Rare earth element geochemistry of South Atlantic deep sea sediments: Ce anomaly change at ~54 My

0016703?/86/53.00

Geochrmrca a Cosmochimrca Acta Vol. 50, PP. 13374355 0 krgamon Journals Ltd. 1986. Rintcd I” U.S.A.

+ .oo

Rare earth element geochemistry of South Atlantic deep sea sediments: Ce anomaly change at -54 My Y. L. WANG*, Y.-G. LIU** and R. A. ScHMrTTt tDepartments of Chemistry and Geology and the Radiation Center and the College of Oceanography, Oregon State University, Cowallis, OR 9733 1. of Atomic (Received February

Abstract-The mainly on

of the from DSDP

of China 1985; accepted

revised,form March

(rare earth

in oceanic

1986)

is discussed,

530A and Leg 75, Hole 525A, 74. The mechanisms for of the into the carbonate phases adsorption, chiefly the carbonate and on Hf, and Fe-Mn hydroxide as carbonate The Ce of marine was used an indicator paleo-ocean water conditions: the water of Angola Basin in a condition in Cretaceous. At 54 My, South Atlantic condition became similar to present seawater condition. This was related the improvement circulation due to the widening of South Atlantic and the subsidence of water circulation barriers such as the Walvis Ridge and perhaps the Romanche Fracture Zone. The younger (Eocene-Recent) and older (Aibian-Santonian) argillaceous sedimentary rocks from 530A (denoted as YSAB and OSAB respectively) show different degrees of ELIdepletion with a transition period in between. The REE patterns of OSAB suggest a basaltic origin. The possible murces are Kaoko basalt in Southwest Africa or Namibia and the basaltic Walvis Ridge itself. The decrease in the area covered by Kaoko basalt due to erosion, the subsidence of the Walvis Ridge, and the improvement of water circulation led to changes in the Eu anomaly from Campanian to Paleocene, and resulted in the YSAB REE pattern. Changes in the Sm/Eu. La/Th, Th/Yb. Ti/A1203,FeO/A1203, and Hf/Al,O, ratios suggestchanges ofaverage source rock composition from andesite to granodiorite. The REE abundances and patterns of younger sediments in the Angola Basin (YSAB) are very similar to those observed in NASC, PAAS, and ES sediments. The YSAB REE abundances and patterns may represent the average REE distribution of the exposed African continental crust. The strong resemblance of REE distributions of YSAB. NASC, PAAS and ES suggeststhorough REE mixing from different sources and the uniformity of the average crustal compositions of different continents: Africa, North America, Australia. and Europe. I_ INTRODUCI’ION

THE ENTIREHISTORY of the Earth is linked dosely to the oceans and studies of oceanic sediments are fundamental to our understanding of oceans and also of the Earth’s evolutionary history. In modem marine geology, the main body of information on oceanic sediments comes from the Deep Sea Drilling Project (DSDP). Figure 1.shows the South Atlantic, the Walvis Ridge and the locations of DSDP Site 525, Leg 74, and Site 530, Leg 75, on which the discussions in the present paper are based. Site 525 at a depth of 2467 m was located near the crest of Walvis Ridge off Southwest Africa (29*04.24’S, 02”59.12’E). Site 530 at a depth of 4629 m is located in the southeastern comer of the Angola Basin, near the eastern end of the Walvis Ridge about 20 km north of the northern escarpment of the Walvis Ridge, (19’ 11.26’S, 9”23.15’E). The initial rift of the South American and African continents occurred somewhere along the Falkland Shear Zone in the early Cretaceous, probably in the Valanginian (- 125 to 130 My) (LARSONand LADD, 1973). The South Atlantic opened from south to the

* Preseni address: Department 3, Chengdu Geological College, Chengdu. Sichuan, People’s Republic of China.

north like a zipper as the tip of a mid-ocean ridge axis moved northward. It had arrived at the Rio Grande Rise-Walvis Ridge position by the Albian (105 My). By the Cenomanian (90-100 My) the tip of the axis had arrived at the equatorial Romanche Fracture Zone (BONATTI and CRANE, 1984). The two continental plates then drifted from each other along the Romanche Fracture Zone, and -20 My later the equatorial Atlantic began to open during the late Santonian (-78 My). Because of the proximity of Africa and South America to the Romanche Fracture Zone, the water connection between South and North Atlantic was considerably more restricted than at present. The sedimentary history in the South Atlantic has been reviewed by MCCOY and ZIMMERMAN (1977) and KENNETT (1982). During most of the Cretaceous, the newly opened basins of the South Atlantic were supplied with ocean water only from the south over the shallow Falkland Plateau, resulting in oxygen-deficient conditions and an absence of significant deep water circulation. Rue to the presence of the Rio Grande Rise-Walvis Ridge which restricted water circulation, this situation continued until the ConiacianSantonian in the Angola-Brazil Basins. The establishment of communication between the South and North Atlantic during the Late Cretaceous ended the stagnant bottom water condition. These paleo-South Atlantic

1337

‘r L, Wang. Y.-C. Liu and R. A. Schmnt

1338

i-

h

300 w

0”

FIG. 1. Site location and index chart of the South Atlantic. 525: DSDP Site 525. Leg 74. located near the crest of Walvis Ridge, 29YM.245, 0.2°59.12’JZ. 530: DSDP Site 530, Leg 75, located in the southeastern comerofthe AngolaBasin, 19”11.26’S. 9”23.152.

water redox condition

studies were based on a study of organic carbon in sediments. LIU and SCHMITT (1984) have discussed the REE pattern in carbonate sediments, and they used the Ce anomaly as a redox indicator to study the paleo-ocean water conditions over the Walk Ridge. They found that the water over the Walvis Ridge achieved oxidation conditions at about 54 My that are similar to the present seawater redox condition in the world oceans. HASKlNand PASTER (1979) and FL,EET ( 1984) have reviewed REE geochemistry in sedimentary and igneous rocks. The REE contents in North American Shale Composite (NASC) (HASKINet al., 1966; HASKIN and PASTER, 1979; GROMET et al., 1984) and postArchean Australian shale (PAAS) (NANCE and TAYLOR, 1976; TAYLOR, 1979; TAYLOR and MCLENNAN. 198 1b) have been suggested to represent the average crustal or upper crustal abundances. PIPER (1974) summarized the REE chemistry in the marine sedimentary cycle. In the present paper we address the following problems: the mechanisms for incorporation of REE into marine carbonate; the Ce anomaly in marine carbonate sediments and its use as a redox indicator for study of paleoocean water conditions; the REE patterns of noncarbonate sediments and their implied sources and their relationship to the evolution of the South Atlantic. These discussions are mainly based on the elemental

data of sediment samples from DSDP Holes 530A and

B. Leg 75, as well as Hole 525A, Leg 74. The initial report on Hole 525A has been published (LIU and SCHMITT, 1984) and has provided the foundation fix many discussions in the present paper. 2. EXPERIMENTAL 2 1 Sample preparation:

