26. CENOZOIC PLANKTONIC FORAMINIFERA —DSDP LEG 39 … · Cenozoic planktonic foraminifera were...

26. CENOZOIC PLANKTONIC FORAMINIFERA1—DSDP LEG 39 (SOUTH ATLANTIC)

Anne Boersma, Lamont-Doherty Geological Observatory, Palisades, New York

ABSTRACT

Tertiary planktonic foraminiferal faunas were recovered at Sites354, 355, 356, 357, 358, and 359 during DSDP Leg 39 in the westernSouth Atlantic; faunas at Site 355 are considered redeposited.

At Site 354 the Tertiary section is characterized throughout bystrong dissolution; the low-latitude planktonic foraminiferal faunasindicate deposition above the CCD. Dissolution across the Mio-cene/Pliocene boundary has resulted in the unique "' Sphaeroidinel-lopsis fauna," typical of the circum-Mediterranean and equatorialAtlantic for this interval. An extensive middle Miocene hiatusoccurs at this site.

Site 356 contains the oldest Tertiary, basal "GlobigerincTeugubina Zone, which includes the ancestor to Globoconusadaubjergensis. An extensive middle Miocene hiatus also occurs atthis site. Some unusual planktonic foraminiferal morphotypes withabundant spines characterize a temperature maximum in the earlyMiocene.

The faunas at Site 357 contain a greater number of high latitudespecies than the adjacent Site 356, particularly in the early Tertiary.

- There is a significant hiatus across the Eocene/Oligocene boundary,preceded by a marked drop in planktonic foraminiferal diversity;this is also the time of cooling bottom and surface temperatures inthe South Atlantic. The very long lower Miocene section, so typicalof the South Atlantic, is followed by a relatively short middleMiocene hiatus. Several unusual planktonic foraminifera occur atthis site. The first appearance of Streptochilus, known previouslyonly from the middle Miocene to Recent, was recorded here in thelatest Oligocene. Unusual spiny morphotypes of Globoquadrina andCatapsydrax appear during a temperature rise in the early Miocene.Globorotalia miozea morphotypes have a long stratigraphic range,occurring from the early Miocene into the Pliocene. Because of thehigh latitude component it was difficult to zone the late Miocene; itwas, however, possible to use these higher latitude elements to inter-relate the Neogene temperate and high latitude zonations with thelow latitude zonation of Berggren (1972).

Site 358 contains an unusual sequence of moderately wellpreserved to poorly preserved Paleocene through middle Eoceneplanktonic foraminifera. This site, deep in the Argentine Basin, wasapparently near the foraminiferal lysocline and CCD throughoutthe early Tertiary until it sank permanently below these levels in themiddle Eocene. Using the paleodepth of the site during this timeperiod, it is possible to estimate the depth of the paleo CCD in thispart of the Southern Atlantic from the Maestrichtian through theEocene.

Site 359 faunas are similar to those at Site 357. Only intermittentcoring was done and only Pliocene, Miocene, and upper Eoceneintervals were recovered. Eocene samples are full of volcanic debrisand displaced foraminifera; Hantkenina is very abundant at this site,which must have lain at about 1000 meters in the Eocene.

'The author has expressed strong preference for using "foraminifera"rather than the common form "foraminifer." Although the DSDP editorsfeel that the common form of the word is preferable in English, and havedecided for consistency to use it in the Initial Reports, they accede here tothe authors wishes.

567

A. BOERSMA

INTRODUCTIONCenozoic planktonic foraminifera were retrieved

from all sites drilled on Leg 39 (Table 1). Theplanktonic foraminiferal faunas from Site 355 in theBrazil Basin are considered redeposited. The locationof Sites 354-359 and their stratigraphy are shown inFigure 1. This chapter gives an introduction to thetypes of planktonic foraminiferal faunas recoveredfrom these sites, and calls attention to some Oceano-graphic problems that may be approached or are raisedby a knowledge of these faunas. Detailed taxonomicanalysis is beyond the capacities of the present writer;hence there is little taxonomic detail included here. Forsuch an analysis of the Neogene of Site 357 seeBerggren (this volume).

TAXONOMYIn the past few years there have been a number of

taxonomic revisions of the planktonic foraminifera(Fleischer, 1974; Premoli Silva, in preparation). Therestill appears to be confusion regarding the Phylogeneticrelationships of species and particularly genera,specifically those of the Oligocene and lower Paleocene.A compromise position is adopted in this study. Wheregeneric relationships are considered established, thenew generic or subgeneric designations are included inquotation marks along with the older generic designa-tion. Otherwise the older generic assignment is used. Asthe species name conveys the most information at thistime, this position should allow understanding of whatforms are being discussed.

ZONATIONThe standard zonation of Berggren (1972) was

applied to all sites in this study. In only a few instanceswas there trouble recognizing the standard zones, forexample in the upper Miocene at Site 357. The locationof Site 357 close to 30° south latitude results in thepresence there of many higher latitude species. Thus itwas also possible to locate several of the higher latitudezonal boundaries of Jenkins (1971) and Kennett (1973).If there is an ecological "delay" effect on the extinctionof taxa between higher and lower latitudes, then zonalboundaries will not correspond in time with thoserecognized at higher latitudes. But we will know whenhigh latitude zonal markers appear or disappear interms of a low latitude zonation and time scale.

TABLE 1Locations and Water Depths

of Leg 39 Drilling Sites

Site

353354355356357358359

Latitude

10°05°15°28°30°37°34°

55'N53.95'N42.59'S17.22'S00.25'S39.31'S59.10'S

Longitude

44°44°30°41°35°35°04°

02.25 "W11.78'W36.03'W05.28'W33.59'W57.82'W29.83'W

WaterDepth

(m)

5165405248963203210950001658

SITE 354Site 354 on the Ceará Rise was drilled at a depth of

4045 meters. The ranges of selected planktonicforaminiferal species in the Tertiary of Site 354 areshown in Figure 2. The planktonic foraminiferalzonation is that of Berggren (1972). However, thelocation of several zonal boundaries was obscured byepisodes of dissolution, recrystallization, and inferreddiagenetic alteration of the foraminiferal faunas.

PreservationPreservation is particularly poor in Cores 11 to 16.

The bottom cores contain dissolved, pitted, and barelyrecognizable planktonic foraminifera, some stronglystained red. In many instances the foraminifera havebeen squashed flat into calcareous pancakes. In Cores11 and 12, foraminifera are often pitted, recrystallized,and fragmented. In these same samples radiolariansand/or diatoms are abundant and often pyritized. Thissuggests that the foraminifera were dissolved duringepisodes of increased productivity, increased organicflux to the bottom, and micro-reducing conditions.

In Core 10 preservation has improved markedly,although there are levels in almost every core wherepreservation again degenerates and forms becomechalky, dissolved, and fragmented.

Cores 4 to 8 contain highly dissolved faunas with"peeled" Sphaeroidinellopsis and reduced faunaldiversity. Above Core 4, preservation is moderate togood.

Sphaeroidinellopsis FaunaAbove Core 8 an unusual sequence of dissolved

faunas occurs. These faunas are often rich in planktonicforaminifers, only a couple of which dominate thefauna. Such faunas typically contain the speciesSphaeroidinellopsis seminulina and Sphaeroidinellopsissubdehiscens in abundance, with occasional Globi-gerinoides preserved along with the more resistantkeeled globorotaliids and Sphaeroidinellopsis spp.

