7. SITE 358: ARGENTINE BASIN The Shipboard Scientific Party1 · SITE 358: ARGENTINE BASIN Core 1 2...

7. SITE 358: ARGENTINE BASIN

The Shipboard Scientific Party1

45°S45°W 15°E

SITE DATA

Date Occupied: 30 November 1974 (0701Z).

Date Departed: 3 December 1974 (2012Z)

Time on Site: 3 days, 13 hours

Position: 37°39.31'S, 35°57.82'W

Accepted Water Depth: 4990 meters (drill pipe measurement)

Penetration: 842 meters

'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 Holes: 1

Number of Cores: 16

Total Length of Cored Sections: 152.0 meters

Total Core Recovered: 89.3 meters

Principal Results: We drilled and cored at Site 358 in thenortheastern Argentine Basin to a total depth of 842meters subbottom. Two major lithologic units occur. Thefirst extends from the sediment surface to 730 meters, andcomprises siliceous mud and mudstone, of mid-Eocene toprobably Holocene age. Terrigenous mudstone and marlychalk of Late Cretaceous to middle Eocene age underliethese sediments.

The top of Horizon A (Ewing and Lonardi, 1971) cor-relates well with the contact between diatom-radiolarianmudstone and siliceous mudstone at 460 meters; at thisspecific site, it is thus a diagenetic horizon of lateOligocene age. The top of Horizon B correlates very wellwith the contact of noncalcareous mudstone to middleEocene marly chalk at 730 meters. Basement wascalculated to lie at 897 meters. Very bad weather condi-

CoredInt. Units Lithology Age

1 0 0 -

200

300-

4 0 0 -

500-

600-

700

800

Δ- • • Z

-•• z

AΔ\ Λ

Λ Λ

— z

_7.Fe

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Maestri chti anCampanian?

329

SITE 358: ARGENTINE BASIN

tions forced us to abandon the site without reachingbasement or adding planned stratigraphic coverage.

BACKGROUND AND OBJECTIVES

Site 358, in accordance with recommendations of theJOIDES Atlantic Advisory Panel, is in the northeasternArgentine Basin at latitude 37°39'S, longitude 35°58'W(Figure 1). A major objective at this site was to date thebasement (presumably oceanic basalt), in order to havea valid date at the older end of the magnetic reversaltime scale of Heirtzler et al. (1968). The site is betweenthe recently determined positions of anomalies 32 and33 in the Argentine Basin (Figure 2). Before Leg 39, theearliest reliable date for the old end of the scale wasMaestrichtian (67 ±1 m.y.B.P., anomaly 30, Site 20,Maxwell, Von Herzen, et al., 1970). At Site 355 in theBrazil Basin, basement was dated at 76-80 m.y.B.P.(early Campanian) between anomalies 33 and 34. Weknew, then, that basement age at Site 358 should bewithin the range determined by Sites 20 and 355, inwhich case we could be confident of having dated truebasement rather than younger sills.

A second objective at Site 358 was to obtain a deep-water section for stratigraphic and biostratigraphicpurposes, and in particular, to determine the natureand age of Horizon A. The stratigraphy of theArgentine Basin, as represented in seismic profilerecords (as, for example, the L-DGO reference profile,Figure 3, and the Glomar Challenger approach profile,Figure 4), is quite homogenous over the area of thebasin, and consists of stratified sediments aboveHorizon A and a transparent section below, with apatchily distributed reflector just above basement. IfHorizon A is analogous to Horizon A in the NorthAtlantic, it should be late Mesozoic or Early Tertiary inage (see discussion in Supko and Perch-Nielsen, thisvolume). The reflector cored at Site 328 on theFalkland Plateau and correlated with Horizon Arepresents increased lithification of an otherwiseuniform clay unit approximate ly at theCretaceous/Tertiary boundary.

The recommended site location was at 0245 hours onL-DGO record 119, Cruise V3101, 21 January 1974(Figure 3). The location is 50 miles east of Site 331, Leg

35°S

Figure 1. Base map of the northeastern Argentine Basin showing the location of Site 358.Contours in corrected meters. From unpublished L-DGO bathymetric chart of theArgentine continental margin.

330

-38°W

-38° -37C -36


-34°

-34°

Figure 2. Location of Site 358 in relation to magnetic anomalies 32 and 33 as identifiedon L-DGO cruise tracks by R. Larson (personal communication).

PROPOSED

SITE 358ARGENTINE

BASIN

05 HRS

Figure 3. Site selection reference profile, 0245 hours, L-DGO Record 119, Cruise V3101, 21 January 74.

100

r01

I02

21 JAN.

103

104

- 1 0

36, which was abandoned for operational reasons aftercoring only the top 18 meters.

OPERATIONSGlomar Challenger approached the vicinity of Site

358 on a course of 182°T from Site 357 on the RioGrande Rise (Figure 5). At 0514Z, 30 November, wechanged course to 268° at a point approximately

37°38'S, 35°55'W, to approximate the heading used byR/V Vema when obtaining the seismic reflectionreference profile (Figure 3), and reduced engine speedto 150 rpm (ship speed about 6 knots). The approachprofile approximated very closely the Vema profile; weselected a site that had about 1.0 sec of sediment abovebasement and showed both reflectors A and B (Figure4). At 0618Z, we executed a Williamson turn and came

331


Figure 4. Glomar Challenger reflection profile obtained onapproach to Site 358. Reflecting Horizons A and Bshown.

37°3O'S

3 1 '

32'

33'

34'

35'

36'

37'

38'

39'

37°40'

Figure 5.358.

1 1 1 I 1 1 1 1 1 1

0456Z 30 Nov 74

S/N*801

0515 c/c 268°pgc

R/S 150 R P M ^ ^

0618Z START ^

\ TURN

\ 0 6 3 0 S/N #803

-

-

-

-

. *-*- ^ 0538Z

S/N *802DROP BEACON 0701

SITE

1 i

158

Glomar Challenger tracks on approach to Site

back on a reciprocal heading at 0627Z. We dropped thebeacon while under way at 0701Z, retrieved geophysicalgear, and returned over the beacon. The final sitelocation, based on 35 satellite navigation fixes, is35°39.31'S, 35°57.82'W.

The bottom-hole assembly used was the same as thaton previous Leg 39 sites (see Site 356 report). The heavecompensator was put in line, but failed to work whenactivated later in the drilling program. Water depth byPDR was 4956 meters, corrected, or 4972 meters to therig floor. We spudded Site 358 at 1845 LCT, 30

November 1974; the driller reported feeling bottom at5000 meters drill pipe measurement. The 28-meterdiscrepancy between pipe measurement and PDRmeasurement is greater than that at other Leg 39 sitesand greater than that normally experienced in general.The driller may have encountered and not felt a softbottom; but we decided to accept a water depth of 4990meters.

In order to ensure reaching basement, we cored theupper section at fairly wide spacing; but spacing wassomewhat closer in the vicinity of Horizon B andapproaching basement. The coring plan was to fillstratigraphic gaps by spudding a second hole at thissite. Depths of cores and recovery statistics are listed inTable 1; coring rates are plotted in Figure 6. The holedrilled and cored very quickly and easily in the rela-tively unconsolidated clay and siliceous clay above 460meters, where coring rates exceeded 40 meters/hour,and drilling rates were higher still. The firmer claysequence between 460 and 750 meters drilled well,coring at a rate of 20-30 meters/hour. Coring anddrilling rates slowed considerably below 750 meters,because the sediment was chalk. Rates of penetration inchalk and limestones were low at earlier Leg 39 sites,and forced abandonment of Sites 356 and 357 becauseof time constraints.

For Cores 9 and above, we attempted to wash awaythe sediment in the drilled interval by using pumppressure, then took the core at the base of the interval.This works well in soft sediment, where it is very likelythat we did collect in the last 9.5 meters, as intended.With a harder formation, however, the barrel isprobably filled, at least partially, in the "washed"interval. So Cores 8 and 9 may have been collectedanywhere between cored intervals 7 and 8 and 8 and 9,respectively. Elsewhere when the formation was hard,we cored at the top of the section and completed thedrilled interval with the core in the barrel, in effectusing the sediment already in the barrel as a center bit.Where recovery was complete, it is fairly safe to assumethat the sediment was collected, as intended, in theuppermost part of the sequence. Where it was less thancomplete, however, as in most of the section belowCore 9, it is more difficult to assign the sedimentcollected to a discrete zone of the cored plus drilledsection.

At 0300 LCT on 3 December, we had just cut Core 16at 817.0-826.5 meters, and were drilling two pipelengths beyond. We were a calculated 50 meters abovebasement. With a higher drilling rate below Core 16, wewere assured of reaching basement in the timeremaining; we had requested a 24-hour extension of ourETA Cape Town, so that we could spud a second holeand add needed stratigraphic coverage at this site.

Weather had been worsening since midnight, and at0400 hours we found we could no longer hold ship'sposition without taking power from the rig floor. Inview of the bad weather, and to avoid the possibility oflosing drillstring should the ship move from the beacon,we tripped to the mud line. Above the mud line, wecontinued to trip pipe slowly until we could get areliable weather report. At 1230 LCT our weather

332


Core

12345678910111213141516

Total

Depth FromDrill Floor (m)

5047.5-5057.05123.5-5133.05199.5-5209.05275-5-5285.05351.5-5361.05418.0-5427.55484.5-5494.05551.0-5560.55589.0-5598.55636.5-5646.05703.0-5712.55750.5-5760.05779.0-5788.55788.5-5798.05798.0-5807.55817.0-5826.5

TABLECoring Summary

Depth BelowSea Floor (m)

47.5-57.0123.5-133.0199.5-209.0275.5-285.0351.5-361.0418.0-427.5484.5-494.0551.0-560.5589.0-598.5636.5-646.0703.0-712.5750.5-760.0779.0-788.5788.5-798.0798.0-807.5817.0-826.5

1, Site 358

Cored(m)

9.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.5

152.0

Recovered(m)

9.56.28.62.62.43.02.68.53.79.55.98.67.15.92.72.5

89.3

Recovery(%)

1006591272532278939

100629175622826

59

forecast, based on two sequential satellite maps, wasbad for at least the next 36 hours, so we had no choicebut to abandon Site 358. We got under way towardCape Town on course 085° at 2012Z, 3 December 1974.

LITHOLOGYWe drilled one hole at Site 358, to a maximum

penetration of 842 meters, and recovered 16 cores atvarious intervals; the lowest core contained UpperCretaceous sedimentary rocks. We distinguish twomajor lithologic units at this site (Figure 7, Table 2).Unit 1 consists of siliceous mud and mudstone ofPleistocene to mid-Eocene age (Core 1 to Core 11,Section 3). Unit 2 consists of terrigenous mudstone andmarly chalk of middle Eocene to Late Cretaceous age(Core 11, Section 4 to Core 16).

Unit 1

Unit 1 is a dark greenish gray diatom-radiolarianmud, which becomes progressively firmer toward thebase. Carbonate content is generally less than 5%. Theunit is divided here into five sub-units on the basis ofdegree of consolidation and diagenetic alteration of thebiogenic siliceous component. Some of the sub-unitcontacts are readily apparent in drilling rate andseismic reflection records, and others are arbitrarilyplaced. Unit 1 extends from at least 50 meters (thedepth of Core 1) to 730 meters, and represents theinterval from the (the Holocene or) Pleistocene to themiddle Eocene.

Sub-unit 1A includes Core 1 (upper Pleistocene andlower Pliocene) through Core 2 (upper Miocene). Thebase of the sub-unit is at 152 meters, the position of aprominent reflector. The sub-unit consists of uncon-solidated diatom-radiolarian mud, generally darkgreenish gray to greenish gray, with occasional blackstreaks and indistinct grayish olive-green layers. Fewclear primary structures are visible; the muds have beendisturbed by drilling.

The major constituent is undifferentiated clay, whichranges from 40% to 70%. Silt-sized quartz decreases

from 5%-15% in the upper portion to less than 5% at thebase. Zeolites and volcanic shards occur throughout,and each makes up about 5%. Siliceous biogenicmaterial, up to 30%, forms the other major component.Diatom remains generally average about 10%, butconstitute 25% of the sediment near the top of Core 1;radiolarians and sponge spicules make up about 10% to15%. Feldspar, mica, heavy minerals, and ferro-manganoan grains occur in trace amounts throughoutthe unit. The coarse fraction consists of approximatelyequal amounts of fecal pellets and siliceous biogenicmaterial.

Sub-unit 1A contains occasional indistinct areas ordisturbed layers where the volcanic glass content isgreater than average (up to 20%) and where the siltcontent is 40%. Blebs of Mn-rich material are present,and are generally smaller than 0.5 cm in diameter.

Sub-unit IB, represented by Core 3 (mid-Miocene), issiliceous mud. It is greenish gray throughout, andcontains black blebs and indistinct layering similar tosub-unit 1A. Clay makes up about 50% to 60% of thesub-unit; quartz, volcanic glass, feldspar, manganeseoxides, and zeolites occur in trace amounts to 5%. Thecoarse fraction, somewhat different from that of sub-unit 1A, contains phillipsite (?), fish debris, and teeth,in addition to fecal pellets.