Samples were broken in an agate mortar, then dried m a freeze-drier for 24 hours. Samples were weighed and dried for another 24 hours, then weighed again, the two weights were consistent. The dried sediment samples, plus pulverized and powdered basement rock samples of - 500 mg, were weighed into polyethylene vials and heat-sealed for neutron activation analysis. -7.2 Acrrvatlon and counting A standard sequential neutron activation analysis (INAAI procedure (LAUL, 1979) was used. Activations were done in the I MW TRIGA reactor at the Radiation Center of Oregon State University. The counting system consisted of a Ge(Li) detector coupled with a ND600 analyzer (4096 channels). A 5 mm thick high purity Ge detector was used in an additional counting for obtaining better “‘Ce data. All data were computer-reduced. Sediment samples from 92 cores of 530A and B, Leg 75. were analyzed and the data are presented in Appendix I. Data for 525A. Leg 74. have been published by LIU and SCHM1l-r f 1984).

1339

Deep sea sediment REE geochemistry 3.

is -3

DI!XXJSBlON

X

106. Because

the K,,,for Fe(OH), is -IO-“.

all Fe”

will be present in SW as Fe(OH)t ‘molecules.

3. I The correlations of REE to other elements and

The K_ for Th(OH), is - 10-45z’. Therefore. the allowed Th in SW is IO-“/loo’* mol/L (-2 X IO-” &L). The observed Th in SW is -4 X IO-’ @L. so - 100% of Th in SW will he Th(OH)! molecules and the Th,Oba,/Th,d, ratio is -2 X IO’. Similarly. the K_ for Zr(OH), is -10-5’ and the allowed Zr m SW is -IO-“/IO-” mol/L f-9 X 10m" @g/L). The observed SW Zr of 3 X 10m” &L indicates that all Zr (and Hf) will he present as Zr(OH)i molecules and will coprecipitate with the Fe-Mn-oxides. The &, for HQOH), is 10-5’, similar to Zr(OH),. The I$, of .Sc(OH), is lOeM; the allowable SCis IO-N/IO ‘* mol/L (-5 X 10-‘~1g/L). while the observed SCis - I X IO&L. Therefore, the SC,& JSc(dcj is -20. Most of the SC m SW should he Sc(OH)t molecules and Sc should coprectpitate to some degree with the Fe-Mn-oxides. The &, for Ti(OH), is -IO-” so that the allowable Ti” in SW is - 10~5’/10~‘4 mol/L (-4 x IO-‘” &L). The oh served amount of Ti. - I rg/L. indicates that all Ti in SW exists as Ti(OH)t molecules and the Ti,h.,/Ti,cllc., ratio is -3 x IO”. Consequently. Ti is also expected in the hydrogenous phase. These observations are consistent with the calculations by TURNERet al. ( I98 I ).

the distribution of REE in carbonate oozes and limestones The abundances of the REE in deep sea carbonate oozes and limestones are given in Table IA. The REE abundances decrease with carbonate contents in the sedimentary sequence; e.g.. the REE in pure limestones (298% CaCOs) are about i/n times the concentrations observed in pure claystones. Negative linear relationships of REE with carbonate contents were also found (Table I B). Correlation coefficients were calculated for pairs of REE and relevant elements. For minimizing the residue detrital contamination, we selected IO pure limestones (CaCOJ 2 90%, 530A. sub-bottom depth: 504-639 m, Maestrichtian-late Paleocene, about 70-55 My) and 20 pure calcareous oozes (also CaCO,, 525A. sub-bottom depth: 34 15 m, late PaIeocene-Quatemary, about 55 My-recent). If it is assumed that all the Al203 measured is in fact due to residue detrital contaminations, and that this detrital material has REE/AlzOj ratios similar to those of argillaceous sediment and rock, the average contamination of detrital REE to the whole REE is calculated to be about 20?&(Table 2A). If we use the same assumption for FeO, the average FeO/A1z03 ratio in calcareous oozes and limestones is 0.40 and lower than observed in argillaceous sediments and rocks (FeO/AlrO, = 0.58); therefore all Fe in carbonate oozes and limestones is attributed to residual detrital material. This conclusion is based on the assumption that the A&O, is only “clay” related and that the Al203 content in the carbonate phase (hydrogenous AI(OHh -xH,O) is insignificant. Correlations between elements and A1203 (Table 2B) yield intercept values that are zero within or near 20 error for Fe, SC. V, Cr, Co. Ni. Zn, Rb. Cs. Hf. Ta. and Th. If we assume a simple two component model of “carbonate” and “clay” phases and that A&O) represents the “clay” phase. it seems evident that these elements are only “clay” related.

Considering

The K,,, for AI( is approximately IO-““. The allowed Al” in SW (seawater) should he - 10~“/10~‘* = IO-” mol/L (-3 X IO-’ *g/L). so essentially all the Al in SW is present as AI( molecules and the ratio of A\&A4,,

Table IA.

CaC03X

t5 5-50 50-80 80-90

l

I.

Sample location*

1

1

2 1 2

33

23 19 20

Holes 53OA and 530,

75 54 :: 38

31 26 19 LB 15

prior to diagenesis.

