4. SITE 355: BRAZIL BASIN The Shipboard Scientific Party · 8/11/1974 · altered in contact with ba-salt. Aphyric tholeiitic basalt with numerous calcite veins. of the unit (Cores

4. SITE 355: BRAZIL BASIN

The Shipboard Scientific Party1

30°N

45°W 15°E

SITE DATA

Date Occupied: 8 November 1974 (1858Z)

Date Departed: 12 November 1974 (1028Z)

Time on Site: 3 days, 15 hours, 30 minutes

Position: 15°42.59'S, 3O°36.O3'W

Accepted Water Depth: 4886 meters (drill pipe measurement)

Penetration: 460 meters

Number of Holes: 1

'K. Perch-Nielsen, Eidg. Technische Hochschule, Zurich, Switzer-land (Co-chief scientist); P.R. Supko, Scripps Institution ofOceanography, La Jolla, California (Co-chief scientist); A. Boersma,Lamont-Doherty Geological Observatory, Palisades, New York;R.L. Carlson, University of Washington, Seattle, Washington; M.G.Dinkelman, The Florida State University, Tallahassee, Florida; R.V.Fodor, University of New Mexico, Albuquerque, New Mexico; N.Kumar, Lamont-Doherty Geological Observatory, Palisades, NewYork; F. McCoy, Lamont-Doherty Geological Observatory,Palisades, New York; J. Thiede, Oregon State University, Corvallis,Oregon; H.B. Zimmerman, Union College, Schenectady, New York.

Number of Cores: 22

Total Length of Cored Section: 207.5 meters

Total Core Recovered: 118.1 meters

Principal Results: At Site 355, sediment 449 meters thickoverlies a typical oceanic tholeiite basalt basement. TheTertiary section comprises muds, mudstones, and zeoliticmuds. Silt and sand laminae indicate that much of thesection was deposited by turbidity currents. Biogenicmaterial is rare, except for bioclastic turbidites in theMiocene and an Eocene radiolarian mud. Zeolites areparticularly common below 150 meters. At 405 meters, themuds and zeolitic muds unconformably overlieCampanian to lower Maestrichtian calcareous corescontaining veins of sparry calcite. Hiatuses occur in theintervals from the middle to upper Miocene, from middleEocene to lowermost Miocene, and from Maestrichtian toPaleocene. K-Ar dating of the basalt gives an age of 78.1±9 m.y., which is in excellent agreement with theCampanian age of the basal sediment determined bycoccoliths, and provides an accurate date for the oceancrust between anomalies 33 and 34.

BACKGROUND AND OBJECTIVES

Site 355 is in the west central Brazil Basin at latitude15°43'S, longitude 30°36'W, in accordance withrecommendations of the JOIDES Atlantic AdvisoryPanel (Figure 1). A primary objective at this site was todate the basement (presumably oceanic basalt), in orderto date the older end of the magnetic reversal time scaleof Heirtzler et al. (1968). This site is between therecently determined positions of anomalies 33 and 34 inthe Brazil Basin (Figure 2). Up to now, the oldest

CoredInt. Units Lithology0

Age

100-

200^

300•

400-

Z

Z

z

Plio-Pleistocene

Miocene

Eocene

MaestrichtianCampanian

101

SITE 355: BRAZIL BASIN

15°S

20°S

40°W 35°W 30°W

Figure 1. Base map, Site 355. Contours are 200, 1000, 2000, 3000, 4000, 4500, and 5000 mNumbers 1, 2, 3, 4, 5 are in thousands of meters. From Connary and Moody, 1975, Bathymetryof the continental margin of Brazil (unpublished).

reliable date for the reversal time scale is probably theMaestrichtian age (67 ±1 m.y., Maxwell, Von Herzen,et al., 1970) obtained by drilling on anomaly 30 in theSouth Atlantic.

A second major objective was to delineate sedimentfacies as a function of time, in order to aid in compilinga circulation history for the South Atlantic. Seismicprofiles in the area (Figure 3) show about 0.5 sec ofsediment near the proposed site. Sections of the records(e.g., 1900-2000 hr, 22 November, Figure 3) showstratified sediment to basement. The more typicalsection, however, as at the proposed site (2010 hr,Figure 3), is transparent, with only slight apparentlayering in the upper layers. We had estimated about300 meters of Cretaceous and Paleogene biogenic sedi-ments, overlain by about 200 meters of Oligocene andNeogene pelagic clays and occasional fine silts; weobtained these figures by using an estimated basementage of 80 m.y.B.P., the sea-floor spreading crustalsubsidence curve of Sclater et al. (1971), the average

Atlantic accumulation rates for clay, marl, and cal-careous ooze facies (Berger and von Rad, 1972), and anestimated carbonate compensation level for the middleand early Tertiary.

We planned to spot core the pelagic clays and silts,core more closely the lower biogenic section, and corecontinuously beginning at least 60 meters abovecalculated basement, in order to ensure coring of thesediment-basalt contact.

OPERATIONSWe approached Site 355 from Recife, Brazil, on a

heading of 154°T (Figure 4). At 1605Z on 8 November1974, at a point 15°42'S, 30°48'W, we changed courseto 077°T to follow the reference profile (Figure 3), andslowed to 6 knots. A good satellite navigation fix at1626Z showed us to be exactly on the Lamont track,and our approach profile (Figure 5) matched thereference profile. We decided to pinpoint the site in asmall depression in the basement (passed at 1812Z), in

102


-32°W -3IC -30°

-15'

-16° -

-17'

ilk ^^*os

1 & SITEf | 355

%^/J-—-

1

M

—^—^_j 200

GAMMAS

-l-o

-29°-14°

-I5C

- -I6C

-17°-32° -31° -30° -29°

Figure 2. Location of Site 355 in relation to anomalies 33and 34 in the Brazil Basin. Position of anomalies identi-fied by Roger Larson (personal communication). TrackC1604 is the reference seismic reflection profile.

order to sample the oldest possible sediments. At 1825Zwe executed a Williamson turn, and came back onto areciprocal heading of 259°T at 1837Z. We dropped thebeacon under way at 1858Z, retrieved gear, and cameback over the beacon.

Coring was intermittent to a depth of 338 meters, andcontinuous below that (Table 1). The entire section cutquickly; fluctuations in coring and drilling ratesresulted mostly from stickiness of the clay formations.

We did not use the heave compensator because (1)the sediment cover was fairly thin and we expected nohard layers, (2) we needed to penetrate basement onlyshallowly, and (3) the weather was fine. We weretherefore able to drill double joints of pipe and reducethe time required for connections. We lost six hoursbecause the positioning computer malfunctioned.

No survey seemed necessary after we finished at thesite; we left Site 355 at 1028Z, 12 November 1974, andheaded toward Site 356 on course 218°T.

LITHOLOGYWe took 21 cores in the 449-meter-thick sedimentary

section overlying basalt in the Brazil Basin. The lower-most core contains basalt and the sediment/basaltcontact. The upper 338 meters (Cores 1-9) werediscontinuously cored, but the remainder of thesediment section (Cores 10-22) was continuously cored.

Two sedimentary units have been defined: muds,mudstones, and zeolitic muds in the upper portion(Unit 1), unconformably overlying a nannofossil ooze(Unit 2); the latter is in apparently conformable contact(see Fodor and McKee, this volume) with tholeiiticbasalt.

Q

—cou•804b

IRO

•8

3g

tK

•2-CS

I

§3

iZ

103


15°20

15°30'

15°40'

15°50

16C

Approach o/c 154°T

S/N #525

S/N #526

S/N #527

1716Z1830Z execute

1605Z

c/c 077°T

r/s to 6 kt

Williamson

1858Z Drop

/Departure o/c 218°Tff 1028Z 12 Nov. 74

Beacon Site 355

30°50' 30°40' 30°30' 30°20'

Figure 4. Glomar Challenger track in the vicinity of Site 355.

In general, the entire Tertiary here (represented byUnit 1) seems to have been characterized by pelagic andturbidity current sedimentation below the carbonatecompensation depth (CCD), after a Late Cretaceousregime of deposition of calcareous material (repre-sented by Unit 2) when this site was above the CCD.The units are summarized in Table 2; the general varia-tion in dominant sediment components is given inFigure 6; detailed variations and changes in thesecomponents from smear-slide analyses are graphed inFigure 7.

TABLE 1Coring Summary, Site 355

Core

123456789

10111213141516171819202122

Total

Depth BelowSea Floor

(m)

53.0-62.5110.0-119.5167.0-176.5214.5-224.0243.0-252.5262.0-271.5281.0-290.5300.0-309.5319.0-328.5338.0-347.5347.5-357.0357.0-366.5366.5-376.0376.0-385.5385.5-395.0395.0404.5404.5414.0414.0423.5423.5433.0433.0442.6442.5452.0452.0460.0

LengthCored

(m)

9.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.58.0

207.5

LengthRecovered

(m)

9.36.97.63.39.59.54.23.06.92.05.66.43.76.35.72.18.04.63.32.01.56.7

118.1

Recovery(%)

98738035

10010044327321596739666022

844835211684

57

Unit 1The upper 405 meters of the Brazil Basin sedimentary

sequence forms Unit 1 (assuming that it extends up-section to the sediment-water interface), which consistsof low-carbonate unconsolidated muds, zeolitic muds,and some mudstones near the base of the section.Colors, generally brown, become an alternatingsequence of yellow-brown and green-gray in the middle

MOO

Lf>O f>

NJO

σ

LOLOCO

LU

' - 6

Figure 5. Glomar Challenger approach profile, Site 355.

104


TABLE 2Lithologic Summary, Site 355

Unit Cores

Depth BelowSea Floor

(m)Thickness

(m) Age Description

1 1-17 (Section 2) 0-405 405

1A 5 (Section 1-2) 234 (?) -245

IB 6,CC-7 271-284 (?)

2 17 (Section 2) -21 405-449

IK?)

21-22 449-

Pleistocene toEocene

Middle Eocene

13(?) Early Eocene

44 Late Cretaceous(Maestrichtian-Campanian)

11+ Cretaceous(Campanian)(78.1±9 m.y., K/Ar))

Unconsolidated mud,zeolitic mud, mudstone(brown, red-brown,green-gray); with turbi-dites in upper portion;increasing zeolite contentdownsection; mudstonesonly near base.

Unconsolidated radiolarianmud (olive-gray).

Unconsolidated dolomitemud-zeolitic dolomite mud(green-gray).

Nannofossil ooze (palebrown); with numerous thincalcite veins, lower portionaltered in contact with ba-salt.

Aphyric tholeiitic basalt withnumerous calcite veins.

of the unit (Cores 3-11), then an alternating sequence ofdark red-brown and brown near the base (Cores 12-17).Except for one hiatus (see Biostratigraphy andSediment Accumulation Rates), the entire Tertiary,from the Eocene to the Plio-Pleistocene, is representedby this unit.

Carbonate content varies from 0 to about 10%;locally higher values up to 80% are associated with bio-clastic turbidite sequences in the Miocene and Plio-Pleistocene (Cores 2 and 3), discussed below.Foraminifers, calcareous nannofossils, and biosiliceoustests are rare, except in the bioclastic turbidites and inthe Eocene radiolarian mud forming Subunit 1A, alsodiscussed below. Abundant coarse micarb occurslocally. Dolomite is abundant only in the dolomite mudof Subunit IB (see below).