A brownish gray layer with a greater than averagequantity of quartz silt and volcanic glass is evident inCore 3. It is about 2 meters thick and grades upwardinto the dominant green-gray sediment, but its lowercontact is sharp. Sub-unit IB also shows infrequentburrow fill material of pale olive or yellowish gray.Smear-slide examination of this material reveals a 50%to 100% content of authigenic carbonate material, andvariable percentages of clay, volcanic glass, and pyrite.

The major difference between the first two sub-unitsis the nature of the siliceous component. In sub-unit 1Athe siliceous material consists of radiolarians, diatomremains, and sponge spicules, whereas in sub-unit IBsilt-sized blebs of amorphous silica occur. This lattermaterial apparently represents a diagenetic or partially

333


100 -

200 -

300 -

400 -

500 -

600 -

700 -

800-

900

-

-

-

-

-

-

-

13

111

1

7

I

8•

10I

111

16

i

9

12•

I

3

5

6

i i

11

2

1

4

I

10 20 30 40

CORING RATE (METERS/HOUR)

90 140+

Figure 6. Coring rates, Site 358.

mobilized phase of the original biogenic silica. Thecoarse fraction contains some chert-like material,

which appears to be altered but recognizable diatomand radiolarian fragments.

Sub-unit 1C includes the mudstones of Cores 4, 5,and 6 (lower Miocene-upper Oligocene), which extendfrom 220 meters to the Horizon A reflector at 460meters. Macroscopically, the sub-unit is similar to theprevious units, but its degree of consolidation differen-tiates it. Microscopically, it mose resembles sub-unit1A, in that its siliceous material is biogenic—radio-larian remains for the most part, with fewer diatomfrustules than in sub-unit 1A. Volcanic shards (10% to20%) also distinguish it from the units above and below.Evidence of burrowing occurs in Core 4 and below, andwell-formed Zoophycos burrows are prominent,especially in the lower sections. Some burrows haveblack halos. Nodular carbonate layers occur in thelower sections.

Sub-unit ID, represented by Cores 7, 8, 9, and 10(upper Oliogence to upper Eocene) is also green-graymudstone. With its (probably altered biogenic) silica, itmost resembles sub-unit IB. Sediments from Cores 9and 10 are almost completely barren; they contain onlysome pyritized radiolarians and palynomorphs.Horizon A at this site (460 m) marks the boundarybetween sub-units 1C and ID, and is apparently adiagenetic change from silica clearly recognized asbiogenic to altered silica present as amorphous silt-sizemasses (Figure 8).

Sub-unit IE consists of ferruginous mudstone and isrepresented only by Sample 10, CC and the upper threesections of Core 11. Identification of the upper contactis based on a clear color change, but coring proceduredoes not allow precise placement; we have arbitrarilyplaced the contact at 690 meters.

Sub-unit IE probably represents a transition fromthe green-gray mudstones above to the colorfulcarbonates below; it shows some characteristics ofboth. Red, blue, and dark brown usually occur asindistinct zones, with no clear sedimentary structures.Sample 10, CC also has a distinct black layercontaining large amounts of fecal pellets. Amorphoussilica and clays are the primary constituents, asthroughout Unit 1. The coloring agents are finelydispersed, but recognizable as iron oxides. In Sample10, CC, the coarse fraction contains phillipsite, fishremains, altered siliceous biogenic materials, volcanicglass, and barite crystals. The contact with Unit 2 is atthe bottom of Section 11-3, and is clearly marked at thebase of Unit 1 by up to 10% dolomite rhombs (Figure 9)and the sudden increase of carbonate constituents inthe unit below (see Figure 10).

Unit 2We assign to Unit 2 the remainder of the section

cored at this site. The position of the Unit I/Unit 2contact is somewhat in doubt, and may be an artifact ofthe coring procedure. The actual position of thisboundary is, we believe, at approximately 730 meters,coincident with Horizon B reflector. Unit 2 is dividedinto two sub-units.

Sub-unit 2A is represented only by Section 11-4, andis responsible for the Horizon B reflector. It consists ofa firmly indurated light brown marly chalk. The totalcarbonate content is about 50% to 60%. Micarb and

334


SEDIMENT COMPONENTS CORE UNIT LITHOLOGY

EOCENE

mid

early

PALEOCENE

I I 1 I I I0 10 20 30 40 50 percent1 A I AmoprhousL ^ J si l ica

Biogenicsi l ica

-J—I Nannofossils L~

^ C 0 3 fragments [ ^ | Dolomite

l Volcanic shards | * / | Fe oxide

|Z Zl Zeolite fc>^Pyrite

Figure 7. Lithologic summary, Site 358.

335


TABLE 2Lithologic Summary, Site 358

Unit

1

1A

IB

1C

ID

IE

2

2A

2B

Cores

1-11 (Sec. 3)

1,2

3

4,5,6

7,8,9.10

10, CC(Sec. 3)

11 (Sec. 4-16

11 (Sec. 4)

12-16

Depth BelowSea Floor

(m)

0-730

0-152

152-220 (?)

220 (?) -460

-HORIZON A-460-690 (?)

690 (?) -730

730-820+

730-740

-HORIZON B -

740-820+

Thickness(m)

730

152

68

240

230

40

90+

10

80+

Age

Pleistocene tomid-Eocene

Pleistocene tolate Miocene

Miocene

Early Miocene tolate Oligocene

Late Oligoceneto late Eocene

Mid-Eocene

Mid-Eocene toLate Cretaceous

Mid-Eocene

Early Eocene toMaestrichtian-Campanian

Description

Radiolarian-mud; unconsolidatedsilt and volcanic ash are common

Unconsolidated, siliceous mud;Amorphous silica and clay dominate

Consolidated, radiolarian-diatommudstone volcanic ash common

Siliceous mudstone, similar to Sub-unit IB, lower portion barren

Ferruginous, siliceous mudstone;with amorphous silica, dolomiterhombs at base

Indurated, marly micarb chalk,(light brown)

Red-brown and blue-green calcareousmudstones and marly nannofossilchalks

1mm

Figure 8. Siliceous masses recognizable as biogenic inorigin (Sample 358-7-2, 75 cm).

silt-sized carbonate fragments constitute 30% to 40% ofthe sediment, and poorly preserved nannofossils makeup the remainder of the carbonate fraction. Claysdominate the rest of the sediment, which contains traceamounts of iron oxides, volcanic shards, and zeoliteminerals.

Sub-unit 2B is represented by Cores 12-16, the finalcores at this site. The sediments are predominantly darkreddish brown, with intercalated areas of grayish blue-green. Intercalations are best developed in Core 12,where the blue-green and reddish brown materialsalternate. The color bands vary in thickness from about10 cm to 1.5 meters, and in some bands appear mixed;the contacts are usually gradational but occasionallysharp. The blue-green color bands progressivelydecrease in abundance until only infrequent andindistinct areas occur toward the base of the section.

Sub-unit 2B consists of two rock types which are notalways distinguished by their color. The first is a marlychalk containing between 50% and 70% carbonatematerial. Nannofossils range from 15% to 50%, andmicrocarbonate material may range from 30% to 60%.Foraminifers constitute 5% in Core 16. Clay makes upabout 30%, and quartz silt occurs in trace amounts.Traces of feldspar, zeolite, authigenic silica, pyrite, anddolomite rhombs constitute the remainder. The facies isusually represented by the blue-green sediment, butmay also be reddish brown, in which case iron oxidesaccount for 5% of the sediment (based on smear-slideestimates).

The second rock type is mudstone consisting of 50%to 75% clay, 5% to 25% quartz, and about 5% feldsparand zeolite. Traces of nannofossils and dolomite

336


0.1mm

Figure 9. Dolomite rhombs located at the base of Unit1, above Horizon B (Sample 358-11-3, 48 cm).

rhombs also occur. The color designation here is thereverse of the chalk facies. This lithologic type isusually reddish brown, but blue-green sediments of thesame type occur. Where reddish brown, the sedimentcontains 5% to 10% iron oxide.

Barite, foraminifers, volcanic shards, mica flakes,and fish debris form the coarse fraction of sub-unit 2B.Core 12 also contains large fragments of carbonatematerial. Sub-unit 2B appears to be burrowed through-out, especially the reddish brown sediment. Sporadiclaminae occur, usually in the blue-green material. Softsediment deformation is also sporadic.

Discussion

The lowermost sediments recovered at Site 358are ferruginous mudstones and marly chalks ofMaestrichtian-Campanian to middle Eocene age. Thechalks and mudstones seem to be intimately inter-bedded and mixed. They are predominantly reddishbrown in the lower portion; indistinct blue-green areasand bands become more prevalent in the upper portion,especially in the lower Eocene (Core 12).

Sediments rich in iron oxides have been recognized atDSDP sites in all the major ocean basins. On this leg,we sampled ferruginous sediments in the Brazil Basin(355) and on the Ceará Rise (354). In most cases, thesesediments were formed at or very close to thesediment/basalt contact. At Site 355, an intervening

nannofossil ooze occurs between the basalt and theferruginous sediments.

Boström and Peterson (1966), Boström et al. (1969),von der Borch and Rex (1970), and von der Borch et al.(1971) attribute the concentration and origin ofamorphous iron oxides to sea water precipitation nearthe mid-ocean ridges as a result of volcanic exhala-tions. For Site 355, we infer hydrothermal meta-somatic alteration of sediment, with the source of boththe ferruginous material and the calcite veins beingvolcanically derived volatiles that pass upward throughthe sediment. This argument requires intimate contactof sediment with basalt basement and, in some cases,bypassing of a lower sediment unit not enriched inferruginous material.

Another plausible explanation is that effusion ofplateau basalts, often with production of associatedlaterite, would be widespread in conjunction with theinitial rifting of the basin. The Kaoko basalts ofsouthwest Africa, with a peak effusion at 125 m.y.B.P.(Siedman and Miller, 1968), and the Serra Geral lavasof Brazil (Amaral et al., 1966) cover extensive areas onthe South Atlantic margins, and may have provided asource of iron oxides, with detrital clay and amorphousiron oxides produced through an intermediate lateritestage. Deposition of ferruginous muds and chalks in theUpper Cretaceous and Paleogene seems usually to havebeen associated with a relatively slow accumulationrate (Sites 358, 355). Comparatively slow and fine-detrital weathering of a basalt-laterite terrain would,therefore, seem reasonable for the South Atlantic atthat time.

The alternating sequence of chalks and mudstones inUnit 2 implies a depositional surface approximatelycoincident with the CCD. Occasional fluctuations ofthe CCD are represented by alternating carbonate-richor -poor sediments. The slow rate of accumulationsuggests a basin with weak circulation and with increas-ingly open marine conditions as the basin developed.

The siliceous and biogenic siliceous mudstones ofUnit 1 represent deposition below the CCD. Therelatively high rates of accumulation imply that theyare not pure dissolution facies, but rather the result ofhigh productivity of siliceous organisms and perhapsintroduction of terrigenous components by currents.The siliceous cement and matrix of sub-units IB andID are presumably products of diagenetic remobiliza-tion of biogenic silica. The scattered pyrite and greenishcolor of Unit 1 sediments indicate a reducing environ-ment. Burrows throughout the unit imply, however,that the water column was oxygenated to the bottom,allowing benthic life. Reducing conditions probablyprevailed within the sediment column as a result of highorganic productivity and consequent high rates ofsedimentation. The Unit 1 sediments show no currentstructures and are fine grained. This is as expected,since the site is in the eastern part of the ArgentineBasin, an area presently under the weak eastern arm(south-flowing) of the Argentine Bottom Gyre (Wüst,1957), where fine-grain deposition from nepheloidlayers is occurring (Ewing et al., 1971). Coarserterrigenous components are currently depositing in themore westerly areas of the basin, under westward-

337


Smear Slide Summary Site 358

% CaCCL

% CaCO3 %Forams %Nannos Fragments

Core Unit Age Lithology 0 100 0 50 0 50 0 50

100

Z2

200

300

400

500

600

70(

80

late

Pleistocene

e a r | y

Pliocene

late

IB

mid

early

1C

late

= 6

Horizon A

= 7

mid

ID

Z10

- 1 0 C C •S

late

Z l l

"12

IE

early

= 1 2 C C 2 B

Paleocene

Maestrichtian

Campanian

mid Λ

'•c?•[-~•-

% Biosiliceous

0 50

% Amorp.

Silica

0 50

Figure 10. Smear slide summary, Site 358.

r

i

338


% Quartz Silt % Clay % Zeolite Fe-Mn Oxide Pyrite Dolomite Vole. Shards Sand:Silt:Clay0 50 0 100 0 50 0 10 0 10 0 10 0 50 0 100

\

l

I i

\ I

J

4

sandsilt

ujk.

Ji•

clay

S H

s I

I

•,

I

i

Figure 10. (Continued).


intensified north-flowing bottom currents. At Site 331,west of Site 358, silty muds and silts were recovered inthe two surface cores.

GEOCHEMISTRY

We measured, aboard ship, the pH, alkalinity,salinity, Ca++, and Mg++ contents of nine interstitialwater samples. Data are presented in Table 3 andFigure 11.

