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Gradstein F. M., Ludden, J. N., et al., 1992Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 123

8. GEOCHEMISTRY OF SEDIMENTS IN THE ARGO ABYSSAL PLAIN AT SITE 765:A CONTINENTAL MARGIN REFERENCE SECTION FOR SEDIMENT RECYCLING

IN SUBDUCTION ZONES

Terry Plank2 and John N. Ludden3

ABSTRACT

Drilling at Site 765 in the Argo Abyssal Plain sampled sediments and oceanic crust adjacent to the Australian margin. Someday, this site will be consumed in the Java Trench. An intensive analytical program was conducted to establish this site as ageochemical reference section forcrustal recycling calculations. About 150 sediment samples from Site 765 were analyzed for majorand trace elements. Downhole trends in the sediment analyses agree well with trends in sediment mineralogy, as well as in Al andK logs. The primary signal in the geochemical variability is dilution of a detrital component by both biogenic silica and calciumcarbonate. Although significant variations in the nonbiogenic component occur through time, its overall character is similar to nearbyCanning Basin shales, which are typical of average post-Archean Australian shales (PAAS). The bulk composition of the hole iscalculated using core descriptions to weight the analyses appropriately. However, a remarkably accurate estimate of the bulkcomposition of the hole can be made simply from PAAS and the average calcium carbonate and aluminum contents of the hole.Most elements can be estimated within 30% in this way. This means that estimating the bulk composition of other sections dominatedby detrital and biogenic components may require little analytical effort: calcium carbonate contents, average Al contents, and averageshale values can be taken from core descriptions, geochemical logs, and the literature, respectively. Some of the geochemicalsystematics developed at Site 765 can be extrapolated along the entire Sunda Trench. However, results are general, and Site 765should serve as a useful reference for estimating the compositions of other continental margin sections approaching trenches aroundthe world (e.g., outboard of the Lesser Antilles, Aegean, and Eolian arcs).

INTRODUCTION

The extent to which the continental crust is recycled back intothe mantle via sediment subduction is crucial to our understandingof how Earth's mantle and crust evolved. Primarily, two lines ofevidence support sediment subduction. One is based on seismicsurveys and drilling that show an absence of accreted sedimentsin some forearcs (e.g., in the Marianas: Hussong, Uyeda, et al.,1982; Guatemala: Moore, Backman, et al., 1982; and Peru: Warsiet al., 1983). Even where well-developed accretionary wedgesoccur, often evidence indicates that some sediment is also beingsubducted beneath décollement structures in the wedge (as in theLesser Antilles: Westbrook et al., 1988) or in grabens developedin the bending plate (as for the Nazca Plate approaching thePeru-Chile Trench: Schweller et al., 1981). Thus, ample geophys-ical evidence exists to show that sediment is subducted, at leastbeneath some forearcs.

A second line of evidence for sediment subduction comes fromthe isotope 10Be. An isotope strongly enriched in soils and marineclays, 10Be is found in measurable quantities in arc volcanics, butnot in volcanics from other tectonic settings (Tera et al., 1986).This means that some surface sediments are taken as far as the siteof arc magma genesis (-120 km deep). The factors that lead tosediment subduction in some situations, and not others, are stillpoorly understood (a modern twist on an old soliloquy providesa recent discussion of the various models; Von Huene, 1986).

The issue of how much sediment gets subducted to great depthsremains open. Arc magmas incorporate some quantity of sediment

1 Gradstein, F. M., Ludden, J. N., et al., 1992. Proc. ODP, Sci. Results, 123:College Station, TX (Ocean Drilling Program).

2 Lamont-Doherty Geological Observatory and Department of GeologicalSciences of Columbia University, Palisades, NY 10964, U.S.A.

3 Département de Géologie, Université de Montreal, C.P. 6128 Succ. A, Mon-treal, Quebec, H3C 3J7, Canada.

and provide our best means for estimating the fluxes involved.However, these calculations require knowledge of the geochemi-cal characteristics of both the influx (sediment and crust ap-proaching trenches) and the output (arc volcanics). Although afairly comprehensive global data base exists of the geochemicalcomposition of arc volcanics, a method has yet to be developedfor estimating the composition of the diverse sediment sectionsapproaching trenches. A considerable amount of geochemicaldata exist for marine sediments. Most chemical analyses of sedi-ments, however, consist of a few elements specific to oceano-graphic problems, and not necessarily solid earth ones. These dataprovide a first-order understanding of the systematics of sedimentcompositions, but do not constrain well what compositions areappropriate for individual subduction zones. Estimates of sedi-ment compositions outboard of trenches usually are based onanalyses of a few surface sediments, whole-ocean averages, oraverage "pelagic sediment." These estimates need to be refined.For example, elements that are used as tracers for sediment in-fluxes to arc magma sources (e.g., K2O; Karig and Kay, 1980)may vary considerably in "pelagic sediments," on the order of alligneous rocks on the face of Earth. This is because sedimentsrepresent mixtures of biogenic carbonate or silica, which aredevoid of most trace elements, and continental detritus or Fe-Mnoxides, which are rich in many trace metals. Thus, although ratiosof certain elements and isotopic compositions of sediments arefairly well constrained, the actual element abundances may varyenormously. Ultimately, it is concentration data, not element orisotopic ratios, that are necessary for answering the question ofhow much!

Here, we discuss the geochemistry of the sedimentary sectionof Site 765, drilled during Leg 123 in the Argo Abyssal Plain,south of Java. These sediments may someday be consumed in theSunda Trench. Full characterization of potential crustal fluxesinto the Sunda Trench should include other sedimentary compo-nents that may be added to Site 765 as it drifts northward: volcanicash derived from the arc itself and clastic material derived from

167

T. PLANK, J. N. LUDDEN

the Ganges-Brahmaputra river system via the Nicobar Fan. Inaddition to sedimentary components, the chemical additions to thebasaltic substrate via seawater alteration constitutes another crus-tal component. Gillis et al. (this volume) present some preliminaryconclusions regarding the geochemical fluxes involved duringalteration of the basaltic crust at Site 765.

Although the data presented here have obvious bearing onproblems specific to the Sunda Arc as well as to the sedimen-tological history of the Australian margin, the thrust of this studyis more general: to provide a reference data set for sedimentsubduction globally. Indeed, Site 765 represents an end-memberof sorts. The site is situated adjacent to a passive margin, and sorepresents the crust first formed when an ocean basin opens, andthe last consumed when an ocean basin disappears down a sub-duction zone. The sediments that have accumulated at Site 765are dominated by detrital material derived from the Australiancontinent. Thus, Site 765 should serve as a reference site for othersubduction zones proximal to continental sediment sources (e.g.,the Lesser Antilles, the American, and the Eolian/Aegean arcs).We hope to provide here a methodology for constraining sedimentinflux to this class of subduction zones, and in doing so, to beginto answer the question of how much?

First, we present a geochemical stratigraphy of Site 765 sedi-ments, attempt to tie the geochemical variability to the lithologicvariability, and briefly speculate about the provenance of thesediments. Next, we devise a method for estimating the bulkcomposition of the entire sediment section. Finally, we discussthe relevance of this site to sedimentary sections globally, as wellas regionally along the Sunda Arc.

GEOLOGIC BACKGROUND

Site 765 is situated in the Argo Abyssal Plain, a triangularregion of some of the oldest crust of the Indian Ocean, sandwichedbetween the northwestern margin of Australia and the Java Trench(see Fig. 1). The crust drilled at Site 765 represents the firstoceanic crust formed during rifting of the Australian margin inthe Earliest Cretaceous. This site is now only 500 km away frombeing consumed at the Sunda Trench, south of Java. The sedimen-tary section that has accumulated is thin for a passive marginsequence owing to the arid climate and low relief of westernAustralia. Although several active and explosive volcanoes arelocated on Java and the Lesser Sunda Islands, Site 765 has yet toenter the region of extensive ash falls determined by Ninkovich(1979). Thus, the ultimate source of much of the sediment at Site765 is the Pilbara and Kimberly blocks of northwestern Australiacraton, which are Archean to Proterozoic in age (Fig. 1). AlthoughSite 765 is at abyssal depths, sedimentation rates have been higherthan typical abyssal rates (see Ludden, Gradstein, et al., 1990),especially during the Neogene (averaging 27 m/m.y.) due to thecontinual supply of material from the Australian Shelf andExmouth Plateau via turbidity flows. Even though well below thecalcite compensation depth, the hole has a high carbonate contentowing to the rapid influx and burial of pelagic carbonates fromthe Australian margin.

At Site 765, roughly 950 m of sediment was cored above thebasaltic basement. The sedimentary section can be divided in two,corresponding grossly to the Cenozoic and Cretaceous sections.The Cenozoic section is dominated by calcareous turbidites, prob-

IIO°EFigure 1. Location map of Site 765 with simplified geology of northwestern Australia. Water depth contoursin meters.

168

GEOCHEMISTRY REFERENCE SECTION FOR SEDIMENT RECYCLING

ably originating on the Exmouth Plateau and fed by the SwanCanyon (Fig. 1). Although calcareous sequences also occurthroughout the Cretaceous section, this lower section is domi-nated by pelagic clays. Within this simple division, however,tremendous lithologic diversity is represented by foraminiferalsands, nannofossil oozes, radiolarites, Mn-rich horizons, and red,green, and black clays.

SAMPLING AND ANALYTICAL DETAILSOur sampling strategy was to take one 40-cm3 sample at each

core that was representative of a dominant lithology in that core.Thus, we have a fairly evenly spaced sampling every 10 m or sodown the entire 930-m section. Some sections of cores weresubsampled (three individual turbidite units and red and greenclay units in the lower half of the hole), and several samples weretaken in adjacent intervals to assess variability at the centimeterscale. Samples were powdered and homogenized by first bakingto 110°C, then pulverizing in either a tungsten carbide shatterboxor an alumina ball-mill.

About 70 samples were analyzed on board the Resolution usingX-ray fluorescence (XRF) for all the major elements and for Rb,Sr, Ba, Y, Zr, Nb, V, Cr, Ni, Cu, and Zn (Table 1). Another 70samples were analyzed at Lamont-Doherty (LDGO) by direct-cur-rent plasma emission spectrometry (DCP) for all the major ele-ments and for Sr, Ba, Y, Zr, V, Cr, Ni, Cu, Zn, and Sc (Table 1).Forty samples were selected for additional instrumental neutronactivation analysis (INAA) at the Université de Montreal, forREE, U, Th, Sc, Cr, Hf, Ta, W, Co, As, Sb, Ba, and Cs (Table 2).The major- and trace-element analyses for these same samples orfor adjacent intervals are presented in Table 1. Details of the XRFand INAA procedures are given in Ludden, Gradstein, et al.(1990) and in Francis and Ludden (1990), respectively. Analysisof sediment samples by DCP required new procedures, which aredescribed below.

Different routines were set up for running clay- and carbonate-rich samples by DCP. The clay-rich samples (with 10% CaO)proved as straightforward to analyze as igneous rocks, and proce-dures were followed similar to those outlined in Klein et al.(1991). For each batch of clay samples (usually 10 unknowns),the USGS standards SCO-1 and QLO, as well as an in-houseAleutian andesite standard, LUM-37, were used to establish thecalibration curves.

The analysis of carbonate-rich samples (>10% CaO) requiredsome modifications to our routine method. Preliminary shipboardwork revealed a problem in alkali loss upon ignition. We over-came this problem on board the ship by analyzing the alkalielements (K, Na, and Rb) on unignited powder pellets, althoughthese measurements are inherently less accurate for K and Na,which are normally analyzed on fused glass disks. A new proce-dure had to be developed for the DCP method as well, becausesamples typically are fused and dissolved after ignition. However,comparison with analyses by total HF-HCIO4 dissolution indi-cated that alkali loss occurred only during ignition of samples (30min at 1000°C), not during LiBθ2 fusion. In the most carbonate-rich samples, some K was lost during the standard 15-min fusionat 1050°C; times were then reduced to 5 min, which seemedsufficient for fusion without alkali loss. Thus, carbonate sampleswere fused and dissolved without first oxidizing or devolatilizing.Total volatile loss on ignition (LOI) was determined for separatesplits.

Significant Ca interferences or enhancements occurred on theAl line and on all the trace-element lines of our multi-elementcassettes (the specific wavelengths used for each element areavailable upon request). With the exceptions of Sc, Y, and Zr,however, the Ca interferences are linear and easily corrected byrunning a pure CaO standard during each run. Calibration curves

for each batch of unknowns were constructed using pure CaO,LUM-37, and mixtures of the two in the proportions 1:1 and 1:3.These CaO-andesite mixtures provided us both with standardsthat closely resembled the unknowns and with dependable valuesfor the trace elements, which is important because few well-char-acterized carbonate standards exist. Sc, Y, and Zr have large Cainterferences and are matrix sensitive (Ca enhances and Si sup-presses). As a consequence, the standards do not form goodcalibration curves, and the Sc, Y, and Zr data are not accurate(10%-20% relative). More recent tests have shown that matrixproblems are reduced by using a factor of 2 greater dilution(1:500) and a greater flux to sample ratio (10:1). With this proce-dure, standards form acceptable lines, and thus the Sc, Y, and Zrdata are more accurate (5%), but because of the greater dilution,the peak-to-background ratios suffer, and the data are less precise(10%).

XRF analyses were presented in Ludden, Gradstein, et al.(1990), but have been reproduced here (Table 1) because anadditional normalization factor was applied. In addition, K2O wasre-run for the powder pellets by XRF at the Université de Mon-treal, and these newer analyses are reported here. On board theship, the standard SCO-1 was run with every batch of samples;the precision based on these replicates is good (generally betterthan 2% relative for the major elements and 4% for the traceelements; see Table 21 in Ludden, Gradstein, et al., 1990). TheDCP data are similarly precise, based on analysis of an IndianOcean brown clay sample (IOBC) that was used to monitor driftduring 10 different runs (Table 3). The Na2θ and MnO valuesdetermined by DCP are more precise than the XRF determina-tions, while the Zr and Y XRF values are preferred because of thematrix problems with the DCP mentioned above.

