21. PALEOCENE AND EARLY EOCENE MICROFACIES, BENTHONIC ... · 21. paleocene and early eocene microfacies, benthonic foraminifera, and paleobathymetry of deep sea drilling project sites

21. PALEOCENE AND EARLY EOCENE MICROFACIES, BENTHONIC FORAMINIFERA,AND PALEOBATHYMETRY OF DEEP SEA DRILLING PROJECT SITES 236 AND 237,

WESTERN INDIAN OCEAN

Edith Vincent, Department of Geological Sciences, University of Southern California, Los Angeles, CaliforniaJames M. Gibson, Texaco Inc., Los Angeles, California

andLélio Brun, Centre de Recherches de Boussens, Laboratoire Exploration ELF-RE, Saint Martory, France

ABSTRACTA significant and abrupt change in the sedimentary regime at

Site 237 provides evidence for an early Tertiary subsidence of theMascarene Plateau area in the western Indian Ocean. Betweenapproximately 62 and 57 m.y.B.P. pelagic sediments weredeposited at Site 237 in upper bathyal (200-600 m) depths withadmixtures of slumped material from nearby shoals at a rate ofabout 68 m/m.y. The sea floor began to sink in the late Paleocene(57-58 m.y.B.P.). Introduction of shallow-water material ceasedand normal pelagic sedimentation proceeded, at a rate about sixtimes slower, at lower bathyal (600-2500 m) depths. Deepeningat Site 237 at this time permitted development of deep-waterbenthonic foraminiferal faunas similar to those at Site 236 to thenorth. A further decrease in the rate of sedimentation occurrednear the end of the Paleocene and in early Eocene, fromapproximately 54 to 50 m.y.B.P. During that period of time aninterval of nondeposition spanned the Paleocene/Eoceneboundary at Site 236. The area at Site 237 has subsidedapproximately 2000 meters over the past 52 m.y.

This sequence of events on the Mascarene Plateau is similar to,and synchronous with, the subsidence history of the Chagos-Laccadive Ridge to the east.

INTRODUCTION

The Mascarene Plateau, a major structural element of theIndian Ocean, forms the foundation for a series of islandsand shallow banks that extend in a gentle northwest tosouth crescent across the western tropical Indian Ocean(Fisher et al., 1967). During Leg 24 of the Deep SeaDrilling Project, Glomar Challenger drilled two holes in theMascarene Plateau area. Site 236, in 4500 meters of water,is located in the outermost foothills southwest of theCarlsberg Ridge, 270 km northeast of the SeychellesIslands, the northern termination of the Mascarene Plateau.Site 237, in 1630 meters of water, was drilled in the saddlejoining the granitic Seychelles Bank to the volcanic Saya deMalha Bank (Figure 1 and Table 1). The thickness of thePaleocene and lower Eocene section is 42 meters at Site236 and about nine times greater (374 meters) at Site 237.Site 236 reached basement, whereas Site 237 was ter-minated before basement was reached for operationalreasons.

The age of the foundation and the petrologic affinity ofthat part of the Mascarene Plateau located betweenPrecambrian granitic Seychelles and volcanic Saya de Malhaare a matter of controversy. Site 237 was drilled in this areato answer these questions and to establish the rate andcontinuity of subsidence of what was thought to be anextensive reef area on a massive igneous base. Drilling atSite 237 failed to determine the age and nature of the

basement, but the thick early Tertiary sedimentarysequence recovered here provides clues to help elucidate thesubsidence history of the area. No coralline section waspenetrated and the area appears to have been a site ofpelagic sedimentation since early Paleocene time. Thepurpose of this study was to gain information on thedepositional environment and paleodepth on the MascarenePlateau during the Paleocene and early Eocene. Thinsections from lithified oozes at Site 237 were examined forthis purpose, as well as to complement the planktonicforaminiferal zonation established at this site based on thefauna extracted from the few soft horizons. Benthonicforaminiferal faunas extracted from these unlithified sedi-ments at Sites 236 and 237 were also studied.

The Paleocene and lower Eocene sequence at Site 236,which underlies 263 meters of Quaternary to late Paleocenenannofossil chalk oozes, consists of nannofossil chalk withchert. It was continuously cored with a poor recovery. Agood sediment/basement contact was obtained within Core33 at 305 meters. The biostratigraphic age of the basalsediments is 56-58 m.y. old (Discoaster mohleri and P.4zones) according to Berggren's (1972) scale; whereas themagnetic age of basement is 9 to 11 m.y. older (approx-imately magnetic anomaly 27, McKenzie and Sclater, 1971)according to the geomagnetic scale of Heirtzler et al.(1968). Two substantial stratigraphic gaps were found, onespanning the late Paleocene/early Eocene boundary and theother representing the entire middle Eocene.

859

E. VINCENT, J. M. GIBSON, L. BRUN

45* 50* 55* 60 65* 7Q ••»*• 7V

Figure 1. Location of DSDP sites on the Mascarene Plateau/Central Indian Ridge/Chagos-Laccadive Plateau complex.

860

PALEOCENE AND EARLY EOCENE MICROFACIES, BENTHONIC FORAMINIFERA, AND PALEOBATHYMETRY

TABLE 1Location of Sites Containing Paleocene and Lower Eocene

Deposits Drilled on Leg 24

Site

236

237

Latitude

l°40.62'S

7°04.99'S

Longitude

57°38.85'E

58°07.48'E

WaterDepth(m)

4504

1640

Paleocene and LowerEocene Section

Thickness(m) Cores

42 29-33

374 35-67

The Paleocene and lower Eocene section at Site 237,which underlies 320 meters of Quaternary to middleEocene nannofossil ooze, consists of partly silicified nanno-fossil chalk with chert, with some glauconitic horizons inthe upper Paleocene. Coring, with poor recovery, wascontinuous in the upper part of that section down to adepth of 585 meters, and from that depth to hole bottomalternate joints were cored.

A summary of the Paleocene and early Eocene lithology,fossil zonations, age assignment, and sedimentation rates atboth Sites 236 and 237 is presented in Figure 2.

MICROFACIES

Folk's (1962) classification was used to describe themicroscopic features of 42 thin sections from the Paleoceneand lower Eocene silicified nannofossil chalks (lithologicUnits 3, 4, and 5) of Site 237 (Table 2 and Figure 3). Thebulk of the rocks consists of sparse to packed biomicrite,often modified by recrystallization and silicification, withplanktonic foraminifera as the main skeletal grain in thePaleocene sequence and radiolarians in the lower Eocene.Recrystallization is very pronounced in the lower 54 meters(below Core 65). The high planktonic/benthonic fora-miniferal ratio clearly reflects a pelagic environmnent,planktonic species usually comprising 90% or more of theforaminiferal population with an increasing trend upsection. Among subordinate biogenic grain types, spongespicules occur commonly while echinoderm spines andmolluscan fragments are rare. Chambers of the skeletalcomponents are infilled either by microspar, spar, micrite,or chert. Radiolarians are often calcified. The variousbiogenic components are regularly distributed throughoutthe sediment, and evidence of bioturbation is not common.Fecal pellets were found in a few horizons. Small quartzgrains and glauconite, which occurs as grains or occasionallyas infilling of foraminiferal chambers, are present in thelower part of the section from 410 to 670 meters, with anabundance of 1 % and 1 % to 5%, respectively.

The high degree of recrystallization precludes identifi-cation of the components of the matrix, which wasprobably composed of nannofossils as indicated by thesmear-slide analyses. These show that nannofossils comprise80% to 95% of the sediments above 516 meters; whereasbelow this level micarb, which may represent alterednannofossils, is the main contributor (80% to 95%) (Figure3).

Interbedded in the Paleocene pelagic deposits are severalhorizons of coarse material. These consist of packedbiomicrite or biosparite with larger foraminifera (D/s-cocyclina, Ranikothaliá), calcareous algae (Archaeo-

lithothamniuni), and fragments of molluscs, echinoderms,and bryozoans. These horizons represent slumped shallow-water deposits, and their contact with the fine-grained rockin which they occur is sharp (Thiede, this volume, Figure30).

Planktonic foraminifera were identified and severalforaminiferal zonal boundaries were defined. The Morozo-vella pusilla-Morozovella angulata (P3)/Morozovellauncinata-Turborotalia spiralis (P.2) boundary, whichseparates the late and early Paleocene, was placed withinCore 61, Section 1, at the lowest occurrence of Morozovellaangulata. The Planorotalites pseudomenardii (PA)/Morozo-vella pusilla-Turborotalia spiralis (P.3) boundary could notbe defined between Cores 45, Section 2 and Core 54,Section 1, because of the co-occurrence in this interval offorms referable to Morozovella velascoensis and Morozo-vella laevigata (younger than P.3) and forms referable toPlanorotalites compressa and Subbotina triloculinoides(older than P.4).