PHYSICAL PROPERTIES

Physical properties measurements at Site 358 aresummarized in Table 4 and Figure 12. The cores wererecovered at such widely spaced intervals that nodetailed data are available on the variation of physicalproperties with depth. Nevertheless, some inferencescan be drawn.

One of the primary objectives of drilling at Site 358was to establish the nature of two prominent reflectorsin the area, Horizons A and B. Horizon A mayrepresent the contact between a diatom-radiolarianmudstone unit and an underlying siliceous mudstone.No significant change in velocity or water contentoccurs in the first of these units. The 2-minute GRAPEdensities for Core 6 (at about 420 m) are anomalouslyhigh. If these data are spurious, no density increaseoccurs above 450 meters either, and the diatom-radiolarian mudstone may be described asuncompacted or uniformly compacted. The average

velocity for this interval is 1.66 km/sec, the density(immersion) is near 1.53 g/cc, and the water content isabout 44%.

The properties of the underlying siliceous mudstoneare markedly different: average velocity, density, andwater content are 1.83 km/sec, 1.88 g/cc, and 25%,respectively. Further, acoustic velocity and densityboth increase with depth through the unit. Thus, thelower mudstone is more highly compacted than theoverlying unit, and the contact between these unitsmost probably correlates with Horizon A.

Horizon B probably represents the boundarybetween the mudstones and a unit, recovered in Core11, consisting of marly chalk. Velocity and bulk densityincrease distinctly across this boundary, from nearly 2.0and 2.2 km/sec and from 2.0 to over 2.2 g/cc,respectively; water content decreases from over 20% inthe mudstone to less than 15% in the chalk unit. Thediscontinuity in lithology and physical propertiesoccurs between Section 11-3 and Section 11-4, which isthought to have been recovered from a depth near 730meters, rather than from the interval intentionallycored.

BIOSTRATIGRAPHIC SUMMARYThe location of this site, in the northeastern part of

the Argentine Basin at a water depth of about 5000meters, is reflected in the nature of the sedimentarysequence and its microfossil assemblages. Figure 13shows the biostratigraphic units at this site.

TABLE 3Summary of Shipboard Geochemical Data, Site 358

Sample(Intervalin cm)

Subdepth Alkalinity Salinity Ca++ Mg++(m) pH (meq/1) (%o) (mmoles/1) (mmoles/1)/

1-4, 144-1502-3,144-150

144-150140-150140-150140-150

10-4, 140-15011-2,140-15012-4,140-150

3-4,6-2,8-5,9-2,

53.5128205.5421558.5592.0642.5706.0756.5

7.517.567.747.938.158.588.607.74

4.707.456.704.532.281.001.000.60

35.234.432.433.633.032.230.830.031.1

11.5620.0922.6427.4630.4931.2535.0635.8940.38

50.2331.9724.4813.149.287.835.005.329.65

Ca Mg

(mmoles/1) mmoles/110 20 30

I 1

50

>o -~ •

ALKALINITY(meq/1)

0 1 2 3 4 5 6 7

Figure 11. Geochemical parameters (pH, salinity, alkalinity, CA++, and Mg++ content) of interstitial waters versus depth;Site 358.

340


TABLE 4Physical Properties Data, Site 358

Sample(Intervalin cm)

4-1, 1404-1, 925-1, 1395-2, 1076-1,76-2, 1366-3, 1477-1, 1497-2, 1458-1, 1478-3, 1478-6, 14610-1, 8110-3, 13710-6, 511-1,3711-3,211-4, 14712-1, 4712-3, 14812-6, 14013-1, 8013-5, 213-0, 014-1, 4614-2, 14714-4, 146

Depth(m)

276.90276.42352.89354.07418.07420.86422.47485.99487.45552.47554.47559.96637.31640.87644.05703.37706.02708.97750.97754.98759.40779.80785.02788.50788.96791.47794.46

Velocity(km/sec)

1.6181.6161.7621.6341.6441.6641.6861.6701.8381.7321.7181.9091.8741.8561.9011.8481.9832.3062.2112.1442.2161.9872.1442.0972.1312.0592.078

Density

S I

- 1.534- 1.542- 1.531- 1.531- 1.539- 1.510- 1.535- 1.536- 1.831- 1.843- 1.823- 1.842- 1.963- 1.966_ _- 1.920- 2.022- 2.203- 2.191- 2.173- 2.179- 2.084- 2.195- 2.172- 2.200- 2.157

2.168

(g/cc)

G

1.6201.6051.3961.6011.7901.7641.8531.6141.8501.8921.8792.0011.9992.015

_1.9442.0382.2452.2542.2132.2312.3692.2202.2372.2532.1922.211

Wt%

42.6643.7344.7144.5843.2345.6244.0643.5025.5827.9128.6726.0122.9422.6222.8822.5020.4813.6313.9912.9014.7516.8513.0715.0212.9114.8814.11

Porosity i

S I

- 69.61- 69.13- 69.79- 69.79- 69.31- 71.05- 69.55- 69.49- 51.88- 51.16- 52.36- 51.22- 44.00- 43.52_ _- 46.57- 40.48- 29.67- 30.39- 31.46- 31.10- 36.78- 30.15- 31.52- 29.85

32.4231.76

G

64.4865.3777.8565.6154.3355.8850.5764.8450.7548.2440.0141.7341.8540.90

_45.1339.5227.1626.6329.0728.0019.7628.6627.6426.6930.3329.19

Acoustic Impedance

S

_————--—__-_-___—_—_______-

I

2.482.492.702.502.532.512.592.573.373.193.133.523.683.65

_3.554.015.084.844.664.834.144.714.554.694.444.51

G

2.622.592.462.622.942.943.122.703.403.283.233.823.753.74

—3.594.045.184.984.744.944.714.764.694.804.514.59

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

Siliceous microfossils occur above 560 meters (Cores1-8), whereas calcareous microfossils occur below 700meters (Cores 11-16) and increase in abundance downthe hole until it bottoms in lower Maestrichtian-upperCampanian marly chalks. The interval between 560meters and about 720 meters (Cores 9, 10 and top of 11)is virtually barren; only infrequent pyritized andrecrystallized radiolarians and some palynomorphsoccur.

Although the cores come from widely spacedintervals, it appears that a fairly complete lower upperPaleocene to Pleistocene section is present at this site.However, there is some evidence for hiatuses or periodsof very slow accumulation in the late Pliocene to earlyPleistocene, the middle to late Miocene, in the lateEocene to the early Oligocene, and in the late earlyPaleocene to the early Eocene, depending on theinterpretation of the timing and spacing of lithologicalchanges (see Sediment Accumulation Rates).Unfortunately, because of poor preservation and/orsolution of all microfossils, biostratigraphic control israther poor for the sediments bracketing theseintervals.

In general, rapid deposition well below the CCDoccurred in the late Oligocene and Neogene (Cores 1-10). The dominance of heavier, robust radiolarians andsponge spicules in the biogenic component of thesediment indicates that solution of silica has occurredthroughout the entire section. The diagenetic removalof biogenic silica has been particularly effective in Core3 of middle Miocene age, and complete dissolution isevident in Cores 9 and 10, which could only be dated by

palynomorphs to "Oligocene" and "upper Eocene,"respectively (see Ioannides and Colin, this volume).Cores 11 to 16 contain no siliceous fossils, and thesediments are characterized by calcareous microfossilsalternating with barren layers. Preservation of thecalcareous microfossils varies from poor to moderate,and every assemblage shows evidence of solution.Intersection of the site with a fluctuating CCD alloweddeposition of calcareous material in parts of theEocene, early late Paleocene, and Cretaceous; solutioncharacterized most of the early Paleocene (Boersma,this volume).

The calcareous microfossils indicate a hiatus orperiod of very slow accumulation at the Creta-ceous/Tertiary boundary. Moderate to good preserva-tion of the foraminifers and calcareous nannofossilsindicates deposition above both the CCD and thelysocline during the late Campanian-earlyMaestrichtian. The benthic foraminifers throughoutthe calcareous sequence (Cores 11 through 16) are allabyssal forms.

The siliceous microfossil assemblages indicate cool totemperate conditions during the late Oligocene. Thepresence of collosphaerids in the early Miocene, as wellas the dominance of tropical radiolarian species,indicates a warming trend in this part of the earlyMiocene. A return to cool conditions is evident inCores 1 and 2 of late Miocene to Pleistocene age.

The predominance of siliceous microfossils in theNeogene sediments is a consequence of the prior events:(a) the great depth of deposition, well below the CCDsince probably middle Eocene; (b) growth of the

341

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

900.0

SILICEOUSDIATOMACEOUSRADIOLARIANMUDSTONE

SILICEOUS

MUDSTONE

XY

460

XY

730

MUDSTONE &CHALKY MARL

w

1.5 2.0 2.5Velocity (km/sec)

3.01.5 2.3

Density (g/cc)

XY

XY

XY X

Xf

3.0 75.0 37.5Porosity(%)

Y Y

0 50.0

V

25.0Water Wt(%)

>r x

××

2.0 3.5 5.0 6.5 8.0Acoustic Impedence

Figure 12. Physical properties versus depth; +, x, andy represent syringe, immersion, and GRAPE values, respectively.


I BLACK-RECOVERY | | UN CORED INTERVAL

Figure 13. Bio stratigraphic Summary, Site 358.

Antarctic Ice Sheet and generation of colder bottomwater from Antarctica; and (c) initiation of theAntarctic Circumpolar Current with its associated highproductivity of siliceous phytoplankton and micro-zooplankton. Northward flow of cold bottom waterinto the Argentine Basin had a profound effect on the(Jeep circulation within this basin, and introduced alarge amount of biogenic silica as an important newconstitutent of the suspended sedimentary load. Therarity of siliceous microfossils in Core 3 (lower tomiddle Miocene) indicates an interruption in thissedimentary regime, possibly coupled with a reductionof surface productivity. An increase in Antarcticdiatom species occurred from the late Miocene throughthe Pleistocene, as a result of cooling of the surfacewaters and intensification of the AABW.

Fish debris is present in varying amounts throughoutthe entire recovered sedimentary section, and mayprove to be stratigraphically useful in the upperEocene-lower Oligocene interval.

ForaminifersWe retrieved a small but interesting assortment of

foraminifer faunas from Cores 11 through 16 at this site.Nearly all have been strongly altered by solution, andin many samples planktonic foraminifers have beenentirely dissolved, leaving only benthic foraminifersand other microfossils in the residues.

Core 7Sample 7, CC contains a few planktonic foraminifers,including Globorotalia (Turborotalia) opima nana andG. (T.) euapertura. This meager fauna occurs in aresidue of organic debris which suggests deposition byturbidity current; it is probably Oligocene in age.

Cores 11-14Cores 11 through 14 contain small assemblages of

planktonic and benthic foraminifers. Both faunas havebeen generally depleted by intensive solution, leavingsolution-resistant assemblages of low diversity.Planktonic species include Acarinina coalingaensis, A.densa, Globigerina (Subbotina) linaperta, G. (S.) primi-tiva, G. (S.) turgida, and Globorotalia (Morozovella)aragonensis. The benthic forms include deeper waterspecies of Bolivinopsis, Nuttallides, Aragonia, Eggerella,and Pullenia. The age assigned to these faunas is earlyto middle Eocene.

In several samples from Cores 13 and 14, faunascontain only benthic foraminifers; they are of Paleo-cene age, NP3/4 and NP5, according to the calcareousnannofossils.

Cores 15-16The top of Core 15 contains no foraminifers. The

lower sections, however, contain assemblages consist-ing only of deep water Cretaceous benthic foramin-ifers, including some very small faunas composed ofAmmodiscus and some primitive agglutinated forms(see Sliter, this volume). We cannot assign ages to thesefaunas.

The bottom of Core 16, by contrast, contains a richforaminifer fauna of a few planktonic species and many

343


benthic species. Preservation of these fossils, however,is only moderately good. The planktonic speciesinclude Globotruncana tricarinata, G. area, G. coronata,and Rugoglobigerina rugosas. Planktonic specimens arevery few, and the entire smaller fraction of planktonicforaminifers is absent. The benthic fauna is rich inGyroidinoides, Nutallinella, Dorothia, Aragonia,Pullenia, and Ammodiscus. The large size of several ofthe benthic specimens, along with a high abundance ofmica in this sample, suggests redeposition of at leastsome of its components. We assign it to the lowermostMaestrichtian G. tricarinata Zone.

Foraminifers and the CCD

If, as we suppose, this site sank according to themodel of oceanic crust of Sclater et al. (1971), then itcan be shown that in its descent from a presumed ridgedepth of 2700 meters in the earliest Maestrichtian (Core16) to 4200 meters in the middle Eocene (Core 11), itintersected the lysocline and/or the CCD several times,thus indicating a fluctuation of the CCD (see Premoli-Silva and Boersma, this volume, for discussion).

Calcareous Nannofossils

Calcareous nannofossils of middle Eocene to lateCampanian-early Maestrichtian age occur in Cores 11through 16. Cores 1 through 10 contain no calcareousnannofossils; this indicates that this site has been belowthe CCD since the mid-Eocene. Figure 13 summarizesthe distribution of coccolith zones; tables in Perch-Nielsen (this volume) show the distribution of coccolithspecies.