Similar small faunas dominated by Sphaeroidinel-lopsis spp. have been reported from the circum-Mediterranean region (Cita et al., 1973) as well as Leg4, Site 29 (Bolli, 1970) Leg 13, Site 132 (Cita et al.,1973), and Leg 14, Sites 141 and 142 (Beckman, 1972).Sphaeroidinellopsis spp. are accompanied by thefollowing species:

Site 29: Neogloboquadrina acostaensis, Globo-quadrina altispira, G. dutertrei, Globigerinoidessacculifer,

Site 132: Globoquadrina acostaensis, Globoquadrinahumerosa, Globorotalia scitula.

Site 141: Globigerina nepenthes, Globoquadrinadehiscens, G. venezuelana, Globorotalia cultrata.

Site 142: N. acostaensis, Globorotalia tumida, Globi-gerinoides obliquus.

In the Mediterranean the fauna characterized by highabundances of Sphaeroidinellopsis spp. has been relatedto the catastrophic transgression of Atlantic waters intothe Mediterranean after the Messinian salinity crisis(Cita et al., 1973).

568

354Cored

I n t . Units Lithology Age

0

355Cored

Int. Units Lithology Age

356Cored

Int. Units Lithology Age

Depths in Fathoms

< 5 ' 5 ' 45% ' ' 30-

Pleistocene

A Pliocene

Maestrichtian

Campani an

357Cored

Int. Units Lithology

i i

.Pleistocene

Pliocene

Oligocene

Campani an

359Cored

Int.Units Lithology Age

E iU 2

inn-π 3

•+-.JL-l.1- -1- - 1 -'+- -1- -L

•J-J^>>J1.

A P l i o - P l e i s t .-\ Miocene

Eocene

358Cored

I n t . Units Lithology Age

VA

ΔΔ

Pleistocene

Pliocene

Maestri c h t i arCampanian?

Figure 1. Locations of DSDP Leg 39 sites in the South Atlantic containing Tertiary sediments. Stratigraphic column for each site: biostratigraphic subdivisions arebased on the zonation and time scale of Berggren, 1972.

Figure 2. Stratigraphic ranges of selected planktonic foraminifera during the Cenozoic at Site 354 on the CeardRise.

570

A. BOERSMA

Site 354 Cenozoic Planktonic Foraminifera

CENOZOIC PLANKTONIC FORAMINIFERA

Figure 2. (Continued).

571

A. BOERSMA

These unique faunas, existing in the circum-Mediterranean area as well as spanning the equatorialAtlantic consistently characterize the uppermostMiocene and lower Pliocene interval.

Stratigraphic BoundariesBecause of the large number of hiatuses and coring

gaps, there were few epoch boundaries to be identifiedat this site. Only the Miocene/Oligocene and theMiocene/Pliocene boundaries were cored. TheOligocene/Miocene boundary was placed within Core9 on the basis of the overlap between Globigerinaangulistuturalis and Globorotalia kugleri, immediatelybelow the abundant occurrence of Globigerinoidesprimordius.

The Miocene/Pliocene boundary was placed in theinterval between Section 4 and the core-catcher sampleof Core 4. Globoquadrina dehiscens last occurs inSection 5-1; however, faunal dissolution above thislevel has removed most diagnostic species so that the"real" top of G. dehiscens is not known. Cita et al.(1973) places her dissolution interval in the top of theMiocene; this may also be the case at Site 354.

Zonal Boundaries and HiatusesZonal boundaries have been determined on the basis

of diagnostic zonal fossils where possible. However,poor preservation and dissolution sometimesnecessitated using other criteria. This was true for theEocene zones which were determined primarily on theco-occurrence of species, not necessarily on thepresence or absence of the zonal markers. As theOligocene through lower Miocene was more complete,most of the zonal markers were present and allowedmore precise zonal assignments.

There are three Paleogene hiatuses: between theEocene/Oligocene, the upper and middle Eocene, andthe lower and upper Paleocene (see Figure 1). Severalhiatuses above the lower Miocene made the recognitionof Neogene zonal boundaries difficult. A middleMiocene hiatus between Zones N.8 and N.I6 is typicalof the South Atlantic, although the duration of thehiatus differs from site to site. Parts of the middleMiocene are absent also from DSDP Sites 14, 17, 19,20, 25, possibly 142, 356, and 357 all in the southernand western Atlantic. This middle Miocene hiatus isconsidered the result of dissolution intensity andcurrent scour related to a shallower CCD with a peakdissolution time in the late middle Miocene.

A second hiatus spans most of the lower Pliocene.The sediments above the hiatus appear to belong to thelower part of Zone N.21, as Globorotalia multicameratais already present in the first sample above the hiatus,and Globigerina nepenthes and Sphaeroidinellopsisseminulina are absent; but there is an overlap betweenSphaeroidinellopsis subdehiscens and G. multicamerata.Higher in this sequence Globorotalia miocenica andGlobigerinoides ßstulosus make their first appearance.However, the top part of Zone N.21 may be missing, asGloborotalia tosaensis was not found. Thus there maybe another hiatus between the lower part of N.21 andthe Pleistocene Globorotalia truncatulinoides Zone(N.22).

Adjacent Sites

Site 142 from Leg 14 lies in the Ceará Abyssal Plainbelow the Ceará Rise (see Figure 4). The followingzones were recognized in the sediments cored at Site142: G. margaritae, G. dutertrei, G. acostaensis, mixedmid-late Miocene, and the G. insueta Zone. Within theupper Miocene/Pliocene interval, there are levels withfew species which may correlate with the Sphaeroidinel-lopsis layers at Site 354. Although a bit of middleMiocene found at this site was mixed in with upperMiocene sediments, there may be a middle Miocenehiatus at this site also. Unlike Site 354, there is a gap inthe lower Miocene down to the G. insueta Zone. Thismay be a stratigraphic gap, except that the unrecoveredinterval may have been contained in the near-40-metercoring gap immediately above the G. insueta Zone andbelow the section generally called lower Miocene, butgiven no zonal designation. Thus the Miocene at Site142 bears close resemblance to that of Site 354 on therise. However, the G. margaritae Zone of Site 141 wasnot found at Site 354. The upper Pliocene may bepresent at Site 142; however, there is a 60-meter coringgap between the lower Pliocene and the Pleistocene, sothat Zone N.19 may occur in the uncored sedimentcolumn.

Site 144 on the Demerara Rise was drilled intoPaleogene sediments at a depth of 2957 meters. There isa hiatus between the lower Oligocene Zone P. 18 and themiddle Eocene within Core 2 in Hole 144A. However,the remainder of the Eocene may be present butuncored in the near-100-meter coring gap between themiddle Eocene and the upper Paleocene (Zone P.4) thatwas recovered.

As fossils from Zone P. 16 were recovered from Site354, the Eocene/Oligocene hiatus on the Ceará Rise isnot as extensive as that on the Demerara Rise. Theupper/middle Eocene hiatus at Site 354 is contained inCore 13 and covers Zones P. 16 to P. 10. Hence, parts ofthe middle Eocene missing here are in fact preserved onthe Demerara Rise nearby. The lower Eocene/upperPaleocene hiatus is also contained within one core atSite 354, but comparison with the Demerara Rise is notpossible because of the extensive coring gap at that site.