The position of the P.3/P.2 boundary at 574 meters inthe section and of the Discoaster mohleri Zone IHeliolithuskleinpella Zone boundary at 403.5 meters, at 60 and 57.5m.y.B.P., respectively (Berggren, 1972), permits the calcula-tion of an average accumulation rate of 68.2 m/m.y. for thesediments deposited between these two points in time(Figure 2). If it is assumed that approximately 100 metersof additional sediments are present between the bottom ofHole 237 and the igneous basement below them (thisvolume, Chapter 8) and that the accumulation rate of 68.2m/m.y. remained constant, then the age of the sediment/basement contact is approximately 63 m.y.B P. (earlyPaleocene).

BENTHONIC FORAMINIFERA

Benthonic foraminifera are very rare at both Sites 236and 237, with the bulk of the coarse fraction (>61µ)consisting of planktonic foraminifera or siliceous com-ponents (radiolarians, sponge spicules) or both. Preservationis generally fair, but, the lower part of the section at Site237 (corresponding roughly to the P.I to P.3 interval) isdominantly recrystallized.

We identified 134 species of benthonic foraminifera.Many of these were described and illustrated in classicalworks on the faunas of the Midway Group of the U. S. GulfCoastal Plain (Plummer, 1926; Cushman, 1951; Kellough,1959, 1965) and the Velasco Formation of the TampicoEmbayment in Mexico (Cushman, 1925, 1926; White,1928, 1929; Cushman and Renz, 1946). The distribution ofspecies at Sites 236 and 237 is shown in Tables 3 and 4.Species diversity, which may reflect bathymetry (Gibsonand Buzas, 1973), was not investigated because the smallvolume of available samples and the low number ofbenthonic specimens precluded a statistically valid study.

PALEOBATHYMETRY

Basis for Paleobathymetric Interpretations

A number of faunal relationships provide good evidenceof depositional environment (Bandy, 1960; Bandy andAmal, 1960). The relative abundance of planktonic fora-minifera in bottom sediments increases offshore (Grimsdaleand Morkhoven, 1955; Bandy and Amal, 1960). Planktonic

861


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Figure 2. Summary of lithology, biostratigraphy, and sedimentation rates of Paleocene and lower Eocene sections at Sites236 and 237.

862


TABLE 2Microfacies of Lithified Calcareous Sediments at Site 237

Cor

34

V

tion

Sec

1

2

1

13

15

Plai

For

Zor

P10-P9

P7-P6

Rock Type

Skeletal Grains(Whole or

Fragments)Identifiable Planktonic

ForaminiferaIdentifiable Benthonic

Foraminifera

~ •g Infilling of= f- Fossil Authigenic and

Chambers Terrigenous Grains

38 1

41 2

43 2

44 2

45 2

46 2

47 2

48 2

49 2

50 1

51 2

52 1

53 2

13 P7-P6

P4

P4-P3

P4-P3

Sparse biomicrite Radiolarians (C)Foraminifera (R)



hacked biomicrite Foraminifera (A)

Packed biomicrite, Foraminifera (A)partially Radiolarians (VR)recrystallized

Sparse biomicrite Radiolarians (R)Foraminifera (C)Sponge spicules (R)

Sparse biomicrite Foraminifera (R)Radiolarians (R)

Packed biomicrite Foraminifera (A)Sponge spicules (R)

Packed biomicrite Foraminifera (A)Radiolarians (R)Echinoderms (R)

P4-P3 Packed biomicrite Foraminifera (A)

P4-P3 Packed biomicrite Foraminifera (A)Radiolarians (R)Sponge spicules (R)

120 P4-P3 Packed biomicrite Larger foraminiferaBryzoansEchinodermsCalcareous algae

2 P4-P3 Packed biomicrite Foraminifera (A)

13 P4-P3

10 P4-P3

Packed biomicrite Foraminifera (C)Radiolarians (C)Sponge spicules (C)

Sparse biomicrite,pellets

13 P4-P3 Sparse biomicrite

P4-P3 Recrystallizedsparse biomicrite,pellets (R)

Foraminifera (R)Radiolarians (C)Ostracodes (VR)Sponge spicules (R)

Foraminifera (C)Radiolarians (R)Echinoderms (VR)

Foraminifera (C)Radiolarians (R)

Acarinina bullbrookiMorozovella aragonensis group

Acarinina broedermanniA. bullbrookiMorozovella aragonensis groupM. quetraPseudohastigerina sp.

Acarinina broedermanniA. wilcoxensisMorozovella aequaM. formosa-gracilis groupsubbotinids

Morozovella aequaM. velascoensis

Morozovella aequaM. laevigataM. cf. velascoensisPlanorotalites pseudomenardii

Chilogumbelina sp.Morozovella aequaM. laevigata

Morozovella aequaM. velascoensissubbotinids

Chilogumbelina sp. RotaliidsMorozovella angulataM. laevigataM. velascoensisPlanorotalites ehrenbergi groupSubbotina triloculinoides

Morozovella angulataM. pusillaM. velascoensisPlanorotalites compressaP. ehrenbergi-pseudomenardiigroupSubbotina triloculinoides

Morozovella angulata LageniidsM. laevigata TextulariidsM. cf. velascoensisPlanorotalites compressa

Morozovella cf. acutaM. angulataM. laevigataM. velascoensisPlanorotalites cf. compressaSubbotina cf. triloculinoides

Chilogumbelina sp.Morozovella acutaM. angulataM. velascoensissubbotinids

Chilogumbelina sp.Morozovella angulataM. cf. laevigataM. cf. velascoensisPlanorotalites cf. compressaSubbotina cf. triloculinoides

Chilogumbelina sp.Morozovella angulataM. cf. velascoensisPlanorotalites cf. compressaSubbotina cf. triloculinoides

Chilogumbelina sp. Robulus sp.Morozovella cf. acutaM. cf. angulataM. cf. velascoensisPlanorotalites cf. compressaSubbotina triloculinoides

Morozovella cf. abundocamerataM. cf. angulataM. cf. laevigataM. cf. velascoensisPlanorotalites cf. compressaSubbotina cf. triloculinoides

Morozovella acuta AnomalinidsM. cf. angulataM. cf. laevigataM. velascoensis

>99% Chert

>99% Chert

>99% Chert

>99% Chert

>99% Micrite

>99% Chert

>99% Calcite

ca 99% Calcite

ca 99% Calcite

Glauconite (VR)

Glauconite (VR)Quartz (VR)

Glauconite (C)Quartz (R)Feldspar (R)

Glauconite (C)Quartz (R)

Glauconite (C)Quartz (R)Pyrite (R)


Discocyclina seunesiMiscellanea sp.Ranikothalia bermudeziRotalia sp.

Robulus sp.

ca 98% Calcite GlauconiteQuartz (R)

> 9 9 % Micrite Glauconiteand chert Quartz (R)

ca 30%

Ca 98% Micrite Glauconite (R)

> 9 9 % Calcite and Glauconite (R)chert Quartz (R)

> 9 9 % Calcite Glauconite (R)Phosphate (VR)

> 9 9 % Micrite and Glauconite (R)calcite

ca 98% Calcite

863


TABLE 2 - ContinuedC

ore

54

56

58

58

58

61

61

62

62

62

63

64

65

65

65

65

66

Sect

ion

1

1

1

1

1

1

1

1

1

2

2

2

1

2

2

3

1

Thin

Sec

tiiN

umbe

r

6

5

6

20

95

5

13

1

6

5

7

7

8

1

12

5

11

Plan

kton

icFo

ram

inif

tZ

one

P4-P3

P3

P3

P3

P3

P3

P2-P1

P2-P1

P2-P1

P2-P1

P2-P1

P2-P1

P2-P1

P2-P1

P2-P1

P2-P1

P2-P1

Rock Type

Packed biomicrite

Recrystallizedpacked biomicrite,pellets (R)

Sparse biomicrite,pellets (C)

Argillaceoussparse biomicrite

Biosparite

Sparse biomicrite

Sparse biomicritepartiallyrecrystallized

Fossiliferousmicrite,partiallyrecrystallized

Sparse biomicrite




Sparse biomicritelargelyrecrystallized


Sparse biomicriteparti allyrecrystallized


Fossiliferousmicrite

Skeletal Grains(Whole or

Fragments

Foraminifera (A)

Foraminifera (C)Sponge spicules (R)Ostracodes (VR)

Foraminifera (C)Radiolarians (C)

Foraminifera (C)Radiolarians (R)Sponge spicules (R)