Eocene (Cores 11 and 12)The uppermost sample containing calcareous nanno-

fossils (Sample 11-3, 135 cm) includes only a few poorlypreserved coccoliths of mid-Eocene age. The presenceof Nannotetrina sp. assigns the assemblage to the N.fulgens Zone (NP15). Surprisingly, the assemblagecontains only very few discoasters among the solution-affected coccoliths. Discoasters usually becomeconcentrated by solution of coccoliths. This mayindicate that very few discoasters actually lived at thesite at that time, and this in turn may indicate a coolenvironment. In the next older sample (11-4, 10 cm),discoasters typical of NP14 are common, and theassemblage shows the "normal" characteristics ofdeposition below the lysocline and near the CCD:concentration of slightly overgrown discoasters, partlydissolved coccoliths, and no small or delicate largecoccoliths. Overgrowth makes the identification ofDiscoaster sublodoensis, and thus the zone of this name,difficult. Marthasterites tribrachiatus is common fromSample 12-3, 54 cm, on down through the rest of Core12, except in the core-catcher sample. It occurs withcommon D. lodoensis only in Sample 12-3, 54 cm, andin one sample just 3 cm below. Below this level, D.lodoensis is absent or very scarce, although coccolithsand/or other discoasters are common; so the preciseextent of the D. lodoensis Zone (NP13) and the top ofthe underlying M. tribrachiatus Zone (NP12) aredifficult to establish. Discoaster binodosus, D.

barbadiensis, and D. kuepperi are the other discoasterspresent in most samples. Chiasmolithusgrandis/eograndis is not so common and large as at Site357 on the Rio Grande Rise, and it is impossible toestimate a discoaster/chiasmolith ratio as a climaticindicator because of poor preservation of the chiasmo-liths, most of which lack their central structure. Thequestion of the significance of this ratio is discussed inPerch-Nielsen (this volume). The generally poorassemblages also lack Zygrhablithus bijugatus, a formcommon in the Eocene at Site 357.

Paleocene (Cores 12 to 14)

The core-catcher sample of Core 12 contains aPaleocene coccolith assemblage. The core-catchersample was probably picked up at the bottom of theinterval drilled with the core barrel in place aftercoring, in which case it represents material as far as 19meters below the rest of Core 12. It is not possible fromour data to conclude whether there was a hiatusspanning up to 7 m.y. of the earliest Eocene and the latePaleocene, or whether accumulation was very slowduring this period. Sample 12, CC and the uppermostsample in Core 13 contain a well-preserved assemblagetypical of the Fasciculithus tympaniformis Zone (NP5).Infrequent and very large forms similar to F. tympani-formis also occur in Sections 13-2 and 13-3, which areconsidered to belong to the Chiasmolithus danicus Zones.l. (including also the Ellipsolithus macellus Zone, sinceno E. macellus or E. distichus were found, probablybecause of solution), as is the rest of the core Core 14.Toward the bottom of Core 14, C. danicus becomesinfrequent, Cruciplacolithus tenuis increases in number,and the size of all coccoliths decreases. This is typicalfor the lowermost part of the Danian sequence, justabove the C. tenuis Zone (NP2) which usually is verythin (less than 1 to 2 m), as is the Markalius inversusZone (NP1). The Danian assemblage here is differentfrom the others seen on this leg (Sites 354, 356, 357), inthat Thoracosphaera, which usually occurs in largeamounts in the Danian of high and low latitudes, hereis very scarce. The same is true for forms of Neo-chiastozygus. This may indicate that both Thoraco-sphaera and Neochiastozygus are genera preferring shelfor slope environments rather than an open oceanenvironment such as is assumed for this site in theDanian. The absence in some samples of small cocco-liths that are usually abundant in the Danian isconsidered to be a consequence of solution or washingrather than other environmental factors.

Cretaceous/Tertiary Boundary and Cretaceous

The core-catcher sample of Core 14 is barren ofcalcareous nannofossils, as are most samples from thetop part of Core 15. The latter core was taken justbelow Core 14, but contained only 2.7 meters of the 9.5meters of sediment cored. The Cretaceous/Tertiaryboundary occurs somewhere in the cored butunrecovered interval, since the uppermost fossiliferoussample of Core 15 includes scarce Maestrichtian formsonly. Site 358 must have been at a depth sometimesabove, sometimes below the CCD during the latest

344


Maestrichtian-earliest Tertiary. The coccolith assem-blages of Core 15 have been strongly affected bysolution, so that only abundant Micula staurophora andvery scarce parts of shields of other coccoliths are left.The presence of parts of Arhangelskiella cymbiformisand the absence of Micula mura and Lithraphiditesquadratus suggest that the youngest Cretaceous calcare-ous sediments in Core 15 and all of Core 16 except thecore-catcher sample belong to the A. cymbiformis Zoneof the middle to early Maestrichtian age. It is possibletha t the absence of M. Mura a n d / o r L.quadratus—indicators of younger Maestrichtian—isnot primary absence but a result of solution. The core-catcher sample of Core 16 again shows an assemblagedifferent from those within the core. We assume thatthe sediment in the core catcher was picked up about 19meters below the interval over which Core 16 wascut—i.e., represents a sample from the very bottom ofHole 358. Sample 16, CC contains a diverse, reasonablywell-preserved coccolith assemblage belonging to theTetralithus trifidus Zone of early Maestrichtian/lateCampanian age. The red as well as the gray marlsamples contain scarce to few Kamptnerius magnificusand A. cymbiformis, species absent or very uncommonat other open ocean sites. Clearly Site 358 was abovethe CCD and probably above the lysocline during lateCampanian-earliest Maestrichtian time.

Radiolaria

Siliceous microfossils of Pleistocene to late Oligoceneage occur in Cores 1 through 8. In these cores, theradiolarians are generally the most abundant siliceousmicrofossils; few to common diatom remains andscarce to few silicoflagellates also occur. Spongespicules are present in varying abundance in all of theabove cores. Preservation of the radiolarians in thesecores varies from moderate to good in Cores 1 and 2and 4 through 6; it is poor in Cores 7 and 8. Extensivedissolution is evident in Core 3. Diversity follows thesame trend. Siliceous microfossils are essentially absentin Cores 9 through 12, except for very scarce pyritizedand recrystallized radiolarians. No radiolarians occurin Cores 13 through 16.

Core 1 contains an assemblage of Pleistocene age;Sample 1, CC is early Pliocene in age. The generalcharacter—for example, the presence of Theocorythiumtrachelium dianae—indicates temperate to cool waters.But most Antarctissa species, which are so common inthe circum-Antarctic sediments of that age, are missing.The radiolarians seem to span only a limited size range.This, coupled with the apparent dominance of fairlyrobust forms, indicates that the assemblage may havebeen modified by current action and dissolutionprocesses at the sea floor.

A late Miocene temperate to cool assemblage of theS. peregrina Zone is present in Core 2. Actinommatanyacantha, Cannartus laticonus, Cannartus sp. cf. C.laticonus, Stichocorys peregrina, Lychnocanoma granderugosum, Lophoconus miocenica, and Cyrtocapsellatetrapera are all present, but again the Antarctissagroup is absent, as is Theocalypytra bicornis spongo-thorax, the late Miocene nominate species for highsouthern latitude radiolarian zonation. As in Core 1, the

robustness of most specimens present may point to theeffects of lateral transport and solution.

Only a few radiolarians are present in the core-catcher sample of Core 3. Infrequent C. tetraperaoccur, along with fragments and spines of oro-sphaerids, mainly of Oroscena sp., O. carolae andscarce Orodapsis sp. All these species range from thelower Miocene to at least the lower upper Miocene.Solution and migration of the biogenic silica has takenplace in this interval; only the most solution-resistantspecies, the orosphaerids, remain, together with spongespicules.

Cores 4 and 5 are assigned to the lower Miocene C.tetrapera Zone of Chen (1975). Collosphaerids occur inboth cores, and this indicates warmer surface waters.

Of the assemblages in Cores 6, 7, and 8, only those ofCore 6 could be assigned to a zone, namely the L.elongata Zone. Radiolarians do, however, indicate alate Eocene age for Section 7-1. The assemblages arequite unlike those from the Eocene-Oligocene tropical-subtropical regions, and seem to bear only superficialresemblance to the Oligocene assemblages recovered onLeg 36 on the Falkland Plateau. But the infrequentoccurrence of Dorcadospyris ateuchus, Cannartusprismaticus, index fossils of Riedel's zonation, andCyrtocapsella semipolita, Cyclampterium sp. aff. C.milowi and Cyclampterium sp. aff. C. pegetrum indicatea late Oligocene age for these assemblages. Since theydo not unequivocally indicate either a warm or a coolenvironment, a region of mixing of cool and warmwater masses may best explain these faunas.

SilicoflagellatesSilicoflagellates occur in samples of Cores 1, 2, 4, 5,

6, and the top of Core 7. They are uncommon in thesesamples, which also contain common diatom remains.No silicoflagellates occur where diatoms are scarce andpoorly preserved.

In Sections 1-1 through 1-3, the assemblage consistsonly of the species Distephanus speculum, Dictyochaaculeata, and D. aspera. In all three samples, silico-flagellates are much too infrequent to conclude muchabout water temperatures, Dictyocha suggests warmerwaters than D. speculum. Diatom remains in Sections 1-1 through 1-4 indicate these sections are of latePleistocene age (Fenner, this volume) and belong to theD. aculeata Zone. No silicoflagellates occur in theremainder of Core 1, which we assign, on the basis ofdiatom remains, to the lower Pliocene to upperMiocene.

In Core 2—which we date as late Miocene on thebasis of radiolarians and diatom remains and thepresence of Mesocena diodon—four samples containinfrequent silicoflagellates and the endoskeletal dino-flagellate Actiniscus pentasterias.

All samples studied from Core 4 contain scarcesilicoflagellates, and are assigned an early Miocene ageon the evidence of radiolarians and the presence ofNaviculopsis lata in Sample 4, CC. The assemblages areslightly richer than in the younger samples. A.pentasterias, Carduifolia gracilis, and infrequentebridians also occur. Scarce Rocella gemma occur inSample 4-2, 130 cm and in Sample 4, CC.

345


Only the core-catcher sample of Core 5 containsscarce silicoflagellates: D. speculum, D. crux, Dictyochamedusa, Cannopilus hemisphaericus, N. biapiculata, N.cf. N. lata and Septamesocena apiculata. A.pentaradiatus, Carduifolia sp., and very infrequent R.gemma also occur.

A relatively rich assemblage occurs in Core 6,especially in Sample 6-1, 46 cm. Common R. gemmaindicates a latest Oligocene age for this sample, whichotherwise contains an assemblage similar to that inSample 5, CC. Additional species here are Corbisemaarchangelskiana and Ammodochium rectangulare.

In Core 7, silicoflagellates occur only in Sample 1, 58cm. The assemblage is similar to the one in Core 6. Thissample also includes a few archaeomonads, whoseabsence is surprising in the other Oligocene andMiocene samples, but which is probably a consequenceof dissolution rather than adverse climatic conditions.Few R. gemma may indicate a late Oligocene age forthis sample.

We may assign the cores to the following silico-flagellate zones of Perch-Nielsen (1975):

Core Zone Age

124, 567

D. aculeataM. diodonN. biapiculataR. gemmaD. medusa (?)

late Pleistocenelate Miocenemid- and early Miocenelate Oligocenelate Oligocene

DiatomsAccording to Fenner (this volume), diatom remains

in Cores 1 and 2 are generally scarce and moderately topoorly preserved, except in Section 1-3, where they arecommon to frequent and moderately to well preserved.The diatom assemblages of Sections 1-1 through 1-4can be assigned to the Coscinodiscus lentiginosus andthe C. elliptiporafActinocyclus ingens zones ofMcCollum (1975), which were correlated with theBrunhes and upper Matuyama epochs. Sections 1-5 and1-6, on the other hand, could be of earliest Pliocene oreven latest Miocene age, on the evidence of Denticulahustedtii and other Miocene species, and the absence ofCoscinodiscus lentiginosus and Nitzschia kerguelensis,which first occur in the upper Pliocene. Thus a minorhiatus, including at least the upper Pliocene and thelowermost Pleistocene, is indicated between Sections 1-4 and 1-5. This unconformity may be a result of anincrease in the AABW flow eroding or at leasthindering deposition at this site. Or the hiatus may be acoring artifact, since Core 1 was taken at 47.5-57.0meters after washing down from the surface to thisdepth with the core barrel in place. The D. hustedtiiZone of McCollum (1975), represented in Core 2,suggests a late Miocene age for that core.

Gradual cooling from the late Miocene to thePleistocene (Shackleton and Kennett, 1975) can betraced by the relative abundance of endemic antarcticspecies. The increase of antarctic species occurring atthis site in the northern part of the Argentine Basin is aconsequence of surface water cooling and of intensifiedgeneration of AABW which transports antarctic floral

elements northward (Burckle, in Groot et al., 1967;Burckle and Stanton, 1975).