In general, Unit 1 is a silty clay with local sand andsilt laminae, and contains substantial amounts ofquartz and feldspar. Zeolites are abundant (5%-60%from smear-slide estimates), particularly in the lower250 meters of the section.

The upper portion of this predominantly terrigenoussequence is brown mud (Core 1), in which colorvariations produce a series of pale yellow-brown, lightbrown, and dark brown. Silt content varies from 5% to50% (all values are from smear-slide estimates); averageis between 5% and 10%. Clays vary from 40% to 95%,averaging 80%. Calcium carbonate values are low (6%).Biogenic debris comprises 5% or less radiolarians,foraminifers, and nannofossils. Dolomite (0-5%) occurswith micronodules (0-5%), ferruginous material (0-5%),and zeolites (1-15%); zeolites become more abundantdown section. Terrigenous detritus, in addition to thecharacteristically high clay content, is present as quartz(0-15%), feldspar (0-10%), and heavy minerals and mica

(both usually in trace amounts). More silt-sizedcomponents occur in thin laminae, as a result of thehigher concentrations of manganese micronodules andanhedral iron oxides (limonite), along with somequartz, feldspar, and biosiliceous material.

Bioclastic turbidite sequences are interbedded andare apparent (Cores 2 and 3) by their light gray andwhite colors. We sampled only a 65-cm-thickundisturbed portion of these turbidites; the remainderoccurs in a drilled breccia. Individual units appear to bethin (2-8 cm). Compositional and textural variationswithin each unit (Figure 8), and the generally fine-grained sediment texture and the thinness of individualunits, imply a distal turbidite sequence. Thin bluishzeolitic muds (containing up to 5% pyrite) at the tops ofthe sequences may represent pelagic brown mudsreduced by rapid burial under successive bioturbidites.Biogenic material is predominantly calcareousnannofossils (up to 60%), coarse micarb (up to 40%),and foraminifers (up to 15%). In some drilling brecciaclasts, disturbed foraminifer sands apparently formedbasal portions of some bioclastic turbidite sequences.Many benthic foraminifers and other invertebratefossils, as well as calcareous nannofossils in these units,are also displaced. (See Biostratigraphic Summary.)

Beneath the turbidite sequence, Unit 1 is character-ized by a higher zeolite content (10%-55%; averageabout 23%), and is alternately red-brown and green-gray. As elsewhere in this unit, calcareous and bio-siliceous material, except the bioclastic turbidites, doesnot form a significant component of these zeoliticmuds. The bulk of the sediment is clay(montmorillonite with some illite and kaolinite; seeZimmerman, this volume); quartz and feldspar arepresent, but in small quantities. Where dolomite is

105


GENERALSEDIMENT COMPONENTS" CORE UNIT LITHOLOGY AGE

:AR CONTACT

Z

0 10 20 30 40 50 60 70 80 90 100

7j-L-n-rurfr-u- i-n_ri-ru-u-•r

-z

Z - -" z .

-z-

2 .

Z

P L I O -PLEISTOCENE

late

early

middle

early

E. MAESTR.

E. CAMPAN IAN

78.1±9 m.y.(K/Ar)

I <*> j Forams

j -±- 1 Nannos [|

*AM0UNTS LESS THAN 5% NOT PLOTTED

Auth. C03 I Z Z | Zeol i tes

Dolomite I_JT-_H Clays

| Fe Ox + Opaques

+ Sand (Quartz,Feldspar, Mica)

Figure 6. Lithologic summary, Site 355.

106


present, it occurs as rhombs with central corescontaining coarse micarb grains similar to those foundelsewhere in the mud.

We define two subunits of the lower to middleEocene: a radiolarian mud (Unit 1A) and a dolomitemud (Unit IB) (Table 2). The radiolarian mud (40%radiolarians) forms the upper 1.5-meter portion of Core5. The actual thickness of this biogenic mud may be 8meters, if the decreased drilling rate at 234 metersmarks the top of the unit. Dolomite mud sampled in thecore catcher of Core 6 is interbedded with the siliceousmuds in Core 7. Assuming continuity of the sedimentbetween cores, this dolomite-rich sequence (average50% dolomite) is about 13 meters thick. Above thedolomitic unit, a fragment of dolomite rock (2 by 4mm) occurs in Core 6.

Intercalated in the zeolitic mud sequence (from about246 m to the base of Unit 1 at 405 m) are numerous thinlaminae of quartz-zeolite sands, silts, and muds. Theirnumber increases markedly toward the base of the unit.They may contain up to 70% sand-sized or silt-sizedgrains; an average texture would be about 25% sand,25% silt, 50% clay, or a sandy mud. Typically, theselaminae contain between 2% and 60% quartz (average40%), between 2% and 50% zeolite (average 25%), up to10% feldspar (average 5%), and less than 5% of heavyminerals, mica, and micronodules. Zeolites tend to beuntwinned and larger than those common in thesurrounding zeolitic muds. They are clinoptilolite (seeMcCoy et al., this volume), and appear to have grownauthigenically in contact with quartz grains (seeKrinsley and McCoy, this volume). We regard thequartz-zeolite laminae as basal portions of individualturbidites, on the basis of their displaced biogenicmaterial (see Biostratigraphy), the surface mor-phologies of some quartz grains (Krinsley and McCoy,this volume), and ratios of clay minerals (Zimmerman,this volume).

At 357 meters (Core 12), Unit 1 becomes analternating sequence of greenish-gray and brown mudcontaining some mudstones. The thin sand and siltlaminae here appear to be less sandy (average 3%) andless clayey (average 30%), but contain considerablymore silt (average 65%). Within a 48-meter interval, atleast 60 of these laminae occur; each is only about 0.5 to2 mm thick.

Unit 2

A calcareous Upper Cretaceous sequence (Unit 2)lies beneath the muds and zeolitic muds of Unit 1. It is alight gray-brown nannofossil ooze, 44 meters thick(Cores 17 through 21), in contact with tholeiitic basalt.The lower contact is altered in large degree to micriticlimestone and may have been baked.

Calcium carbonate is high (44% to 84%);nannofossils range from 20% to 70% (average 40%) andcoarse micarb ranges from 25% to 80% (average 50%).Terrigenous components are relatively scant: 0-20%silt-size detritus (average about 6%), most of which isquartz (0-20%, average about 6%). Clay minerals forman equally sparse constituent (0-20%, average 8%).Trace amounts of micronodules, mica, heavy minerals,limonite, and zeolites are present.

Within Unit 2, 21 veins of sparry calcite occur (X-radiography suggests that more veins may be presentbut extensively broken by drilling). Vein thicknessesrange from 3 to 13 mm. Thirteen veins are within andassociated with reddish-brown ferruginous nannofossiloozes. This suggests an intimate relationship; perhapsmetalliferous components were transferred to the hostsediment by hydrothermal solutions that (may have)formed the calcite veins. These calcite veins also occurin the underlying tholeiitic basalt.

BasaltBasalt was first cored at a subbottom depth of 449

meters, and a total of 7.5 meters was recovered. Theupper 10 cm of the basalt core is yellowish-gray to darkgray, owing to extreme seawater alteration. Below theweathered zone, the basalt is medium to dark gray andin general is aphyric in texture.

The basalt is highly fractured and veined with calcite,particularly at the top; one vein, however, is deep green,and consists of prochlorite. Local areas, generally alongfractures, contain reddish iron staining. Glassy zonesare uncommon and may or may not represent tops ofseparate flows. Where present, they are thin (< 1 cm)and often mixed with calcite. Local brecciated zonesalso occur.

Thin-section examination shows phenocrysts andmicrophenocrysts of Plagioclase and clinopyroxene,sometimes as glomerocrysts, in an intergranulargroundmass of the same phases. Titaniferous magnetiteis also present in the lowermost sections, and relictolivine crystals (highly oxidized) occur infrequently inthe uppermost core. Alteration is most apparent in thereplacement of clinopyroxene by clay minerals.

DiscussionThree findings are particularly significant in the

sediments and sediment associations from this section:(1) the general paucity of calcareous sediments, (2) thehigh concentration of zeolites in the section, particu-larly in the middle and lower portions of Unit 1, and (3)the numerous thin laminae of bioclastic detritus, andzeolites and quartz within the zeolite muds of Unit 1.

The absence of a thick calcareous sediment unit atthe base of the section (the calcareous sequence of Unit2 is only 44 m thick) implies that the sea-floordepositional environment in the Brazil Basin has beenbeneath the CCD since Late Cretaceous time. Pistoncore data and information from other DSDP sites inthis area reinforce this implication (see McCoy andZimmerman, this volume).

Thus, the depositional history in the Brazil Basinbegan during the Late Cretaceous (Campanian) withaccumulation of nannofossil oozes (Unit 2) in contactwith basalt of similar age (see Fodor and McKee, thisvolume). This calcareous material now forms only athin veneer over the basaltic basement, and is separatedfrom the overlying muds of Unit 1 by a hiatus. Biogenicmaterial indicates dissolution of calcareouscomponents as a result of dissolution since the BrazilBasin passed beneath the CCD during the Maestricht-ian. The large variation in carbonate concentrations

107


CORES AGE

Site 355

UNIT LITHOLOGY

SUB BOTTOM

DEPTH

(ml

2 0 0 -

PLIO-PLEISTOCENE

late

late early

early

OLIGOCENE?

late-middle

early

early

PALEOCENE

MAESTRI CHTI AN

CAMPAN I AN

-j

I —

— Z —

— —k^_^*\_

— z —

- z —- z— z

- z —

— z —

— z —

RADIOLARIANMUD

DOLOMITEMUD

NANNOOOZEwith

calcite veins

BASALT

100

200

234(?)

245

271

284 (?)

405

449

% CaCO3

0 20 40 60

CLAY

l:V18-30Biscaye, et a l . ,

t?:V12-12in press

3:V20-224 Zimmermanper. com.

TEXTUREsand/silt/clay

20 40 60 80

CLAY

11

BIOGENIC COMPONENTS

% F0 RAMS

( 5%)

20 40 60 i

% NANNOS

( 5%)

20 40 60 8

% BIOSILICEOUSMATERIAL

20 40 60

Figure 7. Sedimentary components of Site 355 cores. Data are from smear-slide estimate, except CaCOj percentages, whichare based on laboratory analysis.

(see Figure 7) may also reflect differing degrees ofdissolution.

During the Late Cretaceous, hydrothermal solutionsenriched in CO3-2 and metalliferous cations—perhapsimplying proximity to the spreading center—migratedup through the calcareous oozes and produced meta-somatic calcite veins and their associated red-brownferruginous (?) zones.