SITE 355Planktonic foraminifera were recovered in several

layers of presumed turbidite origin. Coarse-grainedshallow water deposits containing larger benthicforaminifera such as Miogypsina are occasionallyintercalated into the foraminiferal ooze layers.

Foraminifera recovered from Core 2 includedGlobigerina nepenthes, Globorotalia mayeri, S.seminulina, and S. subdehiscens at the top, locating thislevel somewhere between Zones N.I3 and N.19. Asecond fauna (Cores 2 and 3), including Praeorbulinaglomerosa, P. transitoria, Globorotalia peripheroronda,and Globigerinoides diminutus, represented the intervalfrom Zones N.7 to N.9. The foraminifera from Section3-1 and Sample 3, CC, representing the interval fromN.5 to P.22 include Globoquadrina dehiscens,Globigerinoides primordius, Globorotalia "7 ." opimanana, G. cuachitaensis, and Globoquadrina altispira.

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SITE 356

Site 356 was drilled at a depth of 3175 meters on theSao Paulo Plateau. At this depth, the plateau presentlylies in the path of the middle North Atlantic DeepWater. Site 356 lies in the southward path of the surfaceBrazil Current in the more steady continentward zoneof this surface current system.

The Tertiary section drilled at this site extends fromthe very oldest Paleocene yet recovered to upperPliocene (see Figure 1). The faunas are subtropical incharacter, but do not include the higher latitudecomponents so abundant in parts of the section at Site357. Otherwise, foraminiferal events at the two sites aresimilar.

HiatusesThere are five significant hiatuses in the Tertiary

section at Site 356. Briefly, the Danian is relativelycomplete, except for a gap covering the interval of ZoneP.lb. The Paleocene sequence above this continues intoZone P.4 above which there is a hiatus (within Core 16)extending into the lower Eocene.

There is a fairly continuous lower to middle Eocenesection; however, poor preservation makes zonationspeculative. There is then a hiatus in Core 6 between theupper middle Eocene and the Oligocene/Miocenetransition. A thick lower Miocene is then followed by ahiatus, within an unrecovered interval between Cores 3and 2. This uncored interval of 19 meters was not longenough to have included the remainder of the Mioceneand lower Pliocene. Further, this is a time of extensiveand geographically widely distributed hiatuses in theSouth Atlantic.

PreservationProbably the most spectacular preservation at this

site can be seen in the Danian (Cores 29-22),particularly in the lower Danian. The basal Tertiary"G." eugubina Zone, as well as other sections of ZoneP.I show excellent preservation. However, significantepisodes of dissolution begin in Core 21 and become sointense in the upper Paleocene and Eocene as to makerecognition of fossils often impossible. Recrystal-lization of forms as well as squashing of individualsbecome common. Increase in siliceous cement in Core16, hence increased induration, leaves residues alteredto the point that the entire sample will contain norecognizable fossils. Beginning in Core 10 there is aninflux of radiolarians and diatoms which precedes amarked improvement in preservation from Cores 10 to6. Dissolution is less obvious except in the top of thissection; nevertheless, faunas appear reduced indiversity by dissolution. A notable exception is Core 6which contains a rich assemblage of the Globorotalia"Af." lehneri Zone.

In Cores 15 through 6 the presence of redepositedfossils of various ages is common. For example, G."Af." palmerae is present as a contaminant in oldersediments (see Figure 3).

Preservation of the Neogene is not much better,although there are several well-preserved levels

scattered throughout the five cores. In lower Miocenesediments, radiolarians, particularly the giant forms,are abundant. Several levels contain pyrite, suggestingmicro-reducing intervals. Preservation improvestoward the top of the lower Miocene and the Pliocene iswell preserved.

Paleogene ZonationThe ranges of the most abundant planktonic

foraminifera at Site 356 are shown in Figure 4. Becauseof unusually bad preservation the zonation of thePaleogene was based on whatever evidence could beused. Paleobiogeographic information supplied by I.Premoli-Silva (personal communication, 1976) helpedimmensely, as faunal events occurring at other sitescould be used to identify the time intervals representedat this site.

The Paleocene at this site is thick. According to Dr.Premoli-Silva, the very base of the "Globigeriná"eugubina Zone is represented in Core 29, Section 3 atthis site; it contains the ancestor of Globoconusadaubjergensis and is dominated by "G."fringa (Plate 1).The top of the "G." eugubina Zone is in Core 29,Section 2. The upper Danian lacks only the Globigerina(S.) triloculinoides interval. Otherwise the G. pseudo-bulloides and G. trinidadensis intervals of Zone P. 1 arewell represented and the faunas are typical ofsubtropical latitudes. The Paleocene sequence iscontinuous to the base of the Globorotalia "P." pseudo-menardii Zone (P.4). This interval contains very rare G."Af." velascoensis, which may not be in place.

Preservation in the overlying Eocene sediments isvery poor and faunas are greatly reduced in diversity.The top of Core 16 is assigned to the base of theGloborotalia "Af." formosa Zone (P.7) primarily on thebasis of right-coiled Globorotalia "Af." aragonensis.The base of the G. "Af." aragonensis Zone (P.8) waslocated in Core 13, as most of the sediments in Core 14yielded no recognizable fossils. Throughout this zonethe faunas are small and the acarininids predominate.Premoli-Silva (in preparation) found in studies on thepaleobiogeography of Paleogene planktonics thatkeeled globorotalids become scarce at mid-latitudesafter the G. "A/." formosa Zone (P.7). This may explainthe lack of those forms at Sites 356 and 357, rather thansimply dissolution. In Core 13, Section 2 the faunaconsists entirely of two acarininid species: Acarininadensa and A. wilcoxensis.

The first bullate forms appeared in Core 10 alongwith increased numbers of globigerinids. However,there are many contaminants in this core. Cores 9 and 8are placed in the Hantkenina aragonensis Zone (P. 10)on the basis of primitive Globigerinatheka sp. as well asthe continuing presence of G. "Af." aragonensis. NoHantkenina sp. was present. The sequence ofappearances, if they are real and not just a function ofpoor preservation, in Cores 9 through 6 parallel thatduring the same time interval at Site 357. The primitiveGlobigerinatheka in Core 9 is accompanied by the firstspecimens of "Globigerina'''' higginsi, and Acarininapseudotopilensis which significantly change the overallaspect of the fauna. Chiloguembelina sp. is first

573

A. BOERSMA

.Epoc

Site 356 - Paleogene Planktonic Foraminifera

P12

20 CC

25

CC

26

27

29

29

29

60

119

60

120

119

50

60

40

30

24

*- '~-irs;

1 ö,

Figure 3. Stratigraphic ranges of selected planktonic foraminifera during the Paleogene at Site 356 on the Sao Paulo Plateau.

encountered also at this level, but this appearance isconsidered a function of the poor preservation ofunderlying samples. Truncorotaloides topilenses andGlobigerina turgida first appear in Core 7, followed inCore 6 by recognizable Globigerinatheka kugleri andTruncorotaloides rohri. Hantkenina alabamensis is also

present; the absence of Hantkenina in older sediments isdue to poor preservation of faunas.