Although both methods are precise, the agreement between thetwo varies for different elements. Powders analyzed using bothXRF and DCP show consistent discrepancies. These differencesare almost always of the same direction and magnitude as thedifferences between the accepted values for SCO-1 (Govindaraju,1989) and those determined by XRF. Thus, normalization factorswere applied to the XRF data based on the DCP duplicates andthe accepted SCO-1 values (see Table 3 for the original XRFaverage for SCO-1, the Govindaraju values, and the values afternormalization). The XRF Ce values and the DCP Sc values werealso adjusted to agree with the more precise INAA values. Thus,the data presented in Table 1 show minimal analytical biases (allelements generally agree among methods to 5% relative).

Analyses of adjacent samples, where one was powdered in theball mill and one was powdered in the shatterbox, indicate con-tamination of a few elements by the tungsten carbide shatterbox(2-4 ppm Co, 0.3-0.4 ppm Ta, and 35-60 ppm W). Aluminumcontamination caused by powdering in the alumina ball mill,however, was negligible. The powdering method is listed alongwith the INAA analyses in Table 2.

GEOCHEMICAL VARIABILITY

The simplest way to estimate the bulk composition of a sedi-mentary section might be to sample continuously down the core,analyze the samples, and then average them. This is impracticalfor a section that is almost 1 km long, such as was cored at Site765. This is certainly an impractical method for estimating theflux of material entering oceanic trenches globally. Because oursampling and analytical efforts were intensive for Site 765, wecan estimate fairly accurately its bulk composition simply byaveraging the analyses reported in Tables 1 and 2. However, ouraim was not only to calculate the bulk composition of Site 765sediments, but also to develop a less analytically intensive methodfor estimating sections elsewhere. One advantage to working withDSDP/ODP cores is the wealth of lithological and mineralogical

169

Table 1. Analyses of major and trace elements in Site 765 sediments. Table 1 (continued).

© 123-765B

Depth:Color:

Lithology:Method:

SiO2TiO2

AI2O3FeO

MnO

MgO

CaO

Na2OK2O

P2O5LOI

CaC03C (Org)

Nb

ZrY

Sr

Rb

Zn

Cu

Ni

Cr

V

Ce

Ba

Sc

123-765B

Depth:Color:

Lithology:Method:

SiO2TiO2

AI2O3FeO

MnO

MgO

CaO

Na20K2O

P2O5LOI

CaCO3C (Org)

Nb

Zr

Y

Sr

RbZnCuNiCrV

Ce

Ba

Sc

1H-4,48-50

4.98Lt ol grayCc. ooze

XRF

22.71.3016.692.54.1982.01

30.97.67

1.26.16432.5

55.23.63

4.7

57.217.2

195451.371.298.7

47

43.358

22.2671

3H-1,33-3519.13

Lt oliveCc. 00Z3

XRF

14.28.2034.401.56.3451.14

40.16.02

.75

.13437.0070.64

.22

3.3

38.515.5138128.743.162.1

31

31.839

6.2

902

2H-3,94-106

13.24Lt ol grayCc. OOZΘ

XRF

23.80.2955.782.08.5151.53

32.39.27

.98

.15232.2156.06

.51

4.9

79.620.9117141.365.1

110.295

34.552

22.51033

4H-3,145-150

32.95

DCP

41.99.538

11.163.57.1002.05

16.791.671.87.120

19.14

150.917.9531

90.5231.2

143

56.8118

750

9.1

2H-3,123-135

13.53Ol gray

ClayXRF

54.26.725

15.025.63.3303.502.214.012.65.16611.53.42

.82

10.3135.2

26.2204

113.7172.7261.8

130

82.7132

46.21383

4H-6,20-2236.20

Red grayClayXRF

56.28.739

14.785.45

1.2173.28

.83

3.752.42.105

11.152.42

.91

10.2150.4

30.8171

100.6142.0192.6

153

77.6110

55.31609

2H-3,145-150

13.75Ol gray

ClayDCP

59.13.742

16.165.11.1122.98

.63

2.762.76.1409.47

143.028.5

143

85.3283.6

152

80.1145

129515.6

4H-6,23-3036.23

Red grayClayDCP

56.97.704

14.886.35.2653.30

.67

3.612.70.115

10.45

145.328.7

163

44.8385.2

324

71.1209

128216.7

2H-4,7-19

13.87Ol gray

ClayXRF

54.15.695

14.514.86.1312.993.633.902.47.15512.55.41

.98

9.8

139.927.1244

104.2158.0223.3

133

82.7114

56.41328

5H-7,40-4247.50

Lt oliveCc. sand

XRF

14.25.1532.951.24.0801.10

41.55.09

.62

.06637.9074.47

.13

2.5

44.79.9

102222.029.946.7

20

16.926

16.8341

2H-4,31-4314.11

Lt oliveCc. OOZΘ

XRF

14.76.2094.341.46.3791.57

39.29.26

.78

.18736.7767.81

.74

3.4

43.516.7

160932.454.389.9

42

33.549

5.8

791

7H-3,38-4360.78

Lt ol grayCc. ooze

XRF

15.25.2274.561.63.1181.75

39.40.44

.85

.17635.6070.31

.58

3.7

46.914.3196731.444.751.7

29

38.641

16.8482

2H-4,91-103

14.71Lt olive

Cc. OOZΘ

XRF

8.74.0971.61

.90

.265.73

46.80.09

.37

.06440.3381.38

.13

1.3

34.06.8

111712.925.441.0

29

6.6

17

3.7

301

8H-6,85-9075.45

Lt ol grayCc. ooze

XRF

28.55.4038.703.22.1222.46

26.461.401.31.142

27.2546.90

.29

6.2

80.920.7998

61.981.3

102.352

49.865

24.61110

2H-4,131-143

15.11Ol gray

ClayXRF

57.50.781

15.925.25.1253.15

.97

3.972.48.1069.751.00

.67

10.9152.8

25.1154

109.6133.6303.6

97

80.3120

53.91099

9H-6,104-105

85.34Gr gray

Cc. oozeXRF

23.16.3517.322.67.1182.51

30.731.081.23.186

30.6555.31

.66

5.1

62.119.0133053.273.974.0

39

51.660

19.3758

2H-6,138-140

18.18Ol gray

ClayXRF

56.68.746

15.385.51.1633.52

.59

4.232.53.127

10.52.58

.72

10.5143.0

25.2152

107.9156.0250.8

143

76.0101

50.31262

10H-3,145-150

90.85

DCP

22.43.3376.042.22.1841.47

34.74.94

1.13.143

31.13

99.720.21142

51.260.3

30

33.442

689

5.7

2H-6,140-142

18.20Ol gray

ClayDCP

56.89.738

15.785.49.1813.37

.57

4.092.81.1449.93

141.226.3

153

42.7193.4

173

85.0117

131417.7

10H-5,89-9593.29

Ltgy blueClayDCP

56.18.889

18.866.47.0443.98

.36

2.073.29.1387.73

198.533.1

160

118.8172.7

95

116.6142

699

18.2

123-765B

Depth:Color:

Lithology:Method:

SiO2TiO2

AI2O3FeO

MnO

MgO

CaO

Na2OK2O

P2O5LOI

CaCO3C (Org)

Nb

Zr

Y

Sr

RbZnCu

Ni

Cr

V

Cθ

Ba

Sc

123-765B

Depth:Color:

Lithology:Method:

SiO2TiO2

AI2O3FeO

MnO

MgO

CaO

Na2OK2O

P2O5LOI

CaCO3C (Org)

Nb

Zr

Y

Sr

RbZnCu

Ni

Cr

V

Cβ

Ba

S c

11H-2,40-4497.90

Lt ol grayCc. ooze

XRF

23.07.3386.552.39.1031.88

33.40.64

1.34.18730.1

61.89.15

4.7

80.019.0

122948.360.258.0

36

44.058

20.1597

15H-3,32-44

137.82Gy olive

ClayXRF

53.89.971

19.077.45.0394.07

.59

1.783.45.1398.561.17

.29

13.1190.4

28.3222

147.8140.7324.9

86

127.3134

69.8810

12H-4,44-48

110.54Lt ol grayCc. coze

XRF

16.17.2594.991.78.1501.32

39.98.35

.85

.15834

69.81.04

4.1

62.216.0

133631.935.148.6

26

35.542

14.1546

15H-5,23-27

140.73Gr gray

Cc. clayXRF

35.56.596

11.824.72.0512.59

20.68.56

2.52.112

20.8036.49

.31

8.1

115.819.6

112899.271.533.6

35

73.985

43.4351

12H-6,105-110

114.15Ol gray

ClayXRF

56.42.967

19.166.93.0483.64

.52

1.263.07.171

7.8

.50

.27

13.8208.9

32.2206

133.1125.7101.2

56

113.3118

65.3820

15H-5,49-54


XRF

58.81.19

5.5

70.915.8

132557.753.942.6

2251.7

5625.5633

13H-2,138-143


XRF

20.29.3356.792.50.1021.79

34.49.77

1.23.20131.5

60.89.31

5.1

74.715.1

150648.351.552.8

47

49.553

25.5378

15H-5,116-121

141.66Lt gr grayCc. ooze

XRF

21.69.3597.912.80.0841.64

32.88.65

1.29.113

30.6058.48

.11

5.9

73.614.8130655.951.564.5

26

45.656

33.0591

14H-4,83-87


XRF

20.93.3497.502.73.0951.65

34.36.27

1.37.13730.6

62.31.12

5.6

70.414.2

134254.448.454.4

24

47.053

23.0513

15H-7,52-56

144.02Lt ol grayCc. sand

XRF

24.42.3417.052.53.0741.44

32.30.62

1.31.123

29.8057.48

.13

5.5

96.916.0

114349.247.064.4

25

42.751

26.7490

15H-2,76-88


XRF

22.80.3285.812.48.0671.68

34.17.75

1.17.156

30.5960.00

.30

4.4

88.017.7

202445.845.270.5

36

61.563

20.7289

16H-1,42-46


XRF

25.16.3346.662.43.0821.43

32.62.46

1.23.106

29.5057.23

.13

5.5

94.015.2113046.745.661.4

21

41.550

28.5462

15H-2,88-100136.88Ol gray

ClayXRF

54.56.971

19.427.51.0393.60

.41

1.893.18.1598.26

.50

.29

13.5199.2

30.1214

139.8117.3260.3

63

125.8150

66.2748

16H-1,42-46


DCP

24.44.3436.772.49.0831.29

32.251.091.15.113

30.26

97.615.61107

49.049.4

25

43.656

435

6.3

15H-2,115-127


XRF

18.50.2946.342.41.1491.48

36.00.66

1.31.109

32.7363.47

.05

4.5

66.117.2140348.846.437.2

18

36.744

22.5687

16H-1,42-46


DCP

24.20.3306.732.43.0801.26

31.981.101.15.100

29.50

94.815.91106

45.347.3

20

38.646

432

7.1

15H-3,1-13

137.51Lt gr yβl

Cc. OOZΘXRF

21.20.3195.822.46.1301.44

34.84.68

1.25.15931.7

59.64.24

4.6

88.919.8

119245.443.344.6

19

31.146

20.2557

16H-1,42-46


DCP

24.45.3406.762.50.0841.32

32.841.101.15.100

30.26

99.015.61106

47.448.9

25

48.960

430

7.2

15H-3,20-32


XRF

14.82.1903.171.25.094

.92

41.79.33

.70

.11136.6473.22

.08

2.9

68.612.8104224.929.157.8

17

31.033

12.7316

17H-5,63-65


XRF

39.75.2002.731.62.048

.48

29.45.50

.95

.07124.2051.98

.08

4.1

112.87.9

782

26.419.850.1

29

9.2

27

15.5251

zr

oFΠ

Z

Table 1 (continued). Table 1 (continued).

