1. INTRODUCTION AND EXPLANATORY NOTES1 · 2007. 5. 3. · 1. INTRODUCTION AND EXPLANATORY NOTES1 T. C. Moore, Jr.,2 Philip D. Rabinowitz,3 Peter Borella,4 Anne Boersma,3 and Nicholas

1. INTRODUCTION AND EXPLANATORY NOTES1

T. C. Moore, Jr.,2 Philip D. Rabinowitz,3 Peter Borella,4 Anne Boersma,3

andNicholas J. Shackleton5

INTRODUCTION

The drilling plan for Leg 74 of the Deep Sea DrillingProject was designed to address three main scientific top-ics: (1) the history of the deep-water circulation in thesoutheastern Atlantic, (2) the nature and geologic evolu-tion of the Walvis Ridge, and (3) the biostratigraphy andmagnetic stratigraphy of this region. In order to studythese subjects, a suite of five sites was drilled on theWalvis Ridge (Fig. 1; Table 1) that extended from itscrest (near 1000 m water depth) down its northwest flankinto the Angola Basin to a depth of 4400 m.

The sites are relatively close together and encompassa transect of approximately 230 km. They span a depthrange of over 3 km and receive approximately the samerain of pelagic debris. Any site to site variation in aver-age accumulation rates for a given interval of time shouldbe a result of two main processes: (1) dissolution rate,which varies as a function of depth, and (2) winnowingand erosion, which may also vary as a function of depthand are likely to be important near large topographicalfeatures. Detailed stratigraphic studies and the analysisof the accumulation rates for different size componentsaid in distinguishing these two processes.

Most classical marine biostratigraphies were estab-lished for tropical sequences; the present suite of sitesserves to establish stratigraphies for more temperate lat-itudes. The usefulness of this material is enhanced by therecovery of several sections within a relatively small geo-graphic area and by the use of the newly developed Hy-draulic Piston Corer (HPC) in three of the five sites.Complete coring of several sites within a small area as-sures nearly complete recovery of the biostratigraphicsequence as well as optimal preservation of both theolder parts of the section (in deeper sites with less over-burden and diagenesis) and the younger parts of the sec-tion (in shoaler sites with less dissolution). The HPC isdesigned to recover relatively undisturbed cores in theupper, unlithified part of the section, thus providing theopportunity for detailed studies of biostratigraphy; pa-

1 Moore, T. C , Jr., Rabinowitz, P. D., et al., Init. Repts. DSDP, 74: Washington (U.S.Govt. Printing Office).

2 Graduate School of Oceanography, University of Rhode Island, Kingston, Rhode Is-land.

3 Lamont-Doherty Geological Observatory, Columbia University, Palisades, New York.Present addresses: Rabinowitz, Department of Oceanography, Texas A&M University, Col-lege Station, TX; Boersma, P.O. Box 404, R.R. 1, Stony Pt., NY 10980.

4 Deep Sea Drilling Project, Scripps Institution of Oceanography, La Jolla, California.5 Godwin Laboratory, University of Cambridge, Cambridge, CB2 3RS, United King-

dom.

leomagnetism; physical properties; and biotic, geochem-ical, and lithologic time series.

Our knowledge of aseismic ridges in general, and ofthe Walvis Ridge in particular, is also enhanced by thistransect. First it allows us to test our hypotheses con-cerning the age and subsidence history of the Ridge, andsecond, it provides a lateral sequence of samples of theupper basement complex. These samples allow us tostudy the magnetic character, petrology, and chemicalcomposition of the crustal rocks as well as the mode ofemplacement of the basement Complex.

OCEANOGRAPHIC SETTINGAll sites lie beneath the generally northward-flowing

surface currents in the eastern part of the central sub-tropical gyre and are approximately 800 km off thecoast of Africa, well outside the main flow of the east-ern boundary current (Benguela Current) and the as-sociated regions of high productivity. With the excep-tion of storm-induced currents, near-surface conditionsare rather uniform over the study area and are assumedto have remained so in the past. Even if surface currentpatterns changed significantly in the past, at any giventime all the sites within this relatively small study areaare expected to have received a nearly uniform supply ofbiogenic and detrital material.

All sites in this region are above the 5-km-deep car-bonate lysocline as defined by Berger (1974). Only Sites527 and 528 lie near both the level of "perceptible dis-solution" (Ro level of Berger, 1977) and the calcite satu-ration level of Takahashi (1975), which in the southeast-ern Atlantic are thought to be close to 4 km. The shal-lowest site (526, at 1054 m) lies within the depth intervalpresently occupied by Antarctic Intermediate Waters(AAIW). The remaining, deeper sites are located atdepths ranging from approximately 2500 to 4400 m (Ta-ble 1). They are all within the depth interval occupied byNorth Atlantic Deep Water (NADW), which presentlydominates the deep and bottom waters of the AngolaBasin. The Walvis Ridge, together with the Mid-AtlanticRidge, form an effective topographic barrier which large-ly isolates the Angola Basin from the Antarctic BottomWater (AABW) to the south and west. Only a smallamount of AABW enters the Angola Basin through thetwo deepest passages: the Romanche Fracture Zone,near the equator (Wüst, 1936), and the Walvis Passage,near the southwestern end (36°S, 7°W) of the WalvisRidge (Connary and Ewing, 1974). Geologic evidencefrom previous Deep Sea Drilling legs (Legs 3, 40, and

T. C. MOORE, JR. ET AL.

W

20° S

25<

30=

35c

Angola Basin

Site 526

- 3

— 8

01" I I I I I

20Time (hr.)

Figure 1. Site localities and index map.

Table 1. Leg 74 coring summary.

15 12 08Ship Course Track 315C

Hole

525525A525B526526A526B526C527528528A529

Date(1980)

10 June10-15 June15-19 June14 July14-16 July16 July16-17 July28 June-4 July4-10 July10-13 July18-20 July

Latitude

29°04.24'S29°04.24'S29°04.24'S30°07.36'S30°07.36'S30°07.36'S30°07.36'S28 "02.49 'S28°31.49'S28°31.16'S28°55.83'S

Longitude

02°59.12'E02°59.12'E02°59.12'E03°08.28'EO3°O8.28'E03°08.28'E03 "08.28 'E01°45.80'E02°19.44'E02°18.97'E02°46.08'E

WaterDepth(m)a

24672467246710541054105410544428380038153035

Penetration(m)

3.6678.1285.6

6.3228.828.3

356.0384.5555.0130.5417.0

Totals

Numberof

Cores

16353

246

52144473044

356

LengthCored

(m)

3.6555.1227.0

6.3200.822.0

185.0384.5441.0130.5417.0

2572.8

LengthRecovered

(m)

3.6406.7181.7

3.6206.6

13.570.9

243.9272.8116.5309.7

1829.5

Recovery

w100738057

100 +613863628974

71

a Water depths from sea level.

73) suggests that the chemical character of the deep andbottom waters of the Angola Basin changed markedlythrough the Cenozoic.

GEOLOGIC SETTING

The Walvis Ridge consists of offset NNW-trendingcrustal blocks connected by ENE-trending blocks. To-gether these segments form a roughly linear ridge which

extends to the northeast from the Mid-Atlantic Ridgeand joins the continental margin of Africa near 20°Slatitude. Within the area of study (Figs. 1 and 2), struc-tural blocks tend to slope steeply into the Cape Basinand to slope more gradually northwestward into the An-gola Basin.

Until recently it was uncertain whether the WalvisRidge was an ocean crustal feature or a fragment of

INTRODUCTION

Figure 2. Bathymetry.

continental crust which had been separated from themain continental blocks during the early phases of rift-ing in the South Atlantic. Seismological and gravitystudies indicate that the average crustal thickness be-neath the ridge is 12 to 15 km and that the seismic char-acter of the crust is consistent with an oceanic origin(Chave, 1979; Detrick and Watts, 1979; Goslin and Si-buet, 1975). Recent geophysical surveys of the studyarea (Rabinowitz and LaBrecque, 1979; Rabinowitz andSimpson, 1979) identified Magnetic Anomaly 32 (lowerMaestrichtian) near the crest of the Walvis Ridge, withyounger anomalies extending to the west into the Ango-la Basin. These results lend support to the idea that theWalvis Ridge was formed at a mid-ocean ridge by sea-floor spreading processes.

Site 526, the shoalest site, is located near the crest ofwhat appears to be a separate structural block. It lies to

the south of the block on which the remaining four sitesin the transect were drilled (Figs. 1 and 2). Site 525 is lo-cated near the crest of the more northern block, in anarea with nearly 600 m of sediment. Site 529 is the nextdeeper site and lies on the eastern flank of a valley whichforms a saddle in the ridge. Sites 528 and 527 are in pro-gressively deeper waters and have somewhat thinner sed-imentary sections.

Acoustic basement in the study area is comparativelysmooth, with pronounced basement highs occurring main-ly in the crestal regions. There appear to be at least threesub-bottom reflectors defining four sedimentary inter-vals which can be traced through the area. The sectionbeneath the deepest sediment reflector thins downslopeand nearly merges with the basement reflector in thearea of Site 527 (Fig. 1). The next shoaler interval ap-pears to be of approximately constant thickness through-


out the transect, whereas the one above that (third fromthe bottom) appears to pinch out between Sites 528 and527. The shoalest interval is dissected between Sites 529and 528 and thins between Sites 528 and 527. The reflec-tion records taken near the edges of the crestal regionand near the valley to the west of Sites 525 and 529 showevidence of erosion and slumping in the study area.

Sediments are composed mainly of calcareous oozes(> 90% CaCO3). Because of the predominance of NADWin most of the Angola Basin, the calcite compensationdepth presently lies below 5500 m (Berger and Winterer,1974). The noncarbonate fraction is dominated by clay,with very little or no biogenic opal.

SEDIMENTOLOGY AND LITHOSTRATIGRAPHYThe overwhelming majority of sediments recovered

from Sites 525-529 are calcareous oozes and chalks.Nannofossils and foraminifers are the dominant micro-fossils identified. Four major lithostratigraphic unitsare recognized and are discussed in the following para-graphs in order of descending depth.

Nannofossil and foraminifer-nannofossil oozes (UnitI) dominate the upper 150-250 m in each hole (Figs.3-7). CaCO3 content is well over 90%. Primary andsecondary sedimentary structures are very poorly pre-served. These calcareous oozes are the only sediment typewhich can be directly correlated from hole to hole, indi-cating a similar and uniform sediment source over thestudy area since approximately the late Oligocene. Theonly exception to this is at the base of Site 527, wherepelagic clay (CaCO3 content approximately 20%) oc-curs in two distinct beds (Fig. 7). These beds, with theirpoorly preserved calcareous microfossils, indicate inter-vals of time when the CCD was elevated. Some slumpswere recognized within the oozes with the aid of veryprecise biostratigraphic age determination. In addition,slump deposits were also clearly seen in seismic sections(Fig. 8).

The uppermost unit grades into alternating ooze andchalk (Unit II) for approximately 100 m, with ooze dom-inant at the top and chalk dominant toward the base ofthe unit. CaCO3 content is still over 90%, but preserva-

Figure 3. Site 526 stratigraphic summary (see Fig. 4 for symbols used).

INTRODUCTION

tion of biogenic sedimentary structures is moderate togood. This preservation is directly related to the chalkcontent. The poor preservation of sedimentary struc-tures in the overlying ooze unit is thus probably the di-rect result of drilling. Stratigraphically the ooze-chalksequence can be correlated from site to site with the ex-ception of Site 526, the shoalest site, where there is onlyabout 30 m of chalk alternating with ooze. The age ofthe ooze-chalk interval ranges from early Oligocene tolate Paleocene at the three intermediate depth sites (525,529, and 528).

Site 526 is located on another crustal block (Rabino-witz and Simpson, 1979), which during the early Oligo-cene to late Eocene was very close to sea level. The pres-ence of shallow-water fossils (e.g., oysters, clams) andalgal oncolites, together with graded sequences of rub-bly limestones tentatively interpreted as a channel fill,support the assumption of a shallow-water, high-energyenvironment in which oozes and chalks could not ac-cumulate because of the winnowing action of waves andcurrents.

At Site 527 the base of the ooze-chalk sequence is latePaleocene in age, which agrees well with the other sites.However, the Oligocene age sediments are drastically re-duced in thickness because of dissolution (see Sedimen-tation History, this chapter). Thus the upper boundaryof the ooze-chalk sequence at Site 527 is not synchronouswith the top of the ooze-chalk sequences at the othersites.

The ooze-chalk sequence passes gradually into UnitIII chalks and highly indurated chalks, which continueto basement basalt. Within this unit, CaCO3 content isextremely variable (20-80%). Although the decrease inCaCO3 is atrributed primarily to increasing amounts ofvolcanogenic materials and dissolution, there were alsocyclic sedimentation patterns. A spectacular turbiditesequence is preserved at the base of this unit, just abovethe basement/sediment contact at Hole 525A. In addi-tion, many other small-scale slumps and cycles of tur-bidites are present at Sites 525, 527, 528, and 529. Theincreased frequency of evidences of slumping and vol-canic activity toward the bottom of the unit indicates achange in sedimentation from a dominantly pelagic to arelatively shallow-water, volcaniclastic mode. Volcan-iclastic layers and ash layers are well preserved. How-ever, the ash layers cannot be directly correlated fromhole to hole. Beautifully preserved primary and sec-ondary sedimentary structures are present throughoutthe entire unit. Some of the better-preserved structuresare graded bedding, cross laminations, convolute bed-ding, and microfaults. Biogenic sedimentary structuresare ubiquitous and indicate that the sediments have beenreworked at least once since deposition. Zoophycos,Planolites, and Chondrites are the most abundant ich-nogenera present.