Neogene ZonationRanges of selected Neogene planktonic foraminiferal

species are shown in Figure 5. The primary problem in

574


the zonation of the Neogene at this site was thedetermination of the Oligocene/Miocene boundary.The lowest Neogene levels at this site could beconsidered either Oligocene or Miocene since the firstappearance of Globigerinoides is no longer a criterionapplicable to the location of this boundary. At this timeCore 5 is placed in the Miocene, Zone N.4, not theOligocene (P.22). In the lowest samples there are still afew individuals of Globorotalia praekugleri; however, itis assigned to the Globigerinoides primordius-G. kugleriZone and hence according to Berggren (1972) belongsto the Miocene (Zone N.4). The sequence offoraminiferal appearances in Cores 5 through 3 parallelthose at Site 357, particularly the appearance(ecological?) of a spiny Catapsydrax sp. and Globo-quadrina dehiscens, along with Globoquadrina altispira,just following the appearance of Globigerinoides spp. inabundance between Zones N.4 and N.5. Then in ZoneN.6 G. altiaperturus and the spiny species appear. AtSite 357 this sequence of events is associated with awarming in the lower Miocene, culminating with thefirst abundance of G. altiaperturus and the spinoseforms. Such a temperature event was apparentlyrecorded also at Site 356.

Core 2, down to Section 2, belongs to the PlioceneZone N.21, specifically the interval above the extinctionof Sphaeroidinellopsis subdehiscens, but below the topof Globorotalia margaritae. The higher sections, as wellas Core 1, contain Globorotalia multicamerata,Globorotalia miocenica, and Globigerinoides ßstulosus,placing them higher in Zone N.21.

SITE 357Site 357 was drilled at a depth of 2086 meters on the

eastern extension of the Rio Grande Rise. The site lieswithin the path of the NADW and the southwardflowing surface Brazil Current. Paleogeographicalreconstructions (Ladd, 1974) indicate that from theSantonian to the present this site has moved fromapproximately 40° to 30° south latitude.

An extensive Tertiary section was drilled at this site,allowing precise biostratigraphic determination as wellas analysis of the oxygen isotopic record at this site(Boersma and Shackleton, this volume). The biostrati-graphic framework and 18O measurements allow us todraw some paleoecological conclusions as to theOceanographic phenomena affecting this site and itsfaunas.

HiatusesThere are nine recognizable hiatuses in the Tertiary

record at this site. As at Site 356, two hiatuses occur inthe Paleocene. The first includes the short Danianinterval P. lb. The second spans the entire upperPaleocene and lower Eocene. There is a 20-meter coringgap between the Paleocene Zone P.4 and the earlyEocene Zone P.7, so it is possible that more of thePaleocene may be present, but was not recovered. Thepresence of well-preserved faunas of Zone P.4corroborates this suggestion.

In addition to the Paleocene/Eocene hiatus, there arethree other gaps in the Eocene. Zones P.9, P. 10, P. 14,

P. 15, and most of P. 16 and P. 17 are all missing at thissite. In the case of zones P.9 and P. 10, part of thisinterval may be present in the 27-meter coring gapbetween Cores 26 and 27. The hiatus between ZonesP. 13 and P. 16 occurs within Core 20. The Oligo-cene/Eocene boundary hiatus is typical of severaladjacent sites (Legs 3, Sites 19 and 20C, Figure 4) andthus represents a widespread and significant Oceano-graphic event at this time in the South Atlantic. Atthese sites, the part of Zone P. 16 corresponding to thenannofαssil Isthmolithus recurvus Zone is all that hasbeen recovered. Zone P. 17 is missing.

The Oligocene lacks the basal Zone P. 18, as well asthe topmost section of Zone P.21. While the lowerMiocene appears complete here, a hiatus spans thelower/middle Miocene interval between zones N.8 andN.I 1 in Core 6. A second hiatus includes parts of ZonesN.14 and N.15. As the Neogene was continuouslycored, all of these hiatuses are considered real and arenot inferred.

The upper Pliocene is missing, along with sections ofthe lower Pleistocene; thus, Zone N.21 and a part ofZone N.22 are not present at this site.

PreservationPreservation varies from sample to sample, but is not

particularly good until the Miocene and parts of theOligocene. The Paleocene and lower Eocene aremoderately preserved, although some levels containbadly recrystallized faunas. Beginning in the lowerEocene samples contain also volcanic glass and asiliceous component, sometimes radiolarians, some-times diatoms. The amount of siliceous material andvolcanic glass increases by Core 25 in which a volcanicbreccia was found embedded in the foraminiferal ooze.Radiolarians are very abundant and the foraminiferaare only moderately well preserved. Preservationimproves slightly above Core 25 and the siliceous andvolcanic components are gone from the residues;however there is abundant fragmentation of theforaminifera. Beginning in Core 22 and continuingthrough Core 20 preservation deteriorates; moreforaminifera are dissolved out of the sediment, and theresidues are chalkly. Within this interval there areoccasional levels where preservation is markedlyimproved, for example, Sample 21, CC. Also through-out this interval mixing of faunas is common andconfusing.

The lower Oligocene shows evidence of dissolution.Occasionally the larger size fraction of the sediments isgone, leaving only small fossils and the brokenremnants of the larger fossils. Preservation improveslater in the Oligocene, although there are still manybroken or corroded specimens. A reincursion of radio-larians occurs in Cores 17 and 18 and continues into thelower Miocene.

The Miocene is generally moderately to wellpreserved, although some levels are particularly chalkyand contain many fragmented foraminifera. Althoughpreservation is generally good in the upper Miocene,episodes of solution of the sediments are attested to bypeeled Sphaeroidinellopsis spp. which have lost their

575

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MVP20

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P17

P16

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P13

P12

PU

P10

P9

P8

P7

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P5

P4

P3

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Leg 3

Site 16

Leg 3

Sites 17,17A, 17B

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Leg 3

Site 19

Leg 3

S i te 20A, B, C

Leg 3

Si te 2 1 ,21A

Leg 3

Site 22

Leg 14

Site143,144

Leg 14

Site 142

Figure 4. Stratigraphic columns of Tertiary age recovered during Legs 39, 3, and 14 in thecentral and south Atlantic. Black areas represent cored interval. Where any part of a plank-tonic foraminiferal zone was recovered, the black area was extended to the upper and

576


Leg 14 Leg 14 Leg 39 Leg 39 Leg 39 Leg 39 Leg 39 Leg 39

Site 141 Site 140 Site 354 Site 355 Site 356 Site 357 Site 358 Site 359

4148 m 4483 m 3366 m 4549 m 3175 m 2086 m 4962 m 1655 m

Hiatuses

(South A t lan t i c )

% of section cored

Figure 4. (Continued), lower limits of that zone. Within-core hiatuses are signified byjagged lines above and below the hiatus. The hiatus curve is based on the percentageof sites where sediment was retrieved and in which some part of the stratigraphicsuccession was missing.

577

A. BOERSMA

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I S1 ε

o oo o

Figure 5. Ranges of selected planktonic foraminifera during the Neogene at Site 356 on the Sao Paulo Plateau.

smoother shiny outer coating and exhibit, rather,rough, porous surfaces. There is also a great deal ofmixing in these faunas, due in part to the "soupy"character of the sediment in the core barrels. Pliocenefossils are well preserved, although some corrosion isevident in nearly every sample.

Paleogene Zonation

Zonation of the Paleocene was based on the standardzonation (Berggren, 1972); ranges of the most im-portant planktonic foraminifera are shown in Figure 6.