With the absence in sediments of a significantcarbonate component, the muds of Unit 1 became thedominant sediment type in the Brazil Basin. By theCampanian, significant influx of terrigenous detritushad already occurred in the northern Brazil Basin (seeSites 23 and 24 in Bader, Gerard, et al., 1970); and bythe Eocene, this influx had also occurred farther south,at Site 355. Our drilling results indicate that the influx

108


\

TERRIGENOUS COMPONENTS

% QUARTZ

20 40 60

% FELDSPAR

20 40 60 8(

% IRON OXIDES

20 40 60 80

s7

AUTHIGENIC COMPONENTS

% ZEOLITES

20 40

% DOLOMITE

20 40 60

% AUTHIGENICCARBONATE

20 40 60 80

Figure 7. Continued.

was strong during the early Eocene (lower portion ofUnit 1) and decreased significantly by the middleEocene (middle portion of Unit 1), as shown by thesmaller number of sand and silt laminae up-section. X-radiography supports this contention. Distal clayturbidite sequences are not apparent, so the decrease inthe number of sand-silt laminae does not reflect

dilution by finer materials. Textural data, in fact, implythat there may have been a progressive increase ofcoarser detritus as turbidity current processesdiminished (note that the laminae become sandier up-section). The material forming the laminae wasapparently derived from continental shelf and upperslope areas, as indicated by biogenic components (see

109


bluishZEOLITIC CLAY

brownZEOLITIC CLAY

TEXTURE MINERALOGY NANNOS

% 100 0 % 100 0 % 100 0

AUTHIGENIC

FORAMS CARBONATE ZEOLITES

% 100 0 % 100 0 % 100

burrows

_Jclayr~tsand

ands i l t

•355-2-5-124*

•355-2-5-121

-355-2-5-122

-355-2-5-123

Haken fromunderlying unit

Figure 8. Compositional variations in a bioclastic turbidite, subunit 1A Sample 355-2-5, 121-124 cm.

Biostratigraphy) and quartz grain surface-morpho-logical characteristics (see Krinsley and McCoy, thisvolume). Sediment accumulation rates werecorrespondingly high (see Sediment AccumulationRates).

Detrital mineral assemblages of the turbidites suggesta chiefly volcanic rock source. Quartz grains containvacuoles and some microlites as inclusions, and showstraight extinction. The predominant feldspar appearsto be twinned Plagioclase. There is evidence of bothextrusive and intrusive vulcanism in Brazilian marginalbasins during the Late Cretaceous-Tertiary (Asmus andPonte, 1973); erosion of these volcanics and the lowerCretaceous Parana and the Serra Geral basalts inBrazil, as well as possible erosion of the ColumbiaSeamount Chain, may have provided a source.Orthoclase, hornblende, and micas, present in smallamounts (see Emelyanov and Trimonis, this volume),imply some contribution from the Brazilian Shield.

Later diagenesis in the muds of Unit 1 led to growthof zeolites. The basal sand-and-silt laminae ofturbidites seem to have been especially conducive totheir formation.

Accumulation rates decreased with the decrease inturbidite deposition, until renewed bioclastic turbiditedeposition during the Miocene. Since this calcareousmaterial was emplaced below the CCD (foraminifersand nannofossils suggest dissolution; see Biostrati-graphic Summary), rapid burial must have occurred.This is also indicated by bluish muds that suggest areducing environment consequent to rapid burial of theunderlying muds by the bioclastic deposits.

There is some evidence for continued turbiditycurrent deposition in the upper portion of Unit 1 in thePlio-Pleistocene. Although X-radiography does notindicate turbidite structures here, displacedforaminifers occur (see Biostratigraphic Summary) inthe core-catcher sample of Core 1, where the quartzcontent increases markedly (see Emelyanov andTrimonis, this volume). Deposition rates also appear toincrease (see Sediment Accumulation Rates). Somevolcanic components occur as volcanic ash or arerepresented by the higher feldspar content (seeEmelyanov and Trimonis, this volume); perhaps theywere derived from the Columbia Seamount Chain orfrom continued erosion of the Brazilian mainland.

GEOCHEMISTRY

We measured pH, alkalinity, salinity, and Ca++, andMg++ contents of 10 interstitial water samples onboardship. Data are presented in Table 3 and Figure 9.

PHYSICAL PROPERTIESThe sediments recovered from Site 355 were in very

poor condition for physical properties determinations.Most of the material consisted of "biscuits" of clay-richmaterial, about one inch thick, and appeared to havebeen compressed in the coring process. The matrix wasmud, presumably derived from drill cuttings. Becauseof the mud surrounding the harder material, weabandoned velocity measurement on materials in splitliners and resorted to the more time-consumingprocedure of cutting and trimming individual pieces of

TABLE 3Summary of Shipboard Geochemical Data

Sample(Intervalin cm)

1-5, 144-1502-4, 144-1503-3,144-1504-2, 144-1505-5,144-1509-4, 144-15011-2, 144-15015-3, 144-15016-2,144-15017-4,140-150

Subdepth(m)

60115170216250325350390398412

pH

7.277.317.126.827.357.707.544.177.127.01

Alkalinity(meq/1)

2.782.713.172.893.763.142.182.082.103.34

Salinity(%o)l

35.234.634.135.233.634.134.234.134.135.2

Ca++(mmoles/1)

14.8817.8224.4327.4433.0938.7240.6150.7645.2944.29

Mg++(mmoles/1)

49.4446.9441.9844.0646.2633.5831.2027.1331.5729.78

110


(mmoles/1)

10 20

Mg++

(mmoles/1)

30 40 50

100

200

Q. 300

400

500

SALINITY

32 33 34 35 36 6.5

pH

7.0 7.5

ALKALINITY(meq/1)

0 1 2 3 4—I 1 1 1

Figure 9. Geochemical parameters (pH, salinity, alkalinity, Ca++, and Mg++ content) of interstitial waters versus depth,Site 355.

hard sediment. The unusually pronounced fissility ofthese sediments posed another difficulty. Manypromising samples were destroyed in trimming, andsampling took a long time. Cut samples were also usedfor 2-minute GRAPE and immersion densitydeterminations. Because of the condition of thesamples, the physical properties measured aboard ship(Table 4) are probably not representative of conditionsin situ.

Downward through the sequence, some correlationsbetween physical properties and lithology are possible(see Figure 10). The transition from mud/clay to zeolitemud at about 150 meters is not apparent, but the zeolitemud shows distinct gradients in velocity (1.54 to 1.80km/sec) and in water content (40% to 26%). That nogradient is apparent in the widely scattered density datamay be a consequence of the poor condition of thesamples.

The mudstone bottom section of Unit 1 and thenannofossil ooze of Unit 2 both show strong gradientsin velocity, density, and water content. The scatteredvelocity data for the mudstone are consistent withobservations for mudstones recovered at other sites (seeSites 356 and 358). The water content of the ooze isdistinctly lower than that of the mudstone unit.

In general, the measured physical properties for Site355 indicate a moderate compaction trend, as shown bythe marked increase in acoustic velocity below about200 meters. A similar trend occurs in water content,and density values increase abruptly below 360 meters.

BIOSTRATIGRAPHIC SUMMARYAt Site 355 we penetrated 449 meters of sediment

which ranges in age from Plio-Pleistocene to

Campanian; hiatuses apparently occur between theupper and middle Miocene, between the lower Mioceneand the middle Eocene, and between the lower Eoceneand the lower Maestrichtian-upper Campanian. Thehole terminated in very fractured and weatheredbasaltic basement. Figure 11 shows the biostrati-graphic units encountered at this site.

The sediments of the first three cores range from thelower Miocene to the Plio-Pleistocene. Planktonicforaminifers and calcareous nannofossils are the mostcommon microfossils; lesser amounts of radiolariansand both larger and smaller benthic foraminifers alsooccur, together with traces of pteropods, ostracodes,diatom remains, sponge spicules, and bryozoan andfish debris.

The nature and associations of these assemblagesstrongly suggest deposition by turbidity currentsoriginating at relatively shallow depths on the Braziliancontinental margin, since Site 355 lay well below theCCD throughout the Tertiary. Mixed with thesebioclastic turbidites are layers of pelagic and hemi-pelagic sediment, but because the cores were intenselydisturbed we could not determine exactly the depth ofthese layers.

Considering the nature of the sedimentarysequence—pelagic sediment interbedded with turbiditycurrent deposits—it is surprising that the data fromboth the planktonic foraminifers and the calcareousnannofossils suggest the middle to upper Miocenehiatus, which also occurs at Site 354 and at severalother South and equatorial Atlantic sites (Leg 3 andLeg 14).

From the top of Core 4 to the bottom of Core 15,radiolarians are essentially the only microfossils

111


TABLE 4Physical Properties Data, Site 355

Sample(Interval in cm)

14,582-5, 982-5, 10234,6534, 1103-5,553-5, 1084-3, 1204-3, 1355-3, 2154,1305-6, 1416-2, 756-3,607-2, 348-2, 958-2, 959-1, 1129-2, 659-3,9594,7510-1, 14210-2, 9111-1, 12112-5, 12614-3, 103144, 8714-5, 14915-2, 7215-3, 2417-1, 12017-2, 13217-3, 126174,6317-5, 6018-1,818-1, 9018-2, 1519-1, 13719-3,65

Depth(m)

58.08116.98117.02172.15172.60173.55174.08218.70218.85246.21248.80251.91264.25265.60282.84302.45302.45320.12321.15322.95324.25339.42340.31348.71364.26380.03381.37383.49387.72288.74405.70407.32408.76409.63411.10414.08414.90415.65424.87427.15

Velocity(km/sec)

1.4871.5281.5711.5391.5421.5571.5591.5871.5781.6421.6411.5751.6551.6291.6821.6811.7251.7141.7351.7161.7591.7591.7461.8031.6741.7811.7191.8061.6141.6511.6441.7431.7311.7541.7751.9005.7911.8441.8681.745

Density (g/cc)

S

1.6711.845

__________

1.840__

1.640_

1.650_—-___

__

1.8401.760

—2.000

_1.9701.9502.030

_

_-

I

———__

1.7001.690

—1.610

—1.640

——

1.640_

1.670———_

1.6501.6101.6901.70

—1.890

—_—__———__—-

G

_

1.7191.9921.6561.6551.6981.6751.7601.771

_1.771

_1.647

——_—

1.727————__——____—_—______-

Wt%

_

37.3343.37

___——_

33.94_

40.15—

31.37———-———

33.3328.3230.0830.97

——

26.9126.2837.8413.2820.3317.1718.1017.6517.98

_17.99

—17.07

S

_

61.4351.04

_—_—_———_—

51.34-—

63.28—

61.69-——_——-—_

51.3456.12

-41.79

—43.5844.7840.00

_

—-

Porosity (1

I

_--———_

59.7060.30

-65.07

—63.28

--

63.28—

61.49--——

62.6965.0760.3054.93

-48.36

—--—-——-_——-

G

_

58.5742.2762.3362.3959.8261.1956.1255.46

-55.46

—62.87

----

58.09--—-——-—-----————-_——-

Acoustic Impedance

S

_

2.552.90

_————---—-

3.00-

2.762.83

-2.86

----—--——

2.972.91

-3.49

_3.463.463.86

_——-

I

_-————-

2.702.67

—2.64

—2.71

——

2.76—

2.86--——

2.882.902.833.17

-3.41

-—-——---——--

G

_

2.633.132.552.552.642.612.792.79

-2.91

-2.73

--—-

2.96--------—---------—---

NOTE: S = syringe technique, I = immersion technique, G = GRAPE.

present. Small numbers of diatom remains occur in theupper part of the section, and fish teeth and fish debrisare common in Cores 14 and 15. Preservation of theradiolarians is generally poor and indicates thatremobilization of opaline silica has occurred. Thesediment ranges from upper middle Eocene in Core 4 tolower Eocene in Core 15. Deposition in this intervalwas continuous and rapid (see Sediment AccumulationRates). The abundant to common radiolarians and thehigh deposition rates agree with the contention ofRamsay (1971) that parts of the Eocene Atlantic wereareas of high productivity, with consequent depositionof siliceous sediments, and that no significantdeposition of siliceous sediments has occurred since.