123-765B

Depth:Color:

Lithology:Method:

SiO2TiO2

AI2O3FeO

MnO

MgO

CaO

Na2OK2O

P2O5LOI

CaC03C (Org)

Nb

Zr

Y

Sr

Rb

Zn

Cu

Ni

Cr

V

Ce

Ba

Sc

123-765B

Depth:Color:

Lithology:Method:

SiO2TiO2

AI2O3FeO

MnO

MgO

CaO

Na2OK2O

P2O5LOI

CaCO3C (Org)

Nb

Zr

Y

Sr

RbZnCu

Ni

Cr

V

Ce

Ba

Sc

18H-1,13-19

163.73Gy olive

ClayDCP

52.18.922

19.646.59.0353.392.271.772.97.198

10.04

196.734.3327

103.7170.1

135

145.5133

579

21.1

26X-3,72-77

244.92Lt olive

Cc. oozeXRF

18.65.3035.601.64.0212.97

36.22.32

.99

.07933.2068.89

.13

4.1

46.38.3

272940.529.239.3

12

52.945

23.6129

18H-3,145-150


DCP

15.68.2875.772.00.0511.11

39.39.71

.83

.12234.4

66.512.2

1564

38.225.1

19

38.638

277

4.8

27X-1,41-46

251.31Gr gray

Cc. oozeXRF

13.75.2254.271.26.0212.96

40.24.33

.73

.10636.1074.89

.26

2.8

47.06.3

284630.336.838.4

10

41.930

14.9110

19X-3,20-26

176.50Lt brown

Cc. sandDCP

15.77.1322.281.56.053

.68

43.281.07

.56

.10535.17

80.19.1

1179

38.655.9

36

20.321

178

2.1

28X-1,34-38

260.94Lt olive

Cc. oozeXRF

10.20.1532.93

.96

.0332.39

44.39.19

.46

.09538.2080.88

.25

1.8

34.55.2

325216.919.649.5

7

24.920

3.2

124

20X-2,125-129

185.75Yel gray

Cc. oozeXRF

14.43.2344.331.69.0421.68

40.97.13

.67

.12335.7

74.72.00

3.3

55.27.7

208625.431.6

160.025

41.039

20.0151

29X-2,21-25

271.91Ol gray

Cc. sandDCP

12.78.1051.50

.45

.0281.39

45.07.50

.31

.05937.85

90.26.6

1625

23.67.7

2

11.810

92

1.4

21X-2,145-150

195.65

DCP

8.01.1302.501.31.0641.69

45.65.53

.40

.11039.27

27.98.2

1861

25.512.8

10

24.927

185

2.4

30X-1,86-92

280.76Lt gr gray

ChalkDCP

12.99.1753.841.35.0273.87

38.73.80

.51

.09236.92

41.18.5

2657

25.312.2

11

36.934

120

5.0

21X-3,64-70

196.34Gy green

ClayDCP

52.69.873

16.545.47.0275.752.661.982.54.287

11.18

184.533.8399

77:3109.0

63

120.9121

511

19.0

31X-3,140-150

294.00

DCP

10.71.1923.661.08.0362.73

43.21.52

.54

.07338.26

40.57.4

2759

25.939.7

13

33.634

136

2.7

22X-1,94-97

203.34Olgray

Cc. sandXRF

18.13.1791.941.65.0291.94

41.10.17

.41

.14334.3

73.80.07

2.3

93.26.1

256513.313.536.5

23

21.716

10.29 3

32X-2,126-129

302.06Lt gr grayCc. sand

XRF

8.91.1542.921.05.0122.92

41.47.25

.49

.07541.7482.22

.13

2.3

38.15.5

318618.818.540.7

11

24.823

9.6

141

23X-2,91-97


DCP

14.26.2404.591.50.0372.79

39.71.91

.70

.09136.74

49.59.0

2194

25.913.9

13

47.933

143

5.4

33X-2,71-73

311.2.1Lt gr gray

ChalkXRF

17.24.2865.981.81.0282.73

36.53.25

1.08.070

34.0068.81

.01

4.0

60.38.3

240542.532.634.3

13

47.446

15.8163

24X-4,77-83

227.07Ol gray

ClayDCP

47.16.697

14.054.30.0247.686.931.562.19.137

15.27

150.121.6541

51.374.2

35

114.7115

202

18.6

34X-CC,17-23

321.90Ol gray

Cc. sandDCP

44.92.1472.06

.51

.014.84

26.96.40

.76

.05423.87

96.56.5

1049

19.49.8

3

13.216

174

1.4

26X-1,69-73


XRF

6.68.062

.69

.22

.0191.12

49.87.08

.19

.06441

91.96.00

1.0

38.72.1

16245.4

4.9

25.71

.0

3

1.5

75

35X-2,37-42

330.17Br gray

Cc. siltst.DCP

12.56.1813.201.22.0202.31

42.11.77

.52

.07937.61

63.79.7

2600

23.577.6

2034.4

27

168

4.5

123-765B

Depth:Color:

Lithology:Method:

SiO2JiO2

AI2O3FeO

MnO

MgO

CaO

Na2OK2O

P2O5LOI

CaCO3C (Org)

Nb

Zr

Y

Sr

Rb

Zn

Cu

Ni

Cr

V

Ce

Ba

Sc

123-765C

Depth:Color:

Lithology:Method:

SiO2TiO2

AI2O3FeO

MnO

MgO

CaO

Na2OK2O

P2O5LOI

CaCO3C (Org)

Nb

Zr

Y

SrRbZnCu

Ni

Cr

V

Ce

Ba

Sc

36X-2,81-86

340.21Lt olive

ChalkDCP

5.51.1082.01

.63

.0262.07

48.87.62

.30

.06241.25

26.36.6

3233

15.913.1

3

24.114

133

2.8

2R-2,90-99

362.00Lt ol gray

ChalkDCP

7.38.1001.89

.61

.0612.88

44.49.57

.21

.05041.77

33.67.8

2794

16.832.0

13

28.831

113

5.2

37X-CC,19-25

350.70Lt gr gray

ChalkDCP

11.57.2143.891.31.0172.94

41.71.68

.47

.05437.87

43.37.8

3671

24.921.1

10

49.234

145

5.3

3R-1,131-133

370.61Br blackDol. clay

DCP

49.77.730

13.753.64.0309.564.431.091.39.181

15.44

166.127.3422

74.655.9

44

129.6139

114

16.9

39X-1,20-26

366.90Gy olive

Dol. dayDCP

41.60.539

10.573.35.0339.15

12.251.281.16.178

19.89

141.229.2903

59.738.9

54

93.797

236

13.2

4R-3,140-150

383.40

DCP

13.50.1523.15

.79

.0403.50

39.93.52

.28

.05237.58

31.96.9

2498

26.39.6

9

38.736

116

2.3

39X-1,86-91

367.56

DCP

3.07.041

.41

.16

.0222.20

50.77.33

.08

.02243

36.14.0

2593.0

6.9

7.2

2

12.912

.0

26

5R-3,45-49

392.05Lt gr gray

Cc. siltDCP

17.67.2564.951.52.0523.85

36.41.57

.52

.05933.93

69.210.01683

39.724.0

19

49.346

171

5.0

6R-1,143-149

399.73Ol gray

ChalkDCP

11.46.1622.69

.83

.0372.19

43.55.79

.37

.05638.00

50.98.8

3630

22.125.0

15

43.638

90

3.5

7R-2,27-32

409.77Gy green

ClayDCP

51.09.810

17.074.82.0446.593.621.402.02.108

12.44

179.227.6447

104.4221.0

74

139.1152

199

18.0

8R-2,114-120

420.34Olive

Cc. oozeDCP

30.45.4669.883.18.0384.25

22.541.11

.85

.03927.20

100.213.1

2486

67.713.6

28

87.487

81

10.1

10R-3,140-150

440.90

DCP

27.04.2836.612.12.0565.47

27.11.70

.53

.04328.84

60.39.0

1950

47.517.2

21

59.057

66

5.0

11R-1,84-88

446.84Ol gray

Cc. clayXRF

36.94.620

12.504.11.0504.33

18.211.031.45.157

20.6032.90

.31

9.2

122.121.4702

64.494.8

119.960

98.192

49.4160

11R-1,91-93

446.91Lt ol gray

ChalkDCP

9.63.1623.131.11.0861.73

45.88.41

.35

.04138.22

39.57.8

1098

25.210.1

15

30.629

89

3.5

O

o

IST

RY

I;F

ER

E

mCΛW

GSz"iiO73CΛ

mö9

o

XIN

G


ts> 123-765C

Depth:Color:

Lithology:Method:

SiO2TiO2

AI2O3FeO

MnOMgOCaO

Na2OK2O

P2O5LOI

CaCO3C (Org)

NbZrY

SrRbZnCuNiCrV

CeBaSc

123-765C

Depth:Color:

Lithology:Method:

SiO2TiO2

AI2O3FeOMnOMgOCaO

Na2OK2O

P2O5LOI

CaC03C (Org)

NbZrY

SrRbZnCuNiCrV

CeBaSc

11R-1,93-96

446.93Lt ol gray

ChalkDCP

9.23.1582.991.09.0961.68

46.38.38.34

.04238.37

36.96.8

1069

25.79.713

29.026

973.4

17R-2,66-68

504.56Lt brown

Cc. oozaXRF

25.48.4549.393.61.2481.04

30.37.72.94

.08427.6854.23

.00

5.784.512.9112537.962.935.0

3956.6

8431.8221

11R-1,96-97

446.96Lt ol gray

ChalkDCP

8.97.1562.861.02.1011.66

47.22.36

.32

.04038.5

36.86.5

1066

23.29.6

13

29.528

105

3.3

19R-1,21-27

521.50Lt gr gray

Silty oozeDCP

24.64.2315.872.62.3611.40

32.88.93

.94

.10430.03

60.723.0729

38.669.5

2638.0

57

3876.6

11R-1,97-100446.97

Lt ol grayCc. ooze

XRF

9.83.1583.001.13.0931.73

45.40.17.40

.05138.0481.80

.00

2.437.3

6.1106813.220.123.0

1328.8

2610.0114

20R-1,77-84

531.57Yel brown

ClayDCP

62.30.439

11.928.33.1193.69

.932.732.61.2836.66

86.536.3666

124.6266.6

5752.6

83

7410.2

11R-1,119-123


XRF

11.17.1592.54

.99

.1061.84

44.72.20

.37

.08137.8280.72

.09

2.7

49.77.5

158512.319.439.9

14

20.430

11.0105

22R-2,28-32

551.88

11R-1,133-137


XRF

11.44.1121.32

.73

.0971.46

46.97.12

.31

.05137.4

83.80.04

1.6

43.24.1

14268.5

10.426.5

9

13.020

9.4

116

23R-4,62-69

564.82Gy olive Gy orange

ClayXRF

62.24.601

14.495.43.0593.871.822.282.12.1416.942.42

.04

10.0127.5

26.6374

70.584.982.2128

97.5152

52.3409

ChalkDCP

16.45.2175.482.36.133

.88

38.98.51

.81

.07134.11

47.519.5763

42.925.0

2530.5

59

12195.9

11R-4,61-64

451.11Gy blue

ClayXRF

55.39.977

18.525.77.0675.82

.41

1.291.94.2009.621.08

.18

15.1199.5

37.6386

93.4160.4313.6

101

135.3148

83.9164

24R-1,92-93

570.22Gy brown

ClayXRF

57.271.01815.709.17.0893.72

.67

1.423.78.2856.87

.33

.03

15.9197.3

48.5130

116.3140.3

67.981

68.9113

101.2213

11R-4,61-64

451.11Gy blue

ClayDCP

55.19.998

18.835.84.0615.72

.40

1.351.95.2229.43

181.834.6362

148.4320.2

109

118.0152

154

18.0

24R-1,92-93

570.22Gy brown

ClayDCP

57.161.01615.56

9.18.0953.82

.661.583.90.2876.74

198.450.5136

133.172.8

9275.9133

22223.9

13R-2,61-64

466.71Gy olive

ClayXRF

54.53.905

18.548.54.0492.961.541.722.14.0978.994.08

.00

10.5156.7

18.3452

92.0126.7

70.656

104.1139

52.7226

24R-4,71-72

574.51Br gray

ClayXRF

55.54.940

15.237.38

1.6984.46

.971.823.54.3398.07

.67

.00

13.6160.4

71.0204

104.6149.5165.5

11866.1137

150.72941

14R-1,97-104475.07

Yel brownClayDCP

52.18.919

20.838.74.1033.83

.42

1.702.13.148

9

174.430.0

334

151.6146.1

113

135.6106

132

16.9

25R-1,92-97

579.92Lt brown

Cc. oozeDCP

10.26.1663.521.45.169

.7045.68

.29

.30.085

37.40

3282

15R-1,86-104484.56

Bl gr gray0

DCP

60.99.964

18.265.58.0342.30

.59

1.452.19.243

7.4

188.145.0313

141.1116.0

45

120.3181

442

16.4

25R-2,92-98

581.42Br gray

ClayXRF

55.721.05516.10

8.99.5253.82

.85

1.653.70.2957.30

.42

.03

12.2168.7

60.3161

113.2162.7178.7

10987.5131

107.7822

123-765C

Depth:Color:

Lithology:Method:

SiO2TiO2

AI2O3FβO

MnOMgOCaO

Na2OK2O

P2O5LOI

CaCO3C (Org)

NbZrY

SrRbZnCuNiCrV

CeBaSc

123-765C

Depth:Color:

Lithology:Method:

SiO2TiO2

AI2O3FeOMnOMgOCaO

Na2OK2O

P2O5LOI

CaCO3C (Org)

NbZrY

SrRbZnCuNiCrV

CeBaSc

25R-3,106-111

583.06Br gray

ClayXRF

56.24.962

16.707.66

1.1383.24

.98

1.763.52.3577.46

.50

.03

15.4175.3

71.7176

108.8165.4183.1

136

78.7134

153.82235

29R-5,70-74

623.10Lt brown

ClayDCP

58.99.884

17.347.20.1272.77

.642.124.25.1025.60

146.424.7166

135.2129.0

8175.5118

23320.5

25R-3,106-111

583.06Br gray

ClayDCP

56.58.958

16.767.70

1.1813.36

.981.703.74.3536.69

175.770.4181

165.1202.1

13883.5147

209023.2

29R-5,124-129

623.64Lt brownCc. clay

DCP

55.04.791

16.816.57.1662.603.892.113.91.1208.00

144.231.4207

112.9122.1

7773.1109

136421.6

26R-4,22-28

593.02Brown

ClayXRF

55.501.00215.06

7.35.1063.713.431.633.51.2768.434.83

.02

14.1176.6

59.1147

100.4127.2105.2

7981.4

9398.2204

30R-2,16-22

627.56Gy brown

Clayst.XRF

59.79.968

17.517.09

1.5422.95

.792.243.84.1233.15

.67

.03

13.2145.3

27.1207

112.1141.8142.4

7965.3120

126.01135

26R-4,42-51

593.22Br gray

ClayDCP

56.801.05816.92

7.721.077

3.59.59

1.683.66.111

6.8

170.326.8145

128.6143.1

9972.9121

165122.5

30R-2,16-22

627.56Gy brown

Clayst.DCP

57.82.937

17.136.85

1.5362.89

.782.033.84.1226.07

145.230.6210

140.8157.1

7969.4130

114321.9

27R-2,34-40

599.34Br grayClayst.