Archeolithothamnium

(A)Foraminifera (R)Ostracodes (VR)Bryzoans(R)Foraminifera (R)Radiolarians (R)Sponge spicules (R)Ostracodes (R)

Foraminifera (C)Bryzoans (R)

Foraminifera (R)Sponge spicules (C)Echinoderms (VR)

Foraminifera (C)Sponge spicules (C)Echinoderms (R)Molluscs (R)

Foraminifera (R)Bryzoans(R)Echinoderms (C)Molluscs (R)

Foraminifera (R)Echinoderms (C)Molluscs (C)

Foraminifera (C)Sponge spicules (C)Ostracodes (R)Echinoderms (C)Lithothamnium,small fragments (R)

Foraminifera (R)Sponge spicules (C)Molluscs (R)Echinoderms (R)

Foraminifera (R)Sponge spicules (A)Echinoderms (R)

Foraminifera (R)Echinoderms (C)

Foraminifera (R)Sponge spicules (R)Echinoderms (R)

Foraminifera (R)SDonee soicules (R)

Identifiable PlanktonicForaminifera

Morozovella angulataM. cf. pusillaM. cf. velascoensisPlanorotalites cf. ehrenbergiSubbotina cf. triloculinoides

Morozovella angulataSubbotina cf. triloculinoides

Morozovella angulataM. cf. pusilla

Chilogumbelina sp.Morozovella angulataM. pusilla

Subbotinids

Chilogumbelina sp.Morozovella angulataM. cf. pusillaM. cf. uncinataSubbotinids

Morozovella cf. pusillaM. uncinataPlanorotalites cf. ehrenbergiP. trinidadensis

GlobogerinidsMorozovella uncinata

Chilogumbelina sp.Morozovella uncinata

GlobigerinidsMorozovella uncinata

Planorotalites trinidadensisSubbotina cf. pseudobulloides

"globigerinids"Morozovella uncinataPlanorotalites trinidadensis

Chilogumbelina sp.Morozovella uncinataSubbotina cf. pseudobulloides

Small globogerinidMorozovella uncinata

Morozovella uncinataPlanorotalites trinidadensis

Morozovella uncinata

Chilogumbelina sp.Planorotalites trinidadensis

Identifiable BenthonicForaminifera

AnomalinidsBolivina sp.Dentalina sp.Nodosaria sp.Robulus sp.

Cibicides sp.Dentalina sp.Valvulinids

Cibicides sp.small rotaliids

Bolivina sp.Cibicides sp.Dentalina sp.

AnomalinidsUrigerinids

Cibicides sp.Discorbis sp.

Bolivina sp.Cibicides sp.Discorbis sp.Small rotaliids

Small rotaliids

Small rotaliids

Small rotaliidsRobulus sp.

AnomalinidsSmall rotaliids

Small rotaliids

Small rotaliidsDentalina sp.

Plan

kton

iivs

Tot

alF

ca 98%

ca 95%

ca 95%

ca95%

<30%

ca 95%

ca 98%

ca 98%

ca 90%

ca 90%

ca90%

ca 90%

ca 90%

ca90%

ca90%

ca 90%

(90%)

Infilling ofFossil

Chambers

Micrite

Calcite

Calcite

Chalcedony

Calcite

Chalcedony

Calcite andmicrite

Calcite

Micrite andcalcite

Calcite

Chalcedony

Micrite

Calcite

Chalcedony

Authigenic andTerrigenous Grains

Glauconite (R)Phosphate (VR)

Glauconite

Glauconite (C)

Glauconite (R)Quartz (R)

Quartz (R)

Glauconite (C)

Glauconite (C)Pyrite (C)Quartz (R)Phosphate (R)

Glauconite (C to A)

Glauconite (C to A)


Glauconite (C)Pyrite (C)

Glauconite (R)

Glauconite (R)Pyrite (C)

Glauconite (R)

Glauconite (R)Quartz (R)

66 2

66 3

14 P2-P1

17 P2-P1

Fossiliferousmicrite, partiallyrecrystallized

Fossiliferousmicrite

Ostracodes (VR)Echinoderms, smallFragments (R)

Foraminifera (R)Sponge spicules (R)Ostracodes (R)Molluscs (R)

Foraminifera (R)Sponge spicules (C)Echinoderms (R)Molluscs (R)

Subbotina cf. triloculinoides

Small "globigerinids"

Planorotalites trinidadensis

(95%) Chert andcalcite

(95%) Chert

864


TABLE 2 - Continued

.S | a ë•S 3 .2 O OHZ Q b N Rock Type

Fossiliferousmicrite, largelyrecrystallized

Sparse biomicrite

Skeletal Grains(Whole orFragments)

Foraminifera (R)Sponge spicules (R)Ostracodes (R)Echinoderms (R)

Foraminifera (R)Sponge spicules (R)Ostracodes (R)Echinoderms (R)

Identifiable PlanktonicForaminifera

Chilogumbelina sp.Small "globigerinids"

Small "globigerinids"Morozovella aff. uncinata

Identifiable BenthonicForaminifera

Robulus sp.Rotalia sp.

Rotalia sp.

Pla

nk U

vs T

ota

ca 95%

ca 95%

Infilling ofFossil

Chambers

Calcite

Calcite

Authigenic andTerrigenous Grains

P2-P1

Note: (A) = abundant; (C) = common; (R) = rare; (VR) very rare; (95%) = foraminifera too rare for a valid estimate of

species comprise less than 50% of the foraminiferal faunaon the continental shelf; their frequency increases to about50% at the shelf edge and to very high values (> 99%) atbathyal depths. However, in an open-ocean environmentnear banks or shoals, or in areas near narrow shelves, a highplanktonic/benthonic ratio may occur closer to shore.Another important faunal relationship providing evidenceas to depth of deposition is that of the relative frequency ofplanktonic foraminifera and radiolarians. Today, radiolarianooze is found primarily at great depths. With increasingdepths, at depths approaching the lysocline (the depth atwhich the preservation of foraminiferal assemblages deter-iorates rapidly), the relative frequency of calcareous fora-minifera decreases while siliceous radiolarians increase inabundance and eventually become dominant below theCCD. Morphological trends in various benthonic speciesalso appear to be correlated with water depth. For example,some species of the bathyal zone show a striking increase insize with increasing water depths (Bandy, 1963; Theyer,1971).

Many modern foraminiferal species show the same upperdepth limit in widely distributed geographic areas. Some ofthese depth indicators have isomorphs that occur in thePaleogene (Bandy, 1960; 1970). Bandy and Chierici (1966)have shown that the upper depth limits of isobathyalspecies are similar in various water masses of the world'soceans and suggested that variations of water depth in thebathyal realm have probably not served to alter the upperdepth of this group of species. Douglas (1973b), however,has provided evidence to suggest that an interpretative errormay result from estimates of paleodepth of fossil assem-blages derived by analogy with modern benthonic assem-blages, because of the migrational displacement ofbenthonic species throughout the Tertiary in response tofluctuations in the temperature and circulation of bottomwater. Caution is especially needed for interpretation ofpopulations older than middle Miocene, the time whenmodern deep-sea benthonic assemblages began to emerge.

Although the number of Paleocene and Eocene Paleo-bathymetric studies of benthonic foraminifera is limited,especially with respect to bathyal and abyssal populations,these studies are of great value for comparison betweengeographic regions. A cosmopolitan distribution ofbenthonic assemblages is expected during early Tertiarytime because of the more uniform thermal structure of theoceans and the more equitable climatic conditions.

Bandy (1970) considered the association of a"Pleurostomella-Nuttalides fauna" with a rich radiolarianassemblage to be indicative of "abyssal" water depthsC> 2000 m) during the late Paleocene and early Eocene ofthe Central America area. In this study we assign apaleodepth of 2000 to 2500 meters to a similar fauna,characterized by Nuttallides truempyi; and robust pleuro-stomellids. Tjalsma (personal communication) investigatedPaleocene faunas from the western Atlantic (Gulf ofMexico and Carribbean) and South Atlantic (Rio GrandeRise) from DSDP sites and recognized deep-water (>IOOOm) assemblages ("Velasco-type fauna") characterized by,among other species, robust anomalinids (Gavelinelladanica, G. velascoensis), Nuttalides truempyi, and variousgyroidinids and buliminids. He has examined material fromour study, which he compared to his material, and founddeep-water species common to both Atlantic and Indianocean assemblages.