Radiolarians are absent below Core 15. Fish teethand fish debris are the principal biogenic componentsin the red clays of Cores 15 and 16, and are stillimportant constituents of the biogenic fraction in Cores17 and 18. Cores 17 to 21 contain calcareous nanno-fossils and benthic foraminifers of early Maestrichtian

to Campanian age. We cannot be certain whether theabsence of any datable upper Maestrichtian-Paleocenematerial is a consequence of a hiatus or of the very slowaccumulation of the zeolitic and ferruginous clays.

ForaminifersIn this area of the Brazil Basin, sediments containing

calcareous foraminifers consist of (1) clay-richturbidites in Core 1, (2) Neogene clay-rich layersinterbedded with foraminifer sands in Cores 2 and 3,and (3) Cretaceous clay-rich nannofossil ooze, withvery small percentages of calcareous foraminifers, inCores 17 through 20. Foraminifers were not found inthe predominately green clay of Cores 4-15 and in thebrick red clay of Core 16, most of which containssiliceous microfossils.

Clay-Rich TurbiditesCore 1 contains a small assemblage of planktonic

foraminifers, including Globigerinoides ruber, G.

112

0 55.6

111.1

Sl66.7C

i j 222.2

I^ 277.8CO-C+JQ.

g 333.3

388.9

444.4

500.0

H-

+ *-H-

-H-

MUD/CLAY

ZEOLITEMUDTO

MUDSTONE

+ NANNO OOZE

BASALT

2.0 2.5Velocity (km/sec)

+Y + Y

XY

× Ya × +

+ Y Y Y

XY

× YX +

VY

405

449

3.01.5 2.3

Density (g/cc)3.0 75.0 37.5

Porosity(%)0 50.0 25.0

Water Wt(%)

Figure 10. Physical properties versus depth; +, x, andy represent syringe, immersion, and GRAPE values, respectively.

•=HY

if

×r

2.0 3.5 5.0 6.5 8.0Acoustic Impedance


Epoch -Series

Stage

Core andDepth (m)

V\aestr-chtian

100-

150-

250-

300-

PlanktonicForaminifer

Zones

unzoned

N16?

N8-N9laçostaensis/merotumid:j . insuèTa

insis/merotumidjta-O. suturans

P22- I G. angulisuturalis-N4 I G. primordius/kuqleri

unzoned

NannofossilZones

\. primuss. heteromorphus

'S . belemnosLD. druggii

T. caπnatus

NN3NN2

NN1

T. trif idus

T. gothicus>

T. aculeus

Radiolarian

Zones

P. mitra

P. ampla

Λ T . triacanthaA

. mongolfieri orP. striata striata

'. striata striata

B. clinata

BASALT B. parca

• BLACK=RECOVERY I 1 UNCORED INTERVAL

Figure 11. Biostratigraphic summary, Site 355.

114


trilobus, Globorotalia scitula, G. tumida, Globigerinitaglutinata, Globigerina pachyderma, and Candeina nitida.Most foraminifers, including the benthic species, arefragmented and dissolved. Those that remain aregenerally small and some are very fragile. Along withthe foraminifers there are sponge spicules, radiolarians,echinoid fragments, fish debris, and several pteropods.

Since the core was taken from water depths close to5000 meters, and the CCD in this area of the SouthAtlantic is estimated at 4600 meters, calcareousmaterial did not seem likely in this core. The presenceof foraminifers and particularly of pteropods indicatesrapid redeposition.

Although not indicative of an age more precise thanPliocene to Pleistocene, the planktonic foraminifersappeared "young"; we assign them tentatively to thePleistocene. The presence of Globigerinoides ruber andabsence of G. obliquus support this age assignment.

Neogene OozesMost residues are composed of about 70% quartz silt

and 30% calcareous foraminifers. The foraminifers areoften broken and corroded, planktonic and benthicspecies alike. The assemblages of planktonicforaminifers are dominated by the fragile globigerinidsand Globigerinoides sp.; globorotaliids are rare andoften fragmented.

The index species include Globigerina nepenthes,Orbulina universa, Globigerinoides obliquus,Sphaeroidinellopsis seminulina, S. subdehiscens, G.bulloides, and Globorotalia menardii. The benthic faunaindicates a deep environment, and contains smooth andhispidocostate uvigerinids, some rotalids, Bulimina,and Bolivina. Also present are cancellate ostracodes andechinoid and fish debris.

The age of the samples is late Miocene. The faunaimplies tropical open marine conditions and apparentflooding with turbidite sands that also may havebrought the ostracodes.

Below approximately 120 cm in Section 2-2, there is alithologic change, reflected also by a change in theforaminifer fauna. Quartz silt is still abundant andforaminifers are fragmented. However, the planktonicfauna now consists of O. universa, Globoquadrinaaltispira, Praeorbulina transitoria, Biorbulina sp., and G.praebulloides. In addition to the deep benthicforaminifers, smooth, cancellate, and ridged ostra-codes, sponge spicules, radiolarians, and diatomremains are present.

This fauna belongs to the lower to middle Miocene.A middle to upper Miocene hiatus is indicated inSection 2 of Core 2, around 120 cm.

The residue from Sample 2, CC, however, containsan older fauna, but does not contain the quartz silt.Planktonic foraminifers are small. The larger globo-rotaliids and globoquadrinids are absent. The faunadoes contain Praeorbulina glomerosa, P. transitoria, G.praebulloides, Globorotalia peripheroronda, and Globi-gerinoides diminutus. Ostracodes are punctate andsmooth, and benthic foraminifers are rare, but of deep-water origin. Echinoid fragments and sponge spiculesare also present.

Because Orbulina is absent and its predecessorPraeorbulina is present, we assign this sample to thelower Miocene, top N7-N9. The fauna indicates openmarine, deep-water conditions and a turbidite origin.

Core 3 contains clay-rich oozes with interbeddedcoarse-grained foraminifer sands. We examined boththe oozes and the sands.

OozesThe clay-rich oozes from Sections 1-5 of Core 3

contain a planktonic foraminifer fauna rich in tinyglobigerinids and Globigerinoides sp. The expectedgloborotaliids and globoquadrinids, typical of this partof the column, are rare to absent. The planktonicspecies include Globoquadrina altispira, Globigerinoidesprimordius, Globigerina praebulloides, Globorotalia (T.)kugleri, Globigerinoides trilobus, Globigerina cipero-ensis, and Globoquadrina sellii. The benthicforaminifers are deep-water species of TVonion, Angulo-gerina, Nuttallides, Lagena, and Nodosaria.

The ooze from Sample 3, CC, contains Globorotalia(Turborotalia) opima nana. Thus, the core apparentlyranges in zone from N5-N6 in the top sections toN4/P22 in the core-catcher sample. The benthic speciesindicate a deep-water origin for this sediment.

Coarse Foraminifer SandsThese sands contain a surprising fauna of larger

benthic foraminifers and other invertebrate fossils,mixed with the oozes described above. Included in thiscoarse material are Miogypsina, Gypsina, Sphaero-gypsina, Amphistegina, large rotalids, large sections ofbryozoans, and possibly calcareous algae.

Such fossil debris is usually associated with a reef orcarbonate platform environment. Depths indicated aresubstantially less than 200 meters. These arepresumably turbidite sands derived from very shallowwaters and intercalated into the ooze sequence.

Cores 4 through 16 contain zeolitic pelagic clays andmudstones which lack foraminifers.

Cretaceous Clay-Rich OozesThe calcareous component of residues of Cores 17 to

20 is minor and consists almost entirely of benthicforaminifers. Although the percentages of the generavary, the faunas are similar and are dominated byReussella, Semivulvulina dentata, Pullenia, Dorothia,and species of the key genera Ammodiscus, Aragonia,Pleurostomella, and Buliminella. Notably absent is thegenus Gavelinella. In these samples the planktonicspecies are entirely dissolved; only a few pieces attest totheir previous existence. The benthic species arecorroded and fragmented. Outer chambers in therotalids have been dissolved, leaving only the umbilicalareas thickened by umbilical nodes. Inoceramus ispresent in Core 19.

This fauna is typical of the Upper Cretaceous andcontains abyssal benthic foraminifers (see Sliter, thisvolume).

115


Calcareous Nannofossils

Three Neogene (Cores 1-3) and six upper Cretaceouscores (Cores 17-22) contain calcareous nannofossils.The remainder of the cores, all probably of middle toearly Eocene age, consist mainly of zeolitic pelagic claysand are barren of coccoliths. The distribution of speciesis shown in tables in Perch-Nielsen (this volume). Thedistribution of coccolith zones is summarized in Figure11.

Pleistocene-Pliocene (Core 1)

The seven samples of brown clay studied from Core 1are barren or contain very few coccoliths. A fewGephyrocapsa sp. without visible bridges and scarceSphenolithus neoabies indicate a Pliocene rather thanPleistocene age for this core, which was taken at 53meters.

Miocene (Cores 2 and 3)

The Miocene material in Core 2 includes rich andwell-preserved assemblages of the upper MioceneDiscoaster quinqueramus Zone (NN 11) in the upperpart of Section 2. In the lower part of this section,below 120 cm and down to the core-catcher portion,assemblages of the lower to middle Miocene Spheno-lithus heteromorphus (NN 5) Zone occur. This indicatesthat a hiatus of about 7 m.y. is present in this section.Caution is necessary, however, in interpreting thissequence. The interval from 62.5 meters to 110 meters,where Core 2 was taken, was drilled with the core barrelin place, so the recovered sediment could have been"picked up" anywhere within this interval.

The assemblages in Cores 2 and 3 contain rare to fewBraarudosphaera bigelowi and Micrantholithus sp.,neither of which is usually fouη^ in open oceansediments. Since part of Core 2 consists of claysdeposited below the CCD and barren of coccoliths, thepresence and relatively good preservation of thecoccoliths may indicate a turbidite origin for thecalcareous layers. The number of reworked oldercoceoliths, however, is very small.

Although the core-catcher sample and samples fromSections 4 and 5 of Core 3 are barren, the three uppersections contain common to a few fairly well preservedcoccolith assemblages of the Sphenolithus belemnosZone (NN3), the Discoaster druggi Zone (NN2), andpossibly the Triquetrorhabdulus carinatus Zone (NN1),all lower Miocene. Since we do not know exactly wherethe core was taken, we cannot be sure whether theproximity of these three zones, which span some 7 m.y.,is a result of very slow accumulation or a hiatus, or is adrilling artifact.

Late Cretaceous

Lower Maestrichtian and Campanian coccolithassemblages of the Tetralithus trifidus, T. gothicus, andT. aculeus zones occur in Cores 17-21. An earlyCampanian age can be assigned to a slightly induratedpink chalk sample recovered from the core catcher ofCore 22 {Broinsonia parca Zone of Perch-Nielsen, thisvolume).

