Dume Canyon. Somefans cover rather extensive areas. The Mugu-Hueneme fan com-plex, which fronts the Hueneme and Mugu Canyons at the
northeastern end of Santa Monica Basin, borders the basin for
a distance of 12 miles and extends some 5 miles into the basin.
The fans contain the coarsest grained sediments in the basin,
particularly in their upper portions where sand is the principal
sediment. Even gravel is common in the Mugu and Hueneme fan
complex. In contrast, clay silts prevail on the basin floor.
Submarine fans and slump aprons. The existence
of submarine fans and slump aprons along the north-ern and eastern margins of the Los Angeles Basin dur-ing the lower Pliocene is postulated, as follows:
1. Montebello-Whittier fan complex is centered at the north-central
margin of the basin. Its outline is identified in figure 10 by
(1) a lobe of conglomeratic strata spreading west and south
from a focal point at the southwestern end of the Puente Hills
and (2) a concentration of coarse-grained elastics in the south-
western Puente Hills area. This complex may represent at least
two fans; one has its locus in the vicinity of location 14, and the
other is centered in the southwestern end of the Puente Hills.
The outline of the two fans is displayed clearly in figure 12.
The existence of this fan complex throughout the lower Pliocene
is indicated by its appearance in the lithofacies maps of lower,
middle, and upper-lower Pliocene.
Olinda fan is indicated at the northeastern edge of the basin by
a concentration of conglomerates (approximately 5 miles long
and 1 mile wide) in the vicinity of locations 39, 40, and 46.
Outlines of this feature appear in the lower and middle-lower
Pliocene lithofacies maps (figures 11—12) but do not appear in
the upper-lower Pliocene lithofacies map. It is possible that the
fan was no longer active in upper-lower Pliocene, and as a
result it was blanketed by sediments from other sources.
Anaheim fan is represented by the broad pattern of conglom-
erates appearing in the vicinity of locations 36, 38, and 61, in
the eastern end of the basin, and the concentration of coarse-
grained elastics at location 61.
Salt Lake fan (?) is suggested, on the basis of meager data, at
the southern flank of the present Santa Monica Mountains in the
vicinity of location 2. The only data available to the writer were
scattered well cores from the basal 200 feet of the Pliocene at
location 2. As a result, little information could be presented on
the lithofacies maps beyond showing a broad trend of increased
amounts of coarse-grained elastics in this general area. How-
ever, supporting data were presented in the petrologic map(figure 27), quartz-feldspar map (figure 25), and sand-grain
roundness map (figure 23). In all of these maps a distinct depo-
46 California Division of Minis \m> Geology SR <•
cu a<L> UQ. C(X -H» H
0-,
El Segundo Inglewood Montebello
28 6 Mi. NNE m 15* Mi. E ^
j—S ' I
Grain Size(Microns)
Grain Size(Microns)
Grain Size(Microns)
Figure 32. Stratigraphic variation of grain size for siltstone and silty shale.
)67 Early Pliocene History, Los Angeles Basin—Conrey 47
im.'IIIIUMMHf 1 1 1
1
1 1 1 1
1
1 1 1 1
1
1 1 1 M 1 1 1 1
HH 1 1| n 1 1 r, l m
11 . i n u 1 1 1
1
! j I
H
1•
\>
'
Figure 33. Pebbly siltstone and cobble from siltstone strata. A (upper
Sampled at location 52 (Malaga Cove). B (upper right). Cobble (8 inches
"anyon). C (lower left). Pebbly siltstone core from location 14. D (lower
sitional trend was displayed from location 2 into the basin. The
distance that these trends spanned suggests an extremely active
depositional feature such as a submarine fan rather than a
more localized slump apron.
5. Puente slump apron is indicated by the appearance of conglom-
erates in a predominantly fine grained clastic section of upper-
lower Pliocene strata along the southern flank of the Puente
Hills between the proposed Montebello-Whittier fan complex andthe Olinda fan (figure 13). These conglomerates probably repre-
sent slumping, and possibly turbulent (low, along an active
Whittier fault that formed the northeastern side of the basin.
These conglomerates are approximately the same composition as
the Miocene conglomerates cropping out in the Puente Hills.
6. Santa Ana-Newport slump aprons are indicated along the south-
eastern margin of the basin, at locations 77 and 86, by the
appearance of sedimentary breccias in the basal portion of anotherwise fine grained clastic section.
i7.Potrero Canyon slump apron is suggested along the southwestern
flank of the present Santa Monica Mountains at location 88by sedimentary breccias and numerous angular clasts scattered
throughout the basal portion of a fine-grained clastic section.
These clasts consist principally of slates and limestones that are
indicative of a local source (discussed in later section).
8. Los Angeles slump apron is indicated by the appearance of
numerous sedimentary breccias in a fine grained clastic section
of lower Pliocene strata at location 3 on the southeastern flank
of the present Santa Monica Mountains. The breccia clasts pri-
marily consist of Miocene limestone from a local source (dis-
cussed in later section).
Submarine margins. The proximity of the north-
ern and eastern submarine margins of the Los AngelesBasin, during at least part of the early Pliocene, is
confirmed by the location of submarine fans and slumpaprons that formed at the base of the marginal slopes
of the basin (paleophysiographic map, figure 39). Also,
left). Cobbles (2'/2 and 4 inches across) displaying animal (?) borings.
across) displaying animal (?) borings. Sampled at location 88 (Potrero
right). Pebbly siltstone core from location 38.
the position of the submarine margins is indicated byangular unconformities. For example, at the Los An-geles City location 3, a 20-degree unconformity be-
tween lower and upper Pliocene strata (Martin, 1952)
may represent a basin slope at the close of the lowerPliocene. In the same manner, a 10 degree angular
unconformity between lower and upper Pliocene strata
north of location 85 in the Newport field (Allan andJoujon-Roche, 1958) may represent a basin slope at
the close of the lower Pliocene. The submarine marginat the eastern end of the basin is indicated by bothangular unconformities and sedimentary pinch-outs, as
follows:
1. A basin slope, ranging from 6—10 degrees, is indicated between
locations 36 and 61. The slope was estimated as 6 degrees on
the basis of the pinching out of successively younger horizons
of lower Pliocene strata from locations 36—61 (figure 40). Anangular unconformity of 10 degrees was recorded between the
Miocene and lower Pliocene strata at location 37, and 8 degrees
was recorded at location 61.
2. A basin slope of approximately 10 degrees is indicated between
locations 77 and 76 by the pinching out of successive basal beds
of lower Pliocene strata (figure 40).
3. A gradual pinching out of basal lower Pliocene beds from East
Coyote (44) to Richfield (49) was reported by Wissler (1941).
This suggests a basin slope of approximately 10 degrees
(figure 40).
Submarine sill. A submarine sill apparently sep-
arated the deep portion of the Los Angeles Basin fromthe open sea along its present coastal margin (figure
39). The clearest cut evidence of its existence is in the
vicinity of the Palos Verdes Hills, as follows:
48 California Division of Mines and Geology SR 9-
0>
a)
a,
Figure 34. Histogram showing variation of sorting coefficients for siltstone and silty shale.