Stratigraphically, Unit III varies in thickness from175 m in Hole 525A to approximately 110 m in holes atSites 527, 528, and 529, with ages ranging from latePaleocene to Late Cretaceous. Excluding Site 526, where

Unit III chalks are absent, the chalks are easily traceablefrom site to site both stratigraphically and seismically.Chert nodules and/or beds are found in the lower por-tions of Units II through III but are confined to Sites525, 528, and 529; the shoalest and deepest sites containno chert. Although the cherts are confined to a certainlithostratigraphic interval, we can make no direct cor-relation of chert beds from site to site. They probablyformed as a result of a silica-rich solutions migratingthrough permeable layers into pockets or voids and even-tually crystallizing as chert.

The much-studied Tertiary/Cretaceous boundary oc-curs within Lithostratigraphic Unit III. At four of thesites (525 A, 527, 528, 529) the Tertiary/Cretaceousboundary is found in zones of high slump activity, tur-bidity deposits, and low carbonate concentrations (Figs.4-7). Quite possibly the high tectonic or current activityevidenced here may have been associated with the world-wide terminal Cretaceous event.

In place of the chalks, volcaniclastic sediments, andstructural slumps, Site 526 contains calcareous sandsconsisting of approximately 60% carbonate and 40%noncarbonate grains. The noncarbonate fraction con-tains angular quartz, feldspar grains (K-feldspar), andvolcanic rock fragments. Recovery of this sand was verypoor, with total drilling penetration only approximately110 m. Drilling was terminated owing to unstable holeconditions. The immature sands indicate that a very shal-low water, high-energy condition existed at or very nearSite 526 from late Eocene to late Paleocene. Shallow-water mollusk, echinoderm, and bryozoan fragmentsare found within the unit but may be contaminationfrom overlying units.

At three sites, 525, 528, and 527 (Figs. 4, 6, 7), base-ment was penetrated. Interbedded with the basalts aresedimentary rocks of varied lithologies. Marly nanno-fossil chalks, limestones, mudstones, and siltstones arethe major rock types. Sediment layer thicknesses rangefrom a few centimeters to several meters. Primary andsecondary sedimentary structures are abundant and verywell preserved. They are the same as those in Unit III.Fairly shallow water fossils—for example, Inoceramus—are also present. Many of the interbeds are identified assmall-scale slump or turbidite deposits. Interstitial porewater analyses of Ca and Mg concentrations show a dra-matic inverse relationship. For example, at Site 528, Caconcentration in pore water increases from 26.3 mM/1above basement to 76.52 mM/1 in the sedimentary inter-layers within the basement. Conversely, magnesium de-creases from 39.33 mM/1 above basement to 1.20 mM/1in the basement sedimentary inter layers. It appears thatthis rapid change is due to seawater-basement interac-tion, possibly at elevated temperatures (Bischoff andDickson, 1975). Magnesium is released during submar-ine weathering of basalt and combines with CO3 to forma precipitant, aiding in the cementation process. Thusmagnesium is depleted in pore waters. Calcium, how-ever, is enriched because of dissolution and weatheringof basalt. The "baked" appearance of many of the in-

Pelagic clay

Nannofossil ooze

Foraminifer-πaπnofossil ooze

Nannofossil chalk

Foraminifer-nannofossil chalk

Insufficient magnetic data

Transitional assemblage

— - Questionable boundaries

Well-defined boundaries

Unconformity or hiatus

Figure 4. Stratigraphic summary, Holes 525A and 525B.

T.C.MOORE, JR. ET AL.

i 200-

Figure 5. Stratigraphic summary, Site 529 (see Fig. 4 for symbols used).

terlayers, especially near the contact with basalts, alsosupports the possibility of seawater-basalt exchange athigher than ambient temperatures.

PHYSICAL PROPERTIES

Gravimetrically determined wet-bulk density andwet-water content, shrinkage (i.e., loss of volume by dry-ing at 110°C), shear strength, sonic velocity, and ther-mal conductivity were routinely determined on samplestaken from the least disturbed sections of the recoveredmaterial. In spite of the site to site differences in waterdepth and physical setting, the results show a distincttrend of slowly increasing diagenesis with depth belowseafloor which is quite similar at all five site locations.

This similarity in physical properties is not surprising,since the sequences of sediment types from site to sitewere also similar.

The general results and trends of the main physicalproperties in the different lithologic units are shown inTable 2.

In the upper 50 m below seafloor, the oozes are un-consolidated. The uppermost samples have very highwater content and porosity and very low wet-bulk den-sity. From 30 to 50 m sub-bottom, the water contentand porosity decrease and wet-bulk density increases.Below that depth, no large changes occur in the oozeunit. Sonic velocity is very uniform throughout thisunit.

10

INTRODUCTION


11


A. cymbiformis zone(upper part)


The next obvious change in the physical propertiesoccurs in the transitional ooze-chalk zone. The watercontent and porosity decrease distinctly, and the wet-bulk density and sonic velocity increase. This trend con-tinues into the next-deeper unit, which is primarilychalk.

Generally there is a larger data scatter in the chalkunit, owing to variable lithology, especially in the lowerpart, where chalks are interbedded with volcanogenicmaterial.

The determination of shrinkage and shear strength ofthe sediments was possible only in the upper two units(ooze and transition ooze-chalk). In the ooze unit thereis little change in shrinkage with sub-bottom depth, andshear strength is very low. In the transition zone, how-ever, there are obvious changes; shrinkage decreases tozero and shear strength increases dramatically. Both ef-

fects show the result of increasing compaction, whichtransforms the oozes into firm chalk layers.

Thermal conductivity measurements show a wide scat-ter of values in all the lithologic units. In a few places,there is a slight trend of increasing conductivity withdepth.

Physical property measurements were also made on afew unusual lithologic units (Table 2). For example, atSite 527 a unit of pelagic clay and clayey ooze occurredbetween the ooze and transition ooze-chalk units. Forthis unit, shrinkage and shear strength were much higherthan in the carbonates.

IGNEOUS PETROLOGY

Although aphyric basalts occur at all three sites,moderately to highly phyric varieties are restricted to thetwo flank sites. Significant compositional differences

12

INTRODUCTION

1500m 1500m to 2200m

Figure 8. 3.5-kHz seismic record of a small-scale slump departing Site 526.

Table 2. Summary of physical properties.

Wet-bulkdensity(gm/cc)

Wet-watercontent(%)

Porosity

m

Sonicvelocity(km/s)(horizontal)

Shrinkage(vol. %)

Vane shearstrength(gm/cm^)

Site

525526527528529

525526527528529

525526527528529

525526527528529

525526527528529

525526527528529

Oozes

0-50 mSub-bottom

1.67-1.711.7

1.62-1.751.62-1.73

1.7536-3440-3440-3342-34

3360-57

6064-5765-56

55

1.61.61.531.551.6

7 - 65

12-98

7 - 5

50

<IOO4050

Below 50 m

1.751.7-1.75

1.751.73-1.81

1.7533-3034-30

3434-31

33

5660-53

5756-53

55

1.61.61.531.551.6

6 - 56

(10)8 - 55 - 4

30< 5 0

<IOO50-200

50

Clay andClayeyOozes

1.75

35

57

1.55

15

800800

TransitionOoze-Chalk

1.75-2.05

1.75-1.91.81-2.01.75-1.9

30-22

34-2831-2433-2650-40

55-5053-4555-451.6-1.9

1.55-1.71 56-1.91.6-1.8

3.5

6 - 05 - 04 - 0

50- > 200

150->40030->3005 0 - > 600

Chalks

2.05

1.9-1.952.0-2.05

1.95-2.222-16

28-2524-2026-1540-35

4745-4145-311.9-2.6

1.71.9-2.01.8-2.5

65-56 =55 =

(10) =

Basement

Sediments

(1.93)

(2.05)2.05

(28)

(21)22

(53)

(42)43

1.8

1.92.4

Basalt

2.47

2.642.85

8

54

20

1310

3.9

4.44.9

Physical Propertiesof Lithologic Unitsestimated averages)

Site

525526527528529

525526527528529

525526527528529

525526527528529

trend top — bottom of unitno trend visibleonly few or one values

exist between these two types. Representative major ele-ment analysis by shore-based XRF, through collabora-tion with A. R. Duncan and D. L. Reid of the Universi-ty of Cape Town, appear in Table 3. The analysis servesto illustrate some features of a probable overall trend inbasalt composition from the ridge crest down into theadjacent ocean basin. The sample from ridge crest Site

525 is an aphyric basalt from a glassy pillow margin. Ithas the chemistry of a quartz tholeiite, with higher K2O,TiO2, P2O5, and FeO content than normally associatedwith a mid-ocean ridge basalt (MORB), consistent withconsiderable differentiation. The sample from the deep-est Site 527 is a highly Plagioclase phyric basalt from aflow interior. Its chemistry is that of an olivine tholeiite

13


Table 3. Representative XRF analyses of basaltsamples from the Leg 74 Walvis transect.

SiO2

Tiθ2A12O3

Fe 2 O 3

MnOMgOCaONa2OK 2 O

P2O5LOIH 2 O

TotalsDeptha

525A-59-4, 25 cm

50.202.49

13.9512.920.195.339.492.491.030.310.900.51

99.8261

527^1-4, 10 cm

48.821.17

16.9110.790.175.86

12.662.520.170.100.190.93

100.2914

a Depth below top of basement in meters.

with K2O, TiO2, and P2O5 contents similar to those en-countered in MORB, although higher FeO and lowerMgO indicate a somewhat more evolved magma.

The major element chemistry of basalts from theWalvis Ridge crest resembles neither that of MORB pre-viously recovered from the South Atlantic nor that ofalkalic basalts on the spatially associated island of Tris-tan da Cunha. The Walvis Ridge has apparently been thelocus of distinctive magma evolution.

PALEOMAGNETIC RESULTS

The results of the paleomagnetic measurements areincluded in Figures 4-7. The white, unlithified ooze ofPliocene to mid-Miocene age at all sites proved to be tooweakly magnetized for measurement even with a super-conducting rock magnetometer. The remaining Neogenematerial was contaminated by a strong viscous rema-nence acquired during sample handling that could notbe reliably removed. Thus an analysis of paleomagneticresults for the HPC material is not reported, and de-tailed study was confined to undisturbed Paleogene ro-tary-drilled cores and especially to the lithified lowerPaleocene to Cretaceous interval at Sites 525, 527, 528,and 529.

The latter proved to be quite stably magnetized, withmedian demagnetizing fields of 200-300 Oe and direc-tional change of less than 20° over a 600-Oe coerciveforce range. We selected 43 pilot samples for detaileda.c. demagnetization in order to determine the optimumfield for cleaning treatment of samples. The resultsshow a record that is completely consistent with the typesection at Gubbio, Italy (Alvarez et al., 1977). The Cre-taceous/Tertiary boundary occurs near the top of thereversed interval between Magnetic Anomalies 29 and30. The complete Paleocene-Cretaceous sequence ofAnomalies 28-31 was recognized at all four sites, andAnomalies 25, 26, 27, and 32 are seen at some sites. Fig-ure 9 shows a summary diagram together with the pre-ferred time scale of Ness et al. (1980). The basement agesderived from these magnetic measurements indicate thatat Site 525 the basement is of Anomaly 32N age; at 527,Anomaly 3IN age; and at 528, Anomaly 3IN. These

D2-

D1+

75

basalt

Figure 9. Summary diagram of Late Cretaceous-early Tertiary paleo-magnetic results from four Leg 74 sites, using the time scale ofNess et al. (1980), with comparisons to the seafloor spreadinganomaly pattern and the paleomagnetic measurements of the Gub-bio section (Alvarez et al., 1977). Black intervals indicate normalpolarity; white intervals, reversed polarity; and diagonal line inter-vals (Leg 74 sites) are areas of no recovery.

data are consistent with the biostratigraphic ages, themapped crustal anomalies, and with the hypothesis thatthe Walvis Ridge was formed by seafloor spreading pro-cesses at a mid-ocean ridge.

SEDIMENTATION HISTORY

The sediments of the Walvis Ridge are dominated bybiogenic carbonate. Only in the late Maestrichtian andearly Paleocene are the sediments rich in volcanogenicmaterial, apparently derived from active centers on theRidge itself. This activity was particularly great duringthe latest Maestrichtian, dropped markedly in the earlyPaleocene, and disappeared from the record in youngertimes.

14

INTRODUCTION

The degree of carbonate preservation and rates ofsediment accumulation varied greatly through theCenozoic. This is evidenced by changes in estimates ofpreservation of the calcareous assemblages and varia-tion in the average carbonate accumulation rates in thestudy area (Fig. 10A, C).