The coccolith assemblages are generally poorlypreserved and of low diversity, and solution-resistantspecies dominate. Kamptnerius magnificus is absent andArkhangelskiella cymbiformis is extremely rare. Bothwere relatively common in the slightly younger chalk ofcomparable age at Site 354 on the Ceará Rise.

The oldest datable sediment recovered at this site is76 to 80 m.y., according to Bukry's (1974) correlationsof coccolith zones, stages, and ages.

RadiolariansRadiolarians are present only in the sediment

recovered between 170 and 390 meters below the seafloor (Section 3-3 to Sample 15, CC). The sediments arezeolitic pelagic clays between Section 3-3 and Sample11, CC, and silty claystones between Core 12 (top) andSample 15, CC. In most samples, radiolarians make upthe bulk of the coarse fraction, except in the lower partof the section (bottom of Core 14 and Core 15), wherefish debris and mineral grains are more abundant.Preservation of the radiolarians is in general ratherpoor, owing to dissolution and remobilization of thebiogenic silica. At several intervals this makes speciesidentification difficult and age assignment uncertain. Inspite of the poor preservation consequent todissolution, the diversity is surprisingly high, whichindicates that perhaps remobilization of the opalinesilica has affected the assemblages for a relatively shortperiod. Fish debris is a constituent of the coarsefraction throughout, and increases in abundance inCores 14 and 15.

Miocene-OligoceneFew specimens of Cannartus prismaticus, Cannartus

sp., Calocycletta sp., and Dorcadospyris sp. occur invery poorly preserved assemblages of Sections 3-4 and3-5 and the core-catcher sample. They indicate a lateOligocene to early Miocene age for this interval.

EoceneA moderately well preserved assemblage of the

middle Eocene Podocyrtis mitra Zone is present inSample 4, CC, and in Section 5-1. The assemblage isdiverse, and the presence of Sethochytris triconiscusindicates that the upper part of the P. mitra Zone isrepresented. The presence of sediments of this age onlyabout 40 meters below the lower Miocene in Sample 3,CC, suggests that a hiatus is probable somewhere inthis interval. In Cores 5, 6, and 7, preservation of theradiolarians deteriorates considerably. Section 5-2belongs to the short P. ampla Zone, and Sections 3, 4,and 6 and Sample 5, CC, can be assigned to theThyrsocyrtis triacantha Zone. Samples from Core 6cannot be assigned to a zone because the assemblagesare poorly preserved, but Podocyrtis sinuosa suggests amiddle Eocene age for this core. The assemblage ofCore 7 belongs to the Theocampe mongolfieri Zone ofthe lowermost middle Eocene, or to the lower EocenePhormocyrtis striata striata Zone, assemblages of whichoccur down to the bottom of Core 11. Cores 12 through15 can be assigned to the lower Eocene Buryella clinataZone. No radiolarians occur in the sediments belowSample 15, CC.

116

Palynomorphs

Ioannides and Colin (this volume) studied palyno-morphs from Sections 15-1, 15-2, 15-3, and 15-4, ofearly Eocene age; Sections 16-1, 16-2, and 17-1, ofunknown age; and Sections 17-2, 17-3, 17-4, 17-5, and17-6, of early Maestrichtian-late Campanian age. Mostsamples are devoid of any acid insoluble microfossils.The two questionable records of the dinoflagellate D.phosphoritica—a species confined to Eocene and Oligo-cene sediments—in Sample 17-1, 135-40 cm, seeminsufficient evidence for dating the ferruginous zeoliticclaystone as early Eocene. It is uncertain whether thereis a hiatus between the lower Eocene and the lowerMaestrichtian-Campanian in Section 17-1, or whether aperiod of slow, more or less continuous sedimentaccumulation occurred.

SEDIMENT ACCUMULATION RATESDrilling results confirm earlier speculation on the

history of sediment accumulation at this site, andconfirm particularly the likelihood of one or morehiatuses, although only intermittent coring was possiblein the upper part of the sequence and biostratigraphiccontrol is lacking in a few cores. A hiatus probablyoccurs in Section 2-2 between the upper Miocene andthe lower to middle Miocene; a hiatus including most ofthe Oligocene and the upper Eocene is also highlyprobable. Another major hiatus or sequence ofextremely slow accumulation seems to represent mostof the Paleocene and the upper Maestrichtian.

The accumulation rate was about 2 cm/1000 yrduring the Pleistocene and the Pliocene. This ratherhigh rate for a brown pelagic mud was probably causedby the contribution of turbidity currents. The same is


true for the lower to middle Miocene sequence, whichseems to have been deposited at about the same rate.

Miocene HiatusThis hiatus occurs at about 120 cm in Section 2-2, a

section highly disturbed by drilling. A major change inlithology occurs at about this depth in the section.Foraminifers and coccoliths indicate an age of lateMiocene and early to middle Miocene for calcareoussediment lumps floating in the non-calcareous brownclays. It is unlikely that this hiatus is a drilling artifact,since the core barrel was not full when recovered andthe sediment seemed soft enough to wash away easily.

Oligocene HiatusCore 3 contains foraminifer zones (N4, P22) and

coccolith zones (NN3, 2) which indicate that the oldestsediment in this core is of early Miocene or possiblylatest Oligocene age. Core 4 was taken at 215-224meters, 38 meters below Core 3, and was dated byradiolarians to be of late middle Eocene age (about 42to 45 m.y., Podocyrtis mitra Zone).

This suggests either (1) continuous accumulation atan average rate of only 0.2 cm/1000 yr or (2) moreplausibly, a higher rate just above Core 4 and a hiatusspanning most of the Oligocene and possibly the latestEocene, since the lithology in Core 4, with accumula-tion rate of about 1 cm/1000 ur (Figure 12, accumu-lation rate in the middle Eocene, between Core s 4 and5), may continue on up to about 190 meters, where adrilling break occurs.

The accumulation rate of the lower Eocene zeoliticmuds was high, presumably because of contribution ofterrigenous material by turbidity currents.

355W.D. 4896 m

Brazil BasinLith. Cores

TERTIARY

P.PLIO MIOCENE OLIGOCENE EOCENE

LATE CRETACEOUS

PALEOCENE MAESTR. CAMPANIAN S. CON. TUR

100-

200--

300-

400-

- Z -

10 m.y. 20 30 40 50 60 70

ca 2 cm/1000 yrs

ivy F,N

ca 2 cm/1000 yrsKJ\.,...:I"

0.2 cm/1000yrs

ca 5 cm/1000yrs

ca 0.1 cm/1000yrsAges derived from Forams

NannosRads

ca 1 cm/1000 yrsT

BASALT

Figure 12. Sediment accumulation history, Site 355.

117


Paleocene-Maestrichtian Hiatus

The lowermost datable Tertiary sediments occur at390 meters in Core 15; on the basis of radiolarians(Buryella clinata Zone), we assign them an age of 52 to52.5 m.y. The uppermost datable Cretaceous sedimentsoccur in Core 17; coccoliths (T. trifidus Zone) indicatean age of 69 to 72 m.y. Thus, the approximately 16meters of red-brown mudstones, for which no age canbe assigned, represent an interval of some 15-20 m.y.,and if sedimentation was uninterrupted, would prob-ably have been deposited at an average rate of less than0.1 cm/1000 yr. This is unlikely in view of the highaccumulation rate of the overlying sediments, whoselithology is basically the same as that found at the topof Core 17. The upper Maestrichtian and at least partof the Paleocene is probably represented by a hiatus.

Late Cretaceous

The coccolith zones in the Maestrichtian andCampanian are too long for more accurate calculationof the accumulation rate for the nannofossil ooze andchalk recovered in Cores 17-21. A rate of 1 cm/1000 yrseems reasonable, on the basis of the age ranges of thezones encountered {Tetralithus trifidus, T. gothicus, T.aculeus, and Broinsonia parca.

CORRELATION OF REFLECTION PROFILEWITH DRILLING RESULTS

The reference reflection profile at Site 355 (LDGOprofile 570 from R/V Conrad Cruise 16-04, Figure 3)shows an acoustically transparent sedimentary column,about 0.47 sec thick, overlying basement. A sonobuoynear the site (Figure 3, sonobuoy #85C16) indicatedthat the average velocity of sediments overlyingbasement is approximately 2.0 km/sec. On the basis ofthis information, a basement depth of 470 meterssubbottom was predicted.

Like the reference profile, the approach profile(Figure 5) shows no well-defined continuous inter-mediate reflectors. The patchily distributed reflectionsare of unknown nature and significance; they mayindicate lateral inhomogeneities in sediment type, ormay be artifacts of acoustics or electronics. Basement isclearly evident, particularly under the transparentsediment sections.

The sonic velocities measured in the first few coresrange from 1.5 to 1.7 km/sec. The measured velocitiesindicated that the basement might be present at ashallower depth than anticipated, i.e., within 380 to 400meters subbottom. The basement was cored at 448meters subbottom. The actual depth to basementsuggests that the average velocity for the column iscloser to that indicated by the sonobuoy than tovelocities measured in the cores (see Table 4). The 0.47-sec two-way time through the sedimentary column and448-meter thickness gives an average velocity for theentire column of 1.91 km/sec, which is close to the 2.0km/sec measured with the sonobuoy. The discrepancybetween the velocities measured in cores and thosemeasured in situ by sonobuoy probably results from therelatively high degree of disturbance in the cores.

The sedimentary section at Site 355 appears to beacoustically homogeneous; most of it is composed ofbrown mud and clay and zeolitic pelagic clay. Theinterbedded layers of gravity-displaced sediment areprobably too thin and too infrequent to createreflectors on the seismic record. Although the claychanges to claystone near the bottom of the section,and the claystone overlies nannofossil ooze, even thesecontrasts are apparently not sufficient to register ascontinuous reflectors on the seismic profile record.

SUMMARY AND CONCLUSIONSThe basalt cored at Site 355 is a typical ocean-ridge

tholeiite (Fodor et al., this volume). It is assumed to bea surface flow, so its age is representative of the age ofocean crust at this distance from the present mid-oceanridge. McKee and Fodor (this volume) have obtained aK/Ar age of 78.1 ±9 m.y. for the basalt, which is inexcellent agreement with the early Campanian agedetermined by nannofossils. The position of the sitewith respect to magnetic anomalies 33 and 34 (Figure 2)provides a calibration point at the older end of themagnetic reversal time scale of Heirtzler et al. (1968).

Unconsolidated Campanian to lower Maestrichtiannannofossil ooze forms the basal sediment sequence,and numerous veins of calcite (satin spar) occur withinthe ooze. The veins are presumably the product of adiagenetic process associated with hydrothermal solu-tions which acted upon the sediments when the site wasstill within the region influenced by crustal generation.A hiatus probably separates the calcareous sedimentsfrom the overlying noncalcareous pelagic clays andterrigenous sediments. The lower Eocene sedimentscontain numerous laminae of sand and silt, whichindicate a period when turbidity currents werecontributing detritus. The laminae contain abundantzeolites, presumably authigenic. Siliceous organismremains occur in significant quantity in the middleEocene. Bioclastic carbonate debris was introduced byturbidity currents in the Miocene.