Leg 75; 2.

based on the

1.31 1.15 0.94 0.63 0.76

including

and rocks

Tb

Oy

Yb

Lu

0.89 0.74 0.59 0.47 0.52

5.6 4.6 3.5 3.2 3.1 1.8 2.1 1.5 1.5 0.7 1.2

2.9 2.2 2.1 1.5 1.6 0.87 1.08 0.78 0.76 0.48 0.61

0.38 0.30 0.31 0.20 0.25 0.13 0.15 0.12 0.10 0.09 0.09

Core 5251, Leg 74.

the prebutial

stage of

From comparisons of element/A1203 ratios

REE abundances of deep sea scdlmnts

6.0 5.0 4.0 3.3 3.6

solubilities

content

diagenesis.

Average REE abundances [pm) La Ce fld Sm Eu

26

the predicted

in seawater, the hydroxides listed above should coprecipitate quantitatively with Fe-Mn-oxides. Therefore. a plot of the (SC, Hf, Ta. etc.) rs. A1203 should yield an intercept of 0. However. the latest &,s for the REE(OH), indicate K&a(OH)j) = 10-.2’ and K,&Lu(OH)~) = IO-*‘. The &,s of the REE(OHh are not exceeded in SW and therefore no appreciable coprecipitation of REEs are expected with the Fe-Mnoxides. But the tiny carbonate organisms that drop through the SW to the sediment SW interface are coated with some Fe-Mn-oxides. At the interface. the organic skin will be disrupted and consumed by deep sea organisms. After the skin is gone. some Fe-Mnoxides (plus Al, Hf. Th. etc. hydroxides) are expected to precipitate from the SW. The REEs are then adsorbed onto the Fe-Mn-oxides. An appreciable fraction of Fe in carbonate is hydrogenous (SHAW and WASSERBURG. 1985: PALMER. 1985: TUREKIAN et al., 1973). We suggest that the Fe is derived from residue detrital materials and that Fe hydroxide is a halmyrolysate. i.e.. a product of submarine weathering. and formed as a result of reactions between Fe detrital materials and bottom seawater OH-

:REE

156 120 96 76 83 42 47 36 27 21 19

No. of Samoles

29 35 14 9 12 4 3 a 13

Y. L. Wang, Y.-G.

1340 Table 18.

The correlations

Liu and R. A. Schmitt

between REE and CaC03 and between REE and Al$j _._.~___

L.3

caco3

A'203

Ce

Nd

Sm

Eu

Tb

Dy

Yb

!.U

Correlation coeffictent

-0.76

-0.78

-Cl 71

-0.75

-0.74

-0.84

-0.75

-0.81

.O.tii

Intercept

32 ?I

71 ?2

32 ti

6.1 to.2

1.36 to.04

0.89 *o.oz

5.5 to.2

2.6 to.1

11.39 '0.05

Regression coefficient

-0.25 to.02

-0.62 '0.05

-0.26 20.02

-0.050 -0.012 -0.007 -0.042 -0.022 -0.030 to.004 *0.001 *0.005 to.004 to.002 to.003

Correlation coefficient

0.82

0.84

O.BZ

Intercept

Regression

coefficient

7.9 '1.5

11 i3

1.8 to.1

4.3 to.3

0.82

0.79

0.87

0.21 to.03

0.78

'4 '1.5

1.4 20.3

0.32 to.07

1.6 to.3

1.e ‘0.1

0.33 ?0.03

0.074 0.048 0.28 iO.006 *0.003 +o.oz

0.89

0.8:

0.68 to.09

0.11 '0.02

0.15 to.01

0.021 to.002

-__

-__-

than the La contents in living sea shells (0.13 ppm) in pure carbonate and in argillaceous sediment and rock (Table ZB), all or an appreciable amount of SC, and the corals of Recent and Pleistocene age (0.08 and 0.052 ppm) (SCHOFIELD and HASKIN, 1964). The avTi, Hf, and Ta are derived from detrital minor phases erage Nd and Sm concentrations in Table 2A are much and in halmyrolysates. larger than those reported in limestones by SHAW and From the discussion above, we contend that most WASSERBURG (1985) by a factor of 40-50. of the REE (about 80%) in pure carbonate ooze and We suggest that the total REE carbonate phases limestone are derived from seawater directly and about l/5 of the REE are derived from residue detrital ma- consist of REE in the CaCO> lattice per se + REE in the Fe-Mn-0 (Fe-Mn-oxyhydroxide coating) + REE terials which have undergone halmyrolysis with bottom adsorbed onto the CaC03 mineral surface. SHAW and seawater. WASSERBURG ( 1985) hypothesized that a major frac3.2 The mechanisms for incorporation of tion of the REE are present on the surfaces of shells REE into marine carbonate phase or tests. PALMER (1985) reported that the Fe-Mn-0 coating is responsible for about 90% of the REE obThe J_a contents of 5-10 ppm in pure carbonate oozes and limestones (Table 2A) are considerably larger served in recent coating + lattice samples. TUREKIAN lable 2A.

The REE and relevant element or oxide concentrations and element/A1203 ratios

Average

Sub-bottom depth (m) No. of samples CaC03(I)

::

(range). ppm

ooze

limestonr

3.2-415.3

504-639

20

10

97(94-99.5)

97(94-991

6.1(4.9-9.9)

8.5(3.8-15.1) 13(4.3-24) 7.0(4.3-10) 1.25(0.6-2.2) 0.27(0.16-0.48)

6.1(2.4-12.6)

Ti02

7.4(4.9-11.7) 1.33(0.86-1.93) 0.31(0.17-0.52) O.Zl(O.ll-0.37) 0.19(0.10-0.32) 1.4(0.8-2.0) 1.4(0.4-2.2) 0.71(0.44-0.99) 0.72(0.31-1.2) 0.09(0.06-0.14) 0.11(0.05-0.18) 0.49(0.28-l.OO)% 0.60(0.25-1.1)X 0.95(0.4-1.3)’ 0.04(0.02-O.lO)% 0.08(0.02-0.16)X

Fe0

0.21(0.09-0.45)X

SC Sr

1.01(0.67-1.94) 1.20(0.41-1.90) 1050(670-1350) 250(180-320) 300(230-2aop 0.13(0.05-0.23)% 0.13(0.050-0.30)X O.lO(O.OZ-0.16)’ 4.3(2.0-8.7) 4.4(2-11) 0.16(0.03-0.52) 0.13(0.05-0.36) 0.21(0.07-0.38) 0.046(0.016-0.16) 0.13(0.04-0.25) 0.42(0.10-0.70) 0.47(0.11-1.7)