Briefly, the Paleocene zonal fossils are all easilyrecognizable. In the Eocene the keeled globorotaliidsare relatively rare. Zone P.7 was recognized by theoverlap between G. "M." subbotinae and very smallspecimens of G. "Af." aragonensis. G. "M." formosawas not found. The fauna of this zone is dominated bythe acarininids. The overlying Zone P.8 contains trueG. "M." aragonensis, the first bullate species, but no G."Af." subbotinae. Above the hiatus spanning Zones P.9and P10, Core 26 contains primitive Globigerinatheka,Truncorotaloides pseudotopilensis, "Globigerina"higginsi, and Hanktenina alabamensis. The evolutionaryappearance of G. "M." lehneri occurs in this core. Alsopresent is the first G. kugleri. An influx of new speciesoccurs in Core 23 and includes Globiginatheka index,Globigerina " 5 . " linaperta, and members of the

Catapsydrax martini group. A few specimens of G."M." lehneri persist, but keeled forms are very rare. Onthe basis of its fauna, the core could be placed in eitherZone P.I 1 or P. 12, but is considered as belonging in thelatter.

The appearance of Globorotalia "77' cerroazulensisand Truncorotaloides rohri in these faunas is slightlyhigher than recorded in other areas (Cita and PremoliSilva, unpublished range charts) as they do not appearuntil Core 21, which is here considered to belong toZone P. 13, whereas Cita and Premoli Silva record theseforms as appearing in the G. kugleri Zone (P.ll).Orbulinoides beckmanni was not found at this site, butdeteriorating preservation has apparently resulted inthe loss of many fossils and perhaps species. However,an assignment of Core 22 through Core 20, Section 3 toZone P. 13 agrees well with the nannofossil evidence forZone NP. 16 (Zλ tanii nodifer).

During this time there is a gradual reduction infaunal diversity. Despite mixing, the faunas from Core21, Section 1, contain about 18 typical upper middleEocene as well as several upper Eocene species. In Core20, Section 3, the fauna is reduced to closer to eightspecies, dominated by large Globigerinatheka spp. InCore 20, Section 1, only six, sometimes fewer speciesare found, so the fauna has the overall appearance of anooze of small balls. The same sequence of faunal

578


reduction can be found in adjacent holes from Leg 3,Holes 19 and 20C, both of which recovered the intervaldescribed here (see Figure 4). Only two species, G. indexand "Globigerina" senni were consistently reported inthe anomalous faunas from those sites. Such faunasstrongly resemble some from the upper Eocene of Site277 (Leg 29), in the South Pacific at 52° south. By thetop of the upper Eocene sequence H. alabamensis,Globigerina "5 . " angiporoides, Chiloguembelina, Globi-gerina praebulloides, and G. "7V' cerroazulensis areoccasionally present, along with abundant Globi-gerinatheka spp. These faunas were placed in Zone P. 16on the basis of the occasional presence of Globi-gerinatheka mexicana. The nannofossil Isthmolithusrecurvus Zone was the only one recognized in the upperEocene of the adjacent Holes 19 and 20C, and is theonly one recovered at Site 357, all of whichcorroborates the placement of these sediments inforaminiferal Zone P. 16.

Above the Eocene/Oligocene boundary hiatus, theOligocene sequence contained the zonal index fossilsfor the recognition of Zones P. 19 through P.22.Globigerina angulisuturalis occurs rather low in thisOligocene succession and resembles the higher latitudeforms of Jenkins (1971). Two forms of Globorotalia"77' nana were found at this site; G. "77' nana pseudo-continuosa was found in Cores 16 through 10. Globi-gerina euapertura occurs from Core 19 into Core 13 inthe lower Miocene. Globigerina "S." angiporoides, firstencountered in the middle Eocene, continues into thebottom of Zone P.21 in Core 18. Also in Core 18 Globo-rotalia "77' opima opima and Chiloguembelina cubensisbecome extinct at the same level. According toBerggren (1972) Chiloguembelina should becomeextinct during Zone P.21, the top of which is char-acterized by the presence of G. "77' opima opima afterthe extinction of Chiloguembelina; Zone P.21 is there-fore considered incomplete. However this sequence ofextinctions may be a function of latitude.

Neogene ZonationThe ranges of selected Neogene foraminifera are

shown in Figure 7. For a more complete discussion ofthe late Neogene foraminifera, see Berggren (thisvolume). The foraminifera were zoned according to astandard low latitude zonation; however because of thepresence of higher latitude forms, it was possible torecognize the limits of several of the higher latitudeNeogene zones of Jenkins (1971) and Kennett (1973).Figure 8 depicts the limits of those recognizable zonesagainst the nannofossil and foraminiferal zonationemployed in this volume, as well as the upper Neogenezones defined in this volume by Berggren. This latterzonation agrees well with the general zonation adoptedin this volume, only it is more precise and proposes theuse of one upper Miocene zone to span parts of whatare designated Zones N.16 and N.I7 in his generalzonation (Berggren, 1972).

The Oligocene/Miocene (P.22/N.4) boundary wasarbitrarily placed in the top of Core 15 just prior to theco-occurrence of Globorotalia kugleri and Globi-gerinoides primordius in Core 14. According to the 1971

zonal scheme of Jenkins, the Oligocene/Mioceneboundary occurs at the top of his Globigerinaeuapertura Zone, whose upper boundary is defined bythe first appearance of Globoquadrina dehiscens. At Site357, the first appearance of G. dehiscens occurs in Core13, thus locating the Oligocene/Miocene boundarysome 35 meters above the boundary used in this report.If the first appearance of G. dehiscens is ecologicallycontrolled, as Jenkins asserts, then there is no reason tosuspect that it will appear anywhere at the same timenecessarily as Australia, and in fact Jenkins (1974)proposes that the G. euapertura, G. dehiscens, and theG. woodi zones all belong in the Oligocene in cores fromDSDP Leg 29.

The three basal zones of Jenkins correlate withplanktonic Zones N.4 and N.5 at this site. TheGlobigerinoides trilobus Zone of both Jenkins (1971)and Kennett (1973) coicides with Zones N.6 throughN.8 at Site 357. Jenkins' O. suturalis Zone correspondsto the base of Zone N.I 1, whereas his G. mayeri Zonecorrelates with all of Zones N.12, N.13, and N.14 atthis site. It then becomes difficult to locate theremainder of Jenkins' zones. The two upper Miocenezones, G. miotumida and G. miozea sphaericomiozea,are defined on the basis of forms not found at Site 357.The uppermost zone, G. inflata, however, can belocated in Core 2 and falls within nannofossil ZoneNN16 at this site. It also correlates with the base ofBerggren's PI.3.

The base of Kennetfs G. trilobus Zone, the lowest inhis 1973 subtropical zonation, occurs within Core 10.The zone spans Zones N.6, N.7, and N.8 as defined inthis report. The O. suturalis Zone falls in the base ofN.ll.