A mid-Miocene hiatus occurs in Core 2, a middleEocene hiatus is probable between Cores 3 and 4, and amiddle Maestrichtian-lowermost Eocene hiatus orinterval of very slow sediment accumulation existsbetween Cores 15 and 17. A mid-Miocene hiatus occurson the Ceará Rise (Site 354, this volume; Site 142, inHayes, Pimm, et al., 1972) and at other Atlantic DSDPsites (Pimm and Hayes, 1972). An Eocene-Oligocenehiatus was also found at Site 354 and at Site 144 on theDemerara Rise; Maxwell et al. (1970) report anOligocene hiatus at the Rio Grande Rise. TheCretaceous-Tertiary hiatus (or at least period of non-deposition of carbonate) also occurs at both theDemerara Rise and the Ceará Rise sites, and isprobably widespread. In a later chapter, Supko andPerch-Nielsen (this volume) discuss the significance ofLeg 39 hiatuses in terms of broad paleooceanographicpatterns.

Figure 13 is a plot of the average depth to basementin the South Atlantic versus age of the oceanic crust,after Sclater et al. (1971). It shows the present basementdepth (corrected for isostatic effect of sediment load)

118


2000

3000

4000

5000

6000

SITE 355EARLY MAESTRICHTIAN

CCD?

ATLANTICCCD

SITE 355EARLY EOCENE

CCD?

crustal curve

MIO. OLIGO. EOC. PALEO CRET.

0 20 60 8040m.y.BP

Figure 13. Average depth to basement in the South Atlanticversus age of the oceanic crust, after Sclater et al (1971)

At the other extreme, we may assume that thesediment directly above the carbonate is as young aslower Eocene, that carbonate deposition continueduntil the early Eocene at the latest, and that carbonatedeposited after the early Maestrichtian wassubsequently removed. The subsidence curve indicatesan early Eocene CCD of ~ 3700 meters (Point B inFigure 13). The missing section in this extreme casewould have to have been removed over a short periodat the Paleocene-Eocene boundary; and sincedissolution facies (pelagic clay) would be absent, thecause of the hiatus would have been current actioninstead of—or at least in addition to—dissolution.

The CCD for the Atlantic is shown by the dashed linein Figure 13, after van Andel (1975) and Berger and vonRad (1972). (Note that the envelope prior to lateEocene is a result of poor control.) Point A falls abovethe CCD curve, and so indicates that carbonatedeposition should have continued after the earlyMaestrichtian. Point B falls considerably below theCCD envelope; this indicates that carbonate depositionprobably ceased before the early Eocene.

Calcareous nannofossils in the uppermost part of thechalk sequence show dissolution effects (dominance ofresistant species, solution, etc. but this may be aconsequence of either synsedimentary processes ordissolution associated with erosional removal.Planktonic foraminifers are absent throughout thecalcareous sequence.

and determined crustal age at Site 355. If we assumethat no subsequent vertical uplift has taken place andthat subsidence was of the normal type described bySclater et al. (1971), then back-tracking of the Site 355data point (solid line, Figure 3) indicates the crustformed at a mid-ocean ridge at a water depth of about2200 meters, as against the present average ridge crestdepth of about 2700 meters.2

Still assuming normal basement subsidence, we mayview the transition from calcareous to noncalcareoussediments in terms of its significance for the level of theCCD by considering two extreme examples. At oneextreme, we assume that the depositional siteaccumulated 45 meters of carbonate in about 8 m.y.(early Campanian to early Maestrichtian), and thatcarbonate deposition ceased in the early Maestrichtianbecause the site subsided below the CCD. Normalsubsidence rate would give an early Maestrichtian CCDlevel of about 3000 meters (Figure 13, Point A). In thiscase, the 16 meters of undated zeolitic and ferruginousclays between the chalk and the next youngersediments, dated early Eocene, could represent a periodof very slow deposition at an average rate of ~O.lcm/1000 yr, or could contain a hiatus.

2This is at odds with the conclusions of McCoy and Zimmerman(this volume), who interpret their data on the distribution ofcarbonates through time as indicating growth of the ridge as apositive feature only in the Cenozoic.

REFERENCES

Asmus, H.E. and Ponte, F.C., 1973. The Brazilian marginalbasins. In Nairn, A.E.M. and Stehli, F.G. (Eds.), Theocean basins and margins, v. 1, The South Atlantic: NewYork (Plenum Press), p. 87-133.

Bader, R.G., Gerard, R.D., et al., 1970, Initial Reports of theDeep Sea Drilling Project, Volume 4; Washington (U.S.Government Printing Office).

Berger, W.H. and von Rad, U., 1972. Cretaceous andCenozoic sediments from the Atlantic Ocean. In Hayes,D.E., Pimm, A.C., et al., Initial Reports of the Deep SeaDrilling Project, Volume 14: Washington D.C. (U.S.Government Printing Office), p. 787-954.

Bukry, D., 1973. Low latitude coccolith biostratigraphiczonation. In Edgar, N.T., Saunders, J.B., et al., InitialReports of Deep Sea Drilling Project, Volume 15:Washington (U.S. Government Printing Office), p. 685-703.

, 1974. Coccolith stratigraphy offshore westernAustralia. In Veevers, J.J., Heirtzler, J.R., et al., InitialReports of the Deep Sea Drilling Project, Volume 27:Washington (U.S. Government Printing Office), p. 623.

Hayes, D.E., Pimm, A.C., et al., 1974. Initial Reports of theDeep Sea Drilling Project, Volume 14: Washington (U.S.Government Printing Office).

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

Maxwell, A.E., Von Herzen, R.P., et al., 1970. Initial Reportsof the Deep Sea Drilling Project, Volume 3: Washington(U.S. Government Printing Office).

119


Pimm, A.C. and Hayes, D.E., 1972. General synthesis. In Sclater, J.G., Anderson, R.N., and Bell, M.L., 1971. Eleva-Hayes, D.E., Pimm, A.C, et al., Initial Reports of the tion of ridges and evolution of the central eastern Pacific:Deep Sea Drilling Project, Volume 14: Washington (U.S. J. Geophys. Res. v. 76, p. 7888-7915.Government Printing Office), p. 955-975. Van Andel, T.H., 1975. Mesozoic/Cenozoic calcite compen-

Ramsay, A.T.S., 1971. Occurrence of biogenic siliceous sation depth and the global distribution of calcareoussediments in the Atlantic Ocean: Nature, v. 233, p. 115- sediments: Earth Planet. Sci. Lett., v. 26, p. 187-194.117.

120

SITE 355: BHAZIL BASIN

APPENDIX ASmear-slide Summary

Site 355

1-2, 501-2,551-5,1351-6, 1251,CC2-1, 1392-3,1112-3, 1382-5, 902-5, 1102-5,1212-5, 1222-5, 1232-5-1242-5, 1382,CC3-1,583-1,633-2, 1223-2,1383-3,1143-3,1193-5, 203,CC4-1,1304-3, 1205-1,605-3, 375-4, 1005-6, 385-6, 1056-1,966-3, 236-3, 1056-4,86-4, 306-5, 316-5, 646-5, 866,CC7-2, 107-2, 507-3, 1008-2, 1209-1,809-2, 1309-3,810-2, 8410-2,11011-1,9811-2,3012-2,2912-3,7012-5,12312, CC13-2,2113-2, 12014-2,514-2,7014-4,2514-5,3215-1,4715-1,9215-2,7515-2, 10216-1, 140

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121


APPENDIX A - Continued

16-2, 10817-1, 13017-2,5017-3,14517-4,2017-4,9817-5,3717-5,8018-2,6518-3,2719-2,9119-3,10520-2, 7220-2, 14721-1,1221-1,2821-1,6021-1,71

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APPENDIX BCarbonate and Quartz Determinations

Section

1-21-31-62-22-32-32-42-42-52-52-52-53-23-23-23-33-43-53-54-34-34-34, CC5-15-15-45-56-26-26-26-46-67-17-27-27-37-38-28-29-29-39-59-511-211-311-312-4

SedimentDepth (cm)

551956706130

1118011370114301152011570116551167011690117101690016938169571711017158173581739021860218702189021925243402435024848250302641026410284502666026982281702831028340284752850030240302953210032207325053261834991350553509236210

CaCO3 (%;

0.250.371.000.633.671.25

13.6012.970.758.32

52.0663.7716.988.50

80.5724.410.300.750.000.000.300.070.190.500.030.240.000.270.855.000.201.370.27

10.532.500.174.500.000.280.000.000.271.030.000.120.030.00

) Org(%)

0.241.100.270.090.120.300.100.400.210.110.510.080.130.510.420.160.070.540.090.360.050.070.100.390.150.450.110.190.170.630.110.870.180.100.300.100.510.480.100.390.110.140.110.210.090.130.42

TotalCarb (%)

0.15

0.170.56

1.731.96

1.106.767.742.17

10.093.09

0.09

0.09

0.090.080.12

0.15

0.110.220.27

0.131.03

0.221.87

0.12

0.14

0.110.170.23

0.100.13

Qtz (%)

9.15

6.65

6.04

5.31

4.25

5.15

4.47

3.76

15.053.604.48

3.65

3.56

122


APPENDIX B - Continued

Section

12-412-513-213-213-314-314-514-514-515-115-115-115-115-215-315-417-217-217-217-217-317-317-317-417-417-417-617-618-118-118-218-218-318-318-319-219-219-219-320-220-220-221-121-1

SedimentDepth (cm)

3625236408368203687036992379933828538287383403863438648386773868038802389683908540605406094062540637408854089040896409054091540925412614132041432415154156841615417364180141820425274258842591427204346843525435654427744311

CaCO3(%)

0.050.280.570.150.000.000.200.000.171.500.000.000.030.160.270.202.55

14.6027.2542.6059.6469.8080.3466.5175.0575.6381.3044.2183.0574.7869.6782.8764.7956.2350.4460.7992.7481.8380.7684.2059.4589.1271.0551.77

Org (%)

0.130.050.040.100.330.271.080.300.090.630.140.510.130.120.060.080.240.050.500.040.680.300.030.930.360.040.390.650.030.510.320.030.150.330.040.660.030.870.040.040.380.480.650.69

TotalCarb (%)

0.130.090.110.12

0.11

0.11

0.13

0.130.140.090.100.551.803.775.157.84

9.688.91

9.12

5.9610.00

8.689.98

7.086.10

11.1610.699.74

10.157.51

9.186.91

Qtz (%)

17.5429.54

6.87

46.6513.786.306.66

6.90

9.81

10.38

6.77

11.85

9.98

10.49

12.15

10.669.88

123

Core 1 Cored I n te r va l : 53.0-62.5 m Core 2 Cored Interval:110.0-119.5 m

FOSSILCHARACTER

- .-.iT=r- —~

CoreCatcher

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2

LITHOLOGIC DESCRIPTION

In general: CLAY/MUD, silty, pale yellowishbrown (10YR 6/2) with light brown (5YR 6/4)mixed in.