Nd Sm :t: BY Vb :;24

1(20 Rb CS Hf Ta Th

11mestone

504439

IO 97(94-991 :: 12 2.1 0.45 0.32 2.3 1.2 0.18

lo-4

argili. sea. and rocks O-1120

bl 50 2.6 5.6 2.6 0.49 0.11 0.07 0.46 0.23 0.031

1300

920

4000

5800

2.0 470

1.5 20

2200

2300

7.3 0.27 0.35 0.22 0.78

9.5 0.42 0.34 0.12 0.73

from Ocrn rnd Parduhn 11984). 8 limestone srm~lcs. awragc (range] Hole 530A. Content: 95(93.4-97.7)X; sub-bottom depth: 516-641 a.

l Calculated

Of WI3

(<0.02-0.2i)’ 0.24(0.10-0.36)X 0.28(0.12-0.32)'

ElementfAl~3,

--

Deep sea sediment REE geochemistry Table 28.

(intercept)

TiO2 Fe0 t4n0 H90 cao Nap0 K20 Cl Br SC V CT CO Ni ;: Sr CS Ba La Ce Nd Sm EU Tb DY Vb LU Hf Ta Th CaC03

0.1310.05 0.7to.3 0.15*0.05 1.3'0.3 47*2 0.51?0.09 0.27*0.09 D.40t0.10

4*3 13tfl 27215 3*4 440+50 0.03?0.22 140*12D 7.9t1.5 11?3 7.451.5 1.4fO.3 D.32*0.07 0.21t0.03 1.6t0.3 D.68*0.09 D.ll*D.O2 0.3tO.2 0.22+D.D7 0.2t0.3 8453

The Correlation between Al203 (x) and elelnents 0')

(coefficient)

O.D54*D.OD4 D.47fD.03 -0.004+D.D04 0.12f0.02 -3.PeO.2 0.098~0.008 D.195+0.008 0.007~0.009 O.ltD.4 1.29f0.05 7.920.7 7.7+0.5 l.SkD.3 4.7tO.6 8.4?1.4 9.3*0.4 -16?4 D.44+0.02 4Dt11 1.8tD.l 4.3tD.3 1.BtO.l D.33eO.03 D.074tO.006 0.048~0.003 0.2Bt0.02 D.150t0.008 0.021t0.002 0.28~0.02 0.077'0.006 0.71kD.03 -5.8tD.3

(correlation)

0.82 0.86 -0.093 0.50 -0.90 0.79 0.93 0.08 0.03 0.95 0.78 0.87 0.49 0.66 0.48 0.94 -0.38 0.92 0.36 0.82 0.84 0.82 0.82 0.79 0.87

_.._

“-78

0.89 0.87 0.89 0.79 0.94 -0.90

1341

precipitated from bottom seawater and/or pore water prior to diagenesis and preburial stage of diagenesis. With exposure of the carbonate to SW within the top l-20 m having -3O-50% interstitial water the time exposure for REE to adsorb onto carbonate could be > 10 My. The better correlations between Ce and (SC, Ti, Fe, Hf, and Ta) than correlations between the other REE and (SC, Ti, Fe, Hf, and Ta) in carbonate oozes (Ap pendix 3) indicate that the Ce is more preferentially adsorbed or precipitated with these very insoluble hydroxides than are the other trivalent REE in an oxidizing environment. It also supports the suggestion and experimental study that Ce+3 in the ocean is oxidized to Cef4 and Ce+4 is precipitated as a colloidal hydroxide at a pH of 8 or more (GOLDBERG, 196 1). PALMER (1985) also found better correlation coefficients between Ce and Fe (r = 0.82) than those between the other REE (La, Nd, Sm, and Eu) and Fe (r = 0.6-0.7) although he did not discuss this correlation. The observation that Ce exhibits similar strong or good correlations with (SC, Hf, and Ta) in 530A limestone suggests that Ce, like the other REE+3, is present as Ce+3 in reducing seawater.

3.3 Reducing conditions of paleo-South et al. ( 1973) analyzed REE and other elements in living Atlantic Ocean water pteropod tests from the South Atlantic Ocean and the Gulf of Agaba. The La contents ranged from under The Ce anomaly in marine carbonate provides a detection limit (0.05 ppm) to 6.1 ppm. They found a new indicator for the study of paleo-ocean bottom wastrong positive correlation between the REE and the ter redox conditions as well as do organic carbon, Fe Fe concentrations and proposed that REE resided in and Mn. However, some REE distributions in carbonsub-microscopic Fe-hydroxide or hydrous Fe-phosates may be consistent with the remobilization of the phate floes which were incorporated into the tests as REE during recrystallization. If the major addition of they grew. PALMER(1985) also found relatively high the REE is trapped during diagenesis, mobilized during recrystallization, and derived from non-seawater correlation coefficients between the non-detrital REE sources, then any record of seawater REE, especially and Fe concentrations which supported the REE-rich Fe-hydroxide mechanism. However, the REE concenCe anomalies, may be obscured. trations in the coating are higher than reported for other The Sr concentrations in calcareous oozes (525A, Fe-Mn-rich deposits. sub-bottom depth: 3.2-4 15 m) are much higher than Sample l-3, Hole 525A, DSDP Leg 74 will suffice they are in limestones (530A, sub-bottom depth: 504as an example. According to the composition of met639 m) by a factor of about 4 (Table 2A). This indicates alliferous sediments reported by DYMONDet al. ( 1976), that Sr in the aragonite structure is mobilized during the average contents of La and Mn of DSDP Site 3 19 recrystallization to calcite. In contrast with Sr, the REE are 180 ppm and 5.8%, respectively. If the Fe-Mn-oxide concentrations in the youngest ooze sample (sub-botin sediments is metalliferous-like, the 166 ppm Mn in tom depth: 3.2 m) and the oldest limestone sample sample l-3 indicates that the La in the Fe-Mn-oxide (sub-bottom depth: 639 m) are roughly the same. The average concentrations in 20 calcareous oozes (subfraction should be 0.5 ppm. Compared with 4.9 ppm La in this sample, the contribution of Fe-Mn-oxide is bottom depth: 504-630 m) are the same with exception of Ce (Table 2A). Also, the average REE patterns of relatively small. HASKIN et al. (1966) found that Eu+~ can be re- carbonate oozes (Quatemary-late Paleocene, Hole moved from solution by CaCOs precipitation, and that 525A) and of limestones (late Paleocene-Maestrichtian, the radioactive Eu on CaCOJ can be replaced by Eu+~ Hole 530A) are quite similar except for the anomalous in solution. SHANBHACand MORSE (1982) have de- behavior of Ce attributed to redox condition. Appartermined the distribution coefficient of 24’Am+3 beently no appreciable REE loss occurred during diatween calcite and seawater and found it to be 22 X 105. genesis of aragonite to calcite as opposed to Sr. The insoluble REE-rich minor phases in carbonate might It is expected that lanthanides as analogs for the actinbe represented by either the REE-rich Sc, Hf, and Ta ides (Nd+3 is the closest analog to Am+3) have similarly oxyhydroxides or REE adsorbed onto Ti-Fe oxyhyhigh distribution coefficients. We suggest that a fraction droxides or phosphates floes which were incorporated of the REE are adsorbed onto carbonate mineral surinto biogenous and hydrogenous carbonate. faces and are adsorbed onto Fe-Mn floes which were