The overlying G. mayeri Zone, defined on the totalrange of the nominate taxon correlates with parts ofN.I 1 through N.14 and extends into an unzoned upperMiocene (called the G. conomiozea-G. mediterraneaZone by Berggren, this volume). Although it is possibleto recognize the base of the overlying G. nepenthes Zoneon the extinction level of G. continuosa, it is not evenbroadly equivalent to the G. nepenthes Zone (N.14)which terminates towards the bottom of Core 5 whileKennetfs G. mayeri Zone begins in section 2 of Core 5.According to the criteria and ranges shown by Kennett,it is impossible to recognize his G. continouosa Zone,which should overlie the G. mayeri Zone, but underliethe G. conomiozea Zone. Similarly, the base of G.conomoizea at this site is equivalent to the base of the G.nepenthes Zone, and thus they are impossible toreconcile. The overlying G. puncticulata Zone can berecognized in Core 3 and corresponds to that part ofCore 3 before the first appearance of G. crassaformis.The G. puncticulata Zone is thus equivalent toBerggren's Pl.lc and P.12, as well with the middleportion of N.19 and nannofossil zones NN.13-NN.15and part of NN.16. Throughout the rest of the zonesthere is little correspondence between the upperNeogene nannofossil foraminiferal zonal boundariesand the zones of Kennett. The exception is acorrespondence between Kennetfs G. truncatulinoides-tosaensis Zone and Zone N.22 as defined in thisvolume.

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Site 357 Paleogene Planktonic Foraminifera

Figure 6. Stratigraphic ranges of selected Paleogene planktonic foraminifera at Site 357 on the Rio Grande Rise.

580



581

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Site 357 Neogene Planktonic Foraminifera

Figure 7. Stratigraphic ranges of selected Neogene planktonic foraminifera at Site 357 on the RioGrande Rise.

582


IS I

o S

S


Kennett considers Jenkin's (1971) G. inflata Zone,based on the first appearance of G. inßata, to cover theentire Pliocene. However, the base of G. inflata both inKennetfs Leg 21 material and at Site 357 lies in theupper Pliocene.

Unusual Neogene Planktonic Foraminifera

Site 357 contains generally well-preserved Neogenesubtropical planktonic foraminiferal faunas. In thelower Neogene there is a predominance of species of thegenus Globoquadrina. At lower levels G. venezuelanaand later G. dehisçens are abundant in most samples.During periods of temperature change there appear tobe fluctuations in the abundance of globoquadrinidsrelative to the genera Globigerina and Catapsydrax. Forexample during times of temperature increaseCatapsydrax decreases in abundance and Globigerinawoodi increases. Such fluctuations during one period oftemperature increase in the early Miocene are shown byBoersma and Shackleton (this volume).

The unusual, large planktonic species, Globi-gerinoides mitra, is present, usually accompanyingGlobigerinopsis spp., from Zone N.7 through theMiocene. Globigerinoides mitra becomes particularlyabundant at the top of the Miocene (for example,Section 3-6).

A unique, spiny form, resembling both the Paleogenegenus Acarinina and the Neogene genus Globoquadrinaappears for a short time in Cores 9 and 10 (Plate 2). Itsspines are actually elongate, sometimes multiplepustules distributed very densely over the test. Thisform appears just during the temperature maximum asrecorded in the early Miocene planktonic foraminifera(see Boersma and Shackleton, this volume.)

In the best preserved samples tiny biserial formsbelonging to the Neogene genus Streptochilus occur.They occur in abundance only in Core 15, Section 2,but are fairly common in samples from the uppermostOligocene into the upper Miocene. These forms areplanktonic, as shown by their 18O values.

DSDP Leg 3 SitesFigure 4 shows the planktonic foraminiferal zones

recovered at Site 357 as well as from several otherwestern Atlantic sites. Hiatuses versus coring gaps aredifferentiated to show that the only hiatus consistentamong these sites occurs across the Eocene/Oligoceneboundary. Most all other Paleogene zones wererecovered at one site or another. The extensive coringgaps in the Neogene allow for little comparisonbetween sites. However, thick Oligocene and earlyMiocene sequences are common to most of these sites.

Paleoecology of Sites 356 and 357The proximity of Sites 356 and 357 suggests that they

may have been subject to the same sort of changingOceanographic conditions through time. As statedbefore, the sequence of events in the planktonic faunas,including change in dominance from one genus toanother, occurs apparently simultaneously at Site 356and 357. We can then briefly reconstruct the changing

583

A. BOERSMA

Core

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Foraminiferal andNannofossil Zones(this volume)

NN17-19

NN16

NN13-15

NN12

unzoned

NN6-7

NN4-5

NN3

NN3?

NN2

NN1

N23

N22

N19

lateMiocene

N13-N14

N12-N11

N7-N8

N6

N5

N4

SubtropicalZonation

Kennett (1973)

Globorotalia

tmmcatulinoides

G. trunβatulinoides-

tosaensis

Globorotaliainflata

Globorotalia

arassaformis

Globorotaliapuntioulata

Globorotalia margaritae

?

Globigerina

nepenthes

Globorotalia

mayeri

Orbulina suturalis

Globigerinoides

tvilobus

New ZealandZonation

Jenkins (1971)

Globorotalia

inflata

Globoratalia

miozea Spheneomiozea

9

9

Globorotalia

miotumida

Globorotalia

mayeri

Orbulina suturalis

Globigerinoides

trilobus

Globigerina

woodi-aonneata

Globigerina

woodii

Globoquadrina

dehisaens

Globigerina

euapertura

(Oligocene)

Foraminiferal ZonesBerggren (this volume)

N23

N22

PI 3

' PI 2 Λ

c

b

a

PI 1

Globorotalia

oonomiozea-

Globorotalia

mediterranea

y MIΛ N

N13N12

Nil

N7-8

Figure 8. Comparison of the temperature zonation (Kennett, 1973) and high latitude zonation (Jenkins,1973) with the zonation of Berggren (1972) as recognized at Site 357. Nannofossil zones (Perch-Nielsen,this volume) and planktonic foraminiferal zonations (Berggren, this volume) are included for the sake ofcomparison.

584


Oceanographic scenario as reflected in the changingplanktonic faunas.

Site 356 lay in the subtropical zone at the beginningof the Tertiary. Contrary to the suggestion of Worsley(1974) that the CCD lay in the photoic zone across theCretaceous/Tertiary boundary, rich faunas of plank-tonic foraminifera were accumulating during the veryearliest Tertiary at a water depth close to 2000 meters(based on a highly speculative model of continuoussinking for this site). Paleocene faunas are rich andwell-preserved and attest to the stability of the site atthis time as well as to moderate temperatures in thePaleocene, in the subtropical zone. Site 357 records atemperature of close to 16° for surface zone waters inthe Paleocene, top of Zone P.I (Boersma andShackleton, this volume).

A fairly continuous Paleocene sequence (at least toZone P.3) accumulated at both sites, althoughpreservation is markedly different between the twosites. At this time both sites must have been movinggradually northward.

The hiatus from the later Paleocene across the Paleo-cene/Eocene boundary suggests a change in bottomcirculation vigor at this time. Loss of sediments of thisage is anomalous with respect to other areas of theAtlantic, where rich foraminiferal faunas of earliestEocene age are preserved in abundance (Premoli-Silva,in preparation). The elimination of keeled forms (ZoneP.7) may reflect either the loss of their niche in thewater column with the cooling temperatures, and/orsolution. As the keeled globorotaliids and Chilo-guembelina consistently record the warmest tempera-tures of the Eocene species tested (Boersma andShackleton, this volume) their resistance to solutionmay be low, and thus they may be lost from sedimentearlier than the cooler-dwelling acarininids, forexample. However, the event does imply changedmovement and stratification of water masses during acooler episode in the early Eocene. The markedincrease in the siliceous component of the sediment andthe increase in induration are further indications of analtered water mass. The later appearance of radio-larians at Site 356 than Site 357 may reflect increasedsurface productivity in this general geographic area byZone P.8, which at least, at Site 356 continues intoZone P. 12, but is much reduced by the later middleEocene.