PalynomorphsIoannides and Colin (this volume) studied palyno-

morphs in Cores 5 through 10, which contain nocalcareous microfossils; they found a general lack ofterrestrially derived microfossils and a limited diversityof the microplankton population indicative of an openmarine depositional environment. Core 5 containsDeflandrea phosphoritica and Tuberculodiniumvancampae; to date, the former has not been reportedfrom Miocene sediments, and the latter is unknownfrom deposits older than upper Oligocene. Thus, a lateOligocene age is suggested on the basis of palynomorphdata for Core 5, which includes a radiolarianassemblage of the Cyrtocapsa tetrapera Zone of earlyMiocene age. Section 6-3 may be assigned a tentativeOligocene age on the evidence of T. succincta, presentlyknown from Oligocene sediments, and C. cf. C.reticulosum, whose type was described from middle toupper Oligocene sediments. A late Oligocene age issuggested for this core by the presence of the radio-larian zone L. elongata and the abundance ofStictodiscus gelidus, a diatom previously studiedalongside such silicoflagellates as Rocella gemma. Core7 contains no stratigraphically significant palyno-morphs, and Cores 8 and 9 contain an assemblagewhich indicates an Oligocene age. The occurrence ofPhthanoperidinium eocenicum may indicate a lateEocene age for Core 10, which is barren of any othermicrofossils. Core 11 contains no palynomorphs.

SEDIMENT ACCUMULATION RATESFigure 14 summarizes the history of sediment

accumulation at Site 358. Age control in the upper 700meters is rather poor, because of spot coring (withintervals of 60 to 70 m), the absence of calcareousmicrofossils (present water depth is 4990 m), and onlymixed high- and mid-latitude radiolarian andsilicoflagellate assemblages are present. Cores 9 and 10contain only pyritized, non-age-diagnostic radio-larians and palynomorphs. We used calcareous nanno-fossils for age assignments in the predominantlycalcareous middle Eocene to upper Cretaceoussequence from 730 meters to the bottom of the hole atabout 840 meters.

During late Campanian-early Maestrichtian times,accumulation of the red clays and marly chalksprobably took place at about 1 cm/1000 years, firstabove and then below the CCD. From the mid-Maestrichtian to about the mid-Danian, accumulationof red clays alone proceeded at a slow rate, about 0.1 to0.3 cm/1000 years. The accumulation rate was aboutthe same or only slightly higher when the site again layabove the CCD, and coccoliths and benthic (but noplanktonic) foraminifers were deposited during theremainder of the Danian and early late Paleocene.From our data we cannot conclude whether or not theuppermost Paleocene and lowermost Eocene arepresent. If they are present in the interval of about 20meters between Cores 12 and 13, they would also have

346


2 cm/1000 yrs.200 m

SITE 355 BRAZIL BASIN

Ages by:R = RadsS = SilicosN = Calc. NannosP = PalynologyD = Diatoms

BASALT

\ SITE 358 ARGENTINE BASIN

10-1 to 6

10CC top10CC btm11-1 to 3

11-412-1 to 612CC

J_J p800 m16-1 to 2

-16CC

ca 1.8 cm/1000 yrsnon CALCAREOUS

ca 0.3 cm/1000 yrs\W

NN

Figure 14. Sediment accumulation history, Site 358. See text for explanation of alternative curves.

deposited at a rate of about 0.3 cm/1000 years. A hiatusin this part of the sequence cannot be excluded,however. Accumulation was still slow during the laterpart of the early Eocene, and perhaps increased toabout 1 cm/1000 years, toward the middle Eocene,when both calcareous nannofossils and planktonicforaminifers were preserved. Horizon B occurs at the

depth where the accumulation rate changes from verylow to about 1 cm/1000 years in the lower Eocene, thelevel of transition from calcareous to noncalcareoussediments. Core 11, the youngest core containingcalcareous microfossils (except for infrequent plank-tonic foraminifers in Core 7), consists of two differentlithologies. Sections 1, 2, and the upper part of 3

347


contain noncalcareous ferruginous mudstones; the restof Section 3 and Section 4 contain much harder, marlychalks. We take the contact of the two lithologies inCore 11 to be a drilling artifact. We suggest that theupper part of the core was taken, as intended, at the topof cored interval 11, but the bottom part of the core wasrecovered well below this level, probably midwaybetween the Core 11 and 12 intervals. In this case, theaccumulation rate in the Eocene would have remainedthe same at least until the middle Eocene (see Figure14). Accumulation may have been continuous (but ofnoncalcareous material) from then until the Pleisto-cene, or interrupted by one, two, or more hiatuses(Figure 14). The hiatuses were chosen as representingabout the same times as in the Brazil Basin, Site 355.

The core-catcher sample of Core 10 contains threedistinct lithologies. The bottom part consists of red clayprobably picked up near the top of Core 11, at thebottom of the interval drilled with the core barrel ofCore 10 in place. The middle part of Sample 10, CCconsists of a dark gray to black mudstone; the top partis the blue-gray siliceous mudstone that is in the coreitself. The dark gray mudstone, like the red clay, wasprobably recovered considerably below the rest of Core10.

Whichever version of the Eocene-early Oligocenesedimentary history of this site we favor, our datastrongly suggest that accumulation was rapid duringthe late Oligocene and the early Miocene. The regionalreflector Horizon A is late Oligocene in age, and seemsto represent a diagenetic change in the siliceousconstituents rather than a change in accumulation rateor a hiatus. The presence or absence of mid-Miocenesediments cannot be established beyond doubt with ourdata. Accumulation rate of sediments seems to havebeen fairly constant at about 2 cm/1000 years, from thelate Miocene to the present. A minor hiatus is,however, indicated in Core 1; diatom remains suggestan early Pliocene to Miocene age below Section 4, and alate Pleistocene age for the upper part of the sequence(Fenner, this volume). Again, it cannot be proven thatthis hiatus is not a drilling artifact.

CORRELATION OF REFLECTIONPROFILE WITH DRILLING RESULTS

The reference profile for Site 358 (L-DGO profileV31-01, #119) showed approximately 1.0 sec ofsediment overlying acoustic basement(Figure 3). Twointermediate reflectors—one at about the middle of thesediment column, another slightly above acousticbasement—are also clearly visible on the referenceprofile.

The approach profile shows an upper transparentzone (0.58 sec thick), an upper reflective zone (0.58 sec-0.69 sec), a lower transparent zone (0.69 sec-0.88 sec), alower reflective zone (0.88 sec-0.98 sec), and theacoustic basement at 1.04 sec. Another discontinuousreflector occurs in the area at a depth of 0.20 sec. Wesaw this reflector on the approach profile soon after wearrived at the turning point enroute to Site 358 (seeFigure 15), but this reflector vanishes immediately atSite 358.

Sonic velocities measured in the cores allow us toestimate thicknesses of the reflective and transparentzones observed on the seismic profile. We have used thefollowing interval velocities here: 1.55 km/sec fromocean bottom to 0.20 sec, 1.6 km/sec between 0.20 to0.58 sec, 1.8 km/sec between 0.58 and 0.69 sec, 1.8km/sec from 0.69 to 0.88 sec, 2.1 km/sec from 0.88 to0.98 sec, and 2.1 km/sec from 0.98 to 1.04 sec.

On the basis of these velocities, the followingsubbottom depths to various horizons can becalculated: 155 meters for the uppermost reflector at0.20 sec, 459 meters for the top of the upper reflectivezone, 729 meters for the top of the lower reflective zone,and 897 meters for the acoustic basement. Unfor-tunately, the hole had to be terminated at 842 metersbecause of adverse weather conditions.

The reflector at 155 meters seems to correlate with apossible hiatus and/or a possible change in accumula-tion rate between Cores 2 and 3. Core 2 is diatom-radiolarian mud, whereas Core 3 is siliceous mud inwhich the biogenic silica has been transformed intoamorphous silica. We assume that the uppermostreflector (155 m) corresponds to the zone of transitionfrom Unit 1A to Unit IB; i.e., from diatom-radiolarianmud to siliceous mud. From its depth in the section, wethink that this reflector is reflector F of Ewing andLonardi (1971).

A similar change from diatom-radiolarian mud tosiliceous mud occurs between Cores 6 and 7. Thecalculated depth of the top of the upper reflective zone(459 m) falls between Cores 6 and 7. We think that thetop of the upper reflective zone marks a diagenetictransition similar to that between Cores 2 and 3.Accordingly, we place the boundary at 459 meters,between Units 1C (diatom-radiolarian mudstone) andID (siliceous mudstone). A sudden decrease in drillingrate at 450 meters also marks the transition.

Even though the upper reflective zone is discontinu-ous in the vicinity of Site 358, it is the most prominentintermediate reflector of the section. Its prominenceand subsurface depth of approximately 7.25 sec (seeFigure 15) suggest that it is probably reflector A ofEwing and Lonardi (1971). So at least in thenortheastern sector of the Argentine Basin, reflector Ais late Oligocene in age and marks a diagenetictransition. The bottom of the upper reflective zone at558 meters probably marks the complete disappearanceof biogenic silica. Cores 9 and 10 of Unit IB contain nosiliceous fossils. The transition from the upperreflective zone to the lower transparent zone is grada-tional, probably because the transition from biogenicsilica to recrystallized silica within Unit ID is alsogradational.

The top of the lower reflective zone at 729 meterscorrelates with the contact of noncalcareous andcalcareous sediments in Core 11 at this depth. Since wecan assign no age to the noncalcareous upper part ofCore 11, the top of this reflective zone may alsocorrespond to a possible major hiatus spanning the restof the middle and the lower upper Eocene, or to asequence of very slow accumulation (see Figure 13)over the same interval. We assume the transition from

348


ARGENTINE BASIN

DIATOM RADMUD (1A)

SILICEOUSMUD (IB)

DIATOM RADMUDSTONE (TC)

b.br UJ TTi^ "

7.0

-

8.0L

SILICEOUSMUDSTONE (ID)

FE MUDSTONEANDMARLYCHALK

METER0

100

200

300

400

500

600

700

800-

900L

EARLY PLIOCENE-PLEISTOCENE

LATE MIOCENE

EARLY-MIDDLE MIOCENE

EARLY MIOCENE

LATE OLIGOCENE

LATE OLIGOCENE

LATE OLIGOCENE

MIDDLE OLIGOCENEOLIGOCENE

LATE EOCENE

MIDDLE EOCENE

EARLY EOCENE[PALEOCENEMAESTRICHTIAN

Figure 15. Correlation of the Site 358 approach profile with the lithostratigraphic interval drilled.

Unit IE to 2 to lie at 730 meters. Because it isdiscontinuous, filling the low areas between basementhighs, we correlate the top of the lower reflective zonewith reflector B of Ewing and Lonardi (1971). Thebottom of the lower reflective zone, at a calculateddepth of 834 meters, may correlate with the transitionfrom marly chalk, deposited near the CCD, to chalkwith well-preserved calcareous microfossils, asrecovered from the bottom of the core catcher of Core16. The acoustic basement, at a calculated depth of 897meters, was not reached.

SUMMARY AND CONCLUSIONSWe did not achieve one of the primary objectives at

Site 358, the dating of basaltic basement betweenanomalies 32 and 33, because bad weather forced us toterminate the hole early. It is possible to estimatebasement age, however, if certain assumptions aremade. The calculated depth to basement (see earlierdiscussion) is 897 meters, or 70 meters below thebottom of Core 16, dated as latest Campanian orearliest Maestrichtian, or about 70 m.y.B.P., accordingto van Hinte (1976). The accumulation rate for theUpper Cretaceous sequence at Site 358 is about 17m/m.y. Assuming accumulation was constant (i.e., nohiatus between basement and Core 16) and proceededat this average rate, and assuming acoustic basementhere is true basement and not a sill, the basement agewould be about 74 m.y.B.P., or mid-Campanian.

The isostatically adjusted depth of basement at Site358 and basement age of 74 m.y.B.P. define a pointwhich falls almost exactly on the empirical elevationcurve defined by Sclater and Detrick (1973) from theNorth Pacific and generally typical of all ocean basins.

The last up-hole occurrence of calcium carbonatesediments is at 730 meters, in a middle Eocene deposit.If we assume that this represents the time at which thedeposition site subsided below the CCD, 30 m.y. ofsubsidence at a normal rate would put the CCD at 4200meters in the middle Eocene; this agrees reasonablywell with the approximately 3700-meter CCD cited forthis time by Berger and von Rad (1972). Alteration ofmuds and chalks in Unit 2 is difficult to explain. It maybe a consequence of the site's proximity to the CCDduring most of the period from the early Maestrichtianto the middle Eocene (see discussion in Premoli-Silvaand Boersma, this volume). The site was subsidingrapidly during this period, with a concomitant generaldownward movement of the CCD. Although thetendency is toward such a trend (see Figure 4, vanAndel, 1975), data are insufficient to draw a finalconclusion.