1342

1'.1. Wang,

Y.-C;.Liu and R. A. Schmitt

These observations indicate that the REE are derived directiy from bottom seawater or indirectly from pore water which is near the seawater-sediment interface and interconnected with bottom seawater. It may, in such a case, be possible to use the Ce anomalies in the carbonate phase to determine the paleo-ocean bottom seawater redox conditions. If seawater is in a reducing state, al1 Ce will be trivalent and will follow other trivalent Ianthanides, resulting in a normal REE pattern in the carbonate phase. If seawater is in an oxidizing condition, Ce will be depleted in seawater, resulting tn a Cedepleted REE pattern in carbonate. Consequently. the REE pattern in biogenic carbonate is an impo~a~t redox indicator of bottom seawater. (See Appendix 2 for a discussion of the Ce oxidation in seawater.) The REE patterns of DSDP 525A carbonate samples from the late Paleocene to Eocene (LIU and SCHMITT. 1984) exhibited a progressive Ce depletion indicating that the bottom seawater redox conditions were changing from reducing to oxidizing during the interval from 60 to 54 My. The progressive Ce anomaly in carbonate revealed that the bottom seawater was anoxic over the W&is Ridge during the late Campanian (before 65 My) and supports the idea that the higher standing Walvis Ridge and the Sao Paula-Rio Grande Rise complex obstructions were the major factors for maintaining stagnant and anoxic bottom seawater in the Angola-Brazil Basins (MCCOY and ZIMMERMAK, 1977). The increasing Ce depletion suggests that as the gap between South America and West Africa widened and the Walvis Ridge subsided during the late Campanian to late Paleocene (65-54 My), the bottom seawater circulation of the South Atlantic improved. The similar Ce depletion in carbonate oozes from the end of the Paleocene to the beginning of the Eocene suggests that the oxidation condition of the bottom seawater over the Walvis Ridge was achieved at about 54 My and is similar to present seawater redox conditions in the world oceans. During the present study four relatively pure carbonate samples of DSDP 530A. between the early Eocene and middle Paleocene, were available to obtain the REE patterns in CaCO3: #38- 1(chalk, 86% CaCO,). #40-4C (limestone, 95% CaCO,), #42-I (limestone. 98% CaCO,), and #46-I (limestone, 95% CaCO& Two relatively pure mudstone samples, #40-2 and #41-l. were obtained from the late Paleocene section near the boundary of the Paleocene-Eocene. We assume that their average REE abundances are an approximation for the non-carbonate fraction in samples of the middle Paleocene to the early Eocene times. By subtracting the contributions of the non-carbonate fraction calculated from the average REE abundances in pure mudstone samples #IO-2 and #4 I- 1, the net REE abundances in the carbonate phase of samples 38- 1. 40-4C, 42-1, and 46-l were obtained. Their Cl chondrite (ANDERS and EB~HARA,1982) normalized REE patterns are shown in Fig. 2. The REE pattern of sample 7- 1 of 530B, late Pleistocene-Holocene, corrected with the average REE contents in Hole 530.A mud sample 6-3 of Pliocene time, is also shown. Due to the

FIG. 2. Chondrite normalized REE patterns of pure carbonate ooze and limestone samples, 530A and B, showing the Ce anomaly changes.

higher non-carbonate content in sample 7-I. rhe errors introduced in subtraction result in somewhat more scattered data for the heavy REE. Samples 46-l (-60 My) and 42-1 t--56 Myj shou the normal REE patterns with no significam Ce depletions. Samples 40-4C (-56 My) and 38” I (h-50 My) exhibit Ce-depicted REE patterns. The REE pattern of sample 7-1 (- 1 My) is similar to the more recent carbonate ooze sample 525A-1-3. These comparative patterns indicate that the change of paleo-bottom seawater redox conditions in the southeastem comer of the AngoIa Basin is consistent with that over the Walvis Ridge, i.e., the bottom seawater of the Angola Basin was anoxic before 56 My, then changed from reducing to oxidizing during the early Eocene (- 54 My) and maintained the oxidizing state until the present time. The history of sediments and water circulation in the South Atlantic Ocean and world oceans reviewed by MCCOY and ZIMMERMAN( 1977) and KENNET?. ( 1982), and the assessments of the paleo-South Atlantic redox conditions based on organic carbon, Mn. and color variation studies in sediment (e.g., BOW et ui.. 1978; RYAN el al., 1978; NATLUND, 1978; BORELLA, 1984: MAILLOT and ROBERT, 1984) can be summarized in the following scenario. The cessation of euxinic conditions in the Angola Basin occurred during the Santonian (-78 My). At this time, the water connection between the North and South Atlantic bad been