The preservation of the calcareous faunas and florasgenerally parallels changes in the CCD. From the mid-dle to late Eocene through the Oligocene, microfossilsare generally poorly preserved; those of the late Oligo-cene to late Miocene are moderately well preserved, andthose of the latest Miocene through Quaternary are wellpreserved. Preservation in the early Paleogene was poor

to moderate, with diagenetic alteration in the thickersections (shallower sites) having the greatest overall ef-fect on the assemblages. Hiatuses are most common inthe late Eocene through late Oligocene parts of the sites(Fig. 10B). In this interval they do not appear to have aclear depth dependency; breaks in the record are foundat the deepest (527) and shallowest (525, 526) sites butnot in between. However, this interval of abundant hia-tuses has a lower accumulation rate, with poorer nanno-fossil preservation at all sites. The increased frequencyof hiatuses in the mid-Paleogene is probably caused by arelatively high ratio of dissolution to supply. Hiatuses inthe late Neogene occur at the mid-depth sites (528, 529).

Avg. Accumulation Rate(g/cm2 per 103y.)

1 2. I , |

No. of Siteswith Hiatuses

1 2 3 4

Avg. Preservation

Figure 10. A. Average foraminifer preservation. B. Abundance of hiatuses. C. Average sediment accumulation ratesfor Leg 74 sites. Preservation is a subjective estimate. Each estimate is given a numerical code and averaged overall five sites. Hiatuses in the sections were considered present only when both calcareous nannofossils and fora-minifers indicated that one or more biostratigraphic zones were not represented. Accumulation rates were calcu-lated for three separate components: coarse-grained (>63 µm) material (dominated by foraminifers and indi-cated by diagonal shading); fine-grained carbonate (>63 µm, dominated by calcareous nannoplankton); andnoncarbonate sediments (indicated by horizontal shading). Accumulation rates for each component were aver-aged over all intervals recovered. Both hiatuses and shallow-water sediments at Site 526 were excluded in the cal-culation of averages (Fig. 11). N.D. indicates lithified intervals where sediments could not be separated into sizefractions.

15


Because they are closely associated with slump depositsand occur near points of peak accumulation (Fig. IOC),they are probably linked to slumping and erosion ratherthan to dissolution.

The record of average accumulation rates from sites inthis region shows the same general features. Carbonateaccumulation averaged about 1 g/cm2/103 y. duringmuch of Cenozoic. There are four maxima in averageaccumulation: (1) in the late Maestrichtian, when vol-canic debris was an important sedimentary componentand contributed nearly 1 g/cm2/103 y. to the sediments;(2) in the late Paleocene to early Eocene, when no hia-tuses occur; (3) in the latest mid-Miocene; and (4) in theearliest Pliocene. Of these four peaks, the one in the earlyPliocene appears to be the largest. The two Neogenepeaks occur at all five sites. Their presence in the shal-lowest site (526), where dissolution effects are thoughtto be negligible, suggests that these maxima result fromincreased carbonate productivity during the late middleMiocene and early Pliocene.

One of the chief purposes of drilling this suite of sitesover a wide depth range was to investigate, in more de-tail than is generally feasible, the history of calcite dis-solution in the water column. Figure 11 shows the esti-mated accumulation rates of sediment broken into threecomponents: greater than 63 µm (almost entirely fora-minifers), less than 63 µm (largely coccoliths), and thenoncarbonate residue. It is apparent from this figurethat the accumulation rate of foraminifers was generallyhighest at the shallowest site; we interpret the reducedaccumulation of foraminifers at deeper sites as a mea-sure of the loss by dissolution. The accumulation of fine-grained material was low at the shallowest sites, high atintermediate depths, and, during parts of the record,low again at the deepest sites. We interpret this as a re-sult of winnowing, which preferentially inhibits the ac-cumulation of fine material on the rises, and of dissolu-tion, which has a significant impact on coccoliths onlynear the CCD.

The recovery of one exceptionally shallow section(Site 526) serves as a standard with no (or minimal) dis-solution effects against which to compare the deepersites. An interesting feature revealed by this comparisonis that the degree of undersaturation with respect to cal-cite in the upper part of the water column (as indicatedby Fig. 11) was considerably greater during periods ofhigh carbonate accumulation (production). This sug-gests that the changes in dissolution rates extend to theshallower parts of the water column and are stronglylinked to large-scale changes in productivity. If the car-bonate dissolution rate at 2500 m water depth had beenas high in the late Miocene and Oligocene (intervals ofrelatively slow carbonate accumulation) or during themid-Miocene (intervals of rapid carbonate accumula-tion) as it was during the last 3 m.y., no foraminiferswould have survived; instead we see that the Oligoceneforaminiferal accumulation at 2500 m (Site 525) was notmuch less than at 1000 m (Site 526).

Figure 12 shows the magnitude of these dissolutioneffects for three time intervals. We divided the foramin-ifers into two fractions on a 150-µm sieve. In the Pleisto-

KEYH i = non-carbonateI 1= fine ( >63µm) carbonate ["coccolith"]^ = coarse ( < 63 µm) carbonate ["foram"]

N. D. = Not determined (i. e., "foram" not separated)

Figure 11. Sediment accumulation rates for the Leg 74 sites, arrangedaccording to water depth from shallow (top) to deep (bottom).Shading and notation as in Figure 10.

cene, the accumulation of larger foraminifers is signifi-cantly affected by dissolution only at the deepest site,but the accumulation of smaller foraminifers is reducedby a factor of 2 between Sites 526 (1000 m) and 525 (2400m), a surprising finding considering that the CCD wasdeeper than 4400 m throughout the interval. Coccolithaccumulation, by contrast, was reduced by a factor of at

16

INTRODUCTION

0.2 0.4 0.2 0.4 0.6 0.8 1.0

0.2 0.4 0.6 0.8 1.0

'0 0.2>150µm

0.2 0.4 0.60.2 0.4150µm -63µm

Accumulation Rate(g/cm2/103y.)

0.8 1.0<63µm

1.2 1.4 1.8

Figure 12. Average accumulation rates of three carbonate-size fractions (<150µm, 15O-63µm, and<63µm) plotted as a function of depth during three time intervals. Data from Site 529 are excludedfrom these plots because slumping in the section gives anomalous accumulation rates.

least 3 at Site 526 as a result of winnowing (the factor isactually somewhat greater, since a significant accumula-tion of foraminifers smaller than 63 µm occurred at Site526). In the late Pliocene, the pattern was somewhatsimilar to that of the Pleistocene, except that even thelarger foraminiferal fraction is affected by dissolutionat 2500 m.

We also show data from the mid-late Miocene (ZonesNN9 and NN10), at which time the CCD was evidentlynot much deeper than the depth of Site 527. Much of theforaminiferal carbonate has been removed at Site 528,

whereas at 527 foraminiferal accumulation is nil and thecoccoliths noticeably reduced.

BIOSTRATIGRAPHY AND EVOLUTION OFWALVIS RIDGE FLORAS AND FAUNAS

Within the Leg 74 area, sedimentation commencedupon the Walvis Ridge in the early Maestrichtian (Globo-truncana tricarinata foraminiferal zone or Tetralithustrifidus nannofossil zone). Sediments were deposited be-tween the basalt layers. (Shallow-water faunas and ap-parent turbidites from shallow pinnacles contain Inocer-

17


amus, often in great abundance.) Both benthic faunasand the ratio of planktonic to benthic foraminifers inthese sediments confirm the approximate depth of for-mation of basalts predicted by normal thermal subsi-dence models. Correlation of foraminiferal datums topaleomagnetics agrees with that in the Gubbio section(Alvarez et al., 1977). The first correlation of standardnannofossil zones to magnetics and foraminiferal da-tums was also possible at the Walvis Ridge sites.

Nannoplankton and planktonic foraminifers of theMaestrichtian are typical of middle latitudes. Preserva-tion varies among the sites and appears to be strongly af-fected by the amount of sedimentary overburden. Nan-nofossils are moderately preserved throughout, but fora-minifers are poorly preserved at the shallow Site 525and intermediate Site 529; the best-preserved faunas arefound at the deepest Site 527.

The Cretaceous/Tertiary boundary interval is includedin four continuous sedimentary sequences and containsdiverse nannofossil and foraminiferal biotas. Substantialvolcanic material was added to sediments below theboundary at all sites—and into the Paleocene at Site 525.Just below the boundary there is a short zone of blue graysediment containing a warmer-water foraminiferal faunathan in the deeper cores, implying the incursion of slight-ly warmer surface waters into this area just before the ter-minal Cretaceous event. All sediments are calcareousoozes with moderately well preserved nannofossils butnot particularly well preserved foraminifers.

The input of volcanic materials in the basal Paleo-cene has altered the sediments to rich hues of brown andgreen at several sites. Fossils are nevertheless well pre-served at all but Site 529, which is strongly lithified. Thebasal Tertiary Globigerina eugubina Zone was recov-ered, attesting to the relative stability of sedimentaryconditions. Paleocene faunas are typical of middle lati-tudes, and floras contain temperate watermass indica-tors. The shallowest Site 526 probably lay close to sealevel at this time and contained a carbonate shelf fauna.Sedimentation through the Paleocene appears to havebeen more continuous at the deeper than at the shallow-er sites, judging by the absence of several foraminiferalzones at Sites 525 and 529 near the end of the earlyPaleocene. However, no significant breaks were foundin the nannofossil biostratigraphic sequence of the earlyPaleocene. Average accumulation rates (Figs. 10 and11) were lower in the early Paleocene than in either thelate Maestrichtian or late Paleocene. Some of the best-preserved nannofossils are found in the upper Paleoceneat Site 529, despite the large overburden at this site. ThePaleocene/Eocene boundary was easily recognized bythe first appearance of the benthic foraminifer Gavel-inella beccariiformis and by the first appearance of thecalcareous nannofossil Discoaster diastypus.

Lower Eocene faunas are relatively well preserved atall sites, and benthic foraminifers indicate deposition atintermediate water depths. Planktonic faunas containsufficient warmer-water elements to indicate warmedsurface waters in this area. Subsequent preservationworsens markedly, and the South Atlantic episode ofpoorly preserved middle Eocene sediments is evidenced

here on the Walvis Ridge. There are few well-preservedsequences from the middle into upper Eocene at anysite. By the late Eocene Site 527 was approaching thepaleo-CCD, and most foraminifers are dissolved. Nev-ertheless the nannoflora was useful for zonation in thisinterval. Little upper Eocene was recovered at any of theother sites. The faunas contain typical middle latitudespecies, and sediments are nearly all carbonate oozes.At this time the shallowest Site 526 lay near the shelf-slope transition; planktonic oozes contain large amountsof shallower-water sediments and fossils. The preserva-tion of the calcareous nannofossils is poor through theEocene interval; only large species are present.

The Eocene/Oligocene boundary is well preserved andappears continuous at Site 529, where a long transitionzone containing moderately to well-preserved biotas wasrecovered. According to the calcareous nannofossilstudy, a very condensed interval containing the Eocene/Oligocene boundary is also present at Site 528. At theshallowest site (526) a regression and consequent sedi-ment removal is indicated for this period.

The Oligocene faunas recovered at Site 529 includedmainly temperate species, which are moderately wellpreserved, as well as several boreal types. Chiasmolithusaltus, an Oligocene nannofossil species preferring coolerwater masses, was also commonly found only at Site526. A nearly complete section was found at the shal-lower Site 526, which, based on the presence of benthicuvigerinid faunas, must have lain at depths of 600-1000m at this time. Shallow-water materials continue to betransported into this area, particularly during a middleOligocene regression which is marked by increased sedi-ment erosion at the shallower site and by the presence ofbryozoan and mollusk debris and a Uvigerina semives-tita-U. mexicana fauna. Other sites apparently lay toodeep to demonstrate the effects of the regression. Site527 lay below the CCD for foraminifers through thistime. Only at Site 526 was an interval of abundant Braa-rudosphaera detected within the Oligocene.

The Oligocene/Miocene boundary was cored at foursites; only Site 527 lay below the CCD at this time. Theboundary is based primarily on the last occurrence ofthe calcareous nannofossil species Sphenolithus ciper-oensis and the Turborotalia kugleri/Globigerinoides pri-mordius concurrent ranges. Foraminifers and nannofos-sils were moderately well preserved except adjacent tohiatuses. Benthic foraminifers indicated that sedimentswere nearly all from intermediate depths, except at Site527, which contained red clays with no foraminifers andfew nannofossils.

It is difficult to use foraminifers to zone the upperlower to middle Miocene intervals because of the lack oftropical index fossils. The nannofossils are generallyamenable to a tropical zonation. The buildup of theAntarctic ice sheet coincident with the NN5/NN6 zonalboundary is evidenced by a large influx of keeled glo-borotalids and forms of Globigerinoides, suggesting in-creased density stratification of the eastern margin ofthe South Atlantic gyre.

Carbonate oozes of late Miocene age contained mid-dle latitude and temperate water floras and faunas; the

18

INTRODUCTION

sections were relatively complete and preservation mod-erate. A change in benthic foraminifers at the end of theMiocene may correlate with the high productivity epi-sode of the post-Messinian time in the Atlantic.