XRF

57.161.03616.60

7.341.898

3.17.52

1.724.06.1316.36

.25

.01

14.4169.1

25.1229

109.7135.7151.5

102

60.9127

132.42610

30R-3,76-83

629.66Brown

Clayst.DCP

59.21.873

17.636.55.1992.58

.70

2.403.86.0995.90

134.221.3212

121.1113.1

67

72.6114

233

19.3

28R-1,55-58

607.55Br gray

28R-3,45-53

610.45

29R-3,76-80

620.16Gy green Gy blue/gr

Clayst. Cc. ClaystXRF

58.06.976

17.187.56.8662.84

.471.774.10.0996.08

.17

.01

13.4157.0

19.3169

115.8165.0142.3

9574.8136

122.3871

30R-4,98-102631.38Brown

Clayst.XRF

59.08.878

16.987.29.1482.62

.712.323.66.0986.21

.17

.05

10.6131.6

19.3227

110.9135.4

97.074

64.3108

92.7232

XRF

45.78.712

12.195.80.1082.53

13.201.693.00.109

14.8822.24

.11

10.1115.7

23.7289

86.8116.1

49.670

55.787

69.61834

32R-1,40-45

645.40Yel brown

Clayst.DCP

63.32.849

14.046.14.1042.90

.682.543.61.0975.71

131.326.4262

112.4146.8

7767.4

91

19916.9

Clayst.XRF

56.62.841

16.225.88.1062.703.542.153.93.106

7.95.33

.06

11.8142.3

21.3172

120.0149.5257.2

8171.1132

89.3539

33R-2,117-124

657.37Gr gray

ClayDCP

62.66.706

14.127.31.1002.73

.832.572.56.1056.30

97.019.9201

94.237.5

3970.5137

81114.9

29R-5,2-6

622.42Lt brown

ClayDCP

57.941.11415.95

8.69.1193.49

.59

1.984.11.117

5.9

172.628.7

129

123.582.4

92

96.9108

221

21.8

34R-3,115-125

668.55

29R-5,26-30

622.66Lt brown

ClayDCP

58.01.964

16.728.10.1313.28

.64

2.094.14.115

5.8

163.428.8

148

128.4130.9

85

82.7104

218

22.1

35R-3,24-29

677.34Lt brown Gy blue/grCc. clay

DCP

61.99.2765.172.07.5011.05

12.411.09

.95.085

13.97

44.613.4185

34.468.2

1537.0

53

20986.0

Clayst.XRF

68.61.740

12.714.83.0402.86

.681.852.13.1325.41

.33

.13

14.0134.4

25.1123

76.4125.0327.5

9155.1113

115.8940

H

r

r

a2


123-765C

Depth:Color:

Lithology:Method:

35R-3,86-90

677.96Black

37R-3,40-43

696.40Ol gray

SIO2TiO2

AI2O3FeOMnOMgOCaO

Na2OK2O

P2O5LOI

CaCO3C (Org)

NbZrY

SrRbZnCuNiCrV

CeBaSc

SiO2TiO2

AI2O3FeOMnOMgOCaO

Na2OK2O

P2O5LOI

CaCO3C (Org)

NbZrY

SrRbZnCuNiCrV

CeBaSc

Siltst. Cc. ClaystXRFXRF

39R-3.101-105715.71Ol grayClayst.

XRF

39R-3,140-150716.10

DCP

40R-3, 42R-2,104-109 41-43724.94 741.71

Br black Gy greenClayst. Clayst.

XRF XRF

44R-2,38-42

760.38OlgrayClayst.

DCP

44R-2,73-77

760.73Ol grayClayst.

DCP

44R-2,95-99

760.95Ol grayClayst.

DCP

80.64.2824.881.72.019

.892.911.16

.74.064

6.74.66

.67

3.2.0

11.288

31.342.835.0

1840.3

4212.4389

43.10.4807.574.57.5771.92

19.661.181.45.140

19.3534.65

.04

7.085.930.1249

47.299.4

104.270

34.265

63.63560

65.71.831

12.447.22.1802.951.071.752.49.1655.191.00

.04

11.3126.728.8138

76.8126.1119.0

7345.2120

111.0613

52.63.5529.145.06.2792.17

11.441.401.82.160

13.51

95.925.9198

105.8121.9

7050.1

79

222312.4

66.79.799

11.587.90.0503.05

.701.582.19.1105.24

.50

.22

12.5138.421.7

9869.4

102.6242.1

7144.9220

72.8153

75.27.5519.414.90.1411.92

.581.241.66.1004.23

.58

.15

7.4100.420.2117

61.477.381.1

3038.3

8760.81927

64.74.835

13.227.49.2932.69

.691.582.68.1975.6

138.331.2100

186.4210.8

9761.7

145

41817.0

67.24.764

12.806.70.0602.51

.461.532.54.1015.3

123.020.788

83.1183.1

3859.0140

48615.4

65.31.672

12.696.52

1.5052.33

.671.532.24.128

6.4

117.924.699

84.3126.2

6355.3130

81815.0

123-765C 44R-4, 45R-2, 47R-5, 50R-1, 51R-1,55-59 70-75 46-55 110-113 84-86

Depth: 763.55 770.40 793.86 816.70 825.84Color: Ol gray Dusky red Gy brown Brown Dk gray

Lithology: Clayst. Clayst. Clayst. Clayst. Clayst.Method: XRF XRF DCP XRF XRF

52R-2,110-118837.10

Gy olive

53R-1, 54R-3,66-72 140-150

844.76 857.90Brown Pink gray

55R-4,2-8

867.52Br gray

Clayst. Rad clayst Rad ooze Rad claystDCP DCP DCP DCP

69.14.700

12.096.55.1402.25

.641.422.18.0894.801.08

.29

10.8136.2

17.698

71.2110.8179.8

5049.8129

67.8492

71.91.670

10.955.83.0402.19

.651.351.91.1544.34

.67

.09

9.9122.527.2122

65.155.6

200.643

56.2120

63.71797

69.02.973

11.846.09.0512.69

.751.372.21.1084.90

122.122.6

95

98.5613.2

5046.3149

51014.4

70.15.7599.348.42.0802.63

.621.311.95.0994.64

.58

.01

11.3126.725.1

9154.490.887.7

4333.5

6578.81257

74.89.7749.055.02.0602.35

.561.241.96.1004.00

.42

.18

10.4

97.221.4

7654.174.1

111.934

29.599

67.2467

71.44.5248.775.67

1.3892.381.021.142.20.2705.20

81.728.9127

57.679.6101

36.884

286012.3

73.39.5548.586.59.2032.45

.751.161.97.1564.20

101.926.5113

80.5127.9

5331.9

49

268815.6

81.08.3155.183.21.0521.36

.49

.941.16.1153.74

61.718.2238

66.8109.4

6325.2

40

966911.3

59.86.3937.192.42

1.5362.07

11.70.99

1.07.174

12.60

130.742.2274

99.9805.9

8826.3130

51859.6

44R-2,119-123761.19Ol grayClayst.

DCP

67.25.730

12.946.53.0662.44

.491.552.51.1005.4

120.919.7

94

89.0176.8

3759.3136

74115.6

57R-1,111-117882.81Brown

Clayst.DCP

72.49.5159.036.00.6442.501.041.231.63.2124.70

134.637.7190

88.685.3

5226.1

45

596111.4

123-765C 58R-4, 59R-4, 60R-5, 60R-5, 61R-4, 61R-5, 61R-5, 62R-3, 62R-3. 62R-4,67-71 39-45 120-123 120-123 92-94 81-85 81-85 73-79 80-84 19-21

Depth: 896.37 902.79 914.70 917.00 922.32 923.71 923.71 930.13 930.20 931.09Color: Brown Gy red Brown Brown Brown Gy brown Gy brown Gy brown Gy brown Gy brown

Lithology: Clayst. Clayst. Ash Ash Ash Cc.Clayst Cc.Clayst Clayst. Clayst. Clayst.Method: XRF DCP DCP XRF XRF XRF DCP DCP XRF DCP

SiO2TiO2

AI2O3FeOMnOMgOCaO

Na2OK2O

P2O5LOI

CaCO3C (Org)

NbZrY

SrRbZnCuNiCrV

CeBaSc

74.20.5438.695.87.2122.48

.681.221.55.1564.41

.33

.01

11.0111.331.9143

48.8114.256.3

5822.7

3196.33870

69.68.537

12.085.54.0432.85

.921.391.83.131

5

84.821.4135

71.8115.6

3931.9

70

284512.8

62.84.235

19.151.11.1085.891.452.37

.56.0756.22

168.08.6136

158.432.7225

18.6528

3507.3

10.7182.7

7.81506.7

191.730.1215

13.3590

17.0241

56.30.865

13.584.24.1134.036.281.652.12.145

10.679.58

.02

90.6432.6

48.3138

46.8230.7

21.7100

14.72297

178.4293

45.56.6878.356.95

1.6272.23

15.35.81

2.28.118

16.0527.32

.00

9.7127.630.6130

54.7102.2141.4

7416.7

9581.4207

44.92.6808.396.88

1.5571.90

15.52.92

2.40.115

18.33

138.731.4129

92.1129.5

6724.7

74

22314.3

65.81.814

10.907.98

2.2572.60

.761.223.06.1724.43

142.230.4139

160.9176.1

14539.6129

188316.3

65.65.829

10.468.00

2.3252.70

.861.173.11.2424.66

.50

.00

13.8179.744.0139

83.3137.1168.4

11424.2138

86.71492

60.25.814

10.4814.46.0922.921.201.193.37.4374.80

143.055.4

82

123.633.8150

38.0490

13516.4

Oxides in wt%; elements in ppm. Abbrev: light (It), dark (dk), olive (ol), gray (gy), green (gr), brown (br), black (bl),yellow (yell), calcareous (cc), claystone (clayst), siltstone (siltst), dolomitic (dol), radiolarian (rad).

O

Table 2. Instrumental neutron activation analyses (EVAA) of Site 765 sediments.

123-765BDepth:Color:

Lithology:Powder:

LaCeNdSmEuTbYbLu

CsBaScHfTaWCr

CoAsSbTh

U

3H-1-3519.15

Lt oliveCc. ooze

Al

13.719.711.42.34.522.3931.42.239

1.93842

5.101.45.2971.2131.76.362.19.5663.771.52

4H-6-2336.23

Red grayClay

Al

30.063.226.95.57

1.259.8822.79.426

6.151212

16.784.49.7673.1973.7

48.6816.94

10.38710.81

1.61

9H-6-9885.28

Gr grayCc. ooze

Al

19.530.816.03.22.707.4681.90.282

3.65719

8.742.21.4422.2153.89.132.92.8176.053.14

10H-5-8993.29

Lt gy blueClay

Al

36.767.227.96.29

1.303.8353.23.466

7.84681

20.215.01.9313.73

105.823.623.48.769

13.571.83

16H-1-42144.62

Lt ol grayCc. sand

we17.630 713.22.78.582.4611.59.245

3.00427

7.412.94.883

65.5742.1

10.762.69.4376.471.37

16H-1-42144.62

Lt ol grayCc. sand

we17.630.713.22.78.582.4611.59.245

3.00427

7.412.94.883

65.5742.1

10.762.69.4376.471.37

16H-1-42144.62

Lt ol grayCc. sand

we17.630.713.22.78.582.4611.59.245

3.00427

7.412.94.883

65.5742.1

10.762.69.4376.471.37

16H-1-42144.62

Lt ol grayCc. sand

we17.630.713.22.78.582.4611.59.245

3.004277.412.94.883

65.5742.1

10.762.69.4376.471.37

16H-1-50144.70

Lt ol grayCc. sand

Al

17.530.813.42.93.550.4041.58.255

3.104687.582.71.4836.9841.26.723.45.4266.391.53

17H-5-56160.46

Lt ol grayCc. sand

Al

8.315.16.6

1.30.280.206

.78.141

1.23197

3.081.87.210

.6121 95.984.12.7973.141.72

18H-1-13163.73Gy olive

ClayAl

41.673.731.56.78

1.376.9023.10.566

7.79553

20.295.98

1.1609.38

119.414.965.09.682

16.872.16

123-765BDepth:Color:

Lithology:Powder:

LaCeNdSmEuTbYbLu

CsBaScHfTaWCr

CoAsSbThU

22X-1-88203.28Ol gray

Cc. sandAl

5.912.96.3

1.16.258.207

.75.114

.68140

2.102.78.2181.0020.22.743.54.4362.452.22

26X-1-63241.83

Lt ol grayCc. sand

Al

3.36.12.0.50

.117

.090.29

.048

.4492.83

1.00.097

.618.7.55.46

.0631.331.00

28X-1-28260.88Lt olive

Cc. oozeAl

7.012.75.3

1.11.265.176

.56.095

1.4416

3.151.13.207

.8634.92.161.05.2012.601.76

39X-1-20366.90Gy oliveDol. clay

Al

20.941.019.64.22.793.5901.90.263

4.04264

11.103.54.6152.2293.19.133.65.6007.751.44

T. PLA

1

•

§

z

Table 2 (continued).