Deep sea sediment REE geochemistry established through a shallow equatorial Atlantic passage. The bottom seawater reducing condition with reference to organic carbon ceased, but it was still reducing with reference to Ce redox conditions as indicated by the normal REE pattern in carbonate of Hole 530A in the Angola Basin at that time. The water supply to the Angola Basin was accomplished by transfer of surface water from both the north and south. During the Paleocene and Eocene (65-54 My) the equatorial area widened and deepened, allowing deepwater exchange between the North and South Atlantic. Also deep water circulation developed between the Angola Basin and Cape Basin. The South Atlantic became an integral part of the world ocean (KENNETT, 1982). This is reflected by the change from normal to &depleted REE pattern in carbonate at both the 525A on the Walvis Ridge and 530A in the Angola Basin (Fig. 3). In the North Atlantic, the oxygen deficiency reached a maximum between late Albian and Cenomanian (95 90 My). Then it returned to a continuous oxygenated condition in deep water throu~out most of the North Atlantic (KJZNNETT,1982). The establishment of a water connection in the late Cretaceous and widening of the Norwegian and Greenland Sea in the early Cenozoic further improved the water circulation. We suggest that a Ce anomaly change may also be observed in the North Atlantic carbonate sediments during this period. 3.4 REE patterns in non-carbonate phases The abundances of REE in deep sea argillaceous sediments and rocks are given in Table 1A. The average REE concentrations in pure argillaceous ooze, mud,

x----_~

Corbonotc OoIc(15sompksHole525A) Quotemary-Lots

0-

-0

FWeocene

Limestone (7 samples Mote LateF4llcocene-Moertrichtion

530A)

2-

t

t I LO cm

t Nd

1 I Sm Eu

I

I

‘ ,

Tb

Dy

Yb tu

FIG. 3. The average REE patterns of ear&mate ooze and limestone, Sites 525 and 530.

1343

mudstone. and claystone (CaC03 2: 5%) are almost equal to the intercept values of the REE-CaC03 regression lines (Table 1B) and, as will be discussed later. are about the same as the values reported for the crust. The REE correlate well with A1203 (r = 0.8-0.9) (Table 1B). The correlations between the REE (La as an example) and other elements are shown in Table 3. We note the excellent correlations (r = 0.8-0.9) between the REE and the terrigenous lithophile trace elements some of which are LIL (large ion lithophile): K, Rb, SC, Hf, Ta, and Th. Also, the REE are well correlated with most of other elements, such as Ti, V. Cr. Fe, Cs (r = 0.7-O.S), Na, Mg, Ni (r = 0.5-0.7). Only a few elements (Mn, Cl, Br, and U) have very poor correlations with the REE. The REE in deep sea sediments have two types of genesis: terrigenous and hydrogenous. The hydrogenesis of REE in marine carbonate sediments and carbonate sedimentary rocks does not reflect the composition of source rocks in any simple manner. Compared to carbonate rocks, the REE in pure argillaceous sediments and rocks (CaC03 - 5%) are terrigenous and preserve a record of the source rock composition. The average REE pattern in argillaceous sediments and sedimentary rocks probably reflects the REE distribution in the exposed continental crust (TAYLOR, 1964. 1977, 1979; NANCE and TAYLOR, 1976: MCLENNAN et al., 1979; TAYLORand MCLENNAN, 198 1a: HASKIN and HASKIN, 1966; HASKIN et al., 1966: HASKIN and PASTER, 1979; GROMET et al.. 1984). The REE patterns in some low CaC03 sediments of different types and age are presented in Fig. 4. Sm/Eu ratios, accurate measures of the degree of depletion. are plotted against age and are shown in Fig. 5. From the Albian to Santonian, the Sm/Eu ratios are basically constant (4.1 ~fr0.4), then the ratio increases gradually from the Campanian to Paleocene. From the Eocene to Recent the Sm/Eu ratio remains constant (5.2 + 0.6) and higher than that observed during the Albian-Santonian period. We will discuss these three periods separately. It can be seen from Fig. 4 that the REE patterns for the argillaceous ooze and mud samples from the Eocene to present (O-54 My), for example sample 221 (mud, - 14 My) and sample 6-3 (ooze, -4 My), are basically identical and the customary Eu depletion is observed. The average Eu/Eu* is equat to 0.70 for 14 ooze and mud samples of Eocene to Recent times, which is consistent with that of the NASC (HASKIN and HASKIN. 1966) composites listed in Table 4. We suggest that the average REE pattern and concentrations in the younger sediments of the Angola Basin (Eocene-Recent (0.5 My)) reflect the REE distribution of the exposed continental crust of western Africa along the Angola Basin. The YSAB have consistent REE patterns and absolute abundances which are very similar to other shales, especially to the North American Shale Composite (NASC) (Table 4). TAYLOR and MCLENNAN ( 198 la) calculated that the average fine grained sedimentary rock ove~timated the REE abundances by about 20%. Therefore. the REE abun-

1’ IL.Wang, \i.-G. Liu and R. A. Schmitt

1344 Table

3.

Element

Ti02 A' 0, Fe?i MnO @JO CaO N 0 K CP Br SC

V Cico Ni 2n Rb Sr CS Ba Ce Nd Sm :: DY Yb LU Zr Hf Ta Th u CaC03

The correlations

between

La and elements

Regression coefficient b

Intercept a 0.07*0.06 0.2?0.8 0.6t0.5 0.08*0.05 1.0+0.3 4813 0.6kO.l 0.2kO.2 0.5to.1 16~5 0.4+1.0 13*10 llt8 1?4 1028 -17klB -3+8 45OC60 -0.1+0.4 0'140 -5*2 2ti 0.220.2 0.05~0.05 0.08kO.03 0.720.2 0.34-+0.09 0.08+0.10 5t9 o.oio.3 0.04*0.08 -0.420.5 l.kO.4 85+6

Sample

Correlation coefficient I-

0.023'0.002 0.83+0.03 0.19t0.03 0.001t0.002 0.06*0.01 -1.350.1 0.03610.005 0.080~0.006 0.001f0.004

0.75 0.82 0.73 0.068 0.52 -0.76 0.63 0.82 0.016

-O.OZ+O.lB 0.53+0.04 3.3to.4 2.9+0.3 0.67kO.13 1.9*0.3 2.9t0.7 3.Bf0.3 -7+2 0.18tO.02 21'5 2.3r0.1 0.92r0.05 0.18t0.01 0.040+0.002 0.024t0.001 0.15+0.01 0.072t0.003 0.009+0.001 4.7eo.3 0.12*0.01 0.037'0.003 0.30t0.02 0.02*0.02 -2.320.2