The sharp facies change in the middle Eocene—frommarls and mudstones to siliceous and biosiliceousmudstones of unknown age (but older than latestEocene)—indicates environmental changes. If sub-sidence below the CCD were the only active process, weshould expect a drop in the rate of deposition. This is

349


one possible interpretation of the sedimentation historybetween Cores 8 and 11 (small dashed line in Figure14). A continued high sedimentation rate into the lateEocene (solid line case in Figure 14), with a hiatus atthe Eocene-Oligocene boundary and well into theOligocene, is, however, equally plausible—indeedexpected in the Argentine Basin since an Eocene-Oligocene boundary hiatus occurs at Sites 354, 355,356, 357, and 359, and since this hiatus is probably aresult of bottom current intensification. Thus the exacttransition from carbonate to non-carbonate sedi-mentation may have been affected by current erosion orcurrent-controlled dissolution as well as a CCD effect,indicating that there may have been a carbonatesequence as young as late Eocene deposited and thensubsequently removed.

Figure 14 shows a sudden increase in the depositionrate, marking an increase in biosiliceous productivity,in the late Oligocene.

We follow Frakes and Kemp (1973) in favoring aclimatic reconstruction for the Antaractic which allowsa limited amount of regional ice formation in theEocene (Geitzenauer et al., 1968). Savin et al. (1975)show a rapid drop of 5°C in bottom temperatures ofthe world oceans at about 43 m.y.B.P., or latest middleto earliest late Eocene (Zones PI4 and PI5 of Berggrenand Van Couvering, 1973). Kennett and Shackleton(1976), using oxygen isotopic analysis of SubantarcticSouth Pacific cores, report this same bottomtemperature drop, but report the sharp temperaturechange to have occurred in earliest Oligocene (38m.y.B.P.) in the Subantarctic and latest Eocene in thetropical Pacific. Presumably these temperature dropsreflect the first intruduction of cold deep water massesfrom the south into the meridional basins. This coldbottom water, formed at high southern latitudes, is heretermed "pre-Antarctic Bottom Water" (pre-AABW).Pre-AABW, with a temperature of 3°-5°C (fromFrakes and .Kemp, 1973; Shackleton and Kennett,1975; Savin et al., 1975), probably circulated in amanner similar to that of present-day Antarctic BottomWater (AABW), but more sluggishly. This late Eoceneformation of bottom water (pre-AABW) is probablyone of the most significant Oceanographic events of theCenozoic, and was enhanced during the Oligocene withthe formation of the circum-Antarctic current in themiddle to late Oligocene (Kennett et al., 1975) andconcomitant extension of the southern ice.

Water as dense as the present AABW cannot formunder any but the most severe climatic isolationconditions, those allowing winter formation ofabundant sea ice. These conditions probably beganwith true thermal isolation of the high southern latituderegions by formation of a truly circum-Antarcticcurrent. On the basis of a sharp drop in bottom paleo-temperatures, Savin et al. (1975) speculate that this didnot occur until the beginning of the middle Miocene, atwhich time the Drake Passage opened (i.e., later thanthe opening cited by Kennett et al., 1975, above).

Note that the siliceous diagenetic mudstones of sub-unit ID cover the late Eocene-early Oligocene period ofsharp bottom temperature drop associated with

establishment of pre-AABW circulation. The top ofthis diagenetic sequence correlates with the Horizon Areflector at this site. Similarly, the siliceous diageneticmud of sub-unit IB covers the mid-Miocene period ofsharp temperature drop perhaps associated with theestablishment of circulation of true AABW. The top ofthis diagenetic sequence correlates with the Horizon Freflector at this site. The diagenetic process alteringbiogenic silica to silica cement may be favored byincreased current activity (see discussion in Supko andPerch-Nielsen, this volume).

REFERENCESAmaral, G., Cordani, U., Kawashita, K., and Reynolds, J.,

1966. K-AR dates of basaltic rocks from southern Brazil:Geochim. Cosmochim. Acta, v. 30, p. 159.

Berger, W. and von Rad, U., 1972. Cretaceous and Cenozoicsediments from the Atlantic Ocean: In Hayes D.E., Pimm,A.C., et. al., Initial Reports of the Deep Sea DrillingProject, Volume 14: Washington (U.S. GovernmentPrinting Office), p. 787-953.

Berggren, W.A. and Hollister, CD., 1974. Paleogeography,paleobiogeography and the history of circulation in theAtlantic Ocean: In Hay, W.W. (Ed.), Studies in paleo-oceanography: Spec. Publ. 20, Soc. Econ. Paleontol.Mineral., p. 126-186.

Berggren, W.A. and Van Couvering, J.A., 1973. LateNeogene chronostratigraphy, biostratigraphy, and paleo-climatology: Woods Hole Oceanographic Institute Tech.Rep. WHOI-73-40.

Boström, K. and Peterson, M.N.A., 1966. Precipitates fromhydrothermal exhalations on the East Pacific Rise: Econ.Geol., v. 61, p. 1258.

Boström, K., Peterson, M.N.A., Joensuu, O., and Fischer,D.E., 1969. Aluminum poor ferromanganoan sedimentson active oceanic ridges: J. Geophys. Res., v. 74, p. 3261.

Burckle, L.H. and Stanton, D., 1974. Distribution of dis-placed Antarctic diatoms in the Argentine Basin. InSimonsen, R. (Ed.), Third Symp. Recent and fossil marinediatoms, Kiel, 1975, Proc.

Chen, P., 1975. Antarctic Radiolaria. In Hayes, D.E., andFrakes, L.A., et al., Initial Reports of the Deep SeaDrilling Project, Volume 28: Washington (U.S.Government Printing Office), p. 437-513.

Ewing, M. and Lonardi, A.G., 1971. Sediment transport anddistribution in the Argentine Basin. 5. Sedimentary struc-ture of the Argentine Margin, Basin and related provinces.In Ahrens, L.H. et al., (Eds.), Physics and chemistry of theearth, v. 5: New York (Pergamon Press).

Ewing, M., Eittreim, S..L., Ewing, J..I., and Le Pichon, X.,1971. Sediment transport and distribution in the ArgentineBasin, 3, Nepheloid layer and processes of sedimentation.In Ahrens, L.H. et al. (Eds.), Physics and chemistry of theearth, v. 8: New York (Pergamon Press), p. 49.

Frakes, L.A. and Kemp, E.M., 1973. Paleogene continentalpositions and evolution of climate. In Tarling, D.H. andRuncorn, S.K. (Eds.), Implications of Continental Drift tothe earth sciences, v. 1; New York (Academic Press),p. 535.

Geitzenauer, K.R., Margolis, S.B., and Edwards, D.S., 1968.Evidence consistent with Eocene glaciation in a SouthPacific deep sea sedimentary core: Earth Planet Sci. Lett.,v. 4, p. 173.

Groot, J.J., Groot, C.R., Ewing, M., Burckle, L., andConolly, G.R., 1967. Spores, pollen, diatoms, and

350


provenance of the Argentine Basin sediments. In Sears, M.(Ed.), Progress in oceanography, v. 4: London (PergamonPress), p. 179-217.

Heirtzler, J.R., Dickson, G.O., Herron, E.M., Pitman, W.C.HI 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.

Kennett, J.P. and Shackleton, N.J., 1976. Osygen isotopicevidence for the development of the psychrosphere 38 m.y.ago: Nature, v. 260. p. 513-515.

Kennett, J.P., Houtz, R.E., et. al., 1975. Cenozoic paleo-oceanography in the southwest Pacific Ocean, Antarcticglaciation, and the development of the Circum-AntarcticCurrent. In Kennett, J.P., Houtz, R.E., et al., InitialReports of the Deep Sea Drilling Project, Volume 29:Washington (U.S. Government Printing Office), p. 1155.

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).

McCollum, D.W., 1975. Diatom stratigraphy of the SouthernOcean. In Hayes, D.E., Frakes, L.A., et al., Initial Reportsof the Deep Sea Drilling Project, Volume 28: Washington(U.S. Government Printing Office), p. 515-571.

Perch-Nielsen, K., 1975. Late Cretaceous to Pleistocenesilicoflagellates from the southern southwest Pacific,DSDP Leg 29. In Kennett, J.P., Houtz, R.E., et al., InitialReports of the Deep Sea Drilling Project, Volume 29:Washington (U.S. Government Printing Office), p. 873-908.

Savin, S.M., Douglas, R.G., and Stehli, F.G., 1975. Tertiarymarine paleotemperatures; Geol. Soc. Am. Bull., v. 86,p. 1499-1510.

Sclater, J.G. and Detrick, R., 1973. Elevation of mid-oceanridges and the basement age of JOIDES Deep Sea DrillingSites: Geol. Soc. Am. Bull., v. 84, p. 1547-1554.

Shackleton, NJ . and Kennett, J.P., 1975. Paleotemperaturehistory of the Cenozoic and the initiation of Antarcticglaciation: oxygen and carbon isotope analyses in DSDPSites 277, 279 and 281. In Kennett, J.P., Houtz, R.E., etal., Initial Reports of the Deep Sea Drilling Project,Volume 29: Washington (U.S. Government PrintingOffice), p. 743.

Siedman, G. and Miller, J., 1968. K-Ar determinations onbasaltic rocks from southwest Africa and their bearing oncontinental drift: Earth Planet. Sci. Lett., v. 4, p. 451.

van Andel, T.H., 1975. Mesozoic/Cenozoic calcite compen-sation depth and the global distribution of calcareoussediments: Earth Planet. Sci. Lett., v. 16, p. 187-194.

van Hinte, J.E., 1976. A Cretaceous time scale. Am. Assoc.Petrol. Geol. Bull., v. 60, p. 498-516.

von der Borch, C.C.and Rex, R.W., 1970. Amorphous ironoxide precipitates in sediment cored during Leg 5, DSDP.In McManus, D.A., Burns, R.G., et al., Initial Reports ofthe Deep Sea Drilling Project, Volume 5: Washington(U.S. Government Printing Office), p. 541-544.

von der Borch, C.E., Nesteroff, W.D., and Galehouse, J.S.,1971. Iron rich sediments cored during Leg 8 of the DSDP.In Tracey, J., et al., Initial Reports of the Deep Sea Drill-ing Project, Volume 8: Washington (U.S. GovernmentPrinting Office), p. 541.

Wüst, G., 1957. Stromgeschwindigkeiten und Strommengenin den Tiefen des Atlantischen Ozeans: Wiss. Ergeb.Deutschen Atlantischen Expedition "Meteor" 1927-1927,v. 6, p. 261.

351

APPENDIX ASmear-slide Summary

1-1, 99

1-1, 145

1-4, 56

1-5, 63

1-5, 87

2-1, 26

2-1,103

2-2, 60

3-2, 80

3-3, 50

3-5, 136

4-1, 131

4-2, 121

5-2, 25

5-2, 90

6-3, 20

6-3, 130

7-2, 75

7-2, 123

7-2, 127

8-2, 40

8-4,100

8-5, 35

9-1, 111

9-1, 111

9-3, 80

10-4, 75

10, CC

10, CC

11-2, 16

11-2,138

11-2, 94

11-2, 148

11-3, 150

11-4,93

12-1, 20

12-2, 40

12-2, 60

GO

5

10

5

5

5

bo

10

25

20

10

40

15

10

10

20

20

15

25

30

25

35

30

20

5

5

5

85

5

95

10

10

10

10

10

10

10

10

10

20

25

25

25

>>

u

90

75

80

90

60

80

90

90

80

80

85

75

70

75

65

70

70

95

95

95

15

95

5

90

90

90

90

90

90

90

90

90

80

70

70

70

S1

t-l

a

5

40

10

5

10

Tr

5

5

10

5

10

5

1

5

5

5

5

Tr

Tr

10

5

Tr

5

5

5

5

5

5

Tr

Tr

u

b

5

5

5

5

1

1

1

Tr

10

Tr

5

5

5

Tr

5

Tr

Tr

s

Tr

Tr

Tr

1

1

Tr

Tr

1

Tr

Tr

!