123-765CDepth:Color:

Lithology:Powder:

LaCeNdSmEuTbYbLu

CsBaScHfTaWCr

CoAsSbTh

U

2R-2-90362.00

Lt ol grayChalk

Al

4.97.14.1.78

.196

.142.48

.058

.70117

2.14.70

.148.13

27.32.41

.73.1261.311.10

7R-2-27409.77

Gy greenClay

Al

31.164.626.35.57.989.7022.51.409

7.10243

15.404.96.8552.63

140.021.69

4.461.17711.22

1.92

11R-1-84446.84Ol gray

Cc. clay

we26.250.221.54.51.916.6862.23.319

5.55204

12.323.82.787

10.8696.2

15.682.84

1.2538.151.92

11R-1-88446.88

Lt ol grayChalk

Al

11.421.9

7.71.75.377.2621.10.185

1.78112

4.191.35.2572.6934.87.163.53.3502.801.54

11R-1-133447.33

Lt ol grayCc. sand

we5.48.64.0.84

.201

.150.52

.063

.58126

1.601.24.997

145.8416.7

19.641.87.1941.621.61

11R-4-61451.11Gy blue

Clay

we39.481.131.96.94

1.450.9963.47.567

7.99164

18.335.69

1.19313.32119.643.75

4.201.54811.02

1.74

11R-4-61451.11Gy blue

Clay

we39.481.131.96.94

1.450.9963.47.567

7.99164

18.335.69

1.19313.32119.643.75

4.201.54811.02

1.74

14R-1-97475.07

Yel brownClay

Al

32.172.722.55.20

1.008.6542.92.509

8.70171

18.295.24.9164.33

138.823.3712.431.0249.531.49

17R-2-60504.50

Lt brownCc.ooze

Al

16.730.511.02.50.515.3671.53.260

3.79206

8.482.48.4982.1758.1

11.419.11.5515.16

.70

22R-2-28551.88Gy olive

Clay

we22.450.018.84.38.877.6202.50.335

4.91477

12.943.63.917

24.8592.5

163.781.52.448

11.901.12

23R-4-62564.82

Gy orangeChalk

Al

17.230.412.32.70.519.3801.40.1.97

1.9611384.861.32.3241.3526.68.685.24.3175.12

.36


123-7650Depth:Color:

Lithology:Powder:

LaCeNdSmEuTbYbLu

CsBaScHfTaWCr

CoAsSbThU

25R-1-92579.92

Lt brownCc. ooze

Al

22.219.117.53.82.883.5142.19.330

1.3931385.39

.95.173

.6317.57.75

.97.1231.70

.25

25R-3-106 25R-3-106583.06Br gray

ClayWC

65.4157.559.1

13.642.8441.7665.10.810

6.322149

22.755.35

1.23113.2981.0

78.516.37.725

12.321.07


123-765CDepth:Color:

Lithology:Powder:

LaCeNdSmEuTbYbLu

CsBaScHfTaWCr

CoAsSbThU

39R-3-101715.71Ol grayClayst.

WC

36.9117.832.68.14

1.452.9382.67.379

4.26691

18.313.86.995

13.6251.7

36.442.90.6799.78

.80

583.06Br gray

ClayWC

65.4157.559.1

13.642.8441.7665.10.810

6.322149

22.755.35

1.23113.2981.0

78.516.37.725

12.321.07

44R-4-55763.55Ol grayClayst.

WC

27.469.923.35.07

1.058.6201.92.317

4.04507

15.093.91.918

28.0954.0

31.3815.39

.5678.53

.91

26R-4-22593.02Brown

ClayWC

50.1101.148.7

11.242.3201.6184.69.733

5.57222

23.245.29.934

12.2184.5

17.074.52.521

11.22.79

45R-2-70770.40

Dusky redClayst.

WC

31.477.729.06.57

1.304.8662.69.437

3.791921

15.213.54.866

19.5155.3

15.585.03.9279.281.34

26R-4-42593.22Br gray

ClayAl

29.2156.023.15.56

1.087.6522.65.342

5.431505

23.704.73.8615.1469.3

37.255.59.6789.78

.96

50R-1-110816.70BrownClayst.

WC

35.388.731.77.06

1.452.9202.72.430

2.921287

15.463.75.931

17.0944.5

22.538.36.7706.81

.65

27R-2-34599.34Br grayClayst.

WC

306131.224.16.04

1.152.7302.80.392

6.332375

22.765.19

1.0808.9266.6

51.625.87.6249.93

.97


WC

38.3113.631.26.65

1.460.8932.79.460

2.56415515.103.26.856

29.0533.3

32.4615.421.0607.56

.53

28R-3-45610.45

Gy greenCcClayst

WC

30.277.324.85.80

1.155.6982.51.387

5.081865

16.803.54.7834.8363.9

20.221.26.6908.69

.79

61R-5-81923.71

Gy brownCcClayst

WC

41.978.334.78.11

1.7711.0833.29.476

3.08227

17.394.39.891

49.1227.3

25.7316.87

.6497.62

.55


WC

31.796.525.55.59

1.172.6772.20.365

7.46243

20.394.33.969

16.6270.4

26.338.21.417

11.55.92

62R-3-73930.13

Gy brownClayst.

Al

43.084.537.08.56

1.7341.1563.55.504

5.24217516.374.85.9114.7433.5

27.9713.39

.8179.89

.99

35R-3-24677.34

Gy blue/grClayst.

WC

44.3122.734.38.42

1.375.9392.46.324

4.73103219.304.04.9955.5064.1

35.5839.671.02013.082.17

62R-3-80930.20

Gy brownClayst.

WC

54.294.247.2

10.812.2481.4824.40.634

5.121473

16.675.42

1.17940.43

34.529.7113.88

.94510.22

1.13

35R-3-86677.96

BlackSiltst.

WC

11.319.69.7

1.88.520.3281.17.195

2.06363

6.181.19.2907.6237.19.94

16.53.4053.661.48

62R-3-80930.20

Gy brownClayst.

WC

54.294.247.2

10.812.2481.4824.40.634

5.12147316.675.42

1.17940.43

34.529.7113.88

.94510.22

1.13

37R-3-40696.40Ol gray

CcClaystWC

30.076.227.86.18

1.289.8262.64.434

2.92357813.322.66.636

12.5639.5

28.821.55.4256.46

.50

All elements in ppm. See Table 1 for major and trace element analyses for samples or adjacent intervals.Powdering method: tungsten carbide shatterbox (WC), alumina ball mill (Al). Other abbreviations as in Table 1.


Table 3. Precision and accuracy of DCP and XRF analyses.

SiO2

TiO2

AI2O3

FeOMnOMgOCaO

Na2OK 2 O

P2O5LOI

Total

NbZrY

SrRbZnCu

NiCrV

CeBaSc

IOBCDCP

n = 10

52.33.864

18.7111.61

2.083.382.034.092.931.179.65

99.19

1871 7 42 0 4

742 6 63 6 8

892 0 7

3 5 824

%st dev

.27

1.67.77

.721.421.041.861.392.222.863.34

4.644.441.24

4.618.041.202.232.72

1.482.12

SCO-1XRF

68.22.750

15.185.72.0602.982.80.9503.00.210

13.01 7 6

24.01 6 4115107

27.034.064.01 4 4

57.05 4 3

SCO-1AcceptedValues

68.74.688

14.975.63.0583.012.87.9903.03.226

11.2163

26.6178114105

29.327.669.5134

63.35 8 2

SCO-1New

68.22.685

15.185.61.0622.892.71

1.0493.00.239

11.3166

22.8177115107

30.528.174.21 3 4

51.26 1 3

Oxides in wt%; elements in ppm.

data that are routinely reported (smear slides, XRD analyses,visual core descriptions, etc.). If geochemical variability can betied to lithologic variability, then potentially accurate estimatesof sediment sections might be made, based only on published coredescriptions and a few chemical analyses. Thus, an important firststep is to examine the relationship between the geochemical andthe lithological variations in Site 765 sediments.

Dilution

The first-order control for variability of almost all the elementsanalyzed in Site 765 sediments is dilution by calcium carbonate

(cc) (Ludden, Gradstein, et al., 1990). An element such as Al, forinstance, is quantitatively diluted by cc. Figure 2 shows that as ccvaries from 0 to 100 wt%, AI2O3 varies from about 20 to 0 wt%.Cc is present in Site 765 sediments largely as nannoplankton andforaminifer skeletons that were transported to the site via turbidityflows. A typical calcareous turbidite consists of a foraminiferalsand at the base (almost 100% cc), and a long interval of feature-less olive nannofossil ooze that grades upward to a white nanno-fossil ooze that is often bioturbated (see Dumoulin et al., thisvolume). Intervals between turbidites typically consist of greenclay, with essentially no cc. Because the cc content may vary from0% to almost 100% in a single turbidite sequence (including theclay-rich interval), the entire compositional range of the hole foran element such as Al can be observed on the centimeter to meterscale of a single graded sequence. Calcareous lithologies are muchless common in the Cretaceous section, and so a first-order depthvariation in most elements is lower concentrations in the Cenozoicsection from dilution by calcareous turbidites and an increase withdepth from the predominance of clay-rich lithologies.

A few elements (Sr, U, Ba, and P) do not show cc dilutionrelationships because they take part in the biologic cycles of theoceans. For example, U and Sr are taken into the carbonate shellsof marine organisms. Ba and P are often enriched below zones ofhigh biological productivity (Schmitz, 1987; Toyoda et al., 1990,and references therein). Mn exhibits a complex distribution thatis not related to cc dilution, but may reflect post-burial mobilityfrom its redox chemistry (Compton, this volume).

Although a large part of the variation in most element concen-trations results from cc dilution, significant variation at low cccontents also exists. Examination of just the low cc samples showsanother dilution effect caused by silica (Fig. 2). Thus, almost allof the AI2O3 variation in Site 765 sediments may be explained bydilution of an end-member with about 20% AI2O3, by cc andsilica. The excess silica reflects either radiolarian-rich intervalsor detrital quartz. Figures 3A and 3C show good agreementbetween Siθ2/Al2θ3 (which is insensitive to cc dilution) andradiolarian abundances in the sediments. The scattered highSi2θ/Al2θ3 values in the upper 500 m of the section mark coarse-grained bases of turbidites, where detrital quartz and heavy min-erals may concentrate (Zr and Ti also may be enriched in these

2 0 -

^ 1 5 -

| •

co 10-O_CM

< 5-I

0

/ 0 20 40 60 80 100

CaCO3 (wt%)

50 60 70 80

SiO2 (wt%)

Figure 2. AI2O3 vs. CaCθ3, and AI2O3 vs. Siθ2 for a subset of low carbonate samples (<6 wt% CaO)

that exhibit dilution effects on Site 765 sediments.

176


εQ-a.

03

en

5000-

4000-

3000-

2000-

1000

5"

crçcöO

TO03OC

o<π

< 2 -

AA

A

iA i A

^ ^ é . AA AA A

c.

200 400 600 800 1000

Depth (mbsf)

Figure 3. Dependence of Siθ2 and Ba on radiolarian abundances at Site 765.A. Siθ2/Ahθ3 (wt% ratio) of sediments vs. depth. Open triangles representturbidite bases enriched in detrital quartz. B. Ba contents of sediments vs. depth.C. Radiolarian abundances in sediments vs. depth (from Table 9 in Ludden,Gradstein, et al., 1990). All three variables are high in the upper 100 m andlower 600 m of Site 765.

intervals). Sediments having high abundances of siliceous fossilsoften have high Ba contents (Schmitz, 1987, and referencestherein). The highest Ba contents in Site 765 sediments (up to10,000 ppm) occur in the radiolarian-rich interval between 800and 900 mbsf, and a rough correspondence exists between Ba andradiolarian distributions (Figs. 3B and 3C).

Although the largest control on concentrations of elements inSite 765 sediments is cc and silica dilution, some elements varysignificantly even after removing the effects of dilution. Most ofthe dilution signal can be removed by normalizing element con-centrations to Al, because Al is quantitatively diluted by cc andsilica. In addition, Al is associated almost exclusively with thedetrital phase in sediments; thus elements that form constantratios with Al are diagnostic of the composition of the detrital

phase. In a later section, we will discuss the provenance of thedetrital phase in Site 765 sediments. First, however, we willdiscuss those elements that do not form constant ratios with Al,but instead reflect changes in sediment mineralogy or lithologydown the hole.

Mg, Cr, and Sr in Diagenetic Clays and Carbonates

Figures 4 and 5 show anomalously high MgO/Al2θ3,0/AI2O3and Sr values in the interval between 200-400 mbsf. This intervalcontains an unusual mineral association: aragonite, dolomite, andthe magnesian clay minerals, palygorskite and sepiolite (Comptonand Locker, this volume). Because of the intimate intergrowths of

1.6

1.2-CO

O_C\J

<

Oen

0.8-

0.4-

A.

A A

A

AAAA

16 - B.

0.8-

:al c

o

CΛ

oen

0

0

0

. 6 -

. 4 -

•

. 2 -

0.0

200 400 600

Depth (mbsf)

800 1000

Figure 4. Enrichment of Mg and Cr in magnesian clay minerals at 200 to 400mbsf at Site 765. A. MgO/Ahθ3 (wt% ratio) in sediments. B. Cr (ppm)/Ahθ3(wt%) in sediments. C. Proportion of magnesian clays (palygorskite, sepiolite,and I/S/C) relative to total clays, as estimated by Compton and Locker (thisvolume).

177


3000"

è 2000 -CD

1000-

<D

• c

11< <

A. Λ •

A *•

• A A A .

B.

200 400 600

Depth (mbsf)

800 1000

Figure 5. A. Sr contents of Site 765 sediments. B. Aragonite abundances fromCompton and Locker (this volume). Sr is enriched in aragonite relative to claysand calcite.

dolomite and fragile palygorskite fibers, Compton and Locker(this volume) favor a diagenetic origin for the magnesian clayminerals. The bulk composition of the sediments reflects thismineral association: Sr is high because aragonite is enriched in Srover calcite (Figs. 5A, 5B); MgO is high because of the presenceof dolomite and the magnesian clays (Figs. 4A, 4C). Compton andLocker (this volume) suggest that diffusion from seawater sup-plies the Mg required to form the diagenetic dolomite and clayminerals. The high Cr/AhCb values (Fig. 4B) are less easilyexplained; either the source of the sediments in this interval wasenriched in Cr, or the diagenetic reactions that led to the formationof the magnesian clays favored Cr enrichment. We are unawareof any published accounts of Cr-rich varieties of palygorskite orsepiolite.