The bathymetric distribution of Paleocene benthonicassemblages from the Tethyan and circum-Atlantic regionswas studied by Berggren (in press, a, b) and Berggren andPhillips (1971) who assigned upper neritic to upper bathyalwater depths to a "Midway-type fauna. '<-For example,faunas including larger foraminifera such as those of a fewPaleocene horizons at Site 237 were interpreted as upperneritic assemblages; whereas faunas composed, as in most ofthe Paleocene section at Site 237, of buliminids, CibicidesGaudryina, Gavelinella, Osangularia, Oridorsalis, andVaginulina were interpreted as representative of lowerneritic to upper bathyal water depths. Douglas (1973a)considered assemblages composed of Aragonia, Gaudryina,Osangularia, and Spiroplectammina to be indicative of"deep-sea assemblages" for the Paleocene in the northwestPacific Ocean. Gibson (1973) arrived at a similar Paleo-bathymetric interpretation (approximately 600 m) for"Midway-type assemblages" of the California coastal area.Early Eocene assemblages in the California basins appear tobe shoaler than that at Sites 236 and 237. Nuttalidestruempyi was not found in the Californian faunas andfurthermore, the amphimorphinids, lagenids, and plecto-frondiculariids characteristic of the California sequences arelacking or poorly developed at the Indian Ocean sites.

Attribution of Depth Assemblages

Four depth assemblages were recognized in the Paleo-cene and early Eocene faunas at Sites 236 and 237. The

865


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a: Larger foraminifera limestone (packed biomicrite)b: Calcareous algal limestone (biosparite); b*: no thin section available

Figure 3. Summary of variations of microtextural components, benthonic foraminiferal assemblages, and bathymetry of

Paleocene and lower Eocene sediments of Site 237.

866


distribution of these assemblages at the sites is indicated onTables 3 and 4 and Figure 3.

Assemblage 1 (Paleocene): Upper neritic (< 50m).Characterized by larger foraminifera (Discocyclina, Rani-khotalià) various rotaliids, and the calcareous algaeArchaeolithothamnium.

Assemblage 2 (Paleocene): Lower neritic to upperbathyal (50-600 m). "Midway-type fauna" characterized byAnomalina midwayensis, Gbicides alleni, Gavelinelladanica, Gyroidina girardana, G. globosa, G. nitida, Loxo-stomum applinae, Marssonella oxycona, Pleurostomellapaleocenica, Pullenia coryelli, Stilostomella spp., andVaginulina longiforma among numerous others.

Assemblage 3 (Paleocene): Lower bathyal (600-2500 m).Dominated by Nuttalides truempyi in co-occurrence withPseudovalvulineria beccariformis and Gavelinella aff. G.danica among others.

Assemblage 4 (Eocene): Lower bathyal (600-2500 m).Dominated by Nuttalides truempyi. Anomalina dorriaragonensis replaces the Paleocene morphotypes (P. beccari-formis and G. aff. G. danica). Forms such as Gyroidinaplanata and Stilostomella kressenbergensis also appear.

The change in morphology of forms assignable toPleurostomella paleocenica to those referred as Pleuro-stomella aff. P. paleocenica suggests a trend of increasingsize and robustness with increasing water depth, becausethis morphological trend parallels the increase in abundanceof the deep-water species Nuttalides truempyi.

DISCUSSION

The Paleocene and early Eocene benthonic assemblages(assemblages 3 and 4) at Site 236 are characteristic of deepwater, as shown by the dominance throughout the sectionof Nuttalides truempyi and the presence of robust pleuro-stomellids. Reconstruction of former water depths at thesite derived from the age/depth constancy of basalticoceanic basement (Sclater et al., 1971) shows that thepaleodepth at Site 236 was approximately 2000 meters forthe upper Paleocene sediments just above basement,deepening to approximately 2500 meters for lower Eocenesediments approximately 50 m.y. old (Figure 4). A deep-water environment interpreted from the foraminiferalassemblages is therefore in good agreement with these lowerbathyal paleodepths.

The benthonic fauna in the lower part of the section atSite 237 between Cores 67 and 49 is poorly preserved andnondiverse, and consists of very few individuals. Howeverthe presence of such elements as Anomalina midwayensis, A.welleri, Pleurostomella paleocenica, Pullenia quinquelobaangusta, Stilostomella paleocenica, and Vaginulina longi-forma suggests a lower neritic to upper bathyal environ-ment. In the interval between Cores 49 and 44 thepreservation is good and the fauna is substantially morecommon and diverse. It contains such typical Midwayfaunal elements as: Anomalina midwayensis, A. welleri,Bulimina arkadelphiana midwayensis, Clavulina asperawhitei, C. midwayensis, Eponides aff. E. bollii, frondi-culariids, Gavelinella danica, Gyroidina globosa, G. nitida,Palmula reticulata, Pleurostomella paleocenica, Pseudoval-vulineria beccariformis, Pullenia coryelli, Stilostomellapaleocenica, Trifarina herberti, Vaginulina longiforma. This

assemblage (assemblage 2) represents lower neritic to upperbathyal depths, and includes no lower bathyal or abyssalindicators. The deep-water species Nuttallides truempyiwhich characterizes assemblage 3, first appears in Sample44, 2, 116-118 cm; it occurs rarely in the first samplesabove this level and increases in abundance upwards until itdominates the Eocene faunas. A transition zone from theshallower assemblage 2 to the deeper assemblage 3 occurs inthe interval between Cores 44 and 42, where the twoassemblages overlap. The early Eocene assemblage (assem-blage 4) is very similar to the early Eocene assemblage atSite 236, differences in preservation account for the minordiscrepancies.

It thus appears that during late Paleocene (later than57-58 m.y.) and early Eocene time a lower bathyal(600-2500 m) environment prevailed at both Sites 236 and237. The sediments contain deep-water benthonic assem-blages (assemblages 3 and 4). The foraminiferal fauna showsa very high planktonic/benthonic ratio, with planktonicspecies comprising more than 99% of the fauna. Depth ofdeposition at Site 236 was on the order of 2000 to 2500meters and may have been of the same order of magnitudeat Site 237. However, as the upper depth limit of Paleogenebenthonic species is not well known, the assemblages at Site237 may reflect a shallower depth as well. It is probablethat the depth at Site 237 during late P.4 and Discoastermolheri Zone time (Core 42) was shallower than thecontemporaneous depth at Site 236, as shown by thegreater abundance of Nuttallides truempyi at the latter site.Site 237, however, may have reached a depth as great asthat at Site 236 in Eocene time, when TV. truempyi becomedominant. The presence of the deep-water ostracodeAbyssocythere in middle Eocene sediments of Site 237(Benson, this volume) support this bathymetric attribution.Populations of Abyssocythere are well developed in Eocenedeep-water sediments of Atlantic DSDP sites. The depthrange of modern representatives of this form is from 2000to 4500 meters, with a peak in abundance at 3000 meters(Richard H. Benson, personal communication). An increasein the radiolarian/planktonic foraminifera ratio in middleand late Eocene sediments of both Site 236 and 237 mayindicate that during that time, a time of shallowing of theCCD (Berger, 1972), the depth at these sites was close tothe lysocline level.

The average accumulation rate for upper Paleocenesediments younger than 57-58 m.y. is approximately 11m/m.y. at Site 237 and 5 m/m.y. at Site 236. Sedimenta-tion slowed significantly near the end of the Paleocene. Aperiod of nondeposition of about 5 m.y. spanned thePaleocene/Eocene boundary at Site 236, whereas at Site237 sediments accumulated at a reduced rate of 7.5 m/m.y.In late early Eocene time, sedimentation resumed at Site236 with a rate of about 13 m/m.y., and at Site 237 theaccumulation rate increased again at the beginning of themiddle Eocene to a value of approximately 17 m/m.y.(Figure 2). The average sedimentation rate for sedimentslaid down at Site 237 between about 57 and 49 m.y.B.P.(latest Paleocene and early Eocene) is approximately 13m/m.y.