.s>>

IseTr2

Tr

Tr

Tr

1

1

Tr

ifu

35

30

25

45

45

25

55

55

35

45

45

40

40

45

40

35

15

45

20

35

15

40

5

65

55

65

55

60

55

60

65

55

45

30

40

45

3'3jj"o

5

20

15

10

10

5

10

5

5

10

15

15

25

10

5

5

5

5

10

Tr

Tr

5

Tr

"2

Oco

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

1

1

Tr

Tr

Tr

1

Tr

Tr

5

Tr

5

5

13

6

„

Tr

5

10

1

Tr

Tr

OH

Tr

40

5

5

Tr

5

5

20

5

10

5

5

Tr

5

Tr

Tr

σ"Pj

&

O

5

5

JS

O

zo0

sTr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

Tr

ü,2oQ

510Tr

TrTr

"o<uN

5

55

51055510555555Tr5

5

Tr5

5

Tr

Tr

<v"So

3o'3α>.SP"3<

5

5

2

50

80

85

100

90

10

40

20

20

20

S•Λ

bo

'3<D

.SP"3<

10

20

15

20

5

5

15

30

25

25

10

10

5

10

5

25

40

40

15

5

30

30

20

30

30

30

30

30

20

εo

1

mof

ossi

ls

cCS

Zo

Tr

Tr

Tr

Tr

5

15

50

35

30

εo

•iQ

25

5

15

10

10

5

15

5

5

15

15

5

1

10

5

Tr

5

Tr

1

5

Tr

c

.23

is-303

DS

5

5

5

5

5

5

5

5

10

10

20

5

5

5

5

oo<u

oOrGO

5

5

5

5

5

5

5

5

1

2

5

5

5

5

5

Remarks

Burrow

Burrow

White crust

Brown crust

Black layer

Red layer

Green pebble

Brown pebble


o g o m v) r*< o © o m

O O O Λ(N Cl ^ -•I ^H

O © in ©

£ no >n © • 0 ""> £

> o o o < n o o o o n>o>o

>n in >n

0 O Oc ~ - o o o o o ^ t— o^ o o r β o

APPENDIX BCarbonate and Quartz Determinations

Section

1-51-51-6

1-62-22-32-43-23-23-23-53-53-54-14-14-15-15-25-26-16-36-37-17-1

7-28-18-28-29-29-310-410-411-211-311-411-411-412-312-312-512-513-113-113-414-114-114-214-214-415-115-115-115-216-216-216-2

SedimentDepth (cm)

542854465582560012540127601289420168201932020120618206402064327648276622768735206353373539241819421334217149019490804923755212552765527959114592296417068769705167060970755708327084675426754307575475760779787803678455788727887279038791357944079865798707987080090819488195181956

CaCO3(%)

0.110.850.000.820.031.170.00

0.270.60

0.370.200.00.500.640.01.100.470.300.71

0.200.56

4.080.520.400.480.100.360.00

47.77

51.8263.3368.9736.6538.0521.9929.5822.0145.0351.2740.0228.5447.111.750.430.1321.7413.5110.2616.72

Org (%)

0.200.380.480.210.210.120.45

0.260.13

0.090.05

0.210.24

0.120.160.160.22

0.180.16

0.170.270.120.200.230.210.04

0.05

0.290.240.040.060.230.210.060.450.180.070.300.370.050.360.000.040.050.200.330.05

Total.Carb (%)

0.220.49

0.310.210.27

0.290.21

0.130.08

0.270.32

0.250.220.190.30

0.200.23

0.660.340.170.260.240.250.08

5.79

6.517.848.324.464.802.852.61

5.586.23

3.795.71

0.060.062.661.83

2.06

Qtz (%)

10.75

10.12

10.64

9.40

9.78

7.84

9.37

7.73

9.85

9.89

18.39

20.75

13.0729.16

13.608.86

11.86

10.21

12.58

14.01

353

Site

3N3G

PLEISTO'

öoa.

<;

358

o

acul

eata

•lole

FOSSILCHARACTER

[ FO

RAN

Barn

—

cocc

c

RM

-

_

_

—

[ RA

DSFM F

FMP

RP

RP

_

—

FM

o

1 SIL

KRM

RM

RM

:ore 1

-

0

1

2

3

4

5

6

25

0 . 5 -

1.0——_-_-

—

I—

Z

i i

i i

1 i

i

:

_

~--

-

-_z~-

CoreCatcher

Cored I n t e r v a l :

LITHOLOGY

•^~ ~^z

—v> —

• 7 " ^ - -

•*—*-c

—^

•J- •‰r•

~^<t ~~H

<zjpjz

r f ^

- v > r —

/z×^y(zr- — j-

- N T " —

r^jj~yz

-̂ _ _

-rv-

O ^

"<>

i

z~z

—• - —

~_~7_~

7_~_—_—_

-z-•

• Z T Z •

Z-Z-

üiüi

..T_171—_—_

hi

—

-_—_—"7"_~—~.

~-T-~~-~-~

!_"_""_.

,"~_"7_~~

.'.~."~.

'_—!

r"Z~Z-

Z~ZrZ

σ

|

oU-a

1

|

I'

I1

11

11|

11I1

L U

.SAMP!

[ LI

THO

99

45

56

63

87

CC

17.5-57.0 m

STR

1 SE

D.

rzz •

- - •

LITH0L0GIC DESCRIPTION

DIATOMACEOUS MUD, dark greenish gray (5GY 4/1)t o greenish gray (5G 6 / 1 ) , blebs of apparentlycoarser m a t e r i a l , greenish gray (5G 6/1) at 8 0 ,90, 136 (Sec. 1 ) .

VOLCANIC MUD, o l i v e gray (5Y 4 / 1 ) , smearedalong side blebs of coarser m a t e r i a l , greenishgray (5G 6 / 1 ) , Sec. 2, 02, 56, 62, 78, 96, 147,some dark streaks - grayish black (N2).SS 99 SS 14535% Clay 40% Quartz s i l t

5% Volcanic glass 25% Clay25% Diatoms 20% Volcanic glass

5% Rads 5% Sponge spicules10% Amorp. s i l i c a TR% P y r i t e , l imon-10% Quartz s i l t i t e , Heavy

5% Heavy minerals minerals5% Z e o l i t e 10% Diatoms

TR% Fe-Mn Oxides

(

\ Grading t o f i r m mud.

SS 565-10% S i l t

TR- 5% Feldspar30% Clay15% Volcanic glass20% Diatoms15% Rads

5% Sponge spiculesTR% Limonite

DIATOMACEOUS RADIOLARIAN MUDf i r m mud, occasional dark s t r e a k s / i n d i s t i n c t

bandi ng.62-92, l i g h t o l i v e gray (5Y 6 / 1 ) , color band.92-97, o l i v e gray (5Y 4 / 1 ) , color band.128-132, o l i v e gray (5Y 4 / 1 ) , co lor band.10-20, s l i g h t l y darker deformed band(?).

SS 63 & 87 CC5-10% Quartz s i l t 25% Amorp. s i l i c a

5% Feldspar 10% Diatoms-Rads50% Clay 5% Quartz s i l t10% Diatoms-Rads 50% Clay

5% Sponge spicules 5% Volcanic shards5-TR% Volcanic glass 5%.Fe Oxides

10% Amorp. s i l i c a5% Z e o l i t e5% Fe-Mn Oxides

C03: Sec. 1 , 100 cm = 3%

Site 358 Hole Core 2 Cored Interval: 123.5-133.0 m

FOSSILCHARACTER

8 g

CoreCatcher

LITHOLOGIC DESCRIPTION

DIATOM-RADIOLARIAN MUDgreenish gray (5G 6/1), s t i f f , p y r i t i f e r o u s blebat 26 (Sec. 1) other black areas throughout,apparently coarse areas (Sec. 1 ) , 0-30, 60-66,78-82, 102-105, 112-115, 127-129, 146-150.Sec. 2 - 0-42.

SS 2640% Pyrite30% Clay10% Volcanic glass10% CO3 frags.10% Diatoms-Rads

SS 60, 70, 103TR- 5% Quartz si I t60-50% Clay

5% Volcanic glass5-10% Zeolite5-15% Amorp. s i l i c a5-25% Diatoms-Rads

TR% Fe Oxides

Somewhat darker area -̂ 100 (Sec. 3) - 21 (Sec. 4).

CO,: Sec. 2, 40 cm =

çç_20% Diatoms-Rads10% Amorp. silica5% Quartz silt5% CO3 frags.

45% Clay5% Zeolite

10% Fe-Mn Oxides

Explanatory Notes in Chapter 1

Hole Core 3 Cored Interval:199.5-209.0 Cored Interval: 275.5-285.0 m

FOSSILCHARACTER

-Δ

CoreCatcher


SILICEOUS MUDgreenish gray (5G 6/1)

becoming firmer

dark bleb at 45 (Sec. 2), dark indistinctlayers at 58 & 69 (Sec. 2).

Occasional dark layers - indistinct.

SS 80 & 50

5% Quartz siltTR- 5% Feldspar

5% Volcanic glass55% Clay25% Authigenic silica5% Zeolite

5-TR% Limonite, Pyrite3-TR% C0

3 frags.

Greenish gray mud (5G 6/1)

grading to

brownish gray clay (5YR 4/1) with some greenish-gray material interspersed.

VOLCANIC MUD

SS 39, 136, CC

10- 5% Quartz silt

5% Volcanic glass

50% Clay

5% Zeolite

5% Sponge spicules

25% Amorp. silica

TR- 5% Fe Oxides

Sharp contactwithgreenish gray (5G 6/1) mud as above.

Two brownish areas interspersed at 15 and 60

(Sec. 6).

CO,: Sec. 2, 93 cm = 0%J Sec. 5, 90 cm • 0%

FOSSILCHARACTER


RADIOLARIAN MUDSTONE, greenish gray (5G 6/1),broken and rotated clumps/drilling breccia,individual clumps are firm with dark blebs andbands, dark green-black bleb at 131.SS 121, 131

5% Quartz siltTR% Feldspar40% Clay

20-15% Volcanic glassTR- 5% Pyr i te10- 5% Zeol i te

5% Diatoms15% Rads

5% Sponge spicules10% Amorp. s i l i c a

Sec. 2, 86-88, three black composite burrows.

CO3: Sec. 1 , 112 cm = 1%

Cored I n t e r v a l : 351.5-361.0 m


VOLANIC RADIOLARIAN MUDSTONE, dark greenishgray (5G 4/1) , broken and rotated d r i l l i n gbreccia; i n d i s t i n c t l a y e r s , grayish o l i v egreen (5GY 3/2); some black blebs - layers;zoophycos burrows, l a r g e ; well formed ( 4 ) ;Sec. 2, 30 cm - large burrow (.7 cm d i a . ) wi thblack ha lo; 40-50 cm - i n d i s t i n c t layers grayishgreen (5GY 3/2).SS 25 8. 9050-60% Clay15-20% Volcanic glass

5% Pyr i te ( i n dark layers)5% Zeol i te

15% Diatoms-RadsTR% Quartz, Mica10% Amorp. s i l i c a

CO,: Sec. 2, 10 cm = 2%Sec. 2, 37 cm = 1%

*LATE OLIGOCENE according to palynology

Explanatory Notes i n Chapter 1

to>CΛ

Cored Interval:418.0-427.5 m Core 8 Cored Interval: 551.0-560.5 m

FOSSIL

CHARACTER

FHG

FMG

FMG

CoreCatcher

a

o


RADIOLARIAN MUDSTONE, dark greenish gray (5GY4/1), dark burrows throughout, drilling breccia.

Burrows throughout, occasional Zoophycos - wellformed, large burrows (•>-l cm dia.) have gray(5Y 5/1) centers with black halo.

Sec. 3 at MOO cm - soft sediment deformationburrows faulted - M cm displacement.47-48, 134-136, nodule or layer of carbonateyellowish gray (5Y 8/1) at 134 distinct butdeformed contact.SS 20, 92

5% Quartz silt40% Clay

10% Volcanic glassTR- 5% Zeolite

10* Diatoms20* Rads

5% Sponge spiculesTR% Limonite, Mica,

Pyrite5% Amorp. silica

CO,: Sec. 1 , 19 cm =

SS 1365% Volcanic g lass

85% A u t h i g e n i c CO,5% Diatoms, Rads

TR% P y r i t e

Core 7 Cored I n t e r v a l : 4 8 9 . 5 - 4 9 4 . 0

FOSSILCHARACTER

CoreCatche


SILICEOUS MUDSTONE, dark greenish gray (5GY4/1) - drilling breccia, dark burrows through-out, occasional large Zoophycos and compositeburrows

grading to

grayish blue green (5BG 5/2).

113-134, lamina (dusky blue-green [5BG 3/2])123 (1-2 mm) disrupted black lamina

SS 123 (Black)25% Clay40% S i l i c a20% Pyri teTR% Quartz,

SS 75, 127TR- 5% Quartz40-45% S i l i c aTR- 5% Volcanic glass45-50% ClayTR- 5% Pyr i te

5% Zeol i teTR% RadsTR% Feldspar

Limonite10% Rads-Diatoms

CO,: Sec. 2, 27 cm = 3%

AGE

:EN

E

o

o

,ATE

ZO

NE

FOSSILCHARACTER

8

FO

R?

rei

CO

-

cocc

LIT

I

—

RP

-R

AD!

-

CP

o

PA

LI

+

+

+

+

IS)

0

I

2

3

4

5

6

-

I0 5—

-

1.0-

_

-

--

Z_--

-

1

:

-

-

z.--_::-

-

-

-:

-

CoreCatcher

LITHOLOGY

VOID

ΔΔ

ΔΔ

Δ

ΔΔ

ΔΛ

ΔΔ

ΔΔ

Δ

. Δ

Δ

ΔΔ

ΔΔ

ΔΔ

Δ

Δ

ΔΔ

ΔΔ

ΔΔ

Δ

Δ

Δ

ΔΔ

Δ

'~-~-~.

1

-•~T r

"~ :

~_7_71_"

r"_~_7.ili

_-_j7_—" _ . j — •

rt

_~_~_7

—Jo—.- ~

Z-I-I-

'. IT

o

|

O.S

AMPL

LIT

H

24

40

100

35

CC

STR

SED

.

o

o

otffci<

§o

o

o

o

o

o


SILICEOUS MUDSTONE, greenish black (5GY 2/1),many burrows - usually filled with black

material or various shades of dark green,many zoophycos and composite burrows.

Sec. 2:35-48, greenish gray area (5G 6/1) with lightolive gray burrows (5Y 6/1).