Potassium and Clay Minerals

K2O/AI2O3 varies by more than a factor of two in Site 765sediments (Fig. 6A), and variations in this ratio appear to reflectvariations in the clay mineralogy (after Compton and Locker, thisvolume). The K2O content of the bulk sediments varies roughlywith the percentage of illite (a high K clay mineral) relative to theK-barren clay minerals, kaolinite and smectite (Figs. 6A, 6B). Thelow K2O/AI2O3 values around 400 m reflect dominance of kao-linite, while the peak around 600 m reflects high illite and K-feld-spar contents.

Iron, Manganese, and Cretaceous Clays

Both FeO/Al2θ3 and Mn/AhCb increase dramatically at about600 mbsf (Figs. 7A, 7B), which corresponds roughly with theCretaceous/Tertiary boundary. The Cretaceous section at Site 765

0.3"

CO

O_CM

5 0.2o

CVJ

0.1 -

0.6-

fSm

ec

+K

aol

II /(

III

0.4-

0.3-

0.2-

0.1-

0.0200 400 600

Depth (mbsf)800 1000

Figure 6. Dependence of K2O content of Site 765 sediments on clay mineral-

ogy. A. K2O/AI2O3 (wt% ratio) of sediments. B. Proportion of illite relative to

sum of illite, kaolinite, and smectite (I/S <10%) from Compton and Locker

(this volume).

is characterized by a decrease in abundance of cc turbidites, adecrease in sedimentation rate, an increase in amount of pelagicclay, and an increase in (volcanogenic) smectite (Ludden, Grad-stein, et al., 1990). Several of these factors may have led to anincrease in the Fe and Mn contents of these sediments. Thesmectite that dominates the lower 600 m is Fe-rich and Al-poorrelative to the detrital illite and kaolinite that dominate the upper600 m (Compton and Locker, this volume). Thus, the increase inabundance of smectite in the lower section is partly responsiblefor the increase in FeO/Al2θ3. The slower sedimentation rates inthe Cretaceous section, in part reflecting a decrease in rapidlydeposited turbidite sequences, favors enrichment and preser-vation of the Fe-Mn oxyhydroxides that constantly rain onto theseafloor. Thus, Cretaceous sediments have a higher hydrogenouscomponent and higher Fe and Mn contents. Finally, FeO and MnOare anomalously high in the clays immediately overlying thebasaltic basement (Figs. 7A, 7B), suggesting a ridge hydrothermalorigin for some of the Fe and Mn.

REE Abundances, Patterns, and Ce Anomalies

Like Fe and Mn, the rare earth elements (REE) increasedramatically in the lower 600 m (Fig. 8A). A higher hydrogenouscomponent in Cretaceous sediments might have led to higher REEcontents because Fe-Mn oxyhydroxide floes scavenge REEs fromthe water column (Aplin, 1984, and references therein) and mayenrich underlying sediments. However, Sm correlates well with

178

0 200 400 600 800 1000

Depth (mbsf)

Figure 7. Increasing FeO and Mn in the lower 600 m of Site 765. A. FeO/Ahθ3(wt% ratio) in sediments. B. Mn (ppm)/Ahθ3 (wt%) in sediments.

P2O5 in Site 765 clays, and the correlation is similar to that ofrecent Pacific pelagic clays (Fig. 9). One might thus speculate thatphosphate phases, such as fish teeth and bones, exert a dominantcontrol on abundances of the REEs in Site 765 sediments, similarto what has been suggested for recent Pacific pelagic sediments(Toyoda et al., 1990). Low sedimentation rates and high biologi-cal activity may have led to higher biogenic phosphate contentsin pelagic clays (Toyoda et al., 1990).

The chondrite- or shale-normalized REE patterns also exhibitdifferences between Cenozoic and Cretaceous samples (Figs. 10Aand 10B). The REE patterns of the Cretaceous sediments aretypically enriched in the middle REEs, producing concave down-ward shale-normalized REE patterns (Fig. 10B) and high Sm/Ybcontents (Fig. 8B). The hydrogenous and phosphate phases, aswell as the volcanic source of the smectites in the Cretaceoussediments, may all contribute different REE patterns, and Sm/Ybdoes not correlate simply with any of these components.

Ce anomalies form in the marine environment as a result of thecontrasting behavior of oxidized Ce 4 + relative to the other domi-nantly trivalent REEs. Fe-Mn floes preferentially scavenge Ce 4 +

from seawater, which leads to positive Ce anomalies in Mnnodules and hydrogenous Fe-Mn crusts and a negative anomalyin seawater (Elderfield and Greaves, 1981, and referencestherein). Site 765 sediments exhibit both positive and negative Ceanomalies, with positive anomalies more common in Cretaceoussediments (Fig. 8C). The magnitude of the Ce anomaly is consis-tent within three different sediment types (Fig. 11). First, sampleshaving the largest positive Ce anomalies are high in Mn, reflecting


1.2

1.0-

coO 0.8-

<

0.4-

CΛ

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2.0-

2.5-

>, 2.0-co

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A.

A Δ

AA

A A '

A A

B.

m A

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A 1

c.

A 4 A

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0 200 400 600 800 1000

Depth (mbsf)

Figure 8. Variations in the REEs with depth at Site 765. Dashed line indicatesapproximate position of the Cretaceous/Tertiary boundary. A. Sm (ppm)/Ahθ3(wt%) is higher in Cretaceous sediments. B. Sm/Yb (ppm ratio) shows greaterheavy REE-depletion in Cretaceous sediments. C. Ce anomaly reflects Cedeviation from La and Nd in chondrite-normalized patterns and may becalculated from [3Cen/(2La« = n + Ndn)], where n indicates chondrite-normal-ized concentrations. Ce anomalies are generally negative (<l.O) in Cenozoicsamples and are more commonly positive (>l.O) in Cretaceous sediments.

a significant hydrogenous component that has scavenged REEsfrom seawater. Second, cc-rich sediments have negative Ceanomalies. Foraminifer tests, although almost devoid of REEsthemselves, may become coated by an authigenic Fe-Mn oxidephase rich in REEs (Palmer, 1985). These oxide phases have been

179


40

3 0 -

E& 20-

10-

• Pacific pelagic claysO Site 765 Clays

•

0.0 0.2 0.4

P 2 θ 5

0.6

(wt%)

0.8 1.0

Figure 9. Sm and P2O5 in recent Pacific pelagic clays (from Toyoda et al., 1990)and Site 765 clays (<6.0 wt% CaO).

shown to possess negative Ce anomalies inherited from bottomwater (Palmer, 1985). Finally, clay-rich samples have Ce anoma-lies that depend upon their P2O5 contents, showing a relationshipidentical to recent Pacific pelagic sediments (Toyoda et al., 1990).Phosphate phases (such as fish teeth) may have large negative Ceanomalies (Elderfield and Pagett, 1986, and references therein),and so increasing amounts of phosphate may lead to larger nega-tive Ce anomalies.

This analysis of the REEs in Site 765 sediments suggests thatdownhole variations in abundances of REEs and their patterns aredependent upon downhole variations in phosphate, Mn, and ccphases. In general, phases enriched in REEs (clay, phosphate, andMn) dominate the Cretaceous, while REE-poor cc dominates theCenozoic sediments (see Fig. 75 in Ludden, Gradstein, et al.,1990). In detail, however, distribution of the Mn and phosphatephases may be complex (Figs. 7B, 12). Nonetheless, high P2O5contents are typical of the 450- to 600-m interval (Fig. 12). Thisinterval is distinguished by the lowest sedimentation rates in thehole (1-2 m/m.y.), where fish debris may not be overwhelmed byother influxes. Even so, the P2O5 contents in this interval requireless than 1% apatite (with about 40% P2O5), which may explainwhy fish debris was not identified in sediment smear slides.Because fish-bone apatite may contain on the order of 100 timesthe REE contents of shales (Elderfield and Pagett, 1986; Staudigeletal., 1985/86; Toyoda etal., 1990), this seemingly trivial amountbecomes significant.

Although minor phases and lithologies may be important foraffecting downhole variations in certain elements, the aim of thisstudy is to characterize the average composition of Site 765sediments. In this regard, the most volumetrically significantcontrol on element concentrations in Site 765 sediments is dilu-tion of a shalelike phase with cc. For example, although subtledifferences in REE patterns may reflect different mineral phases,all Site 765 sediments, and in fact all marine sediments, have REEpatterns remarkably similar to average shale. This justifies thepractice of normalizing REE to average shales. AlthoughK2O/AI2O3 varies with clay mineralogy (Figs. 6A, 6B), the aver-age value is similar to average shale (around 0.2 for Australianshales; Taylor and McLennan, 1985). In the following section, we

25R-3-106

62R-3-80

7R-2-27

22R-2-289H-6-983H-1-35

17H-5-5628X-1-28

2R-2-90

A. Chondrite Normalized

26R-4-42

58R-4-67

1000

:100

LaCe Nd SmEuGdTb YbLu LaCe Nd SmEuGdTb YbLu

Figure 10. REE patterns in selected Site 765 sediments. Gd has been interpolated between Tb and Sm to illustrate Eu anomalies better. Closed circles indicateCenozoic sediments; open circles represent Cretaceous sediments. A. Chondrite-normalized patterns (to values in Taylor and Gorton, 1977). B. Shale-normalizedpatterns (to PAAS in Taylor and McLennan, 1985).

180


>. 2oö

oc:<CD

<•> 1

oMn

O

• Pacific pelagic claysO Site 765 ClaysA Site 765 Cc

•.01 0.1 1

P 2 O 5 (wt%)10

Figure 11. Ce anomalies in Site 765 clays, carbonates (>20% CaO), andMn-rich clays. Carbonates have negative Ce anomalies; Mn-rich clays havepositive anomalies. Other Site 765 clays exhibit a similar relationship betweenCe anomaly and P2O5 content as recent Pacific pelagic clays (Toyoda et al.,1990).

0.0

200 400 600 800 1000

Depth (mbsf)Figure 12. Variation in P2O5 content of Site 765 sediments with depth.

discuss the provenance of this shalelike detrital phase in Site 765sediments.

Provenance of Detrital PhaseSite 765 lies oceanward of the northwestern shelf of Australia,

and thus the likely source of Site 765 sediments is northwesternAustralia. A considerable data base for the sedimentary masseson the Australian continent has been developed overpast decadesby researchers from the Australian National University as a wayof estimating the composition of this exposed continental crust(reviewed in Taylor and McLennan, 1985). Special attention hasbeen paid to the Archean and Archean/Proterozoic boundarysedimentary sequences; thus, a fair amount of data exists forsamples from the Precambrian Pilbara Block of western Australia(see Fig. 1). A more direct source for Site 765 sediments might

be the Phanerozoic rocks of Canning Basin, but these have beenultimately derived from the Archean and Proterozoic blocks ofwestern and central Australia, too (BMR Paleogeographic Group,1990).

Figures 13A through 13D show AI2O3 variation diagrams forSite 765 sediments, along with sediment data from the CanningBasin (Nance and Taylor, 1976), the Pilbara Block (McLennan,1981; McLennan et al., 1983), and the post-Archean AustralianShale (PAAS) average from Taylor and McLennan (1985). ThePilbara Block sediments include both Archean shales from theGeorge and Whim Creek groups, as well as early Proterozoicsediments from the Hamersley Basin. The Archean shales fromthe George and Whim Creek groups are too depleted in Tiθ2 andTh, and too enriched in Ni and Cr, to be an appropriate source forthe Site 765 sediments (Figs. 13A-13D). Furthermore, theArchean shales lack an Eu-anomaly, which is a ubiquitous featurein Site 765 REE patterns (Fig. 10A), and indeed, is the hallmarkof post-Archean sediments (Taylor and McLennan, 1985). Thesecharacteristics of the George and Whim Creek shales are commonto most Archean shales and preclude much of a pure Archeancomponent in the Site 765 sediments. On the other hand, anaverage of three Canning Basin shales (Paleozoic) provides agood fit with the detrital end-member for Site 765 sediments(Figs. 13A-13D) and makes sense geographically (see Fig. 1) asa source for river or wind influxes to the Exmouth Plateau andArgo Abyssal Plain. The Canning Basin average is near the PAAScomposite itself, which is similar to post-Archean shales else-where, owing to the remarkable mixing efficiency of sedimentaryprocesses (Taylor and McLennan, 1985). The early ProterozoicHamersley Basin sediments lie compositionally between the Pa-leozoic Canning Basin shales and the Archean Pilbara shales, butlike the Archean shales, are too Cr-enriched and Tiθ2-depleted tobe a suitable end-member for Site 765 sediments. Thus, despitesignificant exposures of Archean rocks in their presumed source,Site 765 sediments are compositionally like post-Archean shales.The ancient age of the source of Site 765 sediments should bereflected, however, in their compositions of Pb and Nd isotopes.Future isotopic work using these samples should help constrainthe mean age of the source of Site 765 sediments.

For elements that increase down the hole (e.g., REEs, Fe), theCenozoic values are more representative of a purely detrital com-ponent having a composition near PAAS, which is consistent withthe Cenozoic section being dominated by turbidites that quantita-tively deliver continental detrital material to the marine environ-ment. The Cretaceous sediments may be enriched over PAASbecause of additional hydrogenous, volcanic, hydrothermal, orphosphate contributions, as discussed above.

The proximity of active volcanoes of Java and the LesserSunda Islands (Bali, Lombok, Sumbawa, etc.) raises the issue ofthe extent to which arc andesites contributed to the youngest Site765 sediments. Ninkovich (1979) demonstrated that Lesser Sundaash falls extend to only 200 km south of the Sunda Trench. Site765 lies far south of this zone, and indeed, no prominent ash falllayers were cored in the Cenozoic section. However, it is possiblethat a disseminated ash component contributed to Site 765 sedi-ments. Figure 14 shows the K2O and Cr contents of Site 765sediments, modern Indonesian volcanics, and post-Archeanshales. During differentiation of arc magmas, elements incompat-ible in the fractionating mineral assemblage (such as K) increasedramatically, while compatible elements (Cr) decrease dramati-cally. Thus, although arc andesites have high K2O abundances,they are strongly depleted in Cr, unlike marine clays and terrige-nous shales that are enriched in both. These systematics apply tothe compatible element Ni as well, but Ni may be further enrichedin marine sediments from a hydrogenous (Fe-Mn oxide) contribu-tion. The high Cr/K2θ contents throughout the Cenozoic section

181


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TiO

P

(PP

i

E

IfQ_a.