1. A submarine slope is indicated on the northeastern side of the
Palos Verdes Hills (PI. 2) by the pinching out of the basal bedsof the lower Pliocene towards the Palos Verdes Hills. At loca-
tions 52 and 53, middle-lower Pliocene strata rest conformablyon Miocene rock. Furthermore, at location 53 most of the upper-lower Pliocene strata are missing under the cover of upperPliocene rock.
2. Extremely slow deposition is represented by the strata at loca-
tion 52 which is in closest proximity to the sill. Evidence for this
is as follows:
a) The entire middle and upper-lower Pliocene interval is re-
duced to little over 100 feet.
b) Organic hard-parts, iron sulfide minerals, and carbonaceousmatter occur in greater abundance at this location than at
other locations.
3. A much higher proportion of fine-grained rocks occurs imme-diately adjacent to the Palos Verdes Hills than in adjoiningareas (lithofacies map, Fig. 10).
4. The occurrence of minerals and rock fragments similar to thoseforming the core of the Palos Verdes Hills, as well as glau-
conite and cobbles with animal (?) borings, at flanking loca-
tions indicates a submarine sill at the present site of the Palos
Verdes Hills. Examples of these minerals and rocks are as
follows:
a) Considerable quantities of chlorite occur in the samples of
sandstone at locations 50 and 68 (figure 26).
b) Glaucophane occurs in the sand-size fraction of fine-grained
sediments from locations 52 and 53.
c) Localized concentrations of metamorphic rock and shale frag-
ments appear in samples of sandstone from location 50. Muchof the metamorphic rock consists of quartz-mica schist that is
an important constituent of the basement rock in the Palos
Verdes Hills.
d) Considerable quantities of glauconite appear in the fine-
grained sediments rich in organics at locations 52 and 53.
This glauconite probably is displaced from a submarine high
(cited in previous discussion).
e) Cobbles displaying animal (?) borings are scattered through-
out the section at location 52 (figure 33).
67 Early Pliocene History, Los Angeles Basin—Conrey 49
100
Figure 35. Median diameter-sorting coefficient curve for siltstone and silty shale.
iFormer existence of a sill in the Santa Monica Bay is
based principally on the following evidence:
1. Rocks of Miocene age crop out in Santa Monica Bay. Further-
more, at one location on the outer shelf of the Santa Monica Bayschist-basement rock was sampled in dredge hauls during several
marine surveys by the Allan Hancock Foundation, University of
Southern California (Terry, Keesling, and Uchupi, (1956). These
older rocks suggest a continuing trend of the Palos Verdes Hills
structure through the Santa Monica Bay.
2. The thinning of the lower Pliocene strata westward towards the
older rocks in the Santa Monica Bay suggests a sill in this area
(isopach maps).
3. There is also a westward decrease in the quantity and grain size
of coarse grained clastic rocks (figures 10, 17, and 31).
4. A sill through the present site of the Santa Monica Bay would
help explain the oxygen-poor bottom conditions suggested by
the sediments and fossil Foraminifera in the Los Angeles Basin.
50 California Division of Mines and Geology SR 9:
r 11
*>
mdX&>'
Figure 36. Sedimentary structures in siltstone and silty shale. A flop, left). Sandstone mottles in a core of siltstone from location 56. Core is in
an upright position. 8 (top, right). Magnification of the sandstone mottle pictured on the right side of the mottled siltstone shown in "A". C (bot-
tom). Top view of mottled core of siltstone from location 56.
Evidence that a sill formerly existed between the pres-
ent sites of the Palos Verdes and San Joaquin Hills
is, as follows:
1. The thinning of the lower Pliocene strata towards this proposedsill (isopach maps).
2. A submarine slope north of location 85 (previously cited).
3. The foraminiferal assemblages changing from a normal open-
sea fauna at locations flanking the proposed sill to abnormalassemblages in basin locations (previously cited).
At the beginning of the Pliocene the lowest portion
of the sill was located between the present sites of
Palos Verdes and San Joaquin Hills. This assumptionis based upon a measured increase in the number of
hyaline Foraminifera, both in individuals and species,
and a decrease in the number of arenaceous Foraminif-era in a southeast direction from the northwesternend of the basin (figure 38), which suggests that the
deepest subsurface waters entered the basin from thesoutheast. The estimated minimum depth of this sill
is 6,000 feet as previously stated.
The faunal assemblages sampled from the upper-most lower Pliocene at locations flanking the sill at thepresent sites of Santa Monica Bay and south of thePalos Verdes Hills are remarkably similar (locations
10 and 75, Table V). This suggests that at the closeof the lower Pliocene the sill rose at both sites toapproximately the same depth, possibly a 4,000 foot
minimum depth. Now the same rocks are at a depthof approximately 200 feet.
Overlying water
Clues concerning the nature of the water and its
movements can be obtained from the fossil faunas and
sediments. For example, the deficiency in the oxygencontent of the waters at the sediment-water interface
on the basin floor is suggested by (1) abnormal foram-
iniferal assemblages, (2) high organic content of the
fine grained clastic rocks, and (3) presence of free
iron sulfide minerals in the fine grained clastic rocks
and the microfossil tests. In addition, the specific com-position of the microfossil assemblages suggests little
change in temperature, salinity, and oxygen content
of the water from sill depth to a level slightly above
the basin floor. In this regard, the modern represent-
atives of the basal lower Pliocene Foraminifera domi-nate upper abyssal assemblages living in waters off the
coast of southern California that average in tempera-
ture, salinity, and oxygen content; 2.5° C, 34.5 parts
per thousand, and 1.35 ml./L., respectively. In con-
trast, the modern representatives of the uppermostlower Pliocene Foraminifera dominate lower bathyal
assemblages living in waters averaging in temperature,
salinity, and oxygen content; 3.5° C, 34.5 parts per
thousand, and 0.50 ml./L., respectively.
157 Early Pliocene History, Los Angeles Basin—Conrey 51
Locations
1000_
9
1o
2000-
£ 3000-
Uooo_
^b * 30
Figure 37. Stratigraphic variation of acid soluble material in silt-
tone and silty shale.
The abnormally low salinity of the surface waters
h the basin at the beginning of the Pliocene is sug-
gested by the paucity of planktonic Foraminifera in
he basin locations 12, 14, 31, and 44. The works of,:>arker (1954) and Emiliani (1954) on modern foram-
niferal populations demonstrated the lack of tol-
erance of planktonic Foraminifera for fresh water.
|fhe return of normal salinity in the surface waters in
':he later part of early Pliocene is indicated by the
ippearancc of numerous planktonic Foraminifera in
:he basin locations. The sporadic occurrence of plank-
ronic Foraminifera throughout the remainder of the
tlower Pliocene strata suggests continued normal salin-
ity of the surface waters until the end of early Plio-
cene deposition.
Movements of water in the basin are revealed byareal depositional patterns in the strata (isopach, litho-
facies, grain size, and composition maps). The prin-
cipal direction of motion was apparently west andsouth from the northern and eastern margins of the
basin. These movements probably represent a limited
part of the water column, namely bottom water. Thisconclusion is based upon the primary role of turbidity
currents in transporting sediments into and through-
out the basin.