98-120, soft sediment deformation.

SS 40.3580* Authigenic COj

15* Clay

5* Volcanic glass

SS 24, 100 CC10% Quartz, Feldspar silt

60% Clay20% Authigenic silica

5% Pyrite

5% ZeoliteTR% Mica, Limonite

Sec. 5, burrow at 35 cm ( \.l cm dia.) paleolive (5Y 6/3) with black halo.

CO,: Sec. 2, 26 cm = 4%J Sec. 3, 57 cm = 3%


Core 9 Cored I n t e r v a l : 589.0-598.5 S i t e 358 Hole Core 10 Cored I n t e r v a l : 636.5-646.0 m

FOSSILCHARACTER

111B

niw.


SILICEOUS MUDSTONE, dark greenish gray (5G 4/1)to medium bluish gray (5B 5/1), drilling brecciathroughout - with no fine material interspersed.SS 111 (Burrow)90% Authigenic C03, 10% S i l i c a

SS 111 (White)1002! Authigenic C03

burrow"light olive-gray (5Y 6/1)

Srtiite-green-gray

other light olive-grayburrows

Burrowed throughout, but not extensively, 1Zoophycos in top section - none below, burrowsusually with dark material, some with lightolive gray (5Y 6/1).

Sec. 3, large portions undisturbed.

SS 28, 80, CC

25% Authigenic silicaTR% PyriteTR« ZeoliteTR% Limonite5% Quartz, Feldspar silt

C03: Sec. 2, 64 cm = 0% .

FOSSILCHARACTER

ε>

o

ù


SILICEOUS MUDSTONE, dark greenish gray (5G 4/1)to greenish black (5G 2 /1 ) , d r i l l i n g brecciathroughout, black, i n d i s t i n c t layers a t : Sec. 1 -38, 39, 66, i n d i s t i n c t green lamina also associ-ated wi th black ma te r ia l , Sec. 1 , 141-142 -series of burrows wi th l i g h t o l i ve gray (5Y 6/1)mater ia lk , burrows general ly not d i s t i n c t .

Sec. 4 , 136-140, two large burrows of l i g h to l i ve gray (5Y 6/1) mater ia l .SS 75, 125

5% Quartz s i l tTR- 5* Feldspar s i l t

60* Clay30* S i l i caTR% Zeol i teTR% Py r i t e , Volcanic

glass

Sec. 6 , 0-50, s imi lar to above, wi th s l i g h t l yl i gh te r shade of green. Grayish blue-green(5BG 5/2) wi th occasional l i g h t o l i ve grayburrows (5Y 6 /1 ) ; 50-110 cm, extreme d r i l l i n gbreccia; 110-150 cm, t rans i t i ona l upper contactto general ly brownish gray (5YR 4/1) wi thinterspersed i nd i s t i nc t bluish areas.

CC Sequence:Green-gray (as above); black layer ; dark red-brown (5YR 3/3) .SS CC (B)5% Quartz, Feldspar s i l t

65% Clay25% Authigenic s i l i c a5% Pyr i te

SS CC (R)5% Quartz s i l t

80% Clay15-10% Authigenic

s i l i caTR% Limonite,

Pyrite

CO,: Sec. 4 , 70 cm =


Hole Core 11 Cored I n t e r v a l : 703.0-712.5 m Core 12 Cored I n t e r v a l : 750.5-760.0 m

FOSSIL

CHARACTER

CoreCatcher

Δ _-_-_-


FERRUGINOUS MUDSTONE, dark reddish brown (5YR 3/3)dominant, mixed with indistinct areas of grayishblue green (5BG 5/2). Occasionally in layers(largest 2 cm thick). Oval areas resemble alteredburrows, not otherwise burrowed, no clear struc-tures.

SS 16 (Blue-green)5% Quartz silt

65% Clay30% SilicaTR% ZeoliteTR% FeldsparTR% Volcanic glass

SS 138 (Red-brown)5% Quartz60% Clay30% Silica

5% Fe OxidesTR% Nannos

SS 11, 9460% Clay30% Authigenic s i l i c a

5% Volcanic glassTR% Mn-Fe Oxides

Sec. 3, 109-133, gradational to 133-142 -grayish blue-green (5BG 5/2), 142-150 - d r i l l i n gbreccia with many d i s t i n c t clasts in greenishgray (5G 6/1) matrix. Lithology of 2 clasts

S i m 1 • U r • SS 148 » 150

25% Authigenicsilica

10% Dolomiterhombs

TR% Quartz,

Feldspar5% Nannos

Sec. 4, MARLY CHALK, l i g h t brown (7.SYR 6/4),burrowed throughout; 96-108, very f i n e lamina at10° dip with sharp bottom contact.SS 93, 10035-40% Clay

20% Calcareous nannosTR% Dolomite rhombs,

Pyr i te , Zeolite40-45% Micarb, C03 f rags.

CO,: Sec. 3, 11 cm = 2%Sec. 4 , 5 cm = 48%Sec. 4, 102 cm 47%


FERRUGINOUS MUDSTONE AND MARLY CHALKS, dark brown(7.5YR 4/2) a l ternat ing with l i g h t bluish gray(5B 7/1); color bands vary from 10 cm to 1.5meters t h i c k ; occasionally mixed with gradationalcontacts; burrowed throughout but most noticeablein the brown sediment. Three Zoophycos in Sec. 1,none i n rest of core. Sec. 1, 113-123 - sof tsediment deformation, occasional lamina notedespecially i n blue mater ia l . Sec. 2, color bandsdevelope •v20° dip.SS 20, 105, 120 (Blue

30% Clay30-20% Micarb40-50% Nannos

SS 40, 149 (Brown)40% Clay20% Micarb35% Nannos

5% Fe OxidesTR% Volcanic glass,

Dolomite rhombsSS 60 (Brown)45% Clay15% Authigenic CO,35% Nannos

5% Fe OxidesTR% Dolomite

Sec. 3, 47-48, dark brown layer (7.5YR 3/2),sharp bottom contact, faulted

48-70 cm - sof t sediment deformation.78-92 cm - small v e r t i c a l cracks.

SS 47 (Dark-brown) SS 80 (Blue)60% Clay 20% Micarb

5% Fe Oxides 50% Nannos15% Micarb 30% Clay15% Nannos TR% Volcanic glass

5% Quartz s i l t

Sec. 4 , burrows very i n d i s t i n c t .

SS 113 (Brown)40% Nannos20% Micarb, CO, frags.

5% Dolomite35% Clay

Sec. 6, 42-60, sharp contacts - color bandsdip •^10°.

SS 60 (Brown)5% CO, frags

90% Clay5% Volcanic glass

TR% Quartz, silt

Core catcher probably "picked up" above top ofCore 13, 19 m below bottom of 12!CO,: Sec. 2, 22 cm = 59%

Sec. 3. 80 cm = 69%

Explanatory Noces in Chapter

to>XΛ

Hole Core 13 Cored Interval: 779.-788.5 m Core 14 Cored Interval: 788.5-798.0


FERRUGINOUS MARLY CHALK, dark brown (7.5YR 4/4),light bluish gray (5B 7/1) areas at: Sec. 1,41, 46, 52, 125; •x-2 cm in dia. with indistinctoutline; burrowed throughout with slightlydarker brown material.

Sec. 2, slightly lighter in color, brown (7.5YR5/4) to reddish brown (5YR 4/4); indistinctbluish area at 33 cm.

Sec. 3, indistinct bluish area at 60 cm.

Sec. 4, slightly darker areas at 26-36 and 99-115 dark reddish brown (5YR 3/3).SS 70, 115

TR- 5% Fe Oxides5-10% Micarb

60-50% Nannos5% Quartz silt

SS 108, CC (Darker red-brown)50% Clay5% Fe Oxides

40% Nannos5% Quartz silt

C03: Sec. 5, 20 cm =


FERRUGINOUS MARLY CHALK, dark reddish brown(5YR 3/4); light bluish gray layer (5B 7/1)near core top - M50° dip. Burrows cross colorboundary horizontally from blue to brown;burrows throughout.

Sec. 4, 30-55, 80-90, slightly darker shadesof brown - no sharp contacts.SS 10 8, 395% Quartz silt

50% Clay5% Fe Oxides

40% NannosTR% Forams, Volcanic glass,

Dolomite rhombsCO,: Sec. 1, 22 cm = 51%

Sec. 4, 9 cm = 27%Sec. 4, 140 cm - 47%

Core catcher: noncalcareous.


ww>CΛ

2

Core 15 Cored Interval: 798.0-807.5

AGE

MIDDLE

MAESTRICHTIAN

ZONE

Arkhangelskiella

cymbiformis

FOSSILCHARACTER

FORAMS

j no

planktonics

1 1

C0CC0-

LITHS

RP

CP

CP

RADS SECTION

0

1

2

METERS

2

0.5-

1 1

1 1

1 1

1 1

1 1

I I

1 I

CoreCatcher

LITHOLOGY

VOID

>oool —o•o-o•<d-—

— — — -

DEFORMATION

LITHO.SAMPLE|

65

100

140

CC


FERRUGINOUS MUDSTONE AND MARLY CHALK, darkreddish-brown (2.5YR 3/4), Sec. 1, 29-39;Sec. 2, 93-100 - burrows, generally no visiblestructures.SS 65, 10010% Quartz75% Clay10% Fe OxidesTR% Volcanic glass, Heavy

minerals, Dolomiterhombs, Nannos

Sec. 2, 23-26, 75-78, 136-144 - areas ofgreenish-gray material (5G 6/1) withindistinct contacts.SS 140 (Greenish area) SS CC10* Quartz silt 40% Nannos25% Clay 10% Quartz, Feldspar silt60% Nannos 45% ClayTR% Feldspar, Mica 5% Fe Oxides5% Volcanic glass

CO,: Sec. 1, 70 cm = 0%J Sec. 2, 140 cm = 22%

GlwzH

Core 16 Cored I n te r va l : 817.0-826.5 m


FERRUGINOUS MARLY CHALK AND MUDSTONE, darkreddish brown (5YR 3 / 2 ) ; Sec. 1 , 66 -69 , 113-115indistinct dark greenish gray (5G 4/1) occasion-ally other small areas in both sections.SS 67 (Green)35-25% Quartz, Feldspar s i l t

65% ClayTR% Zeolite, Heavy minerals

SS 80 (Red)10% Quartz silt5% Feldspar30% Clay5% Fe Oxides50% Nannos

SS 10735% Nannos15% Quartz silt40% ClaySt Volcanic glass5% Fe Oxides

Core catcher: red and blue layers.SS CC (Brown)10% Quartz50% Clay5% Fe Oxides 5% Forams35% Nannos 45% Nannos

TR% Fe Oxides, Barite5% Dolomite

C03: Sec. 2, 106 cm 17%

* "CC blue" probably came from the very bottomof this hole, at 14 m below the rest of Core16.



I—Ocm

—25

—50

—75

— 100

— 125

1—150358-1-1 358-1-2 358-1-3 358-1-4 358-1-5 358-1-6

361


I—Ocm

1—50

1—75

1—100

125

1—150358-2-1 358-2-2 358-2-3 358-2-4 358-3-1 358-3-2

362


I—Ocm

—25

—50

—75

— 100

— 125

1—150358-3-3 358-3-4 358-3-5 358-3-6 358-4-1 358-4-2

363


i—Ocm

25

•50

— 75

— 100

— 125

1—150358-5-1 358-5-2 358-6-1 358-6-2 358-6-3 358-7-1

364


I—Ocm

—25

-50

—75

— 100

— 125

150358-7-2 358-8-1 358-8-2 358-8-3 358-8-4 358-8-5

365


r—Ocm

—25

—50

— 75

— 100

125

1—150358-8-6 358-9-1 358-9-2 358-9-3 358-10-1 358-10-2

366


I—Ocm

—25

•50

— 75

— 100

— 125

1—150358-10-3 358-10-4 358-10-5 358-10-6 358-11-1 358-11-2

367


i—Ocm

—25

•50

75

-^100

— 125

358-11-3 358-11-4 358-12-1 358-12-2 358-12-3 .358-12-4

368


Ocm - l

—25

—50

A:

— 75

i i

i I

— 100

-

-

— 125

i*n -

1

•

I'

1 1

1

I11

I

L

A

II

• - 1

^ . . . ::;

* * * ? i;

j . v 1

I

•

1 'I

jI1

i

:

11

I

fill

' !

I

ii

-

4

4L

B

1IHI I

11

I

1

i—!•

1••

• j

*358-12-5 358-12-6 358-13-1 358-13-2 358-13-3 358-13-4

369


I—Ocm

K50

1-25

\—75

h~ioo

1—125

*—150358-13-5 358-14-1 358-14-2 358-14-3 358-14-4 358-15-1

370


I—Ocm

—25

- -50

100

— 125

358-15-2 358-16-1 358-16-2

371

7. SITE 358: ARGENTINE BASIN The Shipboard Scientific Party1 · SITE 358: ARGENTINE BASIN Core 1 2...

Documents

Transcript of 7. SITE 358: ARGENTINE BASIN The Shipboard Scientific Party1 · SITE 358: ARGENTINE BASIN Core 1 2...