-0.011 0.85 0.70 0.72 0.48 0.59 0.43 0.83 -0.34 0.79 0.41 0.97 0.91 0.94 0.92 0.92 0.87 0.92 0.83 0.83 0.81 0.82 0.85 0.15 -0.76

dances in the Eocene to Recent exposed African crust (Table 4) are estimated to be 20% lower than the YSAB to account for low REE-bearing rocks which contain more carbonate such as marlstone and limestone. It is shown in Fig. 4 that the REE patterns of Claystone from late Albian to Santonian (103-78 My) are also identical but exhibit only an insignificant Eu depletion. The average Sm/Eu ratio for 2 1 late AlbianSantonian samples is 4.1 + 0.4. It is clear that this value is statistically lower and originates from a different population compared to the 5.2 + 0.6 average ratio for 25 younger ooze and mud samples (O-5 My). An important observation is the remarkable consistency of the REE abundances of elastic sedimentary rocks of post-Archaen age (e.g., TAYLOR. 1979: TAYLOR and MCLENNAN, 1981b). HASIUN er ul. ( 1966) concluded that the relative REE abundances are the same at least within 15% for separate, large areas of the continental crust. SHIMOKAWAet al. ( 1972) analyzed 9 sediment samples from the Pacific Ocean and found that the gross features of the REE patterns were similar to those of the NASC. The ocean ooze and clay (WILDEMAN and HASKIN, 1965), Pacific Ocean clal (SHIMOKAWAet al., 1972) and Australian post-Archean sedimentary rocks (NANCE and TAYLOR. 1976) all

m

Llfhology mud

6-3

O-

-0

X-.-X

mudstone

40-2 -0

o-

ooze mud

22-l

57-I

mudstooe

A.--...A 104-3

cloystone

+-+

cloyslone

87-f

100 -

a, C

_

sot% -

$

c 2

LOcn IO -

5’

’

Lo

’

ce

I

Nd

1

Sm

I

Eu

I

I

fb Dy

1

,

Yb iu

FIG.4. Chondrite normalized REE patterns for 530 argillrc rocks with CaC03 < 5%.

Sm/Cu

show customary negative Eu anomalies. DYPVIK and BRUNFELT( 1976) and FLEETet al. ( 1976) pointed out

that localized input of volcanic material often results in clays having distinct REE contents. The fact that the composition of late Albian-Santonian claystones differs from the YSAB, PAAS. NASC, and ES compositions suggests that the REE pattern in the late Albian-Santonian claystones does

1234567

Sm/Eu

FIG. 5. The Sm/Eu ratios and the degree of tu depletwtr wrsus the geologic age of 530 sediments.

1345

Deep sea sediment REE geochemistry Table 4.

REE abundances

(in ppm) I" sedlnents

and sedimentary

rocks

REE I”

YSAB

L C:

(1) 77 34

OSAB (2) 76 33

NASC (3) 32

PAAS (4) 80 38

Nd sn Eu Tb

33 6.1 1.26 0.90

32 6.6 I.6 0.92

:: 5.7 1.24 0.85

:T6 1.1 0.77

40 7.3 1.52 1.05

26 4.9 1.01 0.72

% L" ZREE Eu/Eu'(a) LaN/YbN(b)

6.0 3.1 0.44 162 0.70 7.4

2.9 5.3 0.43 159 0.86 1.7

3.1 5.8 0.48 175 0.70 7.0

2.8 4.4 0.43 183 0.66 9.2

--3.3 0.58 204 0.70 8.4

2.5 4.5 0.35 129 0.70 7.4

(1)

(a) (b)

ES (5) B:

African upper crat (6) 62 27

Younger sediments in the Angola Basin (Eocene-Recent. CaCo3<5Z. Hole 530A. Leg 75, 14 samples, this wrk. Older sedimentary rocks in the Angola Basin (Albian-Santonlan), CaCos (52, Hole 530A. Lee 75. 8 samoles. this wrk. North; American shale composite (Haskin and Paster, 1979). Post-Archean Australian shale (Nance and Taylor, 1976). European Paleozoic shale canoosite (Haskin and Haskin. 19661. Calculated REE abundances in‘the African exposed uppe; crusi, taken to be 20% lower than YSAB to accwnt for low-REE beanng rocks such as limestone and marlstone. Eu* is the extrapolated Eu abundance between the Sm and Gd values for no chondrite-normalized Eu anomaly. N refers to chondrite-nommlized value.

not reflect the REE distribution in the vast western Africa exposed continental crust. The REE pattern with an insignificant Eu anomaly suggests a basaltic or average andesitic origin. One possible source is the 114136 My Kaoko basalts of the immense Etendeka Plateau in the present day country of Southwest Africa or Namibia (SIEDNER and MILLER, 1968). The Etendeka Plateau may have extended well up to 16’S and perhaps beyond 14”E. HUGHES et al. (1983) determined the composition of 2 1 Brazilian Serra Geral (Parana Basin) basaltic lavas, which may be considered to be related in timespace eruption to the Kaoko basalts, and found an average Sm/Eu ratio of 3.2 + 0.3. If we assume that the average Sm/Eu ratio of 4.1 in the late Albian-Santonian claystones is derived by erosion of two sources, Kaoko basalt and average upper crust with a YSAB composition (which has an average Sm/Eu ratio of 5.2) then the contributions for the terrigenous components of claystones are the erosional products of -55% Kaoko basalt and -4.5% sediment. Another possible source is the basaltic Walvis Ridge. All samples from the Campanian to Paleocene do not show a substantial Eu depletion, but mudstone samples of 530A during this period do show an Eu depletion (Fig. 6). Apparently, the sources ofthese 525A samples were not African continental rocks and, therefore, the non-carbonate fraction in these samples may have been derived from erosion of the basaltic Walvis Ridge itself. Volcanogenic smectite dominates the late Cretaceous at site 525, indicating the proximity of strongly weathered. eroded subaerial basalts. Subsidence led to the disappearance of subaerial volcanic rocks during the late Paleocene (CHAMLEYet al., 1984). This is parallel to the Eu anomaly changing in sediments. By analogy, the erosion of basaltic rock on the Walvis Ridge nearby might also have influenced the REE pattern of Site 530 sediments. 3.5 REE and Th in deep sea sediments and sedimentary rocks The La/Th and Th/Yb ratios of argillaceous sediments and sedimentary rocks also support the hypoth-