Three very well preserved and supposedly completePliocene sections containing boreal and temperate plank-tonic fossils were recovered from this area. A markeddecrease in boreal fossils and their replacement by a typ-ical middle latitude fauna is indicated in all the mid-Pli-ocene faunas coincident within the extrapolated base ofthe Gauss. The CCD sank below the deepest site (527)near the base of the Pliocene; thus this site also containsfossils that are sufficiently well preserved for detailedclimatic studies. This site is on the northwestern end ofthe transect (Fig. 1). That it may have lain under a slight-ly different surface watermass in the Pliocene is demon-strated not only by differing planktonic foraminiferalfaunas but also by a different sequence of changes inthese faunas through the Pliocene. A Pliocene sectionwas recovered at Site 529, but active slumping had dis-turbed the upper Miocene sequence. The upper Pliocenesection accumulated at slower rates and is consistentlythin at all sites drilled.

Portions of the early to late Pleistocene containedwell-preserved temperate floras and faunas in coarse-grained foraminiferal nannofossil oozes. Slumping ofPliocene into lower Pleistocene sediments occurred atSite 529.

CONCLUSIONS

1. As suggested by crustal magnetic anomaly pat-terns, the section of the Walvis Ridge under study wasformed at a mid-ocean ridge spreading center. The ageof the basement rocks is approximately 69-71 m.y.(Magnetic Anomaly 31 to 32 time), with the deeper sitesslightly younger than those upslope.

2. The basement is composed of basaltic pillows andflows intercalated with nannofossil chalks and limestonescontaining a significant volcanogenic component. Themajor element chemistry shows a change from quartztholeiitic basalt at the ridge crest to olivine tholeiiticbasalt down the northwestern flank. The chemistry ofcrestal magmas differs from that of mid-ocean ridge ba-salt previously recovered from the South Atlantic.

3. The lithology of the sections is dominated by car-bonate oozes and chalks. Dissolution is seen to have hada marked effect on accumulation in the deeper sites,particularly in the upper Miocene, Oligocene, and mid-dle to upper Eocene.

4. Volcanogenic material is common in the Mae-strichtian and lower Paleocene and is probably derivedfrom sources on or near the Walvis Ridge.

5. Average accumulation rates suggest that there werethree peaks in the rate of supply of carbonate to the sea-floor: one during the early Pliocene, one in the late mid-dle Miocene, and one in the late Paleocene to early Eo-cene. During much of the rest of the Cenozoic, carbon-ate accumulation averaged 1 g/cm2/103 y.

6. The rates of dissolution as a function of depth canbe calculated by using data from all the sites in the tran-sect. Initial results of such an analysis indicate that the

upper part of the water column showed a greater degreeof undersaturation with respect to carbonate duringtimes of high carbonate accumulation (production).Even when the CCD was below 4400 m, a large amountof carbonate was dissolved in the upper part of thewater column. This may render the "lysocline" and "Ro

level" concepts of Berger (1977) inapplicable for at leastsome parts of the record.

7. The effects of winnowing are shown by a systemat-ic downslope increase in the clay (noncarbonate frac-tion) and coccolith (< 63 µm size fraction) accumulationrates. The coccolith accumulation rate is lowered at thedeeper sites only during intervals of intense dissolution.

8. Standard zonations from the foraminifers and cal-careous nannofossils could be used through much of thesection; however, many of the foraminiferal speciescommonly used in tropical zonations are absent in thisarea, and in some cases the ranges of species appear tobe diachronous through latitude. Foraminiferal datumsand standard nannofossil zones of the Maestrichtian arecorrelated to paleomagnetics for the first time.

9. The faunas and floras of the Walvis Ridge sites aretemperate in nature. An indication of warmer faunas isfound in the uppermost Maestrichtian and lower Eoceneand of cooler faunas in the Oligocene, middle Miocene,and lower Pliocene. The boreal elements of the lowerPliocene faunas are replaced by more temperate formsin the mid-Pliocene.

10. The Cretaceous/Tertiary boundary was well re-covered in four of the five sites drilled, and sedimentscontain well-preserved nannofossils but poorly preservedforaminifers. The basal Tertiary Globigerina eugubinaZone was recovered consistently but was poorly pre-served.

11. The shallowest site (526) did not sink below sealevel until the late Paleocene. Here, benthic faunas aredistinctly different from those at deeper sites and at siteson continental slopes at similar depths.

12. At Site 526, the effect of a middle Oligocene re-gression is recorded by the benthic foraminifers, whichindicate a rapid shoaling followed by a deepening. Othersites were deep enough so that no change was noted inthe benthic fauna.

EXPLANATORY NOTES

Responsibilities of Authorship

The site chapters are authored by the entire scientificparty; ultimate responsibility for content lies with theco-chief scientists. These chapters are organized as fol-lows (authors' names are in parentheses).

Site Data (Moore, Rabinowitz)Principal Results (Moore, Rabinowitz)Background and Objectives (Rabinowitz, Moore)Operations (Rabinowitz)Sediment Lithology (Borella, Duée, Fütterer, Lever,

O'Connell)Inorganic Geochemistry (Borella)X-Ray Diffraction Analysis (Lever, Borella)Biostratigraphy (Boersma, Jiang, Manivit)Sediment Accumulation Rates (Shackleton)

19


Igneous Petrology (Richardson, 0'Connell)Magnetics (Chave, O'Connell)Physical Properties (Kleinert)Downhole! Measurements (Rabinowitz)Summary and Conclusions (Moore, Rabinowitz)The interpretations of individual authors have been

retained in the sections for which they were responsible.As a result, there is sometimes a conflict in interpreta-tion between a particular section and the Conclusions.

NUMBERING OF SITES, HOLES, CORES, ANDSAMPLES

DSDP drill sites are numbered consecutively begin-ning with the first site drilled by Glomar Challenger in1968. Site numbers are slightly different from hole num-bers. A site number refers to one or more holes drilledwhile the ship was positioned over one acoustic beacon.These holes may be located within a radius as great as900 m from the beacon. Several holes may be drilled at asingle site by pulling the drill pipe above the seafloor(out of one hole) and moving the ship 100 m or more tobegin drilling another hole.

The first (or only) hole drilled at a site takes the sitenumber. A letter suffix distinguishes each additionalhole at the same site. For example, the first hole takesonly the site number, the second takes the site numberwith suffix A, the third takes the site number with suffixB, and so forth. It is important, for sampling purposes,to distinguish among the holes drilled at a site, sincesediments or rocks recovered from different holes us-ually do not come from identical positions in the strati-graphic column.

The cored interval is measured in meters below theseafloor. The depth interval of an individual core is thedistance between the point below seafloor that the cor-ing operation began and the point at which it ended.Each coring interval is generally 9.5 m long, which is thenominal length of a core barrel; however, the coring in-terval may be shorter or, sometimes, slightly longer."Cored intervals" are not necessarily adjacent to eachother, but may be separated by "drilled intervals." Insoft sediment, the drill string can be "washed ahead"with the core barrel in place, but not recovering sedi-ment, by pumping water down the pipe at high pressureto wash the sediment out of the way of the bit and up in-to the space between the drill pipe and wall of the hole.However, if thin, hard-rock layers are present, it is pos-sible to get "spotty" sampling of these resistant layerswithin the washed interval and thus have a cored inter-val greater than 9.5 m.

Cores are numbered serially from the top of the holedownward. Core numbers and their associated cored in-terval in meters below the seafloor are normally uniquefor a single hole, unless an interval is cored twice. Whenthis occurs, the core number is assigned the suffix " S , "for "supplementary."6

Full recovery for a single core is normally 9.28 m ofsediment or rock, which is in a plastic liner (6.6-cm ID),

plus about a 0.2-m-long sample (without a plastic liner)in the core catcher. The core catcher is a device at thebottom of the core barrel which prevents the cored sam-ple from sliding out as the barrel is being retrieved fromthe hole. After retrieval the core is cut into 1.5-m-longsections that are numbered serially from the top of thecore (Fig. 13). When there is full recovery, the sectionsare numbered from 1 through 7, with the last sectionshorter than 1.5 m.

When the core liner is recovered full to the top, thecore is still cut into six 1.5-m sections, measured fromthe bottom of the liner, and the extra 0.28-m section atthe top is designated Section 0, or the "zero section."The zero section is ignored in calculations of depth be-low the seafloor.

When there is partial recovery, the original strati-graphic position of the material in the cored interval isunknown. If the recovered material is contiguous we as-sign the top of it to the top of the cored interval andnumber sections serially from the top, beginning withSection 1 (Fig. 13).7 There are as many sections as areneeded to accommodate the material. For example, 4 mof material are divided into 3 sections—2 upper sections1.5 m long and a final lower section only 1.0 m inlength. If the shipboard scientists determine that mate-rial recovered is not contiguous, then sections are dividedand numbered serially, as with contiguous material, andgaps labeled as voids for sediments (Fig. 13) or markedby spacers for igneous rocks (see Igneous Rocks sec-tion).

Samples are designated by centimeter distances fromthe top of each section to the top and bottom of thesample in that section. A full identification number fora sample consists of the following information: leg, site,hole, core number, and interval (in centimeters from thetop of section). For example, a sample identificationnumber of 74-525A-3-3, 12-14 cm is interpreted as fol-lows: 12-14 cm designates a sample taken at 12-14 cmfrom the top of Section 3 of Core 3 from the secondhole drilled at Site 525 during Leg 74. A sample fromthe core catcher of this core is designated as 74-525A-3.CC.

When making a sample request, please refer to aspecific interval within a section of a core. DSDP nowhas sample listings from each leg listed on microfichecards with assigned absolute sample depths in meters.For requests, please write to the DSDP InformationHandling Group.

Handling of Cores

A core was normally cut into 1.5-m sections, sealed,and labeled, then brought into the core laboratory forprocessing. Long core spinner magnetism measurements,gas analyses, thermal conductivity measurements, andcontinuous wet-bulk density determinations using theGamma Ray Attenuation Porosity Evaluator (GRAPE)were made before splitting sections.

The cores were then split longitudinally into "work-ing" and "archive" halves. Samples were taken from

° Note that this designation has been used on previous legs as a prefix to the core numberfor sidewall core samples.

This technique differs from the labeling systems used on Legs 1 through 45, whichdesignated a "zero section" but did not have a "number 7 section."

20

INTRODUCTION

FullRecovery

PartialRecovery

PartialRecovery

with Void

SectionNumber

•Top

inσiii

"8δ

Bottom

SectionMumber

1

2

3

4

5

6

T3

1

:. V

: V

i'{'

1EmptyLiner

j

i

1

0

03

Φ

σiII

>

£T3

oc

1

Top

SectionNumber

Bottom

Core-CatcherSample

Core-CatcherSample

r

EmptyLiner

5<vEin _σi Top

II

1oO

• Bottom

Core-CatcherSample

Figure 13. Diagram showing procedure in cutting and labeling of core sections.

the "working" half, including those for determinationof grain-size distribution, mineralogy by X-ray diffrac-tion, sonic velocity by the Hamilton Frame method, wet-bulk density by a static GRAPE technique, water con-tent by gravimetric analysis, carbon-carbonate analysis,calcium carbonate percentage (Carbonate Bomb), geo-chemical analysis, paleontological studies, and others.

Smear slides (thin sections for lithified sedimentaryand igneous rocks) from each major Lithology, and mostminor lithologies, were prepared and examined micro-scopically. The archive half was then described andphotographed. Physical disturbance by the drill bit, col-or, texture, structures, and composition of the variouslithologies were noted on standard core description

forms. All prime data are routinely microfilmed andsome are digitized for computer retrieval.

After the cores were sampled and described, they weremaintained in cold storage aboard Glomar Challengeruntil they could be transferred to the DSDP repository.Core sections of sediments removed for organic geo-chemistry study were frozen immediately on board shipand kept frozen. All Leg 74 cores and frozen cores arepresently stored at the DSDP West Coast Repository(Scripps Institution of Oceanography).

When the cores arrive at the repository, all hydraulicpiston cores are routinely photographed on 3 5-mm con-tinuous flow microfilm. These films will be made avail-able at the termination of the one-year proprietary hold.

21


Hydraulic Piston Corer (HPC)

On Leg 74 the Serocki-Storms-Cameron HydraulicPiston Corer (HPC) was used successfully to recoverundisturbed sediments at Holes 525B, 526A, 526B, and528A. Recovery averaged 82%; if we eliminate Hole526A, recovery averaged a remarkable 100%. HPC holesare designated in the same way as rotary-drilled holes.

The principles of the operation of the hydraulic pis-ton corer are presented in Figure 14. The hydraulic pis-ton corer is located within the lowermost part of thedrill string and is flush with the base of the drill bit be-fore it is fired. Once fired, the cores ideally penetrate 4.4m into the underlying sediment. The full extension ofthe HPC to this length is reflected on the rig floor bycomplete pressure bleed-off following the shot. Afterpenetration, the HPC is pulled up 4.4 m to a positionwithin the lowermost part of the drill string. The wholedrill string is then raised to a point where a drill stringtool joint appears at the level of the rig floor. The raisedinterval ranges from 0.0-9.5 m (length of one joint of

drill pipe). Thus a total open hole beneath the drill bitcan be.as high as 9.5 m + 4.4 m, or 13.9 meters. Thedrill string is then separated at the tool joint, and the in-ner core barrel with the 4.4 m of sediment is pulled tothe rig floor on the sandline.

After removal of the core, the HPC inner core barrelis reloaded and returned to the base of the drill string.The HPC drill bit then washes down through the sedi-ment interval just cored, but only for a distance of ap-proximately 3.4 m. The last meter of lowering is donewithout washing. At that point the base of the drillstring is at the desired level for the next HPC shot.