Rate of sedimentation
In recent studies of the offshore Santa Barbara andSanta Catalina Basin, Orr and Emery (1956) deter-
mined rates of total sedimentation of 0.064 and 0.044
cm. per year, respectively. These rates are of the samemagnitude as the estimated average rate of deposition
for lower Pliocene sediments in the Los Angeles Basin.
To elaborate, the maximum thickness of fine-grained
lower Pliocene strata is about 3,000 feet; therefore,
assuming a time interval of 5 million years and a maxi-mum compaction of each layer to 25% of their origi-
nal thickness at the surface of the ocean floor, the
average yearly rate of deposition would be 0.07 cm.The amount of compaction was calculated for the
lower Pliocene strata at Playa del Rey (location 10),
4500-foot depth of overburden and 1 1 micron average
grain size, using compaction data on modern marinesediments that were provided bv Emerv and Ritten-
berg (1952).
In considering variations in the thickness of the fine-
grained lower Pliocene strata in the Los Angeles Basin,
the rates of sediment range from a maximum of 0.07
cm. per year (3,000-foot thickness) to 0.015 cm. peryear (600-foot thickness) for complete sections. Tosome extent, these different rates of sedimentation re-
flect unlike transporting agents. That is, the thickest
sections contain deposits representing rapid deposition,
such as; turbidity flows. The turbidity deposits com-prise a significant if not dominant portion of mostof the thick sections; this is discussed in detail later.
In contrast, the thin section portrays slow deposition
of fine grained detrital particles and flocculated clay
by continuous sedimentation from surface waters. Thiscorrelation of rates of sedimentation with transport-
ing agents is reported by Gorsline and Emery (1959)in their studies of the offshore San Pedro and SantaMonica Basins. They reported a rate of sedimentationof 0.019 cm. per year from a continuous sedimentationprocess. They further estimated rates of deposition
for the San Pedro Basin where both continuous sedi-
mentation and discontinuous turbidity current andslump deposition are in operation. The rates rangedfrom 0.06 cm. per year on the central basin floor to
0.24 cm. per year at the margins of submarine fans,
with a maximum of 1.00 cm. per year in upper sub-marine fan locations.
Tectonic activity
The instability of the floor of the Los Angeles Basin
during the early Pliocene probably contributed to the
areal variations in thickness of strata. In the previous
section on submarine topography it was pointed out
52 California Division of Mines and Geology SR9
LOCATIONS
PLAY* DEL
NET
J2
POTNEfc.
It
DOMIMUEZ
81
HUNTINCTOM
•EACMT«
NEWPORT
•EACH
BOTTOM PNOFILE
>7- \T-rrn tttttttttrrrrTrrr>
TT.
-
1 1
-
-
- -
- -
- -
- -
• -
- / OWANFEO"
/ roNAJtlNiFCN*
T 1
-
ENDEMIC
lANCHACCOUil
ENOEMICINTALINEl
Figure 38. Areal variation in composition of microfossil assemblages from basal lower Pliocene strata.
that subsidence of the basin floor was partially respon-sible for the accumulation of thick deposits of sedi-
mentary rocks. A decrease in the depth of the central
floor, approximately 2,000 feet by sedimentation, wasestimated for the early Pliocene; therefore, subsidenceundoubtedly took place at locations where the ac-
cumulation of sedimentary rocks markedly exceedsthis figure, for example: a 4,915-foot section at loca-
tion 14.
The tectonic instability of the basin floor also is
substantiated by the thinning of the lower Pliocene
strata and changes in lithology across existing anti-
clinal trends. The isopach maps (figures 5-8) suggest
the development of structures at Richfield, East and
West Coyote, Torrance-Wilmington, and Playa del
Rev fields (figure 3) during the lower Pliocene as fol-
lows: ( 1) Richfield structure developed either prior to
or during the deposition of lower-lower Pliocene sedi-
ments, (2) Coyote structures developed during the
deposition of the middle- and upper-lower Pliocene
sediments, (3) Torrance-Wilmington structural trend
is recognized first in middle-lower Pliocene deposits,
67 Early Pliocene History, Los Angeles Basin—Conr
SUBMARINE FAN SLUMP APRON BASIN FLOOR SUBMARINE "HIGH"(SILL, SHELF, ETC)
FAULT LAND
2 4 6>^JP MILES
SCALE
^^^^^^Z^ An9e 'eS B° Sin dUri " 9 eaHy P ' iOCene-
THe P*****"** *>* - SU pe rimposed on a ma p shp show-
fATTFORXT* niVKKA" >" MlVFS <\H nFnilll.V
_jifi_ ESR a
NWJ4_DATUM- TOP Of LOWER PLIOCENE
.22. -as. Ji _aa_ _L=_ .62. _£L -SiSE
_±iN
'SO' DEL.SH.
30OO^ 1-
10OO0 2000
NUMBERS IN CROSS-SECTIOMS'FORAMINIFERAL ZONES OF WISSLER(ISAI)
COLUMN-SECTIONS- STRATTORAPHIC SECTIONS
LINE-SECTIONS- ELECTRICAL LOO
SCALE IN FEET
ABBREVIATIONS OEL= OELMONTIAN WOK UOHNIAN
A. TOP FORAMINIFERAL ZONE OF MD0INEIWISSLER,I»4I)
SM.= SHALE VOLC* VOLCANIC ROCK
Eiguro 4 0.—Strat i graphy c rest tec t ie n t d e ploy i n g pi n slvou is.
and (.4) Playa del Rey structure developed during the
early Pliocene. The decrease in the proportion of
clastic rocks, as well as in their grain size, suggests
that the Richfield structure and the eastern portion of
the Coyote trend rose above the basin floor as a
distinct topographic feature. The expression of the
other structures is in doubt. They either formed sub-
marine topography or represented localities on the
basin floor in which subsidence played a less active
role.
The major faults recognized today in the Los An-geles Basin (figure 3) apparently were active duringthe lower Pliocene as follows:
1. Whiftier fault, extending along the southern flank of the Puente
Hills, formed a submarine scarp whose occasional activity trig-
gered the movement of turbidity currents and submarine land-
slides down its slope and down submarine canyons dissecting its
slope. The accumulation of locally derived conglomerates and
sedimentary breccias in fans and aprons along the front of the
fault (figure 39) gives testimony to its activity. The active nature
of the fault is portrayed further by its Quaternary record of
15,000 feet of right-lateral displacement and approximately
10,000 feet of vertical displacement (Woodford and others,
1954).
2. Anaheim fault, trending parallel to the Whiftier fault some 6
miles to the south, apparently formed a submarine scarp facing
north during the deposition of lower- and middle-lower Pliocene
sediments (isopach and lithofacies maps). Limited dip-slip move-
ment along this fault is suggested by (1) variation in thickness
of strata and (2) the sporadic concentrations of coarse-grained
clastic rocks along its border.