.cf

'ÉTi—Q.a.

i _

O

-

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0.4-

10 -

5 •

15

10-

5

-

400-

200-

-

A.

B.

A

A. l

c.

AAA A

D.

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Δ 3fe,r^A ok A P F )

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A

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CB

A PAAS A P

PAAS A °

* A AP

OAP

HBO

1* > / - ^ A

‰Δ^PAASCB

10A I 2 O 3

15(wt%)

20 25

Figure 13. Selected elements vs. AI2O3 in Site 765 sediments (open trianglesCretaceous, closed triangles = Cenozoic), average shales from the Phanero-

zoic Canning basin (CB), the early Proterozoic Hamersley Basin (HB), and theArchean Pilbara Block (AP), and average post-Archean Australian shale(PAAS). A. Tiθ2 vs. AI2O3. B. Sm vs. AI2O3. C. Th vs. AI2O3. D. Cr vs. AI2O3.Data are from Taylor and McLennan (1985); Nance and Taylor (1976);McLennan et al. (1983); McLennan (1981); and Tables 1 and 2.

160

120

Q.Q.

U

PAAS

Arc Andesites

1 2 3 4 5

K 2 O ( w t % )

Figure 14. K2O vs. Cr for Site 765 sediments (triangles), the Canning Basinaverage and PAAS (as in Fig. 13), and andesites from Java and Lesser Sunda(Merbabu volcano, Java, and Batur volcano, Bali). Data for andesites fromWhitford (1975) and Wheller and Varne (1986). Open triangles = anomalouslyhigh Cr sediments in the 200- to 400-m interval at Site 765 (Fig. 4B).

rules out much andesitic ash in Site 765 sediments. As Site 765approaches the Sunda Trench, however, ash may have contributedsignificantly to the upper sedimentary section, and subduction ofthis material leads to interesting speculations about the extent ofcannibalism at arcs (Ben Othman et al., 1989).

CALCULATING A BULK COMPOSITION FOR SITE765 SEDIMENTS

Estimating the bulk composition of Site 765 sediments mightbe as simple as averaging the analyses in Tables 1 and 2. However,this estimate is only as accurate as each sample is representative.Because cc dilution accounts for most of the geochemical varia-bility in Site 765 sediments, this estimate may be refined by takinginto account cc variations. Cc contents are linked to macroscopiclithologies (foraminifer sands and nannofossil oozes); thus, pub-lished core descriptions provide, in effect, continuous downholecc estimates. To determine the bulk composition of the site, weestimated the cc content of each 10-m interval (each core) fromvisual core descriptions, used our analyses to determine the com-position of the noncarbonate fraction, and then diluted this com-position by the estimated cc content. Details of these calculationsare presented next.

The data reported here represent spot analyses that must beweighted by the length of the interval that they represent. Forexample, some sampled clay units are only centimeters thick,while some sampled nannofossil ooze units are meters long. Todetermine the weighting factors, the relative proportions of car-bonate-rich lithologies were estimated for each of the 103 coresfrom the barrel sheets in Ludden, Gradstein, et al. (1990). Becausea sediment described as "nannofossil ooze" is not pure calcite,shipboard CaCθ3 analyses were used to calculate the pure ccfraction for each core. The rest of the core was considered "non-carbonate." Figure 15 presents the downhole variation in thisvalue. This "noncarbonate" factor is simply a way to quantify andsmooth lithologic variations downhole. Moreover, because mostof the geochemical variability is directly linked to carbonatecontent, this value links lithologic and geochemical data.

The data in Table 1 were normalized to a carbonate-free, drybasis (by normalizing by a sum that does not include CaO nor the

182


100

200 400 600

Depth (mbsf)

800 1000

Figure 15. Downhole variation in percentage of noncarbonate per core at Site765. This value has been estimated from CaCθ3 contents and core descriptionsin Ludden, Gradstein, et al. (1990). See text for details.

LOI) and averaged for each core. These values were then "diluted"by multiplying by the noncarbonate percentages in Figure 15 toobtain average compositions for each core.

The method of weighting concentrations by the average non-carbonate content is inappropriate for those elements that arecontained within carbonate (i.e., Sr), or that do not indicatecarbonate dilution relationships (Ba, Mn, P, As, and U). For theseelements, individual samples were assumed to be representativeof each core. Where more than one analysis per core existed,values were averaged, and where no samples from a core wereanalyzed, values were interpolated. This method is limited by theextent to which sampling was representative of the dominantlithologies. Because Sr is contained in appreciable amounts inboth carbonate (usually >IOOO ppm) and clay-rich (usually <200ppm) units, both clay and carbonate Sr contents were estimatedfor each core by interpolation of actual measurements, and thesevalues were weighted by the average carbonate content of eachcore.

Geochemical Logs

These average core compositions provide a smoothed down-hole data set that can be compared with geochemical logs. Thenatural gamma-ray tool (for K, Th, and U), aluminum activationclay tool (for Al), and the gamma-ray spectroscopy tool (for Si,Fe, Ti, and Ca) were run through casing in Hole 765D; the holewas then drilled to set a reentry cone for sampling basement (seealso Pratson and Broglia, this volume). Logging through casingdecreases the quality of the data because it reduces the signal andadds another factor that must be removed when processing thelogs. To smooth these logging data, we applied a five-pointrunning average.

Although logs from the gamma-ray spectroscopy tool provedto have too poor quality to use, the AI2O3 and K2O logs, acquiredusing two different tools, seem to agree with each other, as wellas with the basic lithologic core descriptions. Figure 16 showsK2O and AI2O3 from the logging data for the hole (the upper 170m was not logged), compared with the weighted averages calcu-lated from our analyses of the core samples. Despite simplifica-tion and smoothing of the logging data, the trends agreeremarkably well with the "ground truth" analytical data. Bothexhibit low values in the 200- to 400-m interval, characterized by

low clay content, a peak around 600 m, and lower values deeperin the hole. The average K2O content of the hole calculated fromthe logs is 1.5 wt%, while the average calculated from our sedi-ment analyses is 1.6%. The AI2O3 log in the interval between 200and 400 m is about 6 wt% too high, and this may have resultedfrom a processing artifact, where the highly attenuated signal inthis interval may have been overcompensated (Pratson and Bro-glia, pers. comm., 1990). However, average AI2O3 contents cal-culated for the lower 500 m agree well with the estimate from theweighted core analyses (10.6 vs. 11.1 wt%, from the logs andanalyses, respectively).

Bulk Composition of Site 765 Sediments

A grand average for the entire 930-m section was calculatedfrom the core-by-core averages, and this estimate of bulk compo-sition of the hole is presented in Table 4. Separate compositionsare presented for the Cenozoic and Cretaceous sections.

Even though significant differences exist between the Ceno-zoic and Cretaceous sediments, as discussed previously, the pri-mary difference between the two sections is simply their differentcc contents. For example, while Sm/Yb increases significantlyfrom 1.9 for the Cenozoic section to 2.4 in the Cretaceous section,Sm concentration itself more than doubles as cc decreases frommean values of 60% to 10%. Thus, dilution is still the dominantsignal.

A surprisingly accurate bulk composition for Site 765 sedi-ments may be obtained simply by multiplying an average shalecomposition (such as PAAS) by the average noncarbonate contentof the hole (60%). Table 4 presents the results of these calcula-tions; most elements may be estimated within 30%. Sr can be wellapproximated by assuming 1500 ppm in the carbonate fractionand PAAS values in the clay fraction. A better fit can be obtainedfor elements such as K, Nb, Zr, Rb, and Th by taking advantageof their roughly constant and upper crustal-ratios to Al. Alongwith Al, all these elements are higher in the estimate based simplyon PAAS and the carbonate content. By assuming PAAS ele-ment/Al2θ3 ratios and by multiplying by the mean AI2O3 contentof the Site 765 sediments, better matches for these elements canbe obtained. Elements having poor fits include MnO, Cu, and Ni(due to hydrogenous oxides), MgO (due to the diagenetic mineralsof the 200- to 400-m interval), Ba (due to radiolarian concentra-tions) and Cs. CS/AI2O3 is virtually constant in Site 765 sedimen-ts, but much lower than PAAS.

The success of the PAAS estimate for most elements suggeststhat even though extra hydrogenous, volcanic, phosphate, andhydrothermal phases contribute to the Cretaceous sediments, itscomposition is still dominated by average shales. By assuming anaverage shale composition (PAAS), a relatively accurate estimateof the bulk composition of the hole can be made without relyingon any chemical analyses: the carbonate dilution factor can beestimated from visual core descriptions, and average Al or Kcontents, which constrain crustal ratios, can be determined fromgeochemical logs.

SITE 765 AS A REFERENCE SECTION

Marine sediments are largely mixtures of four components:biogenic, detrital, hydrogenous, and hydrothermal (Dymond,1981; Leinan, 1987). The hydrothermal component is only impor-tant near an active ridge-crest hydrothermal system, althoughdisseminated components may be far reaching (1000 km, Barrett,1987). The hydrogenous component, associated with Fe-Mn ox-ides, dominates only when the other components are absent, suchas is typical for the South Pacific, much of which is below theCCD and far removed from regions of high biologic productivityand terrigenous sources. Site 765 represents the other end-mem-ber. Near a continental margin, the site is dominated by biogenic

183


| 3

o^ 2

°? 3

LoggingData

l

H 1 1 | » I h

*irVH H

• Core Samples

<

AA*A

A

CM p A é * A

A áU

•

20

15

O

15

LoggingData

1 1

Core Samples A £

co 10O

<

i S' -

* ^ À 4 ^ / 4 A

A

200 400 600 800 1000

Depth (mbsf)

0 200 400 600 800 1000

Depth (mbsf)

Figure 16. Downhole logs for K2O and AI2O3 (from Pratson and Broglia, this volume) compared with weighted analyses of core samples. See text for details ofweighting and data processing. Downhole K2O variations from the two methods agree remarkably well. AI2O3 content agrees well in sediments below 400 mbsf.

and detrital material. This leads directly to the success of thesimple calculation based on PAAS and cc content to describe thebulk composition of Site 765. The large biogenic influx meansthat variations in the other components are overwhelmed bysimple quantitative dilution. However, proximity to a continentalso means that the detrital component is relatively constant aswell, owing to the remarkable homogeneity of mature uppercrustal material. Indeed, McLennan et al. (1990), in a survey ofdeep-sea turbidites, found that passive margin turbidites typicallysample average, old, upper crustal material. These two factors,dilution because of biogenic components and average crustaldetritus, should make calculating sedimentary columns adjacentto continents elsewhere just as simple. Results from Site 765suggest that accurate estimates may be made with little analyticaleffort. Continental margin sections exist outboard of other arcsthan Indonesia (the Antilles, Chile, Alaska, Cascades, Mediter-ranean) and thus make up a significant portion of potentiallysubducted material. In contrast, sedimentary sections in the mid-dle of the Pacific, such as outboard of the Tonga Arc, have beenstarved of biogenic and detrital components and may require acompletely different way to calculate bulk compositions. Futureresearch will be dedicated to establishing another reference sec-tion in the central South Pacific.

Although much of the variation in a sedimentary section proxi-mal to a continental margin will reduce simply to dilution ofaverage crustal shales by biogenic material, this still leads to someinteresting systematics for elements that are important tracers ofcrustal recycling:

1. Alkali elements (K, Rb, Cs). These elements are entirelycoupled to the detrital component and will be quantitativelydiluted by biogenic material. Their ratios may be similar to aver-age crustal shales, although K may vary with clay mineralogy(Fig. 6). Deeply weathered source regions may contribute morekaolinite-rich clays, leading to lower K/Al than average shales.McLennan et al. (1990) also suggested that the alkali elementsmay fractionate from each other during weathering, with low K/Cscontents characteristic of highly weathered sources.

2. Alkaline earth elements (Sr, Ba). In contrast, these elementshave little to do with the detrital component, and thus importantfractionations in alkali/alkaline earth elements occur in the marineenvironment. Sr substitutes for Ca in marine carbonates and maybe present in concentrations up to 3000 ppm in some aragonites.Nonetheless, we have shown that the average Sr content of asedimentary section such as that at Site 765 can be well estimatedsimply by assuming average cc and shale values. Although Ba

184


Table 4. Bulk composition of Site 765 sediments.