Assemblage 3, of late Paleocene age, lies directly uponbasalt at Site 236, while at Site 237 it overlies 280 meters

867


TABLE 3Distribution of Benthonic Foraminifera in Paleocene

and Lower Eocene Sediments at Site 236

^> . Epoch

\ v Planktonic Foraminiferal Zone

^ s . Depth Assemblage

^ y . SampleT a X a \ . n * i

^s . (Interval^ ^ in cm)

Ammopalmula sp.Anomalina dorri aragonensis NuttallAnomalina midwayensis (Plummer)Anomalina praespissiformis Cushman and BermudezAnomalina welleri (Plummer)Anomalina sp.Aragonina aragonensis (Nuttall)Aragonina velascoensis (Cushman)Astacolus sp.Asterigerina crassaformis (Cushman and Siegfus)?Bathysiphon eocenicus Cushman and Hanna?Bolivina cf. B. anglica CushmanBolivinoides• delicatula CushmanBulimina beaumonti Cushman and RenzBulimina cf. B. bradburyi MartinBulimina cf. B. eccentricaBulimina excavata Cushman and ParkerBulimina impendens Parker and BermudezBulimina microcostata Cushman and ParkerBulimina cf. B. microcostata Cushman and ParkerBulimina semicostataBulimina aff. B. versaBulimina spp.Cibicides spiropunctatus Galloway and MorreyCibicides cf. C. spiropunctatus Galloway and MorreyCibicides spp.Clavulina cf. C. aspera whitei Cushman and JarvisClavulina cf. C. petrosa (Cushman and Bermudez)Clavulina cf. C. tricarinata (Reuss)Clavulina spp.Dentalina colei Cushman and DusenburyDentalina dusenburyi BeckDentalina cf. D. eocenica CushmanDentalina cf. D. pseudo-obliquistriata (Plummer)Dentalina soluta ReussDentalina spp.Eponides aff. E. bolli Cushman and RenzEponides spp.Fissurina orbignyana SeguenzaGaudryina laevigata FrankeGaudryina aff. G. laevigata FrankeGavelinella aff. G. danica (Brotzen)

Eocene

Early

P8-P7

Assemblage 4

29-1

, 80-

82X

X

X

X

X

X

X

30-2

, 13

0-13

2

X

X

X

X

X

X

X

X

X

X

X

31-2

,70-

72

X

X

X

X

X

X

X

X

32-2

, 70-

72

Paleocene

Late

P4

Assemblage 3

32-3

,50-

52

X

32, C

C

X

X

X

X

X

X

X

X

as©

r~

o

COCO

X

X

X

X

X

X

X

X

X

33-1

, 17

8-18

0

X

X

X

X

X

X

X

33-2

, 90-

92

X

X

X

X

X

X

33-2

, 20-

22

X

X

X

X

X

33-3

, 37

-39

X

X

1èH

CO

cóCO

X

X

X

X

X

X

XX

X

868

PALEOCENE AND EARLY EOCENE MICROFACIES, BENTHONIC FORAMINIFER A, AND PALEOBATHYMETRY

TABLE 3

— Epoch

^ s . Planktonic Foraminifer^ Zone

^ ^ Depth Assemblage

^ s . SampleTaxa ^ - s . (Interval

^ ^ in cm)

Gavelinella hyphalus (Fisher)Globolina sp.Gyroidina girardana (Reuss)Gyroidina globosa (Hagerow)Gyroidina nitida (Reuss)Gyroidina planata CushmanLagena acuticosta ReussLagena cf. L. laevis (Montagu)Lagena spp.Lenticulina cf. L. rosetta (Gimbel)Lenticulina velascoensis WhiteLenticulina aff. L. vortex (Fichtel and Moll)Loxostomum trinitatensis Cushman and RenzMarginulina cf. M. subrecta FrankeMarginulina spp.Marssonella oxycona (Reuss)Marssonella cf. M. oxycona (Reuss)Melonis aff. M. planatus (Cushman and Thomas)Neoeponides hildebrandti FisherNodosarella advena Cushman and SiegfusNodosarella aff. N. attenuata (Plummer)Nodosarella spp.Nodosaria latejugata GùmbelNodosaria sp.Nuttallides truempyi (Nuttall)Oridorsalis umbonatus Reuss?Osangularia culter (Parker and Jones)Osangularia aff. 0. culter (Parker and Jones)Palmula aff. P. delicatissima (Plummer)Pleurostomella aff. P. paleocenica CushmanPseudogloborotalia florealis (White)Pseudonodosaria manifesto (Reuss)Pseudonodosaria spp.Pseudovalvulineria beccariformis (White)Pullenia coryelli WhitePullenia quinqueloba angusta Cushman and ToddPullenia sp.Spiroplectammina excolata (Cushman)Spiroplectammina mexiaensis LalickerSpiroplectammina cf. S. spectabilis (Grzybowskii)Spiroplectammina sp.Stilostomella cf. S. bradyi (Cushman)

- Continued

Eocene

Early

P8-P7

Assemblage 4

29-1

, 80

-82

X

X

XX

X

XXX

X

XX

X

30-2

, 13

0-13

2

X

X

X

X

X

31-2

,70-

72

X

X

X

XXX

X

32-2

, 70-

72

X

X

Paleocene

Late

P4

Assemblage 3

32-3

,50-

52

32, C

C

X

X

X

X

X

XX

X

X

X

XX

XX

ON

o

©

cóCO

X

X

XX

X

X

X

X

X

XX

XXXXX

X

XX

33-1

, 17

8-18

0

XX

X

X

XX

XX

X

33-2

, 90-

92

X

X

X

X

X

X

XX

X

33-2

, 20-

22

X

X

X

X

X

X

XX

X

33-3

, 37

-39 o

èy—I

cóCO

X

X

X

XXX

X

XX

XX

XX

X

X

X

869


TABLE 1

^ v Epoch

^ s . Planktonic Foraminifer al Zone

. Depth Assemblage

Taxa \ \ S a m P l e

\ . (Interval^ N . in cm)

Stilostomella hispidula CushmanStilostomella kressenbergensis (Gümbel)Stilostomella paleocenica (Cushman and Todd)

Stilostomella plummerae (Cushman)Stilostomella spp.Trifarina advena CushmanVaginulina cf. V. longiforma (Plummer)Vaginulinopsis sp.

\ — Continued

Eocene

Early

P8-P7

Assemblage 4

29-1

, 80-

82

X

X

30-2

, 130

-132

XX

X

31-2

,70-

72

X

X

32-2

, 70-

72

Paleocene

Late

P4

Assemblage 3

32-3

,50-

52

32, C

C

o>—H

o

1—1

enen

X

33-1

, 17

8-18

0

33-2

, 90

-92

33-2

, 20-

22

X

X

33-3

, 37-

39

33-3

, 10

5-10

7

XXX

of older sediments. At the latter site the hole wasterminated in sediments approximately 62 m.y. old (P.Iand Cruciplacolithus tenuis zones) and basement was notreached. The lower 280 meters of section at Site 237 showsa sedimentary history different from that of the overlyingsequence. Sediments include a characteristic Midway ben-thonic assemblage (assemblage 2), which reflects lowerneritic to upper bathyal water depths with admixtures inseveral thin horizons of displaced upper neritic fauna(assemblage 1). The environment, however is clearlypelagic, well below shelf depth as planktonic foraminiferaconstitute 95% or more of the foraminiferal populationthroughout the section, except in the few horizons withdisplaced neritic material in which their frequency is muchlower (< 30%). An upper bathyal environment of severalhundred meters (600 m or less) thus appears to havepersisted from approximately 62 to 57-58 m.y.BJP. Thiswater depth is in the range at which glauconite is mostcommonly formed (Porrenga, 1967). The presence ofglauconite (1% to 5%) in the rocks throughout this part ofthe section, as pellets and in some instances as fillings offoraminiferal tests, would thus support the water depthinferred from benthonic assemblages. The presence of finequartz grains (1%) throughout this part of the sequence isalso consistent with this bathymetric interpretation. It ispossible, however, that these components were transporteddownslope and cannot be used as bathymetric indicators.

The very high sedimentation rate which average 68.2m/m.y. for the lower 290 meters of sediments (a rate ofaccumulation about five times higher than for the succeed-ing upper Paleocene and lower Eocene sequence) and theadmixture of slumped shallow-water sediments indicatethat the location of Site 237 functioned as a sediment trapduring the early Paleocene and early late Paleocene. Inaddition to slumping of coarse material from nearby banksor shoals on a few occasions, it is probable that acontinuous influx of fine-grained material was taking place.

The bulk of the rock is very fine-grained calcite, but thedegree of recrystallization prevents identification of itsorigin. Much shallow-water fine-grained carbonate debriswas probably carried downslope into the area, where itaccumulated together with the tests of pelagic organisms.

CONCLUSIONS

The rather abrupt change in sedimentary regime,reflected in the sediments at Site 237 at about 400 metersfrom a higher sedimentation rate below to a lower rateabove and from a shallower environment below to a deeperenvironment above indicates a change in the topographicsituation of the site. This change occurred at approximately57-58 m.y. B.P., a time which may mark the onset ofrupture between the Chagos and Saya de Malha regions.Fisher et al. (1971) suggested that the Mascarene andChagos-Laccadive plateaus were adjacent in pre-Miocenetime prior to the start of the present episode of spreadingfrom the median Central Indian Ridge (Figure 5). Resultsfrom Site 238, located in the Central Indian Ridge area nearthe southern end of the Chagos-Laccadive Ridge (Fig-ure 1), show that sundering of the Chagos region from theSaya de Malha region took place as early as late earlyOligocene (Chapter 9, this volume). It may have startedeven earlier, however, perhaps in late Paleocene time.