Smear at 50 cm (Sec. 2) of light brown material:ZEOLITIC CLAY [0, 5, 95] with:

TR% MicaTR% Heavy minerals85% Clays

5% MicronodulesTR- 5% Dolomite rhombs

Smear at 55 cm (Sec. 2) of darker brown mater ia l :MUD, s i l t y [ 0 , 10-15, 85-90] w i t h :

5% Quartz '2% Heavy minerals

80-90% Claylit Micronodules

1- 2% Zeol i te1- 2% Limonite

122-150 cm, black material mixed i n ; smear at135: MANGANESE MUD, s i l t y [ 0 , 50, 50] w i t h :405! Clay40% Micronodules + Limonite5% Zeoli tes5% Rads10% Quartz5% Feldspar

125 cm, some greenish gray (5GY 6/1) mixed in:CLAY [0, 5, 95] with:10% Feldspar15% Quartz70% Clay

5% Zeol i teTR% Limonite

CC: MUD, s i l t y [ 0 , 15, 85] w i t h :10% Quartz5% Heavy minerals5% Zeolite

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Drilling breccia composed of:

MUD, pale yellowish brown (10YR 6/2) and palebrown (5YR 5/2), silty [0, 40, 60] with:εmear slides at 139, Sec. 1, 111, Sec. 3:10% Quartz, Silt80% Clays

5% Colcsrθous Nδπnos

5% Limonite

Nanno ooze, very light gray (N8), smear slideat 138, Sec. 3:

20% Clay40% Authigenic C0

3

40% NannosTR% Sponge spiculesForam sand at 125, Sec. 4, disturbed.

//MUD, pale brown (5YR 5/2) as above but con-/ taining a sequence of 8 bioclastic turbidites;/ typical sequence is as follows:

/ ©SS 124/ 10% Quartz, Silt

75% Clay

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•-Burrows— (3)ss 121

White 10% Quartz, SiltJ>Nanno Ooze 75% Clay

-T\White Foram 10% Zeolite^Sandy) Ooze 5% Limonite

J)ßluish TR% Nannos/ Zeolitic Mud TR% Opaques/ TR% Dolomite rhombs

/ (jySS 122 ©SS 123/ 15% Clay 20% Quartz, Sand/ 40% Authigenic CO, 5% Feldspar/ 40% Nannos 30% Authigenic C03

/ 5% Sponge spicules 40% Forams—' TR% Fish remains 5% Nannos

TR% Forams

^ ^Nanno Ooze:30% Clay15% Authigenic C03

10% Forams and Sponge spicules45% Nannos

Explanatory Notes in Chapter 1

Core 3 Cored I n t e r v a l : 1 6 7 . 0 - 1 7 6 . 5 Core 4 Cored I n t e r v a l : 214.5-224.0 m

FOSSILCHARACTER

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D r i l l i n g breccia predomiantly composed of(exceptions noted below):CALCAREOUS ZEOLITIC PELAGIC MUD, pale brown(5YR 5 /2) , w i th smear at 58 cm, Sec. 1 :70% Clay

5% Micronodules10* Zeol i te10% Limonite5% Calcareous nannos

FORAM-NANNO OOZE, l i g h t bluish gray (5B 7/1)and greenish gray (5G 6 /1) , w i th smear at63 cm, Sec. 1:

20% ClayTR% Zeol i te30% Authigenic carbonate

5-10% Forams40-45% Calcareous nannos

At 122 cm (Sec. 2) and 136-142 cm (Sec. 2)local clumps of ZEOLITIC FORAM-NANNO OOZE,w i t h :15-20% Clay5-15% Zeol i te

10% Authigenic carbonate10-15% Forams45-50% Calcareous nannosTR- 5% Sponge spicules

TR% Fish teeth

D r i l l i n g breccia of ZEOLITIC PELAGIC MUD,greenish gray (5G 6/1) and ZEOLITIC DOLOMITICPELAGIC CLAY, l i g h t gray (N7); averagecomposition:SS 114 SS 11930% Authigenic C03 40% Clay

20% Quartz20% Zeolite15% Clay10% Dolomite rhombs5% Forams

Note: dolomites

5% Micronodules0% Dolomite

50% Zeolite5% Authigenic carbonate

1- 2% Forams and Calcareousnannos

MARLY ZEOLITIC PELAGIC MUD, predominantlyreddish brown (5YR 5/3) with some greenishgray (5G 6/1) (see above); smears at 20 cm(Sec. 5) and in core catcher:0-10% Quartz

40-50% Clay0- 5% Micronodules10-20% Zeolite

10% Authigenic carbonate5-10% Limonite0-10% Calcareous nannos

FOSSILCHARACTER

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PELAGIC MUD, moderate yellowish brown (10YR 5/4)with minor grayish brown (5YR 3/2) mixed in,with:

75% Clay10% Authigenic carbonate10% Limonite5% Micronodules

0-10% Zeol i te

ZEOLITIC PELAGIC MUD, colors as above, w i t h :60% Clay30% Zeol i te

5% Authigenic carbonate5% Limonite


Site 355 Hole Core 5 Cored Interval: 243.0-252.5 m Site 355 Hole Core 6 Cored Interval: 262.0-271.5 m


RADIOLARIAN MUD, light olive gray (5Y 6/1),with:

5058 Clay40% Rads10% Sponge spicules

0- St Limonite

Transitional between RADIOLARIAN MUD andZEOLITIC PELAGIC MUD; alternating lightolive gray and greenish gray.

QUARTZ-ZEOLITE SAND [50, 30, 20] with:40% Quartz, 20% Zeolite, 10* Feldspar, 10%Sponge spicules and 20% Clay; both quartzand feldspar are fresh and angular.

ZEOLITIC PELAGIC MUD, greenish gray (5G 6/1),with:80% Clay15% Zeolite5% Pyrite

QUARTZ-ZEOLITE SAND [50, 30, 20] with:Quartz, 15% Zeolite, 10% Feldspar, 5%

Pyrite and 30% Clay; both quartz and feldsparare fresh and angular.

QUARTZ-ZEOLITE SILT [0, 50, 50] with: 50%Quartz, 50% Zeolite and Trace of Chlorite,Micronodules, Dolomite and Limonite;

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In general smear 105, Sec. 3 and Smear 30,Sec. 5: ZEOLITIC PELAGIC MUD, greenish gray(5G 6/1), some mottling but difficult to dis-tinguish, with: 60% Clay, 30% Zeolite, 5%Dolomite and 5% Fe-oxide; scattered zones ofbrownish gray (5YR 4/1) Smear at 30 (Sec. 4)•with same composition.DOLOMITE ROCK fragment (<v2 x 4 mm).

SANDY SILTY ZEOLITIC PELAGIC MUD [20, 24, 45],with 30% Clay, 25% Zeolite, 20% Quartz, 5%Feldspar, 5% Micronodules, 1% Mica and Rads,10% Dolomite rhombs.

QUARTZ-ZEOLITE SAND [50, 0, 50], with 45%Quartz, 40% Zeolite, 5% Feldspar and 5%Micronodules.

/qUARTZITIC ZEOLITIC PELAGIC MUD, silt [5,'60, 35] with 50% Zeolite, 35% Quartz, 5%Dolomite, 2% Mica, 3% Heavy minerals.

QUARTZITIC ZEOLITIC PELAGIC MUD, silty [5,70, 25] with 50% Quartz, 15% Zeolite, 15%Opaques, 10% Clay, 5% Feldspar, 5% Dolomite,1% Zircon.

ZEOLITIC PELAGIC MUD, sandy silty [10, 30,60], 60% Clay, 35% Zeolite, 5% Quartz, 2%Dolomite, 1% Micronodules, 1% Fish remains,5% Fe-oxides.

'DOLOMITE MUD, greenish gray (5G 6/1), with45% Dolomite, 40% Clay, 10% Zeolite, 5% Pyriteand rads, pyrite in radiolarian tests.


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"~/.~i~/~'

J- Λ. -L.

zJ- -L. U.

1 i /

terval:

ION

DEFORMAT

W>LE

LITHO.SA

50

100

281.0-290.5 m


Alternating sequences of:DOLOMITIC ZEOLITIC MUD, greenish gray (5G 6/1)with smear at 50 cm:50% Dolomite30% Clay

ZEOLITIC PELAGIC MUD, dark yellowish brown(10YR 4/2) with smear at 100" cm:45% Zeolite40% Clay10% Limonite

"~-~-^_^^ 5% Micronodules

^ X QUARTZ SAND [70, 10, 20] with 60% Quartz, 10%\ . Feldspar, 10% Zeolite, 5% Mica, 5% Heavy minerals,

\ ^ % Clay, 3% Opaques, 2% Micronodules.

Cored Interval:319.0-328.5

Core 8 Cored Interval : 300.0-309.5

AGE

|

EARLY EOCENE

ZONE

Phormocyrtis striata striata

FOSSILCHARACTER

FORAMS

|

no planktonics

COCCO-

RADS

CP

SECTION

0

1

2

CoCa

METERS

-

retcher

LITHOLOGY

VOID

i

2

* -

' -

DEFORMATION j

LITHO.SAMPLE

120


ZEOLITIC PELAGIC MUD, greenish gray (5G 6/1),with some interbedded dark yellowish brown(10YR 4/2); considerably disturbed by coring;with:75% Clay25% ZeoliteTR% Chlorite, Diatoms


ZEOLITIC PELAGIC MUD, greenish gray (5G 6/1).with smears at 80 and 130 cm:65-80% Clay20-30% Zeolite

5% MicronodulesTR% Diatoms and nannos

Some interlayering of dark yellowish brown(10YR 4/2) z e o l i t i c pelagic clay in Sees. 3->6; f iss i le-T ike structure.

D, pinkish gray (5YR 8/1), t h i n layers aret l ined by a "blue" out l ine or "halo"; s i l t y, 10, 90]; w i th:

90% Clay2% Quartz2% Zeolite1% Mica1% Micronodules1% Dolomite1% Rads


Core 10 Cored Interval :338.0-347.5 Core 12 Cored Interval :357.0-366.5 m


ZEOLITIC PELAGIC MUD, in both greenish gray(5G 6/1) and brownish gray (5YR 4/1) alternatinglayers; moderate disturbances due to drillingbut contacts between layers appear to be sharp;with:70-90% Clays10-30% Zeolite

1% MicronodulesTR% Rads

Core 11 Cored I n t e r v a l : 347.5-357.0 m


Alternat ing sequences ( i n about equal amounts)of greenish gray (5G 6/1) and dark greenishbrown (10YR 4/2) ZEOLITIC PELAGIC MUD w i t h :80-90% Clay10-20% Zeo l i te

TR% Limonite and Rads

Appears to be f i ne l y laminated wi th f i s s i l e - l i k es t ruc ture , laminae about 1 mm th ick

FOSSILCHARACTER

CoreCatcher


ZEOLITIC MUD, light gray (N8), 2 irm thicklaminae with 80% Clay, 5% Zeolite, 5% Quartz,5% Feldspar, 3% M1ca, 2% Micronodules; quartznd feldspar both fresh and angular.