The presence of an open hole below the drill stringduring the time the HPC inner core barrel is retrievedand reloaded and the fact that the drill string washesdown 3.4 m and is pushed the last meter begin to explainwhy the upper parts of many of the hydraulic pistoncores are contaminated with material previously coredand disturbed. The raising of the entire drill string asmuch as 9.5 m also explains why a mud line core may betaken twice.

HPC is seated.Seawater pumpedat 350 gpm toactuate.

350 gpm

(length is 36 feet collapsed and50 feet extended)

Stationary sealing top sub

Traveling pistor

, Traveling vent

Dampening port

Stationary pistion head

Locking pins shear at 1700 psi.Pressure on traveling pistondrives core tube. Fluid abovestationary piston is vented.Core tube speed is approximately10-20 ft./s.

At the end of the strokedampening ports are uncoveredto vent the pressurefluid and decelerate the core time.

Figure 14. Operational sequence, DSDP hydraulic piston corer.

22

INTRODUCTION

Sediments and Sedimentary Rocks

Core Description

Drilling DisturbanceRecovered rocks, and particularly the soft sediments,

may be extremely disturbed mechanically. This distur-bance is the result of the coring technique, which uses alarge (25-cm diameter) bit with a small (6.0-cm dia-meter) opening for the core sample. The following dis-turbance categories are used for soft and firm sediment:

1) Slightly deformed: bedding contacts are slightlybent.

2) Moderately deformed: bedding contacts have un-dergone extreme bowing. Firm sediment is fractured.

3) Very deformed: bedding is completely disturbedor homogenized by drilling, sometimes showing symme-trical, diapir-like structure. Firm zones may have relic"drill biscuits" in a breccia or homogeneous matrix.

4) Soupy: water-saturated intervals which have lostall aspects of original bedding.These categories are coded on the core description formin the column headed "Drilling Disturbance" (Fig. 15).

Sedimentary Structures

In the soft, and even in some harder, sedimentarycores, it may be extremely difficult to distinguish be-tween natural structures and structures created by thecoring process. Thus the description of sedimentarystructures was optional. Locations and types of thesestructures appear as graphic symbols in the columnheaded "Sedimentary Structures" on the standard coredescription form (Fig. 15) and the expanded hydraulicpiston core description form (Fig. 16). Figures 17 and 18give the keys to these symbols.

Where distinguishable, bioturbation is noted in thegraphic column. A summary of the most common bio-genic sedimentary structures (ichnofossils) observed inDSDP cores is given in Figure 19.

Color

Colors of the geologic material are determined with aMunsell or Geological Society of America Rock ColorChart. Colors were determined immediately after thecores were split and still wet.

Lithology

The graphic column presented on the core descriptionform is based on the lithologies and represented by asingle pattern or by a grouping of two or more symbols.The symbols in a grouping correspond to end-membersof sediment constituents, such as clay or nannofossilooze. The symbol for the terrigenous constituent ap-pears on the right-hand size of the column, the symbolfor the biogenic constituent(s) on the left-hand side. Theabundance percentage of any component is in approxi-mately equal proportion to the width of the graphic col-umn its symbol occupies. For example, if the left 20%of the column has a diatom ooze symbol and the right80% a silty-clay symbol, the sediment contains 20%diatoms and 80% mud.

Because of the difference in the length-to-width ratiobetween the actual sediment core and the graphic litho-logic column, it is not possible to reproduce structuresas they appeared in the core; they would appear highlyflattened and otherwise distorted. The same is true forrock fragments or pebbles in the cores. Therefore the lo-cations of pebbles are shown by a solid square and thedepth of small "patches" of ash or other lithologicchanges are shown by a triangular inset of the appro-priate lithologic symbol on the right side of the litho-logic column (Fig. 18). This convention applies only tolithologies which do not extend across the entire core.

Format, style, and terminology of the descriptiveportion of the core description forms (Figs. 15 and 16)are not controlled by the "Mandatory Graphic Litho-logic Column Scheme" beyond the minimal name as-signment derived from the lithologic classification (de-scribed in the following section). Colors and such addi-tional information as structures and texture are includedin the text portion of the core description.

Smear slide (or thin section) compositions, carbonatecontent (% CaCO3), and organic carbon content deter-mined aboard ship are listed below the core descriptionon these forms, where two numbers separated by a hy-phen refer to the section and centimeter interval, respec-tively, of the sample. The locations of these samples inthe core and a key to the codes used to identify thesesamples are given in the column headed "Samples"(Fig. 15). Locations and intervals of organic geochem-istry (OG) and interstitial water (IW) samples are givenin the graphic lithology column.

Lithologic Classification of SedimentsThe basic classification system used here was devised

by the JOIDES Panel on Sedimentary Petrology andPhysical Properties (SPPP) and adopted for use by theJOIDES Planning Committee in March 1974. For thesake of continuity the Leg 74 shipboard scientists haveused this basic classification with some minor modifica-tion, which we will point out when those topics are dis-cussed. The general classification (which embraces sev-eral lithologies not encountered during Leg 74) is out-lined in the following section. This classification is de-scriptive rather than genetic, and divisions between dif-ferent types of sediment are somewhat arbitrary. Wetreat lithologic types not covered in this classification asa separate category termed "Special Rock Types."

The sediments recovered on Leg 74 are composed ofcalcareous biogenic components and terrigenous andpyroclastic sediments (Special Rock Types—Fig. 18).

Conventions and Descriptive Data

Composition and TextureIn this classification, composition and texture are the

only criteria used to define the type of sediment or sedi-mentary rock. Composition is most important for de-scribing sediments deposited in the open ocean, whereastexture becomes significant for hemipelagic and near-shore sediments. These data come principally from vis-ual estimates of smear slides using a petrographic micro-

23


SITE

TIM

E -

RO

CU

NIT

o

a.3r

lOS

TR

AT

IGR

>Z

ON

E

iN

θ

)) =

dia

l

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aria

i

oT3CO

II

DC

life

r zo

ne

s

E

JS0

II

IL

Φ

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cII

2

HOLE

FOSSILCHARACTER

OR

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INIF

ER

S

U•

2

_i

ou.

-O

z<z

AD

IOL

AR

IAN

SCC

o «1- 2< •p Φ

> § ?~ o2 tCO II II IILU

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NC

E:

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nd

an

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om

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req

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nt

Z II II ||

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CORE

SE

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ION

1

2

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ME

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RS

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-

_-

-

-

-

-

—

-

——

_

-

-

-

-

-

-

:

-—_-

-

—

-

—--

-

-

CORED INTERVAL Meters below seafloor

GRAPHICLITHOLOGY

IW

PP

OG

18)

.

Φ

3αiI L

Φ

"δi

g•

o

tho

l

u

•apl

α>

, |

SrJCΦΦ

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RIL

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GIS

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lod

era

te;

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ED

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ures

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LES

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°7Λ

ea

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AR

ITY

α.

y

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Φ

1cΦ

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3

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^ers

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DC

ma

oz

LITHOLOGIC DESCRIPTION

Lithologic Description

Smear slide summary (%):Section depth (cm)Lithology: D = dominant; M = minor

. . . Texture:Interstitial _

Composition:water

s a m p e Organic carbon and carbonate (%):Section-depth (cm)Meters below Seafloor

Physicalpropertiessample

Organicgeochemistrysample

Figure 15. Sample core form (sediment).

24

INTRODUCTION

SITE HOLE CORE CORED INTERVAL Meters below seafloorT~

ÜoCC HI H

ui =>

FOSSILCHARACTER

GRAPHICLITHOLOGY

LITHOLOGIC DESCRIPTION

IW

0.5-PP

zO a< -a <o

1.0 OG

IU α o £

zl 1 I.iclout!!^ ii n H ii ii

00< < (J LU CC D0

Interstitialwatersample

Physicalpropertiessample

Organicgeochemistrysample

Lithologic Description

Smear slide summary (%):Section depth (cm)Lithology: D = dominant; M =Texture:Composition:

Organic carbon and carbonateSection-depth (cm)

Figure 16. Sample core form (HPC).

scope. They are estimates of areal abundance and sizecomponents on the slide and may differ somewhat frommore accurate analyses of grain size, carbonate content,and mineralogy (see Special Studies section). From pastexperience, we know that quantitative estimates of dis-tinctive minor components are accurate to within 1-2%,but for major constituents accuracy is poorer (± 10%).All smear slide estimates were done on board. Carbon-ate content is difficult to estimate from smear slides.Therefore, for many cores we determined the percen-tage of carbonate using the "Carbonate Bomb" tech-nique of Muller and Gastner (1971). This method in-volves treating a powdered sample with HCl in a closedcylinder. The resulting pressure of CO2 is proportionalto the carbonate (CaCO3) content of the sample, andthis value is converted to percent CaCO3 using the cali-bration factor of the manometer. The accuracy of thismethod is ± 5 % . Carbonate content determined in thismanner is listed on the core description forms below thelithologic description.

Textures of sediments estimated from smear slidesand listed as percent sand-silt-clay in the smear slidesummary on the core description forms include all con-stituents. Thus, a diatomaceous ooze will have a greaterpercentage of silt-sized particles than a nannofossil ooze

because of the different sizes of the tests of the twoplanktonic groups. This convention causes some confu-sion when naming terrigenous sediments that contain asignificant number of microfossils. For example, a dia-tomaceous silty clay may have fewer silt-sized terrigen-ous particles (e.g., quartz and feldspar) than a nanno-fossil silty clay simply because many diatoms are silt-sized and are included as such in the textural estimate.To minimize this effect, we have chosen fairly broadcompositional class boundaries (see the following) formixed terrigenous and biogenic sediments. For this rea-son we preferred to replace clayey-silt or silty-clay termsby "mud" when used with a biogenic modifier.

Where applicable we used one or several modifiers innaming the type of sediment encountered. In all casesthe dominant component appears last in the name, andminor components precede, with the least commonconstituent listed first. If minor constituents occur inamounts less than 10% they are not included in thename. This convention also holds for zeolites, Fe- andMn-micronodules, and other indicators of very slowrates of sedimentation or nondeposition such as fishbones. Often these minerals are conspicuous eventhough greatly diluted. If deemed important and en-vironmentally significant, as were nontronite, montmo-

25


DescriptionRecommendedSymbol

jjjj.

SL

00AVfI

II

III

Current ripples

Microcross-laminae (including climbing ripples)

® Composite burrow

Inclined bedding

Parallel bedding

Wavy bedding

Flaser bedding

Lenticular bedding

Cross stratification

Slump blocks or slump folds

Load casts

Scour

Normal graded bedding

Reversed graded bedding

Convolute and contorted bedding

Water escape pipes

Mud cracks

Sharp contact

Scoured, sharp contact

Disturbed sharp contact

Gradational contact

Imbrication

Fining-upward sequence

Coarsening-upward sequence

Interval over which a specific structure occurs in core

Bioturbation—minor (0—30% surface area)

Bioturbation—moderate (30—60% surface area)

Bioturbation—strong ( >60% of surface area)

Burrows

Figure 17. Symbols of sedimentary structures used on core descriptionforms (sediment).

rillonite, and smectite on Leg 74, they are sometimes in-cluded in the name of the sediment or mentioned in thelithologic description.

Induration of SedimentsWe recognize three classes of induration or lithifica-

tion for calcareous sediments and sedimentary rocks inwhich the carbonate content is greater than 50% andonly two classes for all other lithologic types.1) Calcareous sediment and sedimentary rocks (cate-

gories after Gealy et al., 1971.)a) Soft = ooze; has little strength and is readily de-

formed under pressure of finger or broad blake ofspatula.

b) Firm = chalk; partially lithified and readilyscratched with fingernail or edge of spatula.

c) Hard = limestone; dolostone; well lithified andcemented; resistant or impervious to fingernail oredge of spatula.

2) Siliceous sediments (silica > 50%)a) Soft = ooze; readily deformed by finger or broad

blade of spatula.b) Hard = radiolarite, diatomite, chert, or Porcel-

lanite; core must be cut with band saw or dia-mond saw.

3) Terrigenous sediments (terrigenous components

a) Soft = sand, silt, clay (or combinations of these);readily deformed by finger or broad blade ofspatula.

b) Hard = sandstone, siltstone, claystone, etc. (i.e.,suffix stone added); core must be cut with bandsaw or diamond saw.

Types of Sediments and Compositional ClassBoundaries

We distinguish five basic types of sediment: siliceousbiogenic sediments, calcareous biogenic sediments, ter-rigenous sediments, volcanogenic sediments, and pyro-clastic and hemipelagic sediments. Each type of sedi-ment is discussed briefly in the following sections. Anadditional category, Special Sediment and SedimentaryRock Types, which was used extensively on Leg 74, isalso included.

Siliceous Biogenic SedimentsThese are sediments in which biogenic silica or authi-

genic silica (opal CT and/or quartz) comprise at least30% of the sediment. If the siliceous component is be-tween 30 and 60%, the terrigenous (mud), calcareousbiogenic, or volcanogenic modifier is retained. For ex-ample, "Muddy Diatomaceous Ooze" describes a softsediment with at least 10% clayey silt and between 50and 90% diatoms. If the siliceous component is >60%,the modifier(s) is dropped. A radiolarian ooze wouldhave < 10% clay or carbonate and >60% radiolarians.If the siliceous biogenic component is between 30 and60%, the names for terrigenous or calcareous biogenicsediments or pyroclastic rocks apply, with the dominantsiliceous constituent as a qualifier. Silica in amounts< 10% is not acknowledged in the name.