The first appearance of bullate forms at both sitesoccurs in Zone P.8 just prior to the temperature declinein the Eocene. The later appearance of A. pseudo-topilensis and eventually Truncorotaloides spp.coincides at Site 357 with a temporary temperature rise.This may also be the case at Site 356 which containscorrelative faunal events.

The later middle Eocene at Site 356 contains diverse,well-preserved faunas accompanied by radiolarians anddiatoms. The section at this site ends low in Zone P. 13;thus, the faunal changes characterizing the coolestintervals of the later Eocene at 357 do not have theiranalogs here.

The early Miocene at Site 356 so resembles that atSite 357 that temperature events at 357 can be

extrapolated to Site 356 also. At Site 357 a temperatureincrease in the surface zone is reflected in the firstappearance of open-apertured, abundant Globi-gerinoides altiaperturus and unusual spinose morpho-types. A change in the ratio of Globigerina woodi toCatapsydrax spp. results in the increased dominance ofthe G. woodi group. As G. woodi is much less abundantat Site 356, the primary difference between the two sitesis the greater abundance of higher latitude species in theearly Miocene of Site 357. Nevertheless, the firstappearance of G. altiaperturus in abundance and thespinose species suggest a temperature increase in ZoneN.6 also at Site 356.

The extensive hiatus at Site 356 spanning theremainder of the Miocene and early Pliocene, includesthe middle Miocene hiatus common to the SouthAtlantic. The hiatus at Site 356 may then in part berelated to a rise of the CCD and increased vigor ofbottom circulation (Berger and von Rad, 1972) causingthe removal of the middle Miocene in several areas ofthe South Atlantic (see Figure 4).

At Site 357 the Miocene section is complicated andnot easily interpreted. After an extensive lowerMiocene, parts of the middle and upper Miocene areabsent; however, the middle Miocene is betterrepresented at Site 357 than at Site 356. As Site 357 isnot within the path of true bottom water, othererosional forces must be considered responsible for theerosion at this site.

SITE 358

From the Cretaceous into the middle Eocene fourdistinctive faunas occur in the sediments at Site 358.These are:

1) planktonic and benthic faunas together, but lowin species and in small residues; faunas are reduced bydissolution and species show evidence of solution;called a near lysocline fauna;

2) faunas containing only benthic foraminifera, andoccasional fragments of the planktonic foraminiferathat were there before dissolution took its toll;calcareous nannofossils would typically be preservedalso in such a sample; called near CCD sample;

3) residue containing no foraminifera, but a mineralresidue: called the below CCD sample;

4) typical open marine planktonic and benthicfaunas slightly reduced in diversity by solution and/orrecrystallization during diagenesis; called abovelysocline fauna.

Elements of the dissolved planktonic faunas areshown in Plate 2; the planktonics include primarilyacarininids and globigerinids.

Using these broad categories and plotting thefluctuations of these faunas against the calculateddepth of the site results in the data presented in Table 2.

For this table the faunas, as described briefly above,were briefly listed according to which core or level theycharacterized. The ages are taken from the zonationand age scale of Berggren (1972), but are basedprimarily on ages given by the calcareous nannofossils(see site chapter, Site 358) as the foraminifera are notdiagnostic.

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A. BOERSMA

TABLE 2Estimates of the Paleo-CCD and Foraminiferal Lysocline Based on a

Continuous Sinking Model for Site 358 in the Argentine Basin

Core

101111,CC12-212, CC13-113-413, CC14-414-151515-1616, CC

Age(m.y.)

49494952526060606063656770

CalculatedDepth(m)

4100410041003800380036003600360036003500330032002700

TypeFauna

Below CCDBelow CCDNear CCDNear lysoclineBelow CCDNear CCDNear lysoclineNear CCDBelow CCDNear CCDBelow CCDNear lysoclineAbove lysocline

LysoclineLevel

<4100<4100near 3800

near 3600<3600

<3500

near 3200>2700

ApproximateCCD

>4100<4100near 4100

<3800near 3600

near 3600<3600>3500 (near)<3300

Site 358 was drilled on basement estimated to liebetween magnetic anomalies 32 and 33 (Ladd, 1974).As the drilling at the site stopped approximately 50meters above basement (see Site 358 Site Summary) asjudged from the seismic profiles, and the oldest fossilsat the site are latest Campanian/early Maestrichtian inage, we can use a rough estimate of 2700 meters for thedepth of the site at the ridge in the latest Campanian.From the age/depth relationships inherent in theMcKenzie-Sclater (1971) model it is then possible toderive the depths of the site at various times as follows:

Core 16, 70 m.y. early Maestrichtian, = 2700 metersCore 15, 67 m.y., middle Maestrichtian, = 3200metersCore 14, 60 m.y., NP.4 (nanno zone) 3500 meters,etc.From the table it is apparent that after the early

Maestrichtian, this site continuously intersects either apaleolysocline or a paleo-CCD, and the times ofintersection give evidence of the paleodepths of thoseOceanographic features in the early Tertiary and latestCretaceous at this site (Table 2).

Comparison of our estimates ot the CCD with thosepublished by Berger and Winterer (1974) and Ramsay(1974) shows that estimates from Site 358 areconsistently shallower than those proposed by Ramsay.According to his estimates for the early Tertiary of theAtlantic, our site would always have lain above hiscompensation depth and should not show this degree ofdissolution, even in the late Eocene when according toour interpretation, Site 358 sank permanently below theCCD.

Berger and Winterer's estimates for the centralAtlantic begin at 50 m.y. and thus overlap by but 7 m.y.with the time of carbonate deposition at our site. Theirestimates for the paleo-CCD at close to 3600-3800meters between 50 and 45 m.y. accord well with theestimates from Site 358 except in the case of our Core11, whose faunas indicated deposition closer to theCCD which, if the depth estimates are nearly accurate,would have lain closer to 4100 meters than Berger andWinterer's estimated 3600 meters.

Our site is considered to have sunk permanentlybelow the CCD by the later Eocene. At this time, the

CCD presumably was located below 4300 meters.Differences between estimates from Site 358 andestimates of Berger and Winterer or Ramsay may resultfrom the roughness of this estimate based on an averagedepth near the ridge or from the fact that this area ofthe South Atlantic had different CCD depths than thegeneral estimates because of its position at higherlatitude and within the direct influence of the bottomwaters generated around Antarctica.

SITE 359Because of the large coring gaps at this site, only

small sections of any one age were recovered. TheMiocene-Pliocene recovered at this site resembled thatat Site 357. This is not surprising as the two sites lie atapproximately the same latitude.

The most interesting sequence of faunas is that of theEocene. The planktonic faunas include Hantkeninaalabamensis, G. angiporoides, Chiloguembelina sp.,Pseudohastigerina micra, Globorotalia "71." centralis,Catapsydrax unicavus, Globigerinatheka kugleri,Globigerinatheka barri, and Globorotalia "7 . " opimanana. The outstanding feature of this fauna is theabundance of H. alabamensis.

Benthic faunas include many species also found atSite 357 as well as a significant component ofpresumably shallower water benthic foraminiferaoriginally described from the Eocene of the AmericanGulf Coast (Cushman, 1935). The benthic fauna lacksthe key genera Nuttallides and Globocassidulina, but hashigh numbers of Robulus and large rectilinear forms.Accompanying this fauna is some invertebrate debris,including bryozoan and pelecypod remains.