3. Newporf-lng/ewood trend, representing a surface-disconnected
series of faults extending from the southeastern edge of the
967 Early Pliocene History, Los Angeles Basin—Conrey 55
basin to its northwestern margin, probably has been an active
fault zone, at least in the basement rock, (Reed and Hollister,
1936) since the middle Miocene. The activity of this fault zoneis suggested in part by sedimentary changes along its boundary(isopach maps and compositional map, figure 25). The existence
of an active dip-slip fault scarp is supported by several observa-
tions as follows: (1) Quaternary history of right-lateral move-ment (Reed and Hollister, 1936) rather than left lateral sug-
gested by the sedimentary trends; (2) present down-faulted
condition of the southwestern (coastal) side of the fault zone(figure 4); and (3) greater accumulation of coarse grained
clastic rocks on the southwestern side of the fault zone.
4. Palos Verdes faulf, extending along the northeastern margin of
the Palos Verdes Hills, undoubtedly formed an active sub-
marine scarp through its dip-slip movement along the basinwardside of the Palos Verdes Hills during the early Pliocene. It pos-
sibly had greater areal extent at that time, representing at least
part of the basinward flank of the sill extending northwest andsoutheast from the Palos Verdes Hills' site (figure 39). The tec-
tonic activity along at least part of this fault is indicated by the
shallowing of the deepest part of the sill from a minimum of
6,000 feet at the beginning of the Pliocene to a minimum of
4,000 feet at the close of early Pliocene (previously discussed
sill depth of basin).
The Los Angeles Basin was initiated as a submarinebasin prior to lower Pliocene deposition. Barbat (1958)suggested that it was blocked out during the mid-Miocene diastrophism. The basin floor progressively
deepened through the late Miocene (Natland andRothwell, 1954). A maximum depth probably was at-
tained either at the close of the Miocene or at the
beginning of the Pliocene, followed by a progressive
shallowing during early Pliocene. There is no evidence
of a sudden deepening at the beginning of the Plio-
cene. This conclusion is based upon similar biofacies
markers occurring in foraminiferal assemblages fromboth uppermost Miocene and basal Pliocene strata and,
secondly, the transitional nature of the Miocene-Plio-
cene contact in the central part of the basin.
MODE OF TRANSPORTATION
The lower Pliocene sediments probably were trans-
ported three ways in the Los Angeles Basin: (1) tur-
bidity currents, (2) submarine slumps, and (3) normal
surface and near surface currents. Each of these modesof transportation will be discussed in the following
i sections, first in terms of a historical resume and
then in regards to the manner in which they wereidentified.
Turbidity currents *
The important role of turbidity currents in the
transportation of marine sediments has been recog-
nized in recent years. Daly in 1936 and Kuenen in
1937 proposed such currents in the formation of sub-
marine canyons. Stetson and Smith (1938) concludedthat turbidity currents may have been important in
carrying fine sediments into the open sea. Bramlette
and Bradley ( 1940) attempted to account for certain
coarse and graded sands in Atlantic deep-sea cores byturbidity currents, and Migliorini (1944) attributed
* Turbidity (density) currents are water currents so heavily laden with
suspended sediments that their density causes them to flow down-
ward along a sloping bottom in a standing body of water. These
currents result from the slumping of sediments in a standing body
of water. They probably pass through brief stages that might
be considered landslides and mud flows. As more water becomes
mixed with the mud flow it is converted from a plastic-solid mass to
the fluid condition of a turbidity current.
great series of graded beds in the Apennines to them.Experimental work on the properties of these cur-
rents was reported first by Bell (1942), and later moreextensive studies were reported by Kuenen and Miglio-rini (1950). Since 1950 there has been a great impetusin the application of turbidity-current deposition bystudents of modern and ancient marine environments.
Turbidity-current deposition was reported in ancient
basins in Europe by several workers. Among these,
Crowell (1955) reported turbidity-current structures
in the Flysch deposits in the Alps. In the Apennines,Kuenen and Migliorini (1950) identified turbidity-cur-
rent deposition from the occurrence of coarse car-
bonate detritals interbedded with shales and fine car-
bonates.
In New Zealand, Mutch (1957) described a tur-
bidity current sequence of thick, banded and gradedgraywackes in Carboniferous geosynclinal sedimentaryrocks. Also, Waterhouse and Bradley (1957) described
slump and turbidity-current features in sedimentaryrocks of several ages and locations in geosynclines of
New Zealand.
In the United States, turbidity-current deposition
was recognized in the Permian Basin of Texas and
New Mexico by Hull (1957). Also, Hawley (1957)
described turbidity and slump features in the Ordo-vician strata of Northern Champlain Valley in Ver-
mont. As far as this study was concerned, the mostsignificant works in the United States were in southern
California, the locale of Los Angeles Basin. Several
workers have identified turbidity-current deposits in
either fossil or modern basins. Natland and Kuenen(1951) demonstrated the role of these currents in the
deposition of the Pliocene sediments in the Ventura
Basin. Kundert (1952) proposed turbidity currents and
submarine slump to explain the distribution of con-
glomerates at the southwestern end of the Puente Hills
in the Los Angeles Basin. Winterer (1954) recognized
sedimentary features representative of turbidity-cur-
rent deposition in the lower Pliocene strata of the
southeastern part of the Ventura Basin. Gorsline
(1958) identified modern turbidity-current deposits
in the San Pedro and Santa Monica Basins.
Evidence of the active role of turbidity currents
The active role of turbidity currents in transport-
ing the lower Pliocene sediments in the Los Angeles
Basin is demonstrated by the following distribution
of coarse-grained clastic rocks:
1. The distribution of conglomerates far beyond the submarine
margin of the lower Pliocene basin indicates a mode of trans-
portation of greater capacity than either surface currents or
submarine slumps. A comparison of the lithofacies map (figure
10) with the paleophysiographic map (figure 39) shows the
occurrence of conglomerates as far as 8 miles from the original
margin of the basin.
2. The distance that the sands were transported in the basin can
only reflect the carrying capacity of turbidity currents. The im-
mediate source of the sands is at the northern and eastern sub-
marine margins of the basin which means that some of the sands
were transported in excess of 20 miles before deposition. Many
of the sands deposited at the distal southwestern (coastal) side
of the basin are very coarse grained "pebbly" sands (figure 41).
Sedimentary features described by Natland and
Kuenen (1951) and Kuenen and Carozzi (1953) as
56 California Division of Mines and Geology
Table VI. Biofacies of modern representatives of lower Pliocene Foraminifera.
SR93'
Neritic Upper bathyal Middle bathyal Lower bathyal Abyssal
Depth range 0-900 feet 900-2000 feet 2000-4000 feet 4000-6000 feet 6000 feet and deeper
Bolivina acuminata Angulogerina angulosa Bolivina seminuda Bulimina rostrata Bulimina rostrata
S Bolivina striatella Bolivina argentea Bulimina spinifera Cassidulina translucens Gyroidina soldanii
rt: Bulimina denudata Bolivina interjuncta Bulimina subacuminata Cassidulina lomitensis Hoglundina elegans
'i Cassidulina californica Bolivina plicata Cassidulina translucens Eponides subtener Nonion barleeanus
Cassidulina limbata Bolivina spissa Cassidulina lomitensis Eponides umbonatus Nonion pompilioides
Uh Cassidulina tortuosa Epistominella bradyana Cassidulina delicata Nonion pompilioides Pullenia bulloides
Planulina ornata Epistominella smithi Eponides subtener Pullenia bulloides Uvigerina proboscidea
Uvigerina hollicki Uvigerina peregrina Eponides umbonatus Uvigerina hispida Uvigerina hispida
Gyroidina altiforrnis Uvigerina hispidocostata Uvigerina senticosa
.2 Uvigerina peregrina Uvigerina proboscidea
O Valvulineria araucana
I
References: Phleger (1951), Crouch (1952). Bandy (1953a), Natland (1957), and Resig (1958).
representative of turbidity-current deposition are iden-
tified in the lower Pliocene strata as follows:
1. Interstratificotion of fine-grained deposits with coarser grained
beds occurs in the strata cropping out at the southwestern end
of the Puente Hills (figure 24). Similar features on a smaller
scale (laminations or banding) appear in cores from the sub-
surface strata. Larger scaled features are suggested by broad
stratigraphic changes in the composition of cores and by elec-
trical log characteristics (pi. 4).