Fisher et al. (1971) suggested that the volcanic founda-tion of the Chagos-Laccadive Ridge and the segment ofthe Mascarene Plateau extending south-southwest fromSaya de Malha was probably formed along the trace of theChagos Fracture Zone, a Cretaceous and early Tertiarytransform fault of major proportion, during a long pause inspreading (Figure 5). The age of the foundation and thepetrologic affinity of that part of the Mascarene Plateaulocated between the granitic Seychelles Bank and thevolcanic Saya de Malha Bank is still controversial, as thedrilling at Site 237 failed to determine the age and natureof the basement. The configuration of the sea floor in this

870

PALEOCENE AND EARLY EOCENE MICROFACIES. BENTHONIC FORAMINIFERA, AND PALEOBATHYMETRY

TABLE 4Distribution of Benthonic Foraminifera in Paleocene

and Lower Eocene Sediments at Site 237

^ v Epoch

^ s . Planktonic Foraminiferal Zone

^ v Depth Assemblage

Taxa ^ v Sample

^ v (Interval^ v in cm)

Ammodiscus incertus (d'Orbigny)

Angulogerina virginiana Cushman

Anomalina cubana Cushman and Bermudez

Anomalina dorri aragonensis Nuttall

Anomalina midwayensis (Plummer)

Anomalina welleri Plummer

Anomalina sp.

Aragonina aragonensis (Nuttall)

Astacolus sp.

Bathysiphon eocenicus Cushman and Hanna

Bolivina aff. B. anglica Cushman

Bolivina crenulata Loetterle

Bolivina midwayensis Cushman

Bolivina cf. B. nacheolensis (Cushman)

Bolivina spp.

Bulimina arkadelphiana midwayensis Cushman & Parker

Bulimina aff. B. arkadelphiana midwayensisCushman and Parker

Bulimina cf. B. bradburyi Martin

Bulimina impendens Parker and Bermudez

Bulimina cf, B. impendens Parker and Bermudez

Bulimina spp.

Cibicides alleni Plummer

Cibicides blanpiedi Toulmin

Cibicides cf. C. blanpiedi Toulmin

Cibicides constrictus (Cushman)

Cibicides cf. C. spiropunctatus Galloway and Morey

Citharina sp.

Clavulina aspera whitei Cushman and Jarvis

Clavulina midwayensis (Cushman)

Dentalina aculeata (d'Orbigny)

Dentalina basiplanata Cushman

Dentalina colei Cushman and Dusenbury

Dentalina cf. D. colei Cushman and Dusenbury

Dentalina cf. D. communis (d'Orbigny)

Dentalina dusenburyi

Dentalina eocenica Cushman

Dentalina pseudo-obliquistriata (Plummer)

Dentalina soluta Reuss

Dorothia cf. D. bulletta Carsey

Dorothia principensis Cushman and Bermudez

Eponides aff. E. bollii Cushman and Renz

Eponides sp.

Eocene

Mid. Early

P.10-P.9 P7-P6

Assemblage 4

r-1—1

iθi-H

i—1

CO

<sCO

X

X

X

X

X

36-1

, 13

2-13

4

X

X

X

X

X

X

38-1

, 90

-92

X

X

X

X

X

Paleocene

Late

P5-P4

Ass. 3

41-2

,48-

50

X

X

X

X

X

X

X

X

X

X

X

X

44-2

,116

-118

X

X

X

X

X

X

X

P3

Early

P2-P1

Assemblage 2

48-1

, 10

0-10

2

X

X

X

X

X

X

X

49-1

,143

-145

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

49-2

, 97

-99

X

X

X

X

X

56-1

, 14

5-14

7

X

X

X

X

X

X

X

X

X

X

58-1

, 70

-72

X

X

X

X

X

X

X

i—i

i—4

oó

X

X

X

XX

X

X

67-2

, 80-

82

XX

XX

67-5

,65-

67

X

X

XX

X

X

871


TABLE 4 - Continued

^ ^ Epoch

\ ^ Planktonic Foraminiferal Zone

^s. Depth Assemblage

Taxa \ .\ . Sample

>s. (Interval^s . in cm)

Fissurina orbignyana SequenzaFrondicularia aff. F. archiacana d'OrbignyFrondicularia midwayensis Cushman

Frondicularia nacheolensis Cushman and ToddGaudryina laevigata FrankeGavelinella danica (Brotzen)Glandulina laevigata (d'Orbigny)Gyroidina globosa (Hagerow)Gyroidina nitida (Reuss)Gyroidina cf. G. nitida (Reuss)Lagena acuticosta ReussLagena laevis (Montagu)Lagena cf. L. vulgaris WilliamsonLenticulina arcuatostriata caroliniana CushmanLenticulina cf. L. arcuatostriata caroliniana CushmanLenticulina degolyeri PlummerLenticulina insulsa CushmanLenticulina midwayensis (Plummer)

Lenticulina velascoensis WhiteLenticulina spp.Loxostomum applinae (Plummer)

Marginulina dubia NeugeborenMarginulina cf. M. exima TerquemMarginulina glabra d'OrbignyMarginulina cf. M. glabra d'OrbignyMarginulina scitula BornemannMarginulina cf. M. scitula BornemannMarginulina spp.Marssonella oxycona (Reuss)Marssonella cf. M. oxycona (Reuss)Melonis aff. M. planatus (Cushman and Thomas)Nodosaria afflnis ReussNodosaria arundinea SchwagerNodosaria cf. N. ewaldi ReussNodosaria grand PlummerNodosaria latejugata GümbelNodosaria cf. N. latejugata GümbelNodosaria velascoensis CushmanNuttallides truempyi (Nuttall)Oridorsalis umbonatus Reuss?Osangularia culter (Parker and Jones)Palmula reticulata Reuss

Eocene

Mid. Early

P.10-P.9 P7-P6,

Assemblage 4

r—1

IΛ*—iT—1

CO

CNCO

X

X

X

36-1

, 13

2-13

4

X

X

X

38-1

,90-

92

X

X

Paleocene

Late

P5-P4

Ass. 3

41-2

,48-

50

X

X

X

X

X

X

X

X

00i-H

vóH^H

CS

XX

XXX

XX

X

X

X

X

X

X

X

X

P3

Early

P2-P1

Assemblage 2

48-1

, 10

0-10

2

XXX

XX

X

X

X

49-1

, 14

3-14

5

XX

X

X

X

X

XX

X

XX

X

X

X

X

X

49-2

, 97

-99

X

X

X

XX

X

I—1

•A

i—i

^£>IT)

X

X

X

X

X

58-1

, 70

-72

X

X

X

X

X

X

i—i

oó>o

XXX

X

X

67-2

, 80

-82

X

67-5

, 65

-67

XX

X

X

X

XX

872


^ v Epoch

>>. Planktonic Foraminifer^ Zone

>v Depth Assemblage

T a x a ^ V Sample^>v (Interval

^ s . in cm)

Palmula sp.Pleurostemella paleocenica CushmanPleurostemella aff. P. paleocenica CushmanPseudonodosaria manifesto (Reuss)Pseudovalvulineria beccariformis (White)Pullenia coryelli WhitePullenia quinqueloba angusta Cushman and ToddQuadromorphina allomorphinoides (Reuss)Ramulina navarroana CushmanSaracenaria cf. S. trigonata (Plummer)Spiroplectammina mexiaensis LalickerSpiroplectammina spectabilis GrzybowskiSpiroplectammina sp.Stilostomella hispidula CushmanStilostomella kressenbergensis (Gümbel)Stilostomella midwayensis (Cushman and Todd)Stilosteomella paleocenica (Cushman and Todd)Stilostomella spp.Textularia plummerae LalickerTrifarina adrena CushmanTrifarina berberti Cushman and RenzVaginulina longiforma (Plummer)Vaginulina sp.Vaginulinopsis cf. V. mexicana

TABLE 4 - Continued

Eocene

Mid. Early

P.10-P.9 P7-P6

Assemblage 4

mi•H

CO

CSCO

X

X

X

X

36-1, 132-134

X

X

X

X

X

38-1, 90-92

X

X

X

Paleocene

Late

P5-P4

Ass. 3

41-2,48-50

X

X

X

X

XX

X

00T—1

V£>

<s

-4

X

XXX

X

X

XX

P3

Early

P2-P1

Assemblage 2

48-1, 100-102

XX

X

X

X

X

49-1, 143-145

X

X

X

X

X

X

49-2, 97-99

X

X

X56-1,145-147

X

X

X58-1,70-72

X

X

«t

Ti"

00

X

X

X

X

67-2, 80-82

X

67-5,65-67

X

X

X

XX

area during early Tertiary time is not fully known. It isclear, however, that at this time the area of Site 237 wasnot a reef-capped bank, as was expected prior to drilling,although there were nearby shoals from which slumpedmaterial was transported and redeposited in the pelagicsediments at Site 237. Between approximately 62 and 57m.y. B.P. this site was probably not deeper than severalhundred meters (perhaps 600 m or less) and was located atthe base of a steep slope where slumped sediments couldaccumulate rapidly. It may therefore have been adjacent tosome shallow-water structure which was probably in exist-ence west of the Chagos Fracture Zone during this time. Inlate Paleocene time (ca 57 m.y. B.P.) a sudden sinking ofthe sea floor took place. The shoal portion of theMascarene Plateau probably subsided below shelf depth,and slumping of shallow-water material into the area at Site237 ceased. This deepening of Site 237 permitted lowerbathyal benthonic faunas, similar to contemporaneousbenthonic assemblages at Site 236 to the north, to develop

in this area of the Mascarene Plateau. Pelagic sedimentationproceeded here during latest Paleocene and early Eocene ata reduced rate averaging 13 m/m.y. During this timeinterval, however, it slowed near the end of the Paleoceneand in early Eocene during a time of nondeposition at Site236. Sedimentation increased to approximately 17 m/m.y.at the beginning of the middle Eocene.