Siliceous microfossils are often absent from hardsiliceous rocks. If they have been dissolved and replacedby opal CT and/or quartz and these minerals make up> 50% of the rock, the terms Porcellanite and chert ap-ply, defined as follows:

chert—a hard, conchoidally fracturing, varicoloredsedimentary rock with semivitreous, vitreous, orwaxy luster and conconsisting dominantly of sil-ica.

Porcellanite—a siliceous sedimentary rock with a dullor matte luster resembling that of unglazed por-celain. It is less hard, dense, and vitreous thanchert and commonly has a lower silica content.

These definitions differ from conventional DSDP usagein that chert and Porcellanite are textural terms indepen-dent of the silica polymorph (see Leg 63 ICD). If two

26

INTRODUCTION

Pelagic

Non biogenic

Pelagic Clay

Siliceous Biogenic

Pelagic Siliceous Biogenic - Soft

Diatom Ooze Radiolarian Ooze

Vertical bar percent(%) designationfor Graphic Log.

6 0 %

40%

Diatom-Rad orSiliceous Ooze

Pelagic Siliceous Biogenic - Hard

Diatomite Radiolarite

Volcaniclastic Sediments

Breccia(Conglomerate)

Tuffaceous Breccia(Conglomerate)

SB3

Porcellanite Chert

Δ Δ Δ Δ ΔΔ Δ Δ Δ Δ



SB6

A A A AA A A A A

A A A A AA A A A A

A A A A AA A A A A

SB7

Transitional Biogenic Siliceous Sediments

Siliceous Component < 5 0 %

VC2

T2

\

Siliceous Component > 5 0 %

IT2 I

Fine Tuff

Siliceous Modifier

Symbol;Hard or Soft.

VC1

Calcareous Biogenic

Pelagic Biogenic Calcareous - Soft

Nannofossil Ooze Foraminiferal OozeNanno-Foram orForam-Nanno Ooze Calcareous Ooze

CB3

3DODDOO

aαoσoσπDC3OOD£

DOODDOOODDODOC3QOOOOQ

CB4

Pelagic Biogenic Calcareous - Firm

Nannofossil Chalk Foraminiferal ChalkNanno Foram orForam-Nanno Chalk Calcareous Chalk

1

1

1

1

_ L

1

I

1

1

1 1

I |

l |l |

l |

1

1

II

1

1

• I : - : : : : : *I I I

I . I . I I

Pelagic Biogenic Calcareous - Hard

Limestone

CB9

1

1

11

11

-1—p

1

11

1!

-1—ri

i

- 1 -

iiii

-r—"-i

i

ii

i

Terrigenous Sediments Qualifers: Letter overprint such as Zeolite A l , Glauconite A3, or Siderite A4 (others may be designated)

Clay/Claystone Mud/Mudstone Shale (Fissile) Sandy Mud/Sandy Mudstone Silt/Siltstone Sand/Sandstone

T 1

Silty Sand/Sandy Silt

Evaporites

Halite Anhydrite Gypsur

E3

Concretions

Circle with Symbol (others may be designated)

Special Rock Types

SRI

Conglomerate Breccia

SR2

BasicIgneous

AcidIgenous

MnManganese

B = Barite P = Pyrite

CarbonaceousClay Dolomite Dolostone

SR3 SR6

Figure 18. Graphic symbols to accompany the lithologic classification scheme.

27


Hollow Cylindrichnus (halo burrow) Solid Cylindrichnus

WAHChondrites Pianolites

Simple Zoophycos

xaacα>o>Fat Zoophycos

Pelleted Zoophycos

Figure 19. Trace fossils most common in DSDP cores.

modifers are used, their order is dependent on the domi-nant fossil type, the dominant component being listedlast.

Calcareous Biogenic Sediments

These are sediments in which biogenic carbonate orcarbonate of indeterminate origin (cement or recrystal-

Pyrite Burrows

lized carbonate) comprises at least 30% of the sediment.If the carbonate component is between 30 and 60%, theterrigenous, siliceous biogenic, or volcanogenic modi-fiers are retained. For example, "Muddy NannofossilOoze" describes a soft sediment with at least 10% clayand between 30 and 60% calcareous nannofossils. Ifthe calcareous component is >60%, the modifers are

28

INTRODUCTION

dropped. A nannofossil ooze would have < 10% clay orsilica and 60% calcareous nannofossils. If the calcare-ous biogenic component is between 30 and 60%, thenames for terrigenous or siliceous biogenic sediments orpyroclastic rocks apply, with the dominant calcareousconstituent as a qualifier. Carbonate < 10% is not ac-knowledged in the name.

For firm and hard calcareous rock with carbonatecontents >50%, the terms chalk, limestone, and dolo-stone, apply. If the carbonate content is between 30 and60%, the terrigenous modifier is retained. The modi-fiers are dropped when the carbonate content is >60%.If the carbonate content is <30%, the terrigenous, sili-ceous biogenic, or volcanogenic names apply, with thedominant carbonate type retained as a qualifier. Car-bonate is not acknowledged in the name if it is present inamounts < 10%.

Terrigenous SedimentsThe textural classification of terrigenous sediments

(Fig. 20) follows that of Shepard (1954), with grain-sizelimits as defined by Wentworth (1922). Sediments andsedimentary rocks are assigned terrigenous names ac-cording to their textural classification when these com-

ponents are > 30%. If the terrigenous component is be-tween 30 and 60%, the biogenic or volcanogenic modi-fier is retained. For example, a nannofossil mud con-tains > 10% calcareous nannofossils and 30-60% siltyclay, with sand-silt-clay proportions of 0-20:25-50: 50-75. The biogenic or volcanogenic modifier is droppedwhen that component is <10%. For hard terrigenoussediments the suffix stone is added. Characteristic com-ponents are noted in smear slide or coarse-fractiondescriptions.

Volcanogenic and Pyroclastic SedimentsWe arbitrarily distinguish pyroclastic rocks from vol-

canogenic sediments, using 50% as the pivotal percent-age, pyroclastic rocks having >50%. Wentworth andWilliams's (1932) textural and compositional classifica-tion applies for the pyroclastic rocks. Textural groupsare as follows:

> 32 mm—volcanic breccia;4-32 mm—volcanic lapilli (lapilli tuff when indur-

ated);<4 mm—volcanic ash (tuff when indurated).The compositional breakdown is vitric (glass), crys-

talline, or lithic, according to the most common con-

BiogenicSiliceous Components

100%

Figure 20. Hemipelagic and textural classification of clastic sediments (Shepard, 1954).

29


stituent. Qualifiers are used when volcanic componentsare between 50 and 90%. For example, "Clayey VitricAsh" contains > 10% clay and 50-90% ash composedmainly of glass shards. Terrigenous and biogenic modi-fiers are dropped if < 10%.

When the volcanic component is <50%, the termi-nology and class boundaries for terrigenous (and, lessoften, biogenic) sediments apply. The modifier tuffa-ceous encompasses both ash and lapilli when either orboth of these components occur in amounts between 10and 50%. Thus "Tuffaceous Clayey Sand" (stone) con-tains 10-50% ash and/or lapilli and 50-90% clayeysand.

Hemipelagic SedimentsFigure 20 (top) shows the standard DSDP hemipe-

lagic sediment classification.

Special Sediment and Sedimentary Rock TypesThe special sediment types from Leg 74 are gravels,

conglomerates, and breccias containing varying amountsof volcanogenic and biogenic sediments. Symbols aregiven in Figure 17.

BIOSTRATIGRAPHYNannofossil, planktonic, and benthic foraminifers

were studied from all cores containing sediments. Bio-stratigraphic zonation of the Neogene (Fig. 21) is basedon the time scales and zonations of Vincent (1977) andMartini (1971); of the Paleogene (Fig. 22) on the timescales and zonations of Hardenbol and Berggren (1978)and Martini (1971); and of the Cretaceous (Fig. 23) ofthe time scales and zonations of Thierstein (1976) andSliter (unpublished).

Special Studies of Sediments

Organic Carbon and Carbonate ContentMeasurements of organic carbon made on selected

samples were done on board using the Hewlett-PackardCHN analyzer. In addition we selected samples to beanalyzed at the DSDP sediment laboratory on a LECOWR-12 carbon analyzer. Some of the data were notavailable at the time of this compilation, but should bein the near future.

Carbonate content was determined on board usingthe "Carbonate Bomb" method already described. Thesedata appear on the core description forms as "%CaCO3."

Grain-size AnalysisSediment samples selected for grain-size analyses at

the DSDP sedimentary laboratory, using standard sieveand pipette methods, were not available at the time ofthis compilation.

X-Ray DiffractionAn X-ray diffraction unit is now on board the Glo-

mar Challenger. Preliminary XRD results are availableupon request.

IGNEOUS ROCKS

Visual Core Description FormsAll igneous rocks were split by rock saw into working

and archive halves described and sampled on board.Figure 24 shows a composite visual core descriptionform used for the description of igneous rocks recov-ered on Leg 74. On this form, each section of a core isdescribed under a set of five column headings: (1) PieceNumber, (2) Graphic Representation, (3) Orientation,(4) Shipboard Studies, and (5) Alteration.

In the graphic representation column each piece is ac-curately drawn and different features, such as texture,glassy margins, or vesicles, coded according to the sym-bols given in Figure 25. Two closely spaced horizontallines in this column indicate the location of styrofoamspacers taped between pieces inside the liner. Each pieceis numbered sequentially, beginning with 1, from thetop of each section. Pieces are labeled on the rounded,not the sawed, surface. Pieces which fit together beforesplitting are given the same number but are consecutivelylettered (1A, IB, IC, etc.). Spacers were placed only be-tween pieces which did not fit together; those pieceswere given different numbers. In general, spacers mayor may not indicate material missing (not recovered) be-tween pieces. All cylindrical pieces longer than the dia-meter of the liner have arrows in the Orientation col-umn, indicating that top and bottom have not been re-versed as a result of drilling and recovery. Arrows alsoappear on their labels on both archive and workinghalves.

The Shipboard Studies column designates the loca-tion and the types of measurements made on a sampleon board. The Alteration column gives the degree of al-teration, using the code given in Figure 25. Below eachset of five descriptive columns is the designation forcore and section for which these data apply.

Figure 24 gives the outline for core descriptions of ig-neous rocks in the right-hand margin of the visual coredescription form. If more than one core appears on theform, these data are listed below the description of thefirst core, using the same format. As many cores asspace allows are included on one visual core descriptionform. Data that do not fit on this form appear on theverso or on a facing page. However, in no case does in-formation from one core appear on successive coreforms.

For each core, the core number, sections, and depthinterval recovered are listed first, followed by the majorand minor rock types and a short description, thin sec-tion data, and, finally, shipboard data.

Classification of Igneous RocksWe informally classified igneous rocks recovered on

Leg 74 according to mineralogy and texture determinedfrom visual inspection of hand specimens and thin sec-tions. The following conventions were agreed uponwhile at sea, and we realize they are generalized. It ispossible that gradations exist within and among texturalgroups in a single sample.

30

Epoch

Plank.ForamZonesBlow

(1969)

N20

N19

Calcareous Nannoplankton Zones

Martini (1971)

NN21

D. pentaradiatus

R. pseudoumbilica

D. asymmetricus

C. rugosus

C. tricorniculatus

D. quinqueramus

C. coalitus

D. kuglen

S. heteromophus

H. ampliaperta

S. ciperoensis

Gartner (1974)

D. surcu/u

R. pseudoumbilica

D. asymmetricus

C. rugosus

C. tricorniculatus

D. quiπQuβramus

D. neohamatus

D. kuglen

S. heteromorphus

S. ciperoensis

Bukry (1973)

G. caribbeanica

D. pentaradiatus

D. asymmetricus

C. rugosus

T. rugosus

C. primus

D. berggrenii

D. kuglen

C. miopelagicus

S. heteromorphus

H. ampliaperta

D. druggi

S. ciperoensis

INTRODUCTION

RadiolarianZones

Riedel andSanfilippo (1978)

L. haysi

P. prismatiun

S. pentas

S. peregrii

O. penultimus

O. antepenultimus

C. petterssoni

S. delmontensis

C. tetropera

L. elongata

Figure 21. Biostratigraphic time scale and zonation of the Neogene, after Vincent (1977) and Martini (1971).

31

T.C.MOORE, JR. ET AL.