2. Graded bedding occurs in the coarse-grained beds interstratlfied
with fine-grained deposits (figure 24); it also appears in inter-
beds of conglomerates (figure 14) in the strata cropping out at
the southwestern end of the Puente Hills. This bedding is visible
in only a few of the sandstone cores from the subsurface strata
due either to the smallness of the cores or their poor consolida-
tion.
3. Sharply defined basal contacts appear in the outcrops of coarse-
grained clastic rocks (figures 14 and 24). In the subsurface
strata these were difficult to identify due to the nature of the
cores (previously stated); however, a few examples of such
contacts were found (figure 24).
4. Horizontal grading of sediments is displayed in a generalized
manner on the grain-size maps (figures 17 and 31). For ex-
ample, figure 17 demonstrates grading of sandstones across the
basin from an average-medium grain, adjacent to the source
area, to a very fine grain at the distal portions of the basin.
5. Mixed (mottled) structures of siltstone with sandstone pockets
and flakes occur in the strata at all subsurface locations (figure
36). Some of the samples do not show sign of deformationwhereas others do. Undoubtedly, many of the mottles showinglittle deformation were created by benthonic organisms.
6. Orientation and imbrication of clasts occur in the conglomeratescropping out at location 22 (figure 15).
7. Occasional fragments of whole shells of shallow benthonic life
forms and displaced microfaunas occur in the lower Pliocene strata.
Woodring (1938) identified whole shells of shallow-water mega-fossils at several locations in the basin. A large number of dis-
placed microfossils appear in assemblages taken from strata atthe top and bottom of the lower Pliocene section at severallocations throughout the basin (figure 38).
Competent sorting capacity, characteristic of tur-
bidity currents, is displayed by the well-sorted condi-tion of the sandstones (average 1.90 to 2.00) and goodsorting of the fine-grained clastic rocks (average 2.60
to 2.70). These sediments are better sorted than sedi-
ments of comparable texture described as turbiditvdeposits in the Santa Monica and San Pedro Basins byGorsline (1958). For example, gray silts in the SantaMonica Basin with an average median diameter of11 microns have a sorting coefficient of 3.23; this
compares with 2.85 for siltstones of the same mediandiameter in the lower Pliocene.
Source and direction of movement of turbidity currents
The sources of the turbidity currents are displayed
on the paleophysiographic map (figure 39) by sub-
marine fans and slump aprons. The principal sources
were at the northcentral margin of the basin, second-
ary sources at the northeastern and eastern margins,
and minor contributions from other sides of the basin.
The directions of movement of the turbidity cur-
rents are shown on the lithofacies maps by the pat-
terns of coarse-grained clastic rocks. To summarize,
the principal directions of movement probably weresouth and southwest; secondary directions were west
and northwest.
Submarine slumps
Submarine slumps, ranging from rolling and sliding
of particles down slopes to the sudden slumping of
larger masses, have been reported by many investiga-
tors throughout the world. The principal studies prior
to 1950 were summarized by Kuenen (1950) in his
textbook on marine geology. Later works include
studies in New Zealand by Waterhouse and Bradley
(1957); in Venezuela by Renz, Lakeman, and Vander Meulen (1955); and in the United States byHaw ley (1957). All of these studies dealt with fossil
marine basins.
Investigations in and adjacent to the Los AngelesBasin are of more immediate interest to this report.
Kundert (1952) proposed submarine slumping as a
partial explanation for the mode of emplacement of
lower Pliocene conglomerates at the northcentral mar-gin of the Los Angeles Basin. Winterer (1954) identi-
fied slump structures in lower Pliocene sediments of
the southeastern part of the Ventura Basin. In studies
of offshore basins, Emery and Terry (1956) identified
submarine topography, which possibly resulted fromslumping, at the base of the coastal slope. More con-
clusive evidence of submarine slumping was presented
by Gorsline (1958) in his investigation of submarine
fans and slump aprons in the Santa Monica and San
Pedro Basins.
Evidence of the active role of submarine slumps
The active role of submarine slumps in transporting
the lower Pliocene sediments into the Los Angeles
Basin is demonstrated by the following features:
>>6~ Early Pliocenk History, Los Angeles Basin—Conrey 57
Figure 41. Sandstone cores. A (top). Medium-grained sandstone con-
taining pebble-sized siltstone. Core sample from location 38. 8 (bot-
tom). Pebbly sandstone from location 56.
1. Sedimentary breccias occur along the periphery of the basin at
locations 3, 22, 77, 86, and 88 (figure 42). Note that the clasts
display a random arrangement in the breccias.
2. Rapid basinward pinch-outs of clasts are displayed by several
of the conglomerates at the western end of the Puente Hills
(figure 15).
3. Pebbles and cobbles occur in a massive-siltstone matrix at loca-
tions 14, 22, 38, 50, and 88 (figure 33). This feature suggests
small-scale slumping of individual particles down submarine
slopes.
4. Siltstone clasts in a sandstone matrix at location 22 (figure 42)
also suggest small-scale slumping.
The sources of submarine slumps are indicated onthe paleophysiographic map (figure 39) by the loca-
tion of the submarine fans and slump aprons.
Normal surface and near surface currents
Normal surface currents were considered the sole
transporting agent of marine sediments until earth
scientists recently recognized the important role of
turbidity currents and submarine slumps. Althoughsurface currents were by no means the sole mode of
transportation of sediments in the lower Pliocene LosAngeles Basin, the proximity of land (figure 39) sug-
gests that they were an important transporting agent.
Evidence of the active role of surface currents
Gorsline (1958), in his studies of the offshore SanPedro and Santa Monica Basins, identified the follow-ing properties as characteristic of surface-current de-posits.
1. Massive sediments with no discernible bedding.
2. Finest grained sediments (clay silts as compared to silts andsands of other transporting agents).
3. More organic matter than other types of deposits (5.7 percent
organic matter as compared to less than 1 percent for turbidity-
current deposits in San Pedro Basin).
4. Organic particles of sand size (tests, spines, and spicules) scat-
tered throughout the mass of sediment without order of preferred
orientation.