CLAY [0, 5, 95] greenish gray (5G 6/1), somefissile-like structure (drilling disturbance?),with:95% Clay10% Zeolite1% Rads

PUARTZ MUD, light gray (N8), silty [0, 80, 20]n 22 thin laminae from 2 to 0.5 mm thick, with60% Quartz, 10% Mica, 10% Clay, 10% Zeolite,5% Feldspar, 5% Heavy minerals; quartz andfeldspar both fresh and angular.CLAY as above, but with some thin laminae ofQUARTZ MUD [5, 80, 15] sandy silty, light gray,with 90% Quartz, 5% Feldspar, 5% Clay, TR%Zeolite, mica and heavy minerals.


Site 355 Core 13 Cored Interval: 366.5-376.0 m Core 14 Cored Interval: 376.0-385.5 m

FOSSILCHARACTER

CoreCatchei


ZEOLITIC QUARTZ MUD, greenish gray (5G 6/1)with some layers of brownish gray (5YR 4/1);silty [0, 70, 30]; with:45% Quartz20% Clay20% Zeolite10% Chlorite5% Opaques

QUARTZ SILT, very light gray (N8) [TR, 90, 10]containing 90% Quartz, 2-5% Heavy minerals,1-5% Zeolite, 1% Mica, 1% Micronodules, 1%dolomite; these occur in a series of very thinlaminae, 0.5-2 mm thick.

FOSSILCHARACTER

CoreCatche


Alternating sequences (in about equal amounts)of:ZEOLITIC PELAGIC MUD, medium bluish gray(5B 5/1), with 30% Clay, 20% Zeolite, TR%Quartz, Silt and Opaques.

FERRUGINOUS ZEOLITIC PELAGIC MUD, moderatereddish brown (10R 4/6) with 65-70% Clay,10-15% Zeolite, 10-25% Limonite and Opaquesand 0-5% Quartz, Silt.

.QUARTZ SILT, very light gray (N8), in packetsof numerous thin (M-2 mm thick) laminae,[5, 90-80, 10], with 80% Quartz, 10% Clays,5% Zeolites, 1-2% Heavy minerals, 1% Dolomite.


Cored Interval: 385.5-395.0 m Core 17 Cored Interval: 404.5-414.0 m

FOSSILCHARACTER

CoreCatche


Alternating sequences (with red-brown layersmore prevalent):FERRUGINOUS CLAY-CLAYSTONE, dark reddish brown(10R 3/4), silty [0, 10, 90] containing:60% Clay, 10% Feldspar and Quartz, 30% Limonite.

CLAY-CLAYSTONE, pale blue (5B 6/2), slightlymottled, containing:9058 Clay5% Zeolite5% Opaques

TR% Limonite and Mica

ZEOLITIC QUARTZ SILT, white (N9) [ 0 , 80-90,10-20], contain ing: 70-80% subangular Quartz,10% Clays, 5-10% Zeo l i t e , 2-10% Heavy minerals,1-5% Micas, 0-5% Opaques, 0-1% Fish debr is ;occurring as th in (i.0.5-2 mm) laminae.

Site 355 Hole Core 16 Cored I n te r va l : 395.0-404.5 m

AGE

ZONE

C

<c

-

FOSiARA

o^

-

SILCTER

o

s

-

PALY

NO | |

SECTION

0

1

2

CoCa

METE

RS

0.5-

1.0-

retcher

LITHOLOGY

VOID

2 _

1

:---– -z"---‰

- — - z •

DEFORMATION

LITH

O.SA

MPLE

|

140

108


FERRUGINOUS MUD-MUDSTONE, dark reddish brown(10R 3/4), [0, 0, 100], containing:70% Clay20% Limonite10% Zeoliteand one lone larqe volcanic shard; someZEOLITIC PELAGIC MUD-MUDSTONE occurs as afew M cm thick layers that are distinctiveby somewhat more brilliant red color of theferruginous clay-claystone near the upper andlower contacts of the pelagic clay, the pelagicclay is medium bluish gray (5B 5/1), and con-tains:50% Clay15% Quartz20% Zeolite15% FeldsparTR% Micarb

FOSSILCHARACTER

: Z -– —

CoreCatcher


FERRUGINOUS ZEOLITIC MUD-MUDSTONE, verydusky red (10R 2/2) containing: 45% clay, 25%Quartz and Feldspar, 15% Limonite, 10% Zeolite,5% Dolomite.

NANNO OOZE, moderate yellowish brown (10YR 5/4),containing: 40% Authigenic carbonates ("micarb"),30% Nannos, TR-1% Heavy minerals, Micronodules,Dolomite; with interbedded: also with 5-10%Quartz, Silt.

CALCITE VEINS, eight in all, thickness varyingfrom 1 mm->•5 mm (average -v3.5 mm), frequentlybroken by coring, composed of sparry calcitewith numerous inclusions, [denoted by I H I H I J I ] ;

NANNO CHALK, 124-130 cm (Sec. 2) and 139-9 cm(Sees. 3 and 4 ) , white (N9), with 40% Nannos,40% Authigenic carbonate, 20% Clay, TR% Dolomite.

FERRUGINOUS NANNO OOZE; pale reddish brown(10R 5/4) to reddish brown (2.5YR 5/4); whichoccurs in contact with, and both above andbelow the calcite veins and the white nannochalk; [denoted by closely-spaced short dashes];with: 40% Nannos, 40% Authigenic carbonate,10% Clay, 10% Limonite.

NANNO OOZE, alternating grayish brown (10YR 5/2)and pale brown (10YR 6/3), with: 50-60% Nannos,20-45% Authigenic carbonate ("micarb"), 20%Clay, TR-1% Dolomite, Mica, Micronodules andLimonite.


Cored I n t e r v a l : 414.0-423.5 Si te 355 Hole Core 20 Cored I n te r va l : 433.0-442.5 m


NANNO OOZE, grayish brown (10YR 5/2) and palebrown (10YR 6/3) in Sec. 1 , both colors a l t e r -nate, in Sec. 2, grayish brown more prevalent,and in Sec. 3, the grayish brown predominatesw i th :40-30°/ Nannos10-20% Quartz S i l t25-40% Authigenic carbonates ("micarb")

20% Clay5% Micronodules

TR% Dolomiteand with interbedded:

CALCITE VEINS (as described in Core 17),denoted by [ M U M ], surrounded (only upperfive veins) by FERRUGINOUS NANNO OOZE (alsoas described in Core 17).

AGE

CAMPANIAN

ZONE

T. aculeus

FOSSILCHARACTER

FORA

MSbo

planktonics

1

COCCO-

LITHS

CP

CP

CM

RADS SECTION

0

1

2

CoCa

METERS

™ 1

1 1

1 1

1 1 M

1

1 1

1 1

1 1

1 1

1 1

1 1

1 1

1 1

1 1

1 1

LITHOLOGY

VOIDmm

DEFO

RMAT

ION

1

1

11111!1t

LITHO.SAMPLE |

72

147

SED. STRUCT.

1


NANNO OOZE, brown (1OYR 5/3) with somescattered disturbed light brown (7.5YR 6/4),with:50% Nannos40% Authigenic carbonates10% Clays

/NANNO OOZE, light brown (7.5YR 6/4),/ with:

/ 60% Nannos' 30% Authigenic carbonates

10% Quartz SiltTR% Limonite

Core 19 Cored Interval: 423.5-433.0

FOSSILCHARACTER

CoreCatcher


NANNO OOZE, thin zone of grayish brown (10YR 5/2)in upperportion of Sec. 1, but generally analternating sequence (mixed) of pale yellowishbrown (10YR 6/2), pale brown (10YR 6/3), andmoderate brown (5YR 3/4) with:30-50% Nannos (lower amount in lighter browns)40-60% Authigenic carbonates

TR% Dolomite and Micronodules5%-15% Quartz Silt , 5-10% Clay

with interbedded:CALCITE VEINS, as described previously (Core17), none noticed in Sec. 3 perhaps due todisturbed core; these veins not associatedwith ferruginous nanno oozes as in Cores 17and 18; veins denoted by [ n i m ] .

Site

AGE

EARL

Y CAMPANIAN

355

ZONE

T. aculeus

-lole

FORAMS |o

FOS«RA

CP

CP

SILCTE

SECT

ION

0

1

e 21

METE

RS1

1 1

1 1

1 1

1 1

1 1

1 1

1

LITHOLOGY

. _ 1 _ " " • _ 1 _ • "ü

DEFO

RMAT

ION

ll: 442.5-452.0 m

LITHO.SAMPLE


NANNO OOZE, altered dusky brown (5YR 2/2),with authigenic carbonates, nannos, micro-nodules, quartz silt, clays, limonite.

APHYRIC BASALT (rare phenocrysts of Plagioclase,high Ca-pyroxene, and altered olivine). Topportion is highly altered, varying in color fromgrayish orange (10YR 7/4), to moderate yellowishbrown (10YR 5/4), to medium dark gray (N4);calcite veins present. Remainder is medium darkgray to dark gray (N3); some glass present;mineralogy consists of Plagioclase laths andhigh-Ca pyroxene in subophitic texture and asglomerocrysts. Much of groundmass highly altered.Olivine phenocrysts occur as highly altered andoxidized relicts. Plagioclase and pyroxene rangefrom fresh to moderately altered. Oxides presentas dust-sized material.

Plagioclase>pyroxene>altered olivine>oxides.


Site 355 Core 22 Cored Interval: 452.0-461.5 m

FOSSILCHARACTER


APHYRIC BASALT (rare phenocrysts of Plagioclase,high Ca-pyroxene, and altered olivine).Medium dark gray (N3) to dark gray (N4) basalt;highly fractured and veined with calcite (greenveins, possibly prochlorite, also present).Mineralogy consists of Plagioclase laths, high-Ca pyroxene in subophitic texture and as glomero-crysts. Much of groundmass is highly altered.Olivine phenocrysts occur as highly altered andoxidized relicts. Plagioclase and pyroxene rangefrom fresh to moderately altered. Oxides presentand best displayed in lowermost portion.

PIagioclase>pyroxene>altered olivine>oxides.

Olivine (altered) absent from lower half.

*lump of limestone



355-9-5 355-10-1 355-10-2 355-11-1 355-11-2

133


I—Ocm

—25

•50

— 75

— 100

— 125

150355-11-3 355-11-4 355-12-1 355-12-2 355-12-3 355-12-4

134


I—Ocm

—25

—50

— 75

— 100

— 125

1—150355-12-5 355-13-1 355-13-2 355-13-3 355-14-1 355-14-2

135


I—Ocm

—25

—50

— 75

— 100

— 125

1—150355-14-3 355-14-4 355-14-5 355-15-1 355-15-2 355-15-3

136


I—Ocm

—25

—50

— 75

— 100

125

1—150355-15-4 355-16-1 355-16-2 355-17-1 355-17-2 355-17-3

137


I—Ocm

—25

—50

— 75

— 100

125

—150355-17-4 355-17-5 355-17-6 355-18-1 355-18-2 355-18-3

138


i—Ocm

—25

—50

75

100

— 125

»—150355-19-1 355-19-2 355-19-3 355-20-1 355-20-2 355-21-1

139


I—Ocm

—25

—50

—75

100

125

^ 1 5 0355-22-1 355-22-2 355-22-3 355-22-4 355-22-5

140

Documents

4. SITE 355: BRAZIL BASIN The Shipboard Scientific Party · 8/11/1974 · altered in contact with ba-salt. Aphyric tholeiitic basalt with numerous calcite veins. of the unit (Cores