The basal sediments at Site 237 are presently found at2334 meters below the sea floor. If they were deposited inwater depths of a few hundred meters, then the area hassubsided about 2000 meters over the past 62 m.y.indicating a mean subsidence rate of 32 m/m.y. This valueis similar to the mean subsidence rate (36 m/m.y.) obtainedat Site 219 located at the northern end of the Chagos-Laccadive Ridge (Figure 1). At the latter site, shallow-water sediments were deposited in a water depth ofapproximately 100 meters during late Paleocene at a rate of70 m/m.y. The seabed began to sink probably toward theend of the Paleocene and after a period of nondeposition of

873


AGE (m.y.)

20 30 40 60 70

3000 -

4000 -

Figure 4. Depth as a function of age at Site 236 (derivedfrom Sclater et al, 1971; and Berger, 1973).

about 5 m.y. spanning the Paleocene/Eocene boundary (asat Site 236), pelagic sediments were deposited at bathyaldepths with a slower rate of 18 m/m.y. Total subsidencewas of the order of 2100 meters (Whitmarsh, Weser, et al.,1974, Chapter 3). There is, therefore, a remarkablesynchroneity and similarity in the subsidence history of theMascarene Plateau and the Chagos-Laccadive Ridge.

ACKNOWLEDGMENTS

The authors have benefited greatly, in the preparation ofthis report, from discussions with W. A. Berggren and R. C.Tjalsma (Woods Hole Oceanographic Institution), I. PremoliSilva (Universita di Milano), and R. L. Fisher (ScrippsInstitution of Oceanography). R. L. Fleisher (University ofSouthern California) kindly reviewed the manuscript. Wewould also like to thank L. Dmitriev (Academy of Sciencesof the USSR) for his assistance in the preparation, aboardthe Glomar Challenger, of the thin sections analyzed in thisstudy.

We thank the management of Texaco Inc. and ELF-REfor permission to publish the article.

This study was supported under Oceanographic Section,National Science Foundation NSF Grand GA-34145 andrepresents Contribution No. 348, Department of GeologicalSciences, University of Southern California.

REFERENCES

Bandy, O. L., 1960. General correlation of foraminiferalstructure with environment: International GeologicalCongress, XXI Session, Norden, Party XXII, Interna-tional Paleontological Union, p. 7-18.

, 1963. Larger living foraminifera of the conti-nental borderland of southern California: Contrib.Cushman Found. Foram. Res., v. 14, pt. 4, p. 121-126.

, 1970. Upper Cretaceous-Cenozoic paleo-

Bandy, O. L. and Amal. R. E., 1960. Concepts offoraminiferal paleoecology: Am. Assoc. Petrol. Geol.Bull.,v. 44, p. 1921-1932.

Bandy, O. L. and Chierici, M. A., 1966. Depth-temperatureevaluation of selected California and Mediterraneanbathyal foraminifera: Marine Geol. v. 4, no. 4, p.259-271.

Berger, W. H., 1972. Deep-Sea carbonates: Dissolutionfacies and age-depth constancy: Nature, v. 236, p.392-395.

, 1973. Cenozoic sedimentation in the easterntropical Pacific. Geol. Soc. Am., Bull., v. 84, p.1941-1954.

Berggren, W. A., 1972. A Cenozoic time scale—someimplications for regional geology and paleobio-geography: Lethaia, v. 15, p. 195-215.

., in press, a. Late Paleocene—early Eocene ben-thonic foraminiferal biostratigraphy and paleoecology ofRockall Bank: Micropaleontology.

., in press, b. Paleocene benthonic foraminiferalbiostratigraphy, biogeography, and paleoecology ofLibya (Sirte Basin) and Mali: Micropaleontology.

Berggren, W. A. and Phillips, J. D., 1971. Influence ofcontinental drift on the distribution of the Tertiarybenthonic foraminifera in the Caribbean and Mediterra-nean regions: Symposium on the Geology of Lybia,Faculty of Science, University of Lybia, Beirut, (Cath-olic Press), p. 263-299.

Douglas, R. G., 1973a. Benthonic foraminiferal biostrati-graphy in the Central North Pacific, Leg 17, Deep SeaDrilling Project: In Winterer, E. L., Ewing, J. I., et al.,Initial Reports of the Deep Sea Drilling, Volume 17:Washington (U.S. Government Printing Office), p.607-672.

.,1973b. Evolution and bathymetric distribution ofTertiary deep sea benthic foraminifera: Geol. Soc. Am.,Abstracts with programs, v. 5, p. 603.

Cushman, J. A., 1925. An Eocene fauna from the Mocte-zuma River, Mexico: Am. Assoc. Petrol. Geol. Bull., v. 9,p. 298-303.

, 1926. The foraminifera of the Velasco Shale ofthe Tampico embayment: Am. Assoc. Petrol. Geol.Bull.,v. 10, p. 581-612.

., 1951. Paleocene foraminifera of the Gulf Coastal

bathymetric cycles, eastern Panama and northernColombia: Gulf Coast Assoc. Geol. Soc. Trans., v. 20, p.181-193.

Region of the United States and adjacent regions: U. S.Geol. Surv., Prof. Pap. 232, 75 p.

Cushman, J. A. and Renz, H. H., 1946. The foraminiferalfauna of the Lizard Springs Formation of Trinidad,British West Indies: Cushman Lab. Foram. Res., Sp. Pub.18, p. 1-48.

Fisher, R. L., Johnson, G. L., and Heezen, B. C, 1967.Mascarene Plateau; western Indian Ocean: Geol. Soc.Am., Bull., v. 78, p. 1247-1266.

Fisher, R. L., Sclater, J. G., and McKenzie, D. P., 1971. Theevolution of the Central Indian Ridge, Western Indian:Ocean: Geol. Soc. Am. Bull., v. 82, p. 553-562.

Folk, R. L., 1962. Spectral subdivision of limestone types.In Ham, W. H. (Ed.), Classification of carbonate rocks-asymposium: Am. Assoc. Petrol. Geol., Memoir 1, p.62-84.

Gibson, J. M., 1973. Foraminiferal biostratigraphy of theAnita Formation, Western Santa Ynez Mountains, SantaBarbara County, California: M. S. Thesis, Univ. SouthernCalifornia, Los Angeles, Calif.

Gibson, T. G. and Buzas, M. A., 1973. Species diversity:Patterns in modern and Miocene foraminifera of theeastern margin of North America: Geol. Soc. Am. Bull.,v. 84, p. 217-238.

874


Cαrlsberg

25

- 2 8

1 Seychelles

A

Ridge

«i

zon

•

rαct

uiα

go

s

u

11

i \ . India Jr

i

[30

30

25

23 ;

South - east

15

Indian Ridqe

Carlsberg Ridoe (

25

28

σ

B

30

2523

- east

Indian Ridae

Figure 5. Schematic diagram of the Central Indian Ocean.

875


Grimsdale, T. F. and Morkhoven, F. P. C. M. van, 1955.The ratio between pelagic and benthonic foraminifera asa means of estimating depth of deposition of sedimen-tary rocks: World Petrol. Congr., 4th, Proc, Sec. I/D, p.473-490.

Heirtzler, J. R., Dickson, G. O., Herron, E. M., Pitman,W. C, and Le Pichon, X., 1968. Marine magneticanomalies, geomagnetic field reversals and motions ofthe ocean floor and continents: J. Geophys. Res.,v. 73,p. 2119-2136.