SiO2

TiO2

AI2O3

F Θ O

MnOMgOCaO

Na2OK 2 O

P 2 O 5

total cc

NbZrY

SrRbZnCu

NiCrV

BaSc

LaCeNd

SmEuTbYbLu

CsHf

Ta-W-

Co*AsSbTb

U

Site 765Ceno

26.8.37

7.4

2.8.112.9

32.2.9

1.3

.13

57.5

5.4931 7

1285485671425366

3197.2

173113

2.8.59.411.5.24

3.32.7.412.3

94.3

.95.81.8

Site 765Crβt

65.6.70

11.26.0.462.65.51.4

2.2

.14

9.8

10.4125

29274

7295

1977145

112191313.8

369331

7.01.44

.912.9.46

4.33.8.744.0

278.0

.78.9

.9

WholeHole

42.5.50

8.9

4.1.252.7

21.41.1

1.6

.14

38.2

7.4106

21871

5872

122545085

9639.9

245620

4.5.94.612.1.33

3.73.1.673.5

215.8

.97.0

1.5

PAAS

64.21.0219.3

6.6.112.21.31.2

3.8

.16

19.4215

28204163

875156

112153664

16

398233

5.721.12

.792.86

.44

15.35.1

23.5

14.93.2

Calc765

39.66.63

11.934.10

.071.39

21.39.76

2.34.10

12.0133

17699101

5432356995

4 1 010

245120

3.54.69.49

1.77.27

9.53.2

14.5

9.22.0

Calcfrom Al

.47

8.90

(from cc)

1.74

8.999

(from cc)75

52

8

7.12.4

6.9

% diff

-7-7

0

0-73-49

0-30

6

-26

21-7

-20-2031

-25-74-35

412

-57

-24

-2-10

-1-22-26-21-14-17

90

-25

-30

-231

* Samples powdered in WC excluded from estimate for these elements.PAAS from Taylor and McLennan (1985), rβnormalized to 100%.

exhibits complex behavior in the marine environment, Ba con-tents may be enormously high (10,000 ppm levels) in siliceousoozes. A rough association exists between Ba and radiolarianabundances in Site 765 sediments (Figs. 3B and 3C). This asso-ciation may result from barite nucleation on decaying siliceousskeletons in the water column (Bishop, 1988). Predominance ofsiliceous organisms is a characteristic of regions of high produc-tivity maintained by active upwelling, such as in equatorial re-gions. Thus, Ba has been used as a paleoproductivity indicator, aswell as an equatorial reference frame for charting plate motions(Schmitz, 1987).

3. REEs. The REEs typically display post-Archean shale pat-terns and are quantitatively diluted by cc and silica. REEs maybecome enriched, however, by phosphate or Fe-Mn oxide phases.Positive Ce anomalies are characteristic of sediments rich inFe-Mn oxides, while negative Ce anomalies are characteristic ofsediments rich in biogenic cc or phosphate. A few arc volcanicspossess negative Ce anomalies (Heming and Rankin, 1979),which might have been inherited from REE-rich phosphates.

4. High field-strength elements (HFSE; Nb, Ta, Hf, Zr). Theseelements, like the alkalis, are completely coupled to the detritalcomponent, although they may become enriched in turbidite sandsfrom heavy mineral concentrations. The high concentrations ofHFSE in sediments and the notoriously low concentrations in arcvolcanics provide convincing evidence against bulk assimilationof sediment in subduction zones. The transfer of material from the

subducting slab to the asthenosphere beneath arcs must be oneselective to certain elements (Morris and Hart, 1983).

5. Parent/daughter ratios. Although carbonate dilution has hada dramatic effect on concentrations of elements, the ratios ofseveral elements remain relatively constant throughout Site 765sediments, especially in the Cenozoic sequence. Indeed, we tookadvantage of the constant and upper crustal ratios for severalelements to refine our estimate of the bulk composition of Site765 sediments. For example, the Sm/Nd ratio is remarkably con-stant in Site 765 sediments, even though Sm concentrations mayvary by a factor of 20 because of cc dilution. Important radioactiveparent/daughter ratios, however, will vary significantly with car-bonate content. The most obvious is Rb/Sr, which decreasessignificantly in carbonate-rich lithologies as a result of bothdilution of Rb and incorporation of Sr in marine carbonates. TheU/Th ratio will vary in an inverse way, because Th is quantita-tively diluted, while U is somewhat taken up in carbonates (BenOthman et al., 1989). Thus, first-order variations in these importantparent-daughter ratios may also be controlled by carbonate content.

SEDIMENT SUBDUCTION ALONG THE SUNDATRENCH

Although not the specific aim of this study, these data for Site765 sediments have obvious applications to sediment recycling atthe Sunda Arc. Geophysical observations along the Sunda Trenchare ambiguous regarding structural evidence for sediment subduc-

185


tion. A large gradient in sediment thickness occurs along theSunda Trench (Fig. 17). In the northwest, south of Sumatra, theremay be as much as 5 km of sediment, much of which is beingaccreted in the forearc (Moore et al., 1980). Farther east, south ofJava, only a thin veneer of sediment approaches the trench: aslittle as 200 m in places (Moore et al., 1980). Available seismicdata, however, show little resolvable structure within the JavaTrench slope and thus leave open the question of sediment accre-tion (Curray et al., 1977).

The isotope 10Be was measured in samples from 10 volcanoeson Java and on Bali, and abundances were indistinguishable fromlavas in other tectonic settings (Tera et al., 1986). A lack of 10Beenrichment in Indonesian volcanics does not prove that sedimentswere not subducted beneath Java. Because 10Be has such a shorthalf-life (about 1.5 m.y.), it is present only in Neogene sediments,and the absence of 10Be in Java volcanics might simply mean thatNeogene sediments were not subducted and erupted within 10m.y. (the time over which 10Be decays). It is entirely possible thatolder sediments are being subducted. Whitford and Jezek (1982)suggested that sediments were incorporated in the source of Javamagmas, based on the radiogenic Pb isotopic compositions andsteep 207Pb/204Pb vs. 206Pb/204Pb trend defined by Java volcanics.These data have long served as one of the classic examples forsediment incorporation, even though no sediment data were avail-able at the time Whitford and Jezek (1982) formed their model.However, new Pb isotopic data for piston core samples of sedi-

ments outboard of Java overlap with the volcanics (Ben Othmanet al., 1989) and provide new support for the original interpreta-tion. Thus, the most compelling argument for subduction comesfrom Pb isotopic data.

Some data exist with which to extrapolate the lithologic andgeochemical stratigraphies developed at Site 765 regionally alongthe Sunda Arc. Several holes that penetrated basement were drilledduring DSDP Legs 22 and 27, and although recovery was poor(often less than 20%), data from these holes do provide a means ofestimating the lithologic sections around the Sunda Trench (seeFig. 17). These holes include two around the Australian margin(Sites 261 and 260), two farther west in the Wharton Basin (Sites212 and 213), and one just south of the Sunda Trench (Site 211).From descriptions in the Initial Reports volumes of these cruises,it appears that calcareous turbidites from the Australian marginextend as far north as Site 261 and as far west as Site 212 in theWharton Basin. Site 213 contains little carbonate, but has accumu-lated siliceous oozes since the Miocene. An extensive section ofSite 211 is composed of clastic turbidites of the Nicobar Fan.

A small amount of geochemical data has been published forsediments from Sites 261 and 260 (largely major elements; Cook,1974), Sites 211 through 213 (transition metals; Pimm, 1974), andfor a few piston cores outboard of the Sunda Trench (trace ele-ments and isotopes; Ben Othman et al., 1989; see Fig. 17). Be-cause no shared set of elements exists, one finds it difficult to drawmany regional conclusions. Future research will include isotopic

10°N

-\ 10°S

80°E 100 110° 120° 130c40°

Figure 17. Location map of other DSDP and ODP holes (closed circles) throughout the region outboard of the SundaTrench. Water depth in meters. Open circles are piston cores V34-47, V34-45, V28-341, and V28-343 from BenOthman et al. (1989) that are discussed in the text (other piston cores from Ben Othman et al., 1989, are on the northside of the Sunda Trench and are not discussed here).

186


analyses of Site 765 sediments, as well as analyses of major andtrace elements in the piston core samples for which Ben Othmanet al. (1989) analyzed isotopes. These data will allow for moreconfident extrapolation of information along the entire SundaArc. However, the following preliminary observations can bemade. Sites 260 and 261 along the Australian margin are similarto Site 765 in that the Cretaceous section is dominated by clays,the Cenozoic section contains calcareous turbidites, and the detri-tal end-member, at least based on the K2θ/Tiθ2 ratios (Fig. 18),appears similar to PAAS. Although one would wish to analyzemore clay samples for more elements, calculating the bulk com-position of these two sites may be as simple as estimating the ccand Al contents, as we demonstrated for Site 765 sediments.

MnO-rich clays may be more common from the Wharton Basinsites than from those sites nearer the Australian margin (Fig. 19).

O

A

oD

765260261 A ^ ^ A

Cfc>A D PAASU O A

A .

0.0 0.2 0.4 0.6 0.8 1.0 1.2

TiO2 wt%Figure 18. K2O vs. Tiθ2 for sediments around the Argo Abyssal Plain. Datafor DSDP Sites 260 and 261 from Cook (1974).

2 -

O

1 "

A••

ML

765212213

mm

•

•

toCL

A

A

#

-

8 10 12FeO (wt%)

Figure 19. FeO* vs. MnO for sediments from DSDP Sites 212 and 213 in ornear the Wharton Basin and Site 765. Data for Sites 212 and 213 from Pimm(1974).

Although no higher in concentration than the most manganiferoussediments from Site 765, almost all of the samples analyzed fromSites 212 and 213 are rich in MnO, perhaps reflecting a. greaterhydrogenous/detrital fraction in the clays. This interpretation isconsistent with these sections being farther from the Australiancontinent and their detrital sources. The isotopic compositions ofthe piston core samples near the Australian margin are distinctiveof old cratonic material (i.e., high ^ P b / ^ P b , low 1 4 3 Nd/ 1 4 4 Nd),while those west of the Wharton Basin are distinctly less enriched(Fig. 20), perhaps reflecting influx of younger material from theNicobar Fan. The Wharton Basin sample has higher Lu contentsthan any sample from Site 765, while other piston core samplesas far west as the Ninetyeast Ridge and as far east as the BandaIslands overlap completely with Site 765 sediments (Fig. 21).

Existing data are patchy, but suggest it may be possible toextrapolate at least certain aspects of Site 765 sediments acrossthe entire basin from the Banda Islands to Ninetyeast Ridge.Australian continental detritus is most likely an important com-ponent of sediments at least out into the Wharton Basin. Keyanalyses of other important components, such as Mn-rich clays ofthe Wharton Basin, clastic material fed from the Nicobar Fan, andash from the active arc, coupled with careful consideration of thelithologic characteristics of the DSDP holes (e.g., carbonate vs.clay fractions), might yield good first-order estimates of elemen-tal fluxes into the Sunda Trench.

CONCLUSIONS

1. The dominant signal in the geochemical variability of Site765 sediments is dilution of a detrital component by biogeniccalcium carbonate and silica. This dilution leads to enormousvariations in the concentrations of most elements. Dilution fromcarbonate or silica may be a long-lived feature of the sedimentarycolumn, even if subducted to great depths because of the relativelyhigh temperatures required for decarbonation reactions (Gill,1981; Abbott and Lyle, 1984).

Q_^ J •

oCVJ

JOQ_

h~oCO

CO

15.75

15.71

15.67

0.51228

0.51224

0.51220

0.51216

H—i—I—i—h

0 Wharton Basin

Ninety East Ridge

N Australia margin -•80 90 100 110 120 130 140

Longitude (°E)

Figure 20. Pb and Nd isotopic compositions for surface samples outboard ofthe Sunda Trench (from Ben Othman et al., 1989).

187


α.Q.

1 0 -

5"

Δ Indonesia Piston Cores

° 765 Cenozoic

• 765 CretaceousA

WB

Δ 90E

Ban AAP

0.0 0.2 0.8 1.00.4 0.6

Lu (ppm)Figure 21. Sm and Lu concentrations for Site 765 sediments and the four piston

core samples shown in Figure 20 from the Banda region (BAN), Argo Abyssal

Plain (AAP), Ninetyeast Ridge (90E), and Wharton Basin (WB).

2. Significant differences occur between Cenozoic and Creta-ceous clays, involving increases in Fe, Ti, Mn, Ba, REEs, changesin REE patterns, and development of positive Ce anomalies downthe section. These variations may result from increases in hy-drogenous, hydrothermal, phosphate, and/or volcanic phases dur-ing the Cretaceous. Although important for identifying changesin the provenance, sediment supply, or rate with time, these phasesled to small deviations from the average composition of the hole,which is dominated by dilution of an average shale composition.

3. The K2O and AI2O3 downhole logs correspond well with"ground truth" chemical analyses. The bulk composition of thehole can be calculated by using the visual core descriptions toweight the individual analyses over appropriate intervals. Thiscomposition, however, agrees remarkably well (to 30% for mostelements) with an estimate based simply on average Australianshales and the average cc and AI2O3 contents of the hole. Thisresult suggests that estimating other sections dominated by car-bonate and continental detritus may require minimal analyticaleffort. Ideally, only core descriptions and logging data shouldprovide estimates of cc and Al contents that are accurate enoughto characterize a site.

4. Although Site 765 is an important reference section forsedimentary columns along the Sunda Arc, our results are moregeneral. Site 765 sediments are well described by dilution ofaverage shale by biogenic phases, and because average shalecompositions are remarkably similar around the world, resultsfrom Site 765 are general, not restricted to provenances or pro-cesses about the Indonesian region. Site 765 should thus serve asa useful reference for calculating other continental margin sec-tions approaching trenches around the world (e.g., the Antilles,Americas, Mediterranean). A recent study by Hay et al. (1988)about global distribution of sediments on the ocean floor esti-mated that roughly 40% of ocean sediments is calcium carbonateand roughly 45% is terrigenous detrital material. Therefore, Site765 sediments, dominated by cc and terrigenous detritus, is repre-sentative of a large part of the global marine sedimentary reservoir.

ACKNOWLEDGMENTS

We thank Ginger Eberhart, Gilles Gauthier, and BettinaDomeyer for technical assistance with the DCP, INAA, and XRFanalyses, respectively. Scott McLennan kindly provided unpub-

lished data and a preprint. We thank Charlie Langmuir for helpfuldiscussions and support, and S. M. McLennan and C. R. Czernafor useful reviews. Mitch Lyle and John Compton are especiallyappreciated for making themselves available for an onslaught ofquestions. T. Plank gratefully acknowledges financial supportfrom USSAC and from a JOI/USSAC Graduate Fellowship.

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Date of initial receipt: 19 July 1990Date of acceptance: 16 August 1991Ms 123B-158

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