Paleogene Time Scale

fi

30 —

35 —

40 —

45—

50 —

5 5 —

6 0 —

6 5 —

MagneticPolarityHistory

8

- 2 4

Epochs StandardAges

Rupelian

- 4 0 -

Ypresian

- 6 0 -

Plankton Zones

Foraminifers

AfterBolli, 1957a, b, c

1966,Stainforth

et al., 1975

Globigerinaciperoensis

"Globorotatia"opima opima

Globigerinaampliapertura

Cassigerineliachipolensis

Pseudohas tigerinamicra

Turborotaliacerroazulensis s. I.NP2J

Globigerinathekasemiinvoluta

Truncorotaloidesrohri

Orbulinoidesbeckmanni

Morozovellalehneri

Globigerina thekasubconglobata

Hantkeninaaragonensis

Acarininapentacamerata

Morozovellaaragonensis

M. formosa formosa

NI. subbotinae

M. edgari

Morozovellavelascoensis

Planorotalitespseudoemenardii

Planorotalitespusilla pusillaMorozovella

angulata

Morozovellauncinata

Subbotinatrinidadensis

J S. pseudobulloides

IUI1

[NP14

18

NP11

NP1

NP9

NP8

NP7

NP6

NP5

NP4

Position StageStatotypes

Martini, 1971Martini and

Muller, 1971Roth, 1970

Roth et al., 1971Radiolarians*

h

II

If

1.2If

— 45

— 50

! Normal polarity>Riedel and Sanfilippo, 1970, 1971; Moore, 1971: Foreman, 1973; Theyer and Hammond, 1974

Radiolarian zones(numbers refer to footnotes only)12. Dorcadospyris ateuchus13. Theocyrtis tuberosa14. Theocyrtis bromia15. Thyrsocyrtis tetracantha16. Podocyrtis goetheana17. Podocyrtis chalara18. Podocyrtis mitra19. Podocyrtis ampla20. Thyrsocyrtis triacaπtha21. Theocampe mongolfieri22. Theocotyle cryptocephala23. Phormocyrtis striata striata24. Buryella clinata25. Bekoma bidartensis

Figure 22. Biostratigraphic time scale and zonation of the Paleogene, after Hardenbol and Berggren (1978) and Martini (1971).

32

Age

Ma

65

7 0 -

75-

80-

85-

9 0 -

9 5 -

100

105-

110-

115

Stage

Maestrichtian

Campanian

Santonian

Coniacian

Turonian

Cenomanian

Albian

Aptian

Barremian I

Biohorizons

First occurrenceLast Occurrence

Micula murus

Lithraphidites quadratus

Tetra I ith us trifidus

Tetralithus trifidus •—*

Broinsonia parca

Marthasterites furcatus

Micula staurophora

Corollithion e×iquum '—*•

Lithraphidites alatus

Eiffelithus turriseiffeli '—*•

Prediscosphaera cretacea '

Parabdolithus angustus

Chiastozygus litteraius

Zone

Micula mura

Lithrophidites quadratus

Arkhangelskiella cymbiformis

Teralithus trifidus

Eiffellithus e×imius

Marthasterites furcatus

Micula staurophora

Corollithion exiguum

Lithraphidites alatus

Eiffelithus turriseiffeli

Prediscosphaera cretacea

Parhabdolithus angustus

Chiastozygus litterarius

Micrantholithus haschulzii

Figure 23. Biostratigraphic time scale and zonation of the Cretaceous, after Thierstein (1976)and Sliter (unpublished).

INTRODUCTION

33

.§ I I I c I c I

I I .1 l | c 1 I I s 1 I J B i I I g i J L i! II I | i I !l i l l 1 !l I I I i !l i l l i !l I I I 1 ft I ! |C < S I T O M < C C D E C O W < C O C C O K < i ‰ α o c o c o < i σ i o a < ò . o c c o c o <

H

n

8δa

>

Leg, Core, Sβction(s), Depth (mbif IDominant LithologyMacroscopic Description(s)Thin Section Description(s)

Shipboard Studies:T = thin section

CORE/SECTION

Figure 24. Visual core description form (igneous rock).

INTRODUCTION

Textureused in graphic representation column

oo

XX

G

G

G

D

DD

X

X

G

G

G

D

D

DD

' O

i

D

o

1

Aphyric basalt

Olivinephenocrysts

Porphyritic basalt

Plagioclase phenocrysts

Clinopyroxenephenocrysts

Vein with alteredzone next to it

Gabbro

Dolerite

O

Serpentinite (shearorientation appro×. asin core; augen showntoward bottom)

Fractures

Figure 25. List of symbols for igneous rocks.

A. Quench textures recognized and described:1. Glassy—matrix is amorphous, basaltic glass with

no visible, incipient crystallization.2. Variolitic—texture characterized by the presence

of varioles, which are spherical bodies, usuallyconsisting of radiating Plagioclase and/or clino-pyroxene microlites or crystals; individual crys-tals are indistinguishable with the microscope.

3. Sub variolitic—texture in which varioles coalesce.4. Immature sheaf—a bundled arrangement of

small crystals (which cannot be individually dis-tinguished with the microscope) assuming asheaflike appearance; a central axis of crystalgrowth often occurs.

Glass on edge

Weathering: Alterationused in alteration column

Very fresh

Weathered rindon rounded piece

Breccia(as graphicas possible)

Moderatelyaltered

Badlyaltered

Almost completelyaltered

Moderatelyaltered(slight discoloration)but has fresh core oris partly fresh

B.

5. Mature sheaf—same as (4), but discrete skeletalcrystals (usually > 0.005 mm wide) can be dis-tinguished with the microscope.

6. Plumose—plume-or feather-like arrangement ofmicrolites or crystals; may grade from immatureto mature (as in sheaf texture) according to crys-tal size.

Major textural classification for basaltic samplesused during Leg 74 includes the following terms:1. Phyric—describes igneous rocks in which larger

crystals (phenocrysts) are set in a finer ground-mass which may be crystalline or glassy, or both.Aphyric: no phenocrysts.Sparsely phyric: 1-2% phenocrysts.

35


Moderately phyric: 2-10% phenocrysts.Highly phyric: > 10% phenocrysts.

2. Glomerophyric—applied to phyric rocks con-taining clusters of equant crystals larger than thematrix crystals.

3. Ophitic—applied to a texture in which euhedralor subhedral crystals of Plagioclase are embed-ded in a mesostasis of pyroxene crystals.

4. Subophitic—characterizing the ophitic texture ofan igneous rock in which the feldspar crystals areapproximately the same size as the pyroxene andonly partially included by them.

5. Intergranular—applied to volcanic rocks in whichthere is an aggregation of clinopyroxene grains—not in parallel optical continuity (as in sub-ophitic texture)—in a network of feldspar lathscharacterized by the absence of interstitial glassor other quenched places which may fill the inter-stices.

6. Intersertal—applied to volcanic rocks wherein abase of mesostasis or glass and small crystals fillsthe interstices between unoriented feldspar laths,the base forming a relatively small proportion ofthe rock. When the amount of the base increasesand the feldspar laths decrease, the texture be-comes hyalophitic; with still greater increase inthe amount of the base, the texture becomes hy-alopilitic.

Paleomagnetic data taken on board are not listed butwill appear in a more comprehensive study by shipboardscientists.

PHYSICAL PROPERTIESThe following physical properties were determinedroutinely:

Measurement/Determination

Gravimetric procedureBulk densityWater contentPorosityApproximate grain density

ShrinkageBulk density by 2-minute GRAPEVane shear strengthPenetrometer strengthSonic velocityThermal conductivity

Sediment

XXXXXXXXXX

Basalt

XXXX

X

XX

In general, we tried to perform these measurements atleast once on every core. Water content samples weretaken in every section unless the cores were highly dis-turbed. All samples were taken from, and measure-ments made on, the least disturbed section(s) of eachcore.

Gravimetric ProcedureThe methods used here are described by Boyce

(1976a). Bulk density and porosity were gravimetricallydetermined, either by the cylinder technique or by mea-suring chunks cut from the split core. The cylinder

technique was used on soft or stiff sediments. Sampleswere taken with stainless steel or brass cylinders ofknown volume (about 5 cm3 and 15 cm3) and weight andwere tightly enclosed until they could be weighed. On in-durated sediment and hard rock, samples were cut incube-shaped pieces from the split core halves and storedunder seawater. Before the gravimetric measurementswere made, sonic velocity and 2-minute GRAPE densitywere obtained on the samples (see GRAPE section);Their volume was determined by weighing both in airand suspended under water. A number of samples with-out defined volume were taken for determination ofwater content alone.

Sample volume and weight yield the wet-bulk densitywithout a buoyancy correction. Wet water content andporosity were calculated from the water loss after dryingat 110°C for 24 hr. Water content is related to theweight of the wet samples and therefore is defined hereas wet-water content. All wet-water content and poros-ity data are corrected for salt content, using the correc-tion factors for seawater (Boyce, 1976). The approxi-mate grain density was calculated from the gravimetricdata (as it is only an approximation, no correction forsalt content was applied). The porosity is calculated as-suming that the sediments are water-saturated. Thismay not be true of all samples, because some undergoadiabatic expansions if the in situ pressure is releasedwhen the cores are brought from the seafloor to theshipboard laboratory. The effect of the volume increaseof the samples due to elastic rebound, caused by the re-moval of in situ overburden pressure (Hamilton, 1976),was not taken into account.

ShrinkageShrinkage is the loss of volume expressed as a per-

centage of the original volume (vol.wet) of the wet cyl-inder sample after drying at 110°C. The volume of theshrunken cylindrical sample (vol.shr) was calculatedfrom its mean height and diameter as determined by atleast three caliper or dial micrometer measurementseach of height and diameter. The shrinkage is defined as

s = vol.wet - vol,hr,

VOl. wet

The measurement is inaccurate, because after shrinkagemost samples are not ideal cylinders. Nevertheless, theshrinkage data may provide valuable information withrespect to composition and early diagenesis of the sedi-ments.

GRAPEAnother method for determinating wet-bulk density

is by the shipboard Gamma Ray Attenuation Poros-ity Evaluator (GRAPE). In addition to the continuousGRAPE density determinations on the unsplit core sec-tions, special 2-minute counts were taken on either thecylinder samples (WCS samples for shorebased deter-mination of gravimetric physical properties) or on thepieces of lithified material used for the shipboard gravi-

36

INTRODUCTION

metric procedures (Boyce, 1976). On these pieces,GRAPE density could be measured in directions bothparallel and perpendicular to the core axis. GRAPEporosity was not determined, because good porositydata could be obtained by gravimetric methods and be-cause porosity determinations from GRAPE data mayhave a large error if grain density is not accuratelyknown (Boyce, 1976).

Vane Shear and Penetrometer StrengthShear strength was measured on the split core halves

applying a torque to the sediment using the modifiedWykeham Farrance Laboratory Vane Apparatus (Boyce,1977). The vane used had an average height of 1.27 cm,a diameter of 1.28 cm, and a vane constant of 0.2273.The blades were buried about 0.5 cm below the sedimentsurface of the split core halves with the vane axis orien-ted parallel to the bedding plane of the sediment. A fewdeterminations of remolded shear strength were per-formed.

Penetrometer measurements were made both by al-lowing the needle to drop from 1 cm directly above thesediment surface at 0 cm. The needle axis was orientednormal to the split half surface.

The determination both of vane shear strength andpenetration was impossible when the sediments were in-durated or lithified, as the sample cracked when thevane was inserted. At all sites only the upper two-thirdsof the cored sediment sequence could be tested.

Sonic VelocityCompressional sound velocity of both sediments and

basaltic rocks was measured with the Hamilton FrameVelocimeter at 400 kHz (Boyce, 1976). By measuringaluminum, Lucite, and brass standards, the correctionfactors for the oscilloscope were determined at the be-ginning of Leg 74. They were K = 0.99866 for the 2-µssetting and K = 1.00575 for the 5-/xs setting. These fac-tors were applied on all sound velocity measurements.The sound velocity of weak sediments was determinedparallel to bedding on split core halves, through the coreliner, with corrections for liner thickness (2.56 mm) andtravel time (1.18 µs) through it. On the indurated sedi-ments and basalts, measurements of sonic velocity weremade on the samples used for gravimetric procedure.The pieces were stored under seawater to prevent dry-ing. Sonic velocity could be determined in horizontal(i.e., perpendicular to the core axis) and vertical (i.e.,parallel to the core axis) directions. All samples weremeasured after they had reached room temperature.

Acoustic impedance was calculated as the product ofsonic velocity and wet-bulk density, using both gravi-metrically determined density data and GRAPE densityvalues.

Thermal ConductivityThermal conductivity was determined using a needle

thermistor probe (No. 28) on weak and stiff sedimentand a flat needle block thermistor probe (No. 1) on in-durated or lithified sediments and hard rock, followingthe shipboard laboratory manual. It was sometimes dif-ficult to obtain a stable zero reading in air, and the in-

Table 4. Thermal conductivity measurements of shipboard semistan-dárds

Blue Plastic Standard(used with needle

probe No. 28)

W/m°C

2.501.531.501.421.701.372.241.471.601.49

Mean x =Standard deviation s• =

W/m°C

.48

.47

.48

.47

.39

.461.461.411.49

= 1.58= 0.29

Granite StandardCeramic Standard

No. 30146(used with flat block probe No. 1)

W/m°C

3.033.053.023.253.093.773.683.05

x = 3.24s = 0.31

W/m°C

3.363.363.333.393.353.393.37

x = 3.365 = 0.01

strument drift during measurement was often very large,which affected the quality of the data. Still, several con-trol measurements performed on shipboard standardsyielded reproducible data with an acceptable scatter(Table 4). Measurements were taken after the sampleshad come to equilibrium temperature.

On unlithified sediments, thermal conductivity wasmeasured on split core halves by inserting the needleprobe obliquely into the sediment. This procedure is lesstime-consuming than inserting the probe through theunsplit liner, and it allows measurements at undisturbedsections of the core.