Kellough, G. R., 1959. Biostratigraphic and paleoecologicstudy of Midway foraminifera along Tehnacana Creek,Limestone County, Texas: Gulf Coast Assoc. Geol. Soc.Trans., v. 9, p. 147-160.

, 1965. Paleoecology of the foraminiferida of theWills Point Formation (Midway Group) in northeastTexas. Gulf Coast Assoc. Geol. Soc. Trans., v. 15, p.73-153.

McKenzie, D. and Sclater, J. G., 1971. The evolution of theIndian Ocean since the Late Cretaceous: Geophys. J.Roy. Astron. Soc, v. 15, p. 437-528.

Plummer, H IT., 1926. Foraminifera of the Midway Forma-tion in Texas: Univ. Texas Bull., v. 2644, p. 3-206.

Porrenga, D. H., 1967. Glauconite and chamosite as depthindicators in the marine environment: Marine Geol., v. 5,p. 495-501.

Sclater, J. G., Anderson, R. N., and Bell, M. L., 1971.Elevation of ridges and the evolution of central easternPacific: J. Geophys. Res., v. 76, p. 7888-7915.

Theyer, F., 1971. Size-depth variation in Cyclamminacancellata Brady, Peru-Chile Trench area: Antarctic Res.Ser. (Oceanology I), v. 15, p. 309-313.

White, M. P., 1928, Some index foraminifera of theTampico Embayment area of Mexico: J. Paleo., v. 2, p.280-317.

, 1929. Some index foraminifera of the TampicoEmbayment area of Mexico: J. Paleo., v. 3, p. 30-58.

Whitmarsh, R. B., Weser, O. E., et al., 1974. Initial Reportsof the Deep Sea Drilling Project, Volume 23: Washing-ton (U. S. Government Printing Office).

876


PLATE 1

Figure 1 Sparse biomicrite with radiolarians. Sample 237-37-2(15),X130.

Figure 2 Sparse biomicrite with planktonic foraminifera andradiolarians. Morozorella cf. subbotinae (Morozova).Sample 237-38-1 (13), X63.

Figure 3 Sparse biomicrite with planktonic foraminifera andradiolarians. Morozorella gr. velascoensis (Cushman).Sample 23741-2 (13), X63.

Morozorella aequa (Cushman and Senz). Sample 237-44-1 (12), X130.

Packed biomicrite with planktonic foraminifera.Planorotalites ehrenberghi (Bolli). Morozorella gr.pusilla (Bolli). Sample 23745-2 (6). X44.

Planorotalites gr. ehrenberghi (Bolli). Sample 237-46-2 (6), X130.

Packed biomicrite. Valrulinid. Sample 23747-2 (2),X44.

Morozorella gr. velascoensis (Cushman). Sample 237-47-2 (2), X130.

Morozorella angulata (White). Sample 23747-2 (2),X130.

Morozorella gr. velascoensis (Cushman). Sample 237-48-1 (4), X130.

Packed biomicrite with larger foraminifera, bryozoan,mollusc, and echinoderm debris. Discocyclina seunesiDouvillé, Ranikothalia bermudezi (Palmer). Sample23748-2 (120),X39.

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

4

5

6

7

8

9

10

11,12

878


PLATE 1

879


PLATE 2

Figure 1 Morozorella angulata (White). Sponge spicule. Sam-ple 237-50-1 (13), X130.

Figure 2 Sparse biomicrite with radiolarians and planktonic fo-raminifera. Sample 237-51-2 (10), X44.

Figure 3 Sparse biomicrite. Pellets. Sample 237-51-2 (10),X44.

Figure 4 Morozorella gr. velascoensis (Cushman). Sample 237-51 2(10),X130.

Figure 5 Morozorella cf. angulata (White). Sample 237-52-1(13), X130.

Figure 6 Planorotalites cf. compressa (Plummer). Sample 237-54-1 (6), X130.

Figure 7 Packed biomicrite with planktonic foraminifera. Len-ticulina sp. Sample 237-54-1 (6), X44.

Figure 8 Archaeolithothamnium. Mollusc and echinodermdebris. Sample 237-58-1 (95), X44.

Figure 9 Planorotalites cf. compressa (Plummer). Sample 237-61-1 (13), X130.

Figure 10 Morozorella inconstans (Subbotina). Glauconitegrains. Sample 237-64-2 (7), X130.

Figure 11 Sparse biomicrite. Morozorella inconstans (Sub-botina). Sample 237-61-1 (13), X130.

Figure 12 Fossiliferous micrite. "Globigerinid." Sample 237-67-3 (7), X130.

880


PLATE 2

881


PLATE 3

Paleocene, Site 236

Figure 1 Marssonella oxycona (Reuss, 1860). Sample 33-3,105-107 cm. X50.

Figure 2 Gaudryina laerigata Franke, 1914. Sample 33-3,105-107 cm. X 50.

Figure 3 Spiroplectammina excolata (Cushman, 1926). Sam-ple 33-3, 105-107 cm ×IOO.

Figure 4 Spiroplectammina spectabilis Gryzbowski, 1898.Sample 33-1,107-109 cm X100.

Figure 5 Aragonia valascoensis (Cushman, 1926). Sample 33-3,105-107 cm X55.

Figure 6 Bolivinoides delicatula Cushman, 1927. Sample 33-3,105-107 cm X100.

Figure 7 Melonis planatus (Cushman and Thomas, 1930).Sample 33-3,105-107 cm XI10.

Figure 8 Palmula delicatissima (Plummer, 1926). Sample 33-1,107-109 cm X100.

Figure 9 Pseudogloboro florealis (White, 1928). Sample 33-1,107-109 cm X50.

Figure 10 Gyroidina depressa (Alth, 1850). Sample 33-3, 105-107 cm.a. Umbilical view XI00b. Apertural view X100.

Figure 11 Osangularia aff. O. culter (Parker and Jones, 1865).Sample 33-3, 105-107 cm X50.

Figure 12 Loxostomum trinitatensis Cushman and Renz, 1946.Sample 33-1, 107-109 cm X100.

Figure 13 Nuttallides truempyi (Nuttall, 1930). Sample 33-3,105-107 cm.a. Umbilical view XI00.b. Dorsal view XI00.

Figure 14 Pullenia coryelli White, 1929. Sample 33-1, 107-109cm XI00.

Figure 15 Bulimina velascoensis (Cushman, 1925). Sample 33-1,107-109 cm X50.

Figure 16 Gyroidina girardana (Reuss, 1851). Sample 33-1,107-109 cm. XI00.

Figure 17 Lenticulina velascoensis White, 1928. Sample 33-3,105-107 cm. X100.

Figure 18 Gavelinella aff. G. danica (Brotzen, 1940). Sample33-3, 105-107 cm. X100.

Figure 19 Pseudovalvulineria beccariiformis (White, 1928). Sam-ple 33-3, 105-107 cm X100.

Figure 20 Gyroidina globosa (Hagenow, 1842). Sample 33-1,107-109 cm X100.

882


883


Figure 1

Figure

Figure

2

3

Figure 4

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

5

6

7

8

9

10

11

12

PLATE 4

Paleocene and Early Eocene, Sites 236 and 237

Anomalina uelleri (Plummer, 1926). Sample 236-33-1,107-109 cm.a. Umbilical view XI00.b. Apertural view XI00.

Clavulina aspera Cushman, 1926. Sample 237-49-1,143-145 cm. X50.

Pleurostemella paleocenica Cushman, 1947. Sample237-67-5, 65-67 cm. XI00.

Bolivina midwayensis Cushman, 1937. Sample 237-56-1, 145-147 cm X100.

Bulimina arkadelphiana midwayensis Cushman andParker, 1936. Sample 23749-1, 143-144 cm X100.

Vaginulina longiforma (Plummer, 1926). Sample 237-67-5,65-67 cm X50.

Palmula reticulata (Reuss, 1851). Sample 237-44-2,116-118 cm X100.

Aragonia aragonensis (Nuttall, 1930). Sample 236-31-2, 70-72 cm X100.

Anomalina dorri aragonensis Nuttall, 1930. Sample236-31-2,70-72 cm X50.

Pleurostomella aff. P. paleocenica Cushman, 1947(robust form). Sample 236-29-1, 80-82 cm. X100.

Bulimina sp. Sample 236-29-1, 80-82 cm. X100.

Nuttallides truempyi (Nuttall, 1930). Sample 236-29-1, 80-82 cm. X100.

884


885

Documents

21. PALEOCENE AND EARLY EOCENE MICROFACIES, BENTHONIC ... · 21. paleocene and early eocene microfacies, benthonic foraminifera, and paleobathymetry of deep sea drilling project sites