Similar properties were recognized in the lowerPliocene strata of the Los Angeles Basin. Samples frommassive units of clay siltstone contain appreciable
quantities (7 to 10 percent) of organic matter. Further-
more, they often display a random arrangement of
microfossil tests. Although there was no detailed studyof the entire clay siltstone section, at any one location,
for the characteristic properties described by Gorsline,
the writer doubts that all of the clay siltstones repre-
sented surface-current deposition. Undoubtedly, someof these rocks represented distal ends of turbidity-
current deposits, particularly the light-colored units ofclay siltstone which contained only minor quantities
of organic matter. On the other hand, many of the
massive siltstones which form the finest grained units
in the northeastern portion of the basin represented
normal surface-current deposition. Their coarseness
and low organic content reflected the proximity of the
source area.
Other evidence of the activity of surface currents in
the Los Angeles Basin is the paucity of planktonic
Foraminifera in fossil assemblages from lower andmiddle lower Pliocene strata. Modern ecologists cor-
relate this phenomenon with surface waters of abnor-mally low salinity, commonly associated with offshore
currents (Parker, 1954).
SOURCE AREAS
Detrital material in the sedimentary rocks
Previous studies of potential source areas for the
detrital material in the lower Pliocene strata were con-
fined to the sedimentary rocks, principally conglom-
erates, cropping out along the periphery of the present
Los Angeles Basin. Edwards (1934), in a basin-wide
study of outcroppings of Pliocene conglomerates, rec-
ognized the similarity between clasts in the conglomer-
ates and bedrock cropping out in the Perris Uplands,
the Santa Ana Mountains, and the Santa MonicaMountains. Two additional source areas, San Gabriel
Mountains and the eastern end of the San Jose Hills,
were recognized in studies of conglomerates cropping
out at the western end of the Puente Hills by Bellemin
in 1938 and from studies of conglomerates exposed at
the western end of the San Jose Hills by Olmsted in
1948. In 1952, Kundert reiterated Bellemin's suggestion
of a San Gabriel Mountain source for the conglom-
erates appearing at the southwestern end of the Puente
Hills; however, he designated the San Gabriel Moun-
California Division of Mines and Geology SR 93
--.\
-«.-
sh !
-S•~
Figure 42. Sedimentary breccia. A (upper left). Limestone clasts at location 3. 8 (lower left). Sedimentary breccia outlined by dots is composed of
siltstone clasts. Location 22. C (upper right). A close-up of sedimentary breccia pictured in 8. D (lower right). Clasts of limestone (Is), shale (sh), and
basalt (b). Location 86.
tains as the ultimate source, proposing an immediatelocal source—Puente Hills (?).
This writer's basin-wide study of the LowerPliocene sedimentary rocks corroborated the pre-
viously proposed areas as sources of detrital material.
In addition, a southeastern source was recognized at
the present site of the San Joaquin Hills and a south-
western source at the existing Palos Verdes Hills. Thesource areas were identified primarily on the basis ofdepositional patterns displayed by the sedimentaryrocks in the basin. These patterns are expressed in
terms of areal variations of (1) thickness of strata, (2)lithofacies, (3) texture of sedimentary rocks, and (4)composition of sandstones. Unfortunately, the petrol-
ogy of the conglomerate clasts, which proved themost effective for previous workers, was of less im-portance in this study. This is due to the subsurfaceposition of the strata at most of the locations whichpermitted very limited sampling.
The remainder of the discussion will deal withevidences, secured principally in this study, that iden-
tify the source areas. These source areas will be dis-
cussed individually in a clockwise order, beginningwith the Santa Monica Mountains and concluding withthe Palos Verdes Hills.
Santa Monica Mountains source
A source area at the present site of the Santa MonicaMountains was recognized by Edwards (1934). This
was on the basis of large amounts of Miocene lime-
stone clasts, ranging up to 1 foot long, appearing in
sedimentary breccias along the southern flank of the
Santa Monica Mountains, vicinity of locations 3 and88 of this report. Edwards considered the source rockof these clasts to be the .Miocene strata cropping out
in the Santa Monica Mountains.The appearance and size of the limestone clasts in
the sedimentary breccias at location 3 were reaffirmed
by this study (figure 42). Moreover, at location 88
additional sedimentary breccias were recognized that
consisted almost entirely of slates. These slates pro-
vided the best evidence of a local source by their
similarity to the Santa iMonica slates that form the
core of the Santa Monica Mountains. In addition, a
local source was indicated by the size of the slate
clasts—6 inches long. Additional evidence of a Santa
Monica Mountains source is as follows:
1. Basinward disappearance of the breccias and conglomerates that
appear along the southern flank of the Santa Monica Mountains.
2. Thinning of lower Pliocene strata towards the Santa Monica
Mountains.
Early Pliocene History, Los Angeles Basin—Con
3. Increase in the angularity of the granule- and pebble-sized
grains in the sandstones towards the Santa Monica Mountains(figure 23).
4. Increase in the quartz-feldspar and potash feldspar-plagioclase
ratios towards the Santa Monica Mountains (figure 25).
,n Gabriel Mountains source
As previously stated, Bellemin (1938), Olmsted948), and Kundert (1952) identified the present site
' the San Gabriel Mountains as the principal source' the conglomerates appearing at the western end of
ie San Jose Hills and the southwestern end of the
uente Hills. Bellemin identified the source primarily
y a comparison of the general assemblage of rock
pes comprising the conglomerate clasts and those
ropping out as bedrock in the potential source areas.
However, he did correlate the dacite-porphyry clasts
l the conglomerates with the dacite-porphyry bed-' ock cropping out in the southeastern San Gabriel
lountains and at the eastern end of the San Jose Hills.
)lmsted's identification of the source was based pri-
larily upon a correlation of rock types occurring in
he conglomerates with their "parents" in the Sanjabriel Mountains. His principal correlations werevith the Mt. Waterman plutonic suites of bedrock
' :ropping out in the central San Gabriel Mountains.
-Ie also recognized the similarity between dacite-
)orphyry clasts in the conglomerates and bedrock of
he same composition in the southeastern San Gabriel
Mountains. The third investigator, Kundert, proposedin ultimate San Gabriel Mountain source for a major-ity of the conglomerate clasts. This was based upon the
' similarity of the general assemblage of rock types ap-
pearing as clasts in the conglomerates at the south-
western end of the Puente Hills to those in the SanJose Hills (Table VII), which previously were as-
signed a San Gabriel source by Olmstead.
Additional data that substantiated the previous as-
sertions of an active source at the present site of the
San Gabriel Mountains were brought forth by the
writer's study. The best indicator is the "orangequartzofeldspathic" grains occurring in the sandstonesat several locations in the Los Angeles Basin. The dis-
tribution of these grains (figure 28) outlines a de-positional trend from the present site of the SanGabriel Valley into the Los Angeles Basin through its
northcentral margin in the vicinity of location 14. Inthe San Gabriel Valley the "orange quartzofelds-pathic" grains occur in the matrix of conglomeratescontaining orange alkali granite clasts at the westernend of the San Jose Hills (location 87). A geneticrelationship between the "orange quartzofeldspathic"grains and the alkali-granite clasts is indicated by their
chemical and mineral composition (previously stated).
These orange granules and pebbles also were identified
in the recent stream-channel deposits of Lytle Creek,which drains the extreme southeastern end of the SanGabriel Mountains.