On indurated sediment and basalt, the flat block probewas used. Pieces of split core were stored in seawaterwhile reaching room temperature. At times the sectionsurface was ground to obtain a smooth interface. Themeasurement itself was performed with the probe andsample immersed in seawater.

PHOTOGRAPHYAs supplements to the core descriptions, sets of color

and black and white slides and photographs of wholecores are available for consultation at both repositories.In addition, negatives in color and black and white forclose-up documentation of special structures are ar-chived at DSDP. Table 5 lists those from Leg 74. Photo-graphs are available on a charge and time availablebasis.

DOWNHOLE LOGGINGOwing to bad weather and equipment failure the de-

tailed logging program planned for Leg 74 was ab-breviated. Nevertheless, we did successfully log holes atSites 527 and 528. We obtained a density log at Site 527and a sonic log with gamma ray traces at Site 528. A de-tailed analysis of the logging results is given in the re-spective site chapters and in Rabinowitz and Borella,this volume.

REFERENCES

Alvarez, W., Arthur, M. A., Fischer, A. G., Lowrie, W., Napoleone,G., Premoli-Silva, I., and Roggenthen, W. M., 1977. Upper Cre-taceous-Paleocene magnetic stratigraphy at Gubbio, Italy v. typesection from the late Cretaceous-Paleocene geomagnetic reversaltime scale. Geol. Soc. Am. Bull., 88:383-389.

37


Berger, W. H., 1977. Carbon dioxide excursions and the deep-sea rec-ord: aspects of the problem. In Anderson, R. N., and Malahoff,A. (Eds.), The Fate of Fossil Fuel CO2 in the Oceans: New York(Plenum Press), pp. 505-542.

,1978. Sedimentation of deep-sea carbonate: maps andmodels of variations and fluctuations. / . Foram. Res., 8:286-302.

Berger, W. H., and Winterer, E. L., 1974. Plate stratigraphy and theflucuating carbonate line. In Hsü, K. J., and Jenkyns, H. S.(Eds.)» Pelagic Sediments on Land and under the Sea. Spec. Publ.Int. Assoc. Sedimentol., 1:11-48.

Berggren, W. A., and Van Couvering, J. A., 1974. Biostratigraphy,geochronology, and paleoclimatology of the last 15 m.y. in marineand continental sequences. Palaeogeogr. Palaeoclimatol., Palaeo-ecol., 16:1-216.

Bischoff, J. L., and Dickson, F. W., 1975. Sea water-basalts interac-tion at 200°C and 500 bars: Implications for origin of sea floorheavy metal deposits and regulation of sea water chemistry. EarthPlanet Sci. Lett., 25:385-397.

Blow, W. H., 1969. Late middle Eocene to Recent planktonic fora-miniferal biostratigraphy. In Brönnimann, P., and Renz, H. H.(Eds.), First Internat. Conf. Plankt. Microfossils, 1:199-421.

Bolli, H. M., 1957a. The genera Globigerina and Globorotalia in thePaleocene-lower Eocene Lizard Springs Formation of Trinidad,B.W.I. U.S. Natl. Mus. Bull., 215:61-81.

, 1957b. Planktonic Foraminifera from the Oligocene-Mio-cene Cipero and Lengua Formations of Trinidad, B.W.I. U.S.Natl. Mus. Bull., 215:97-123.

, 1957c. Planktonic Foraminifera from the Eocene Navetand San Fernando Formations of Trinidad, B.W.I. U.S. Natl.Mus. Bull., 215:155-172.

Boyce, R. E., 1976. Definitions and laboratory techniques of com-pressional sound velocity parameters and wet-water content, wet-bulk density, and porosity parameters by gravimetric and gammaray attenuation techniques. In Schlanger, S. O., Jackson, E. D., etal., Init. Repts. DSDP, 33: Washington (U.S. Govt. Printing Of-fice), 931-958.

, 1977. Deep Sea Drilling Project procedures for shear strengthmeasurements of clayey sediment using modified Wykeham Far-rance laboratory vane apparatus. In Barker, P. F.< Dalziel, I. W.D., et al., Init. Repts. DSDP, 36: Washington (U.S. Govt. PrintingOffice), 1059-1068.

Bukry, D., 1973. Coccolith stratigraphy, Leg 13, Deep Sea DrillingProject. In Ryan W. B. F., Hsü, K. J., et al., Init. Repts. DSDP.,13, Pt. 2: Washington (U.S. Govt. Printing Office), 817-822.

Chave, R. D., 1979. Lithospheric structure of the Walvis Ridge fromRayleigh wave dispersion. J. Geol. Res., 84:6840-6848.

Connary, S. D., and Ewing, M., 1974. Penetration of Antarctic Bot-tom Water from the Cape Basin into the Angola Basin. /. Geo-phys. Res., 79:463-469.

Detrick, R. S., and Watts, A. B., 1979. An analysis of isostasy in theworld's oceans. 3. Aseismic ridges. /. Geophys. Res., 84 (No. B7):3637-3655.

Foreman, H. P., 1973. Radiolaria of Leg 10 with systematics andranges for the families Amphipyndacidae, Artostrobiidae, andTheoperidae. In Worzel, J. L., Bryant, W., et al., Init. Repts.DSDP, 10: Washington (U.S. Govt. Printing Office), 407-474.

Gealy, E. L., Winterer, E. L., and Moberly, R., 1971. Methods, con-ventions, and general observations. In Winterer, E. L., Riedel W.R., et al., Init. Repts. DSDP, 7, Pt. 1: Washington (U.S. Govt.Printing Office), 9-26.

Goslin, J., and Sibuet, J.-C, 1975. Geophysical study of the eastern-most W. R., South Atlantic: deep structure. Geol. Soc. Am. Bull.,86:1713-1724.

Hamilton, E. L., 1976. Variations of density and porosity with depthin deep-sea sediments. /. Sediment. Petrol., 46:280-300.

Hardenbol, J., and Berggren, W. A., 1978. A new Paleogene numer-ical time scale. Am. Assoc. Petrol. Stud. Geol., 6:213-234.

Heirtzler, J. R., Dickson, G. O., Herron, E. M., Pitman, W. C , andLePichon, X., 1968. Marine magnetic anomalies, geomagneticfield reversals, and motions of the ocean floor and continents. / .Geophys. Res., 73(6):2119-2136.

Martini, E., 1970. Standard Paleogene calcareous nannoplanktonzonation. Nature, 266(5245):560-561.

, 1971. Standard Tertiary and Quaternary calcareous nanno-plankton zonation. In Farinacci, A. (Ed.), Proc. IIPlankt. Conf.Roma: Rome (Edizione Tecnoscienzia), pp. 739-785.

Martini, E., and Worsley, T., 1970. Standard Neogene calcareousnannoplankton zonation. Nature, 225(5229):289-290.

Moore T., 1971. Radiolaria. In Tracy J. I., Jr., Sutton G. H., et al.,Init. Repts. DSDP, 8: Washington (U.S. Govt. Printing Office),727-775.

Muller, C , 1974. Calcareous nannoplankton, Leg 25 (Western IndianOcean). In Simpson, E. S. W., Schlich, R., et al., Init. Repts,DSDP, 25: Washington (U.S. Govt. Printing Office), 579-633.

Muller, G., and Gastner, M., 1971. The "Karbonate Bomb," a sim-ple device for determination of the carbonate content in sediments,soils, and other materials. Neues Johrb. Miner. Monatsh., 10:466-469.

Ness, G., Levi, S., and Crouch, R., 1980. Marine magnetic anomalytime scales for the Cenozoic and Late Cretaceous: a precis, cri-tique, and synthesis. Rev. Geophys., 18:753-770.

Premoli-Silva, I., Napoleone, G., and Fisscher, A. G., 1974. Risultatipreliminari sulla stratigrafia paleomagnetica della scaglia Creta-ceo-Paleocenia della sezione di Gubbio (Appennino centrale).Soc. Geol. ItalianaBoll, 93:64-659.

Rabinowitz, P. D., and LaBrecque, J., 1979. The Mesozoic South At-lantic Ocean and evolution of its continental margins. /. Geophys.Res., 84(No. Bll):5973-6002.

Rabinowitz, P. D., and Simpson, E. S. W., 1979. Results of IPODsite surveys aboard R/V Thomas B. Davie: Walvis Ridge survey.L-DGO Tech. Rept., JOI, Inc.

Riedel, W. R., and Sanfilippo, A., 1970. Radiolaria, Leg 4, DSDP.In Bader, R. G., Gerard, R. D., et al., Init. Repts. DSDP, 4:Washington (U.S. Govt. Printing Office), 503-575.

, 1971. Cenozoic Radiolaria from the western tropical Paci-fic, Deep Sea Drilling Project, Leg VII. In Winterer, E. L., Riedel,W. R., et al., Init. Repts. DSDP, 7, Pt. 2: Washington, (U.S.Govt. Printing Office), 1529-1672.

_, 1978. Stratigraphy and evolution of tropical Cenozoic ra-diolarians. Micropaleontology, 24(l):61-96.

Sclater, J. G., Jarrard, R. D., McGowran, B., and Gartner, S. 1974.Comparison of the magnetic and biostratigraphic time scales sincethe Late Cretaceous. In von der Borch, C. C , Sclater, J. G., et al.,Init. Repts. DSDP, 22: Washington (U.S. Govt. Printing Office),381-386.

Shephard, F. P., 1954. A scale of grade and class terms of clastic sedi-ments. / . Geol., 30:337.

Stainforth, R. M., 1975. Cenozoic planktonic foraminiferal zonationand characteristics of index forms. Univ. Kansas Paleont. Contr.62:1-45.

Takahashi, T., 1975. Carbonate chemistry of sea water and the calcitecompensation depth in the oceans. In Sliter, W. V., Be, A. W. H.,and Berger, W. H. (Eds), Cushman Found. Foram. Res., 13:11-26.

Theyer, F., and Hammond, S. R., 1974. Paleomagnetic polarity se-quence and radiolarian zones, Brunhes to polarity Epoch 20. EarthPlanet. Sci. Lett., 22:307-319.

Thierstein, H. R., 1976. Mesozoic calcareous nannoplankton biostra-tigraphy of marine sediments. Mar. Micropaleont., 1:325-362.

Vincent, E., 1977. Indian Ocean Neogene planktonic foraminiferalbiostratigraphy and its paleoceanographic implications. In Heirt-zler, J. R., Bolli, H. M., Davies, T. A., et al. (Eds.), Indian OceanGeology and Biostratigraphy: Washington (Am. Geophys. Un-ion), pp. 469-548.

Wentworth, C. K., 1922. A scale of grade and class terms of clasticsediments. J. Geol., 30:337.

Wentworth, C. K., and Williams, H., 1932. The classification and ter-minology of the pyroclastic rocks. Rept. Comm. Sedimentation,Bull. Nat. Res. Covnc, 80:10-53.

Wüst, G., 1936. Das Bodenwasser und die Gliedering der AtlantischenTiefsee. Wiss. Ergeb. Dtsch. Atl. Exped. Meteor., 1925-1927,6(l):3-107.

38

INTRODUCTION

Table 5. Leg 74 detail core photographs (black and white).

NegativeNo.

123456789

10111213141516171819202122232425262728293031

Sample(interval in cm)

525-22-6, 100-115525A-42-2, 5-20525A-40-2, 0-25525A-41-4, 72-83525A-51-2, 35-50526A-2-3, 50-65526A-2-3, 85-100527-13-2, 70-80527-13-3, 75-95527-13-3, 115-130527-14-4, 70-95527-14-4, 95-120527-14-4, 120-145527-24-2, 15-40527-24-2, 40-65527-30-1, 132-145527-30-2, 35-50527-31-1, 145-150527-32-4, 40-60527-36-4, 110-125527-37-5, 60-75527-41-5, 40-68528-4-4, 55-70528-4-4, 95-115528-4-4, 115-135528-16-3, 32-38528-17-3, 70-80528-28-1, 10-20528-28-1, 20-26528-28-2, 35-48528-29-2, 20-25

NegativeNo.

323334353637383940414243444546474849505152535455565758596061

Sample(interval in cm)

528-29-2, 55-60528-29-2, 65-75528-29-4, 42-52528-29-4, 60-80528-29-4, 79-90528-30-2, 43-63528-30-2, 60-80528-30-4, 52-62528-31-2, 19-29528-31-5, 69-76528-33-1, 22-41528-33-1, 126-129528-33-1, 135-139528-43-1, 64-74528A-2-2, 71-91529-8-5, 130-135529-33-3, 19-40529-33-3, 90-107529-33-3, 135-150529-34-3, 115-135529-35-1, 20-30529-36-3, 140-150 (A)529-36-3, 140-150 (top)529-36-3, 140-150 (mid)529-36-3, 140-150 (btm)529-36-4, 65-75529-40-2, 90-100529-41-1, 5-15529-42-1, 10-35529-42-2, 70-85

39

Documents

1. INTRODUCTION AND EXPLANATORY NOTES1 · 2007. 5. 3. · 1. INTRODUCTION AND EXPLANATORY NOTES1 T. C. Moore, Jr.,2 Philip D. Rabinowitz,3 Peter Borella,4 Anne Boersma,3 and Nicholas