In order to lend some evidence toward the sinkinghistory of this site, an estimate of the depth of Core 3was made based on the benthic faunas as well as thehigh abundance of Hantkenina. Based on the problemof redeposited material, two solutions are possible. Ifthe large benthics and invertebrates are out of placethen the site could have lain at a depth less than 357;i.e., less than 1500 meters but greater than the shelf orupper slope. A realistic estimate then would be about900 meters.

586


If, on the other hand, all the fauna is in place, thenthis site must have lain close to the shelf break or upperslope. The great abundance of planktonic fossils is hardto reconcile with this idea, although the prominence ofHantkenina is not. The depth of the site then in the lateEocene would have been closer 300 meters.

Paleotemperature measurements were made onbenthic foraminifera from Site 359 (3, CC) as well asfrom Site 357 (Core 21, Section 1). According to theplanktonic foraminifera, both samples belong to thelate Eocene Zone P. 16. At this time Site 357 has anestimated paleodepth of close to 1600 meters and abottom temperature of 5.5°C (+1.5O°/oo). The bottomtemperature at 359 was about 9.5°C (+O.41°/oo). A 4°Ctemperature difference today in the water columnwould mean a depth difference of from 300-500 metersin the Atlantic and closer to 500 meters in the Pacific.The temperature differential, then, would place 359 notat outer shelf depths, but closer to 1000 meters.

The age of Core 3 based on nannofossils andforaminifera is approximately 41 m.y. The age reportedby Fodor et al. (this volume) on the underlyingvolcanics (Core 4) is 40 ± 1 m.y. Thus, given the degreeof error in each estimate, the sediments in Core 3 andthe underlying volcanic rocks are the same age. Fodoret al. consider the volcanics of subaerial origin.However, the foraminiferal evidence suggests that at 41m.y. this site lay at bathyal depths, receivingredeposited shelf or slope material as well as volcanicash from an adjacent volcanic source.

If the site lay close to 1000 meters in the late Eocene,it would have sunk those remaining 655 meters duringthe remainder of the Tertiary. This rate is reasonableaccording to a crustal subsidence model.

ACKNOWLEDGMENTSI would like first to thank Isabella Premoli-Silva who

helped in the preparation of this report not only in hercapacity as shore lab, but out of great kindness and generosityto the writer. Discussions with Bill Berggren, Maria Cita, andJeanne Aubert were very helpful in analyzing faunas. Mycolleagues on the ship N. Kumar, F. McCoy, and H.Zimmerman shared many useful insights and interpretationsof sedimentologic and seismic problems; J. Thiede and H.Zimmerman kindly provided additional calcium carbonateanalyses. Enrico Bonatti provided information on geo-chemical analyses of sediments and sea-floor tectonics,among other things.

Trudy Wood, Anne Gilbert, Mark McCoy, EricTrachtenberg, and Jo Ann Weinrib all kindly gave technicalassistance. Dee Breger provided the SEM photographs. The

author is supported by Grant Des-74-24110 from theNational Science Foundation.

REFERENCES

Beckmann, J.P., 1972. Foraminifera and some associatedmicrofossils of Sites 135-144. In Hayes, D.E., Pimm, A.C.,et al., Initial Reports of the Deep Sea Drilling Project,Volume 14: Washington (U.S. Government PrintingOffice), p. 389-421.

Berger, W.H. and Winterer, E.L., 1974. Plate stratigraphyand the fluctuating carbonate line. In Hsü, K.J. andJenkyns, H. (Eds.), Pelagic sediments on land and underthe sea: Spec. Pub. Internat. Assoc. Sedim., v. 1, p. 11-48.

Berggren, W.A., 1972. A Cenozoic time-scale—some implica-tions for regional geology and paleobiogeography:Lethaia, v. 5, p. 195-215.

Cita, M.B, Nigrini, C , and Gartner, S., 1973. Bio-stratigraphy. In Ryan, W.B.F., Hsü, K.J., et al., InitialReports of the Deep Sea Drilling Project, Volume 13:Washington (U.S. Government Printing Office), p. 391-413.

Cushman, J.A., 1935. Upper Eocene foraminifera of theSoutheastern U.S.: Washington (U.S. GovernmentPrinting Office), Prof. Paper 181.

Fleisher, R.L., 1974. Cenozoic planktonic foraminifera andbiostratigraphy, Arabian Sea, Deep Sea Drilling ProjectLeg 23A. In Whitmarsh, R.B., Ross, D.A., et al., InitialReports of the Deep Sea Drilling Project, Volume 23:Washington (U.S. Government Printing Office), p. 1001-1072.

Jenkins, D.G., 1971. New Zealand Cenozoic planktonicforaminifera, New Zealand Geol Surv. Paleontol. Bull.,v. 42, p. 1-278.

Jenkins, D.G., 1974. Cenozoic planktonic foraminiferalbiostratigraphy of the southwestern Pacific and TasmanSea—DSDP Leg 29. In Kennett, J.P., Houtz, R.E., et al.,Initial Reports of the Deep Sea Drilling Project, Volume29: Washington (U.S. Government Printing Office),p. 449-469.

Kennett, J. P., 1973. Middle and Late Cenozoic PlanktonicForaminiferal Biostratigraphy of the SouthwestPacific—DSDP Leg 21. In Burns, K.E., Andrews, J.E., etal., Initial Reports of the Deep Sea Drilling Project,Volume 21. Washington (U.S. Government PrintingOffice), p. 575-639.

Ladd, J.W., 1974. South Atlantic sea floor spreading andCaribbean tectonics: Ph.D. Thesis, Columbia University,New York.

McKenzie, D. and Sclater, J.G., 1971. The evolution of theIndian Ocean since the late Cretaceous: Geophys: J. Roy.Astron. Soc, v. 25, p. 431-528.

Worsley, T., 1974. The Cretaceous-Tertiary boundary eventin the Ocean, Studies in Paleo-oceanography: In Hay,W.W. (Ed.), Soc. Econ. Paleontol. Mineral. Spec. Publ.,v. 20, p. 94-125.

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PLATE 1

Figures 1-3 Transitional forms to Globoconusa daubjergensis;Site 356, Core 29, Section 3.

1. ×705.2. X695.3. X745.

Figures 4, 5 Globigerina "Subbotina" triloculinoides; Site 356,Core 29, Section 3.4. X570.5. X600.

Figures 6-8 "Globigerina" eugubina; Site 356, Core 29, Section3.6. X500.7. X475.8. X500.

Figures 9-12 "Globigerina" fringa; Site 356, Core 29, Section 3.9. X500.

10. X640.11. X475.12. X450.

PLATE 2

Figures 1,2 Acarinina primitiva; Site 358, Core 12, Section 2,both X248.

Figures 3,4 Bullate Globigerina trilocularis', Site 358, Core 12,Section 2.

3. X232.

4. X193.

Figure 5 Hantkenina alabamensis; Site 359, 3, CC, X128.

Figures 6, 7 Globorotalia plesiotumida; Site 357, 3, CC, X270.Figures 8-10 Globoquadrina sp., spiny form; Site 357, Core 10,

Section 1.8, 9. X137.

10. XI16.

(see page 590)

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PLATE 1


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A. BOERSMA

PLATE 2

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26. CENOZOIC PLANKTONIC FORAMINIFERA —DSDP LEG 39 … · Cenozoic planktonic foraminifera were...

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