An indication of a San Gabriel Mountain source is
reflected also in the areal distribution of magnetite in
the heavy-mineral fraction of the sandstone (figure
26). As in the previous "orange quartzofeldspathic"rocks, a depositional trend is recognized from the pres-
ent site of the San Gabriel Valley into the Los Angeles
iREY 59
Table VII. Clast composition of lower Pliocene conglomerateat San Jose and southwestern Puente Hills.
Locations
Southwestern WesternPuente Hills San Jose Hills
Kundert, Olmsted,
1951 1948 Rock types
35.0 38.0 Mica-quartz-feldspar plutonics
0.5 5.0 Alaskite .v;
5.0 1.5 Pegmatite o7.5 14.5 Aplite a
9.0 0.0 Vein (?) quartz 0.
5.0 0.0 Unidentified plutonics
6.0 7.0 Andesite, andesite porphyry, basalt
5.5 7.5 Dacite, dacite porphyry, latite, rhyolite •g
1.0 1.0 Unidentified volcanics ft
o>
u8.0 25.5 Quartz-feldspar gneiss rt ^1
1.0 0.0 Quartzite si
2.5 0.0 Sedimentary1 s
12.0 0.0 Unknown
98.0 100.0 Total percentage of clast
Shallow intr ves included.
Basin through its northcentral margin, in the vicinity
of location 14. In the San Gabriel Valley, magnetite
composed 60 percent of the heavy-mineral fraction
of sandstone beds sampled at the western end of the
San Jose Hills. This compares favorably with the mag-netite content of the heavy-mineral fraction of sands
of recent channel deposits that drain the southeastern
and the southcentral end of the San Gabriel Moun-tains (60 and 75 percent, respectively).
Less direct evidence of a San Gabriel Mountainsource is presented by other sedimentary changes
along the same depositional trend outlined by the con-centrations of "orange quartzofeldspathic" and mag-netite grains in the sandstone, as follows:
1. A thick tongue of lower Pliocene strata (isopach maps), a lobe
of medium sandstone (figure 17), and a concentration of sand-
stone and conglomerate (figures 12—13) extend into the basin
from its northcentral margin.
2. A trend in the sandstone of about equal amounts of quartz andfeldspar and potash feldspars in excess of plagioclase feldspars
extends into the basin from its northcentral margin (figure 25).
3. A concentration of metamorphic-rock fragments occurs in the
sandstones at the northcentral margin of the basin (figure 27).
Puente Hills source
In 1951, Kundert postulated a local source for the
conglomerates cropping out along the southwestern
margin of the Puente Hills. Kundert suggested that
the lower Pliocene conglomerates represent reworkedupper Miocene conglomerates, which had been re-
deposited by either turbulent flow or submarine slumpdown an active submarine fault scarp formed by the
Whittier fault. A local source was supported by the
appearance of sedimentary breccias, containing clasts
over 1 foot long (figure 42), among the lower Pliocene
conglomerates.
60 California Division of Minis and Geology SR ?
The importance of the Puente Hills as a source of
detrital rock debris was brought out in this study. De-
positional trends were recognized along most of the
southern margin of the Puente Hills as follows:
1. Concentrations of conglomerate flank the Puente Hills and ex-
tend into the basin in a westward lobe from the southwestern
end of the Puente Hills (figure 10). In addition, concentrations
of sandstone extend south into the basin from the southwestern
end of the Puente Hills.
2. A concentration of strata fronts the Puente Hills as a basinward
extending tongue and as a blanket paralleling the hills (figures
16 and 29).
3. A broad lobe of siltstone spreads across the basin from a Puente
Hills source (figure 30).
4. Subrounded granules in sandstones display a southward trend
from the Puente Hills (figure 23).
5. Sandstone spreading across the basin from a Puente Hills source
is suggested by the areal distribution of dacite-porphyry gran-
ules and pebbles in the sandstone (figure 28). This rock type
abounds as clasts in the conglomerate at the southwestern end
of the Puente Hills and is identified in pebbles at locations 33,
43, 44, and 49. In more distant locations its identification is
questionable due to the small size of the rock fragment.
Perris Uplands source
In 1934, Edwards identified the Perris block (Perris
Upland of this paper) as the principal source area for
the Pliocene conglomerates cropping out in the Los
Angeles Basin. His conclusions were based upon the
appearance in the conglomerates of "characteristic
rock types" such as white pegmatite, white aplite, andfeldspathic porphyry. In later studies Bellemin (1938),
Woodford and others (1946), and Olmsted (1948)pointed out that the "characteristic rock types" de-
scribed by Edwards also occurred in other potential
source areas. Furthermore, they identified a SanGabriel Mountains source for most of these rock typesoccurring in the conglomerates cropping out alongthe northeastern margin of the basin.
This study suggests that the large amounts ofdetrital-rock debris entering the basin from the east
may have come from the Perris Uplands. Granulesdescribed as "weathered quartzofeldspathic" appear in
the sandstone at various locations in the basin. Theareal distribution and the fluctuation in the concentra-tion of these granules suggest a point of entry into thebasin at its eastern margin, possibly east of location 49(figure 28). A petrographic analysis of the granules(previously stated) suggests a weathered parent ofgranite or possibly quartz monzonite. Igneous rocksof this composition comprise approximately 8 percentof the basement rock in the Perris Uplands; none wererecognized in another potential eastern source, "SantaAna Mountains" (Woodford and others, 1946). Gran-ules similar to the "weathered quartzofeldspathic"granules appear in Upper Cretaceous sandstone crop-ping out in the Santa Ana Mountains.
Santa Ana Mountains source
An active Santa Ana Mountains source was rec-ognized in this study by ( 1 ) the composition of rockfragments in conglomerate, breccia, and sandstone and(2) depositional trends outlined by other sedimentaryparameters. These are described as follows:
1. The conglomerate clasts sampled from locations flanking theSanta Ana Mountains (38, 61, and 64) are rock types similar tothose exposed in the Santa Ana Mountains.
s-
2. Pebbles and granules from sandstone at locations flanking tl
Santa Ana Mountains are rock types similar to those exposed
the Santa Ana Mountains. Note in figure 28 the local accumlotion of slate fragments in the sandstone at these locations.
3. A depositional trend into the basin from a Santa Ana Moutains source is suggested by the distribution of sphene and manetite in the heavy-mineral fraction of sandstone in the easte
part of the basin. This is displayed on figure 26 by a progr
sive decrease of both minerals in a basinward direction fro
the Santa Ana Mountains. Both sphene and magnetite form c
important part of the heavy-mineral fraction in sand of rece
stream deposits in the Santa Ana Mountains (location SAfigure 26).
4. A Santa Ana Mountains source is indicated on the lithofaci
maps (example, figure 13) by a tongue of conglomerate exten
ing northwestward into the basin from location 61 and a co
centration of coarse-grained clastic rocks in the vicinity of loi
tion 61. This same trend is displayed to a limited degree in tl
stratigraphic section (PI. 3).
5. The lobe of medium sandstone extending into the basin from tl
east (figure 17) suggests a source at the present site of tr
Santa Ana Mountains.
San Joaquin Hills source
The present site of the San Joaquin Hills is th
logical location of the source area for 95 percent o
the clasts (sedimentary and volcanic) in the sedimert
tary breccia cropping out at Newport Bay (locatioi
86 of this paper). This conclusion is based upon th
following observations:
1. Seventy-five percent of the clasts are in the nature of blocl
and chips of diatomaceous shale and limestone with seconder
amounts of sandstone. The size (up to 1 foot long), angularit)
and composition of these clasts indicate a local source in th
San Joaquin Hills where bedrock of similar composition cror.
out. The clasts are displayed on figure 42 (D).
2. The volcanic clasts, which comprise 15 to 20 percent of the roc
debris, consist of angular to subangular cobbles and pebbles c
basalt (figure 42-D). Miocene volcanics of similar compositio
crop out as bedrock in the adjacent San Joaquin Hills.
Palos Verdes Hills source
An active source at the present site of the Palo
Verdes Hills is indicated by the appearance of localh
derived erosional products in the strata at location
flanking the Palos Verdes Hills. The exposed core othe Palos Verdes Hills contains a basement comple:of chert, quartzite, and schist (amphibole, glauco
phane, and chlorite). Concentrations of erosiona
products of these rocks are displayed on two maps a:
follows: (1) petrology map (figure 27) shows a con-
centration of granules of metamorphic rock in the
sandstone at location 50, and (2) mineralogy map(figure 26) displays a concentration of hornblende anc
chlorite in the heavy-mineral fractions of sandstone al
locations 50 and 68. In addition, glaucophane wa«identified in the sand-size fraction of samples of fine-
grained clastic rocks at locations 52 and 53.
Cobbles displaying animal (?) borings are scattered
through the strata at location 52 (figure 36-A), andlarge amounts of glauconite appear in the fine-grained'
clastic rocks at both locations 52 and 53. The cobblesand glauconite suggest a relatively shallow waterdetrital source.
Subaerial erosion of source areas
There is undisputable evidence that many of the
source areas were undergoing subaerial erosion. This
consists of the appearance of weathered detrital-rock
.7 Early Pliocene History, Los Angeles Basin—Conrey 61
d'ris in the subsurface strata at several locations in
m Los Angeles Basin, as follows:
1. San Gabriel Mountains subaerial erosion is indicated by the
highly weathered clasts, enclosed in part by a ferruginous
cement, appearing in the conglomerate at locations 14 and 17;
the depositional trend from a San Gabriel Mountains source
was identified previously at these locations.
2. Santa Ana Mountains subaerial erosion is suggested by the
highly weathered nature of conglomerate clasts at locations 38
and 61. Previous studies disclosed a Santa Ana Mountains source
for the detrital-rock debris at these locations.
3. Perris Uplands subaerial erosion is suggested by the large
amounts of "weathered quartzofeldspathic" granules and peb-
bles in sandstone. A Perris Upland source for these granules
and pebbles was stated previously.
,4. Subaerial erosion of the Santa Monica Mountains and the San
Joaquin Hills is indicated by the amount of detrital-rock debris
coming from these areas (previously stated) and the depth of
their erosion. Depth of erosion is exemplified in the Santa
Monica Mountains by the metamorphic- and plutonic-rock debris
supplied from the core rock of the Santa Monica Mountainsduring lower Pliocene deposition.
Volcanic sediments
(hi 1941 Wissler reported the occurrence of bentonite
iid ash beds in the lower Pliocene strata of the Los
Angeles Basin. The observations of Wissler were con-firmed by this study (previously stated). In addition,
distinct stratigraphic horizons of volcanics were rec-ognized at various locations, particularly in the upper-lower Pliocene strata (Table III).
Source
Centers of Pliocene volcanism were not identified in
prior works concerning the Los Angeles Basin andsurrounding region. The extensive volcanic deposits
cropping out in the highlands surrounding the basin
were dated as Miocene by Larsen (1948), Shelton
(1954), and Eaton (1958). Larsen also identified vol-
canic deposits of Quaternary and late Tertiary age to
the southeast of the basin.
The thickness of ash beds, maximum of 2 feet in
the Dominguez field reported by Wissler, in locations
of active marine sedimentation suggests to the author
that the volcanic sediments had a local source. It is
possible that in the surrounding highlands some of the
centers of volcanism identified as Miocene are actually
Pliocene since usually only a minimum of stratigraphic
information is often available for their dating.
62 California Division of A^inf.s and Geology
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SR
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California: U. S. Geol. Survey
A 75047—650 6-67 3,500 printed in California office of state printing
DIVISION OF MINES AND GEOLOGYIAN CAMPBELL, STATE GEOLOGIST
STATE OF CALIFORNIATHE RESOURCES AGENCY
DEPARTMENT OF CONSERVATION
fWi y
4u -},-ff
^chui .Mt^touxju
iiVERsirySPECIAL REPORT 93
1/2MI.W5MI.SE OF 1/2MI.SE
LEG
Conglomerate
Interbedded conglom-erate and sandstone
Pebbly sandstone
Sandstone
Interbedded sandstoneand siltstone (shaleyin part)
END
o ° o o r—z-z Siltstone(Shaley in part)
?o -o-o- r^jfSClay siltstone(predominantly shaley)m CCEs Limestone(lentils and nodules)
. . . 1
LJ > ) ) ) I1 1U 1 Bentonite or volcanic ash
-=-: * A Chert
Vert ical Scale- Displayed along margin of stratigraphic columns.
(One division equals one hundred feet)
STRATIGRAPHIC SECTIONS A TO D
1W^-I tf*S3 /u^,. 7a . 99 c-fyj^fi'LkxMJ
DIVISION OF MINES AND GEOLOGYIAN CAMPBELL, STATE GEOLOGIST
STATE OF CALIFORNIA
THE RESOURCES AGENCYDEPARTMENT OF CONSERVATION
'""""' l'WM'rn<-,Tv nr m , Fn„„ sfffq)AL REp0RT MPLATE 2
MAR 13 1968
ICOVT. DOC5 .„a,,.y
STRATIGRAPHIC SECTIONS F TO B
DIVISION OF MINES AND GEOLOGYIAN CAMPBELL, STATE GEOLOGIST
STATE OF CALIFORNIATHE RESOURCES AGENCY
DEPARTMENT OF CONSERVATION
/^.dMt^u^eJ^SPECIAL REPORT 93
PLATE 3
UNSVSRS7T ~'--NbSf .
: \
MAR 13 £68
GOV'T. DOCS. - horary
STRATIGRAPHIC SECTIONS E TO C
DIVISION OK MINES AND GEOLOGYIAN CAMPBELL, STATE GEOLOGIST
STATE OF CALIFORNIATHE RESOURCES AGENCY
DEPARTMENT OF CONSERVATIONSPECIAL REPORT 93—
" PLATE 4 I
LONG BEACH FIELD
ELECTRICAL LOG STRATIGRAPHIC SECTION
INGLEWOOD FIELD
STRATIGRAPHIC SECTION ELECTRICAL LOG
(1/4 MILE EAST OF 56) (LOCATION 56 (LOCATION 11) d/2 MILE SOUTHEAST OF 11)
r 500
400
300
- 200
100
[
UNIVEFiSirr
MAR 13 1368
GOVT. DOCS. - LIBRARY
CORRELATION BETWEEN ELECTRIC WELL LOGS ANDSTRATIGRAPHIC SECTIONS