esis of a source change for the deep sea sediments from local (78-103 My) to a wider area (O-54 My) as revealed in 530A and B cores in the Angola Basin. The correlation coefficient between La and Th is good (r = 0.85) and the data include samples covering an age range of 103 My to present. Most of the argillaceous sediments and sedimentary rocks of widely varying ages from Australia and Greenland fall between La/Th = 2 and 4 (NANCE and TAYLOR, 1976, 1977; MCGREGOR and MASON, 1977: BAVINTONand TAYLOR, 1980). Most of the carbonate ooze, marlstone and limestone (CaC03 < 50%) have ratios which fall between 5 and 50. In general, the La/Th ratio increases with increasing carbonate contents in sediments. We attribute this increase to a larger partition coefficient of La for the CaC03 phases. On closer inspection of “pure” argillaceous sediments and rocks (CaC03 < 5%) in the time span of 103 My, the La/Th ratios for the younger argillaceous oozes and muds from the Eocene to the present are essentially constant. The average La/Th ratio for 13 samples is 2.7 +- 0.1 which is equal to the average postArchean La/Th ratio of 2.7 (MCLENNANef al., 1980). He notes that the La/Th ratio of YSAB, like PAAS, is similar to that of relatively felsic igneous rocks (Table 5). The Th/Yb ratios for the YSAB (O-54 My) are also essentially constant. The average Th/Yb ratio of 13 YSAB samples is 4.1 + 0.5. The post-Archean samples cluster around Th/Yb = 4.5-5.5 (MCLENNAN et al.. 1980). The fact that the La/Th and Th/Yb ratios of YSAB are equal or similar to that of PAAS confirms

Samplr

Lilhology

Pol0OCene

chalk

79%

Moeslr~cht

chalk

57%

Moestnchtlon

51-5

l~meslone

51%

Componlon

53-l

mudstone

100%

C0lllpolWn

36-3

chalk

w

44-4

A---d

48-I * -0

tcl-

carObaatr 16%

+---•+

IO”

IOO-

50-

0) .z g

-

20-

Y 0 e

IO-

x

5-

La

Ca

Nd

Sm

Eu

rb Or

Yb Lu

FIG. 6. Chondrite normalized REE patterns for argillic recks of 525A core.

\I’.L. Wang. Y.-G. Liu and R. A. Schmitt

1346 Table 5.

The distributions of soa? elements in Sedmenfary igneous rocks'

_-~_Sample

Llthology

OSAB YSAB PAAS PCC-1 Bat-1 U-l AGV-1 GSP-1 G-2

Claystone Mud ooze. mud Shale Perldotitr Basalt Diabase Andes~te

l

La iK

and

7h %

& A'203

feO A'203

Zr A'@3

2.Y 4: 5.8 0.4 1.r ;.I 3.2 42 27

0.085 0.051 -0.025 0.16 0.063 0.039 0.031 0.035

0.71 0.45 __ 11.9 0.90 0.70 0.35 0.28 0.14

16.8 11.8 _. 11.7 12.5 6.8 11.2 36 17.9

4.0 2.7 27 ii 7.0 70 5.7 1.9 23

Data SOUI-ces: Abbey (1973). Flanagan (1976). McLennan St.

Hf i;Tza3 0.41 0.26 0:; 0.35 0.18 0.32 1.08 0.44 (lw:

From De.% and Parduhn (19SS) data for the respecttve 33 ud (CaCCQ <5X) YSAB sanples and 64 claystones KaCO3 <5X) OSA8 saqles, *e ca‘lcirlate: TiDp'Al203 0.095 and 0.053; FeO,'Al& 0.64 and 0.46; &/A1203 14.8 and 9.7.

again that the REE and Th distributions reelect the REE and Th distributions in the exposed continental crust of western Africa and support the suggestion of a granodiorite present day upper continen~i crust (MCLENNAN et al., 1980). There were also no significant changes in La/Th ratios and Th/Yb ratios in late Albian-Santonian claystones (78-103 My). but these older claystones appear to have higher La/Th ratios (4.9 ? 0.2) and lower Th/Yb ratios (2.9 + 0.3) than the younger sediments. The La/Th and ThjYb ratios are similar to that of andesite (Table 5). suggesting a more mafic source. 3.6 Ti, Fe, and Hf in deep sea sediment.s Changes of the (FeO, Ti, Hf)/A1z03 ratios are similar to the changes in Sm/Eu ratios. There are no significant changes of FeG/A1203, TifAllOj and Hf/A& ratios in deep sea sediments and sedimentary rocks from early Eocene to the present (O-54 My). There are also no significant ratio changes in the late Albian to Santonian claystones. The average ratios of older sampfes (OSAB) are higher than younger samples (YSAB) as shown in Table 5. The above fact confirms again that for the Angola Basin Site 530 (only about 300 km west of the present African coast) the dominant terrigenous sedtment source (78-103 My) has been the local African continental exposed crust, which had an average andesitic com~sition, or a mixture of half basalt and half YSAB composition. From 54 My onward. the FeO/Ai203 ratio etc. of the deep sea sediments and sedimentary rocks represent the distributions of these elements in the exposed crust which differ from those of the older ones (OSAB).

(78- 103 My) to granodiorite after the Paleocene (54 My-Recent). The simultaneous volcanism of Kaoko basalt tn Southwest Africa or Namibia and Parana basalt tn Brazil has been interpreted as being functionally related to the separation of Africa and South America in the final breakup ofGandwanaland (SIEDNER and MILL~K. 1968). During the early stage of sedimentary histon at Site 530, it is expected that the weathering Qroducis from the southwestern African continent, which was largely covered by Kaoko basalt during that period, would be a major source of terrigenous sediments. Also. the weathering products from the basaltic Walvis Ridge could be transported down the northern slope to thr Site 530 by turbidity currents. The sediments exhibit the characteristics of ma& source rocks. As the area covered by Kaoko basalt decreased due to erosion and the Walvis Ridge subsided, the input of mahc weathering products decreased and the input of felsic products increased due to the increasing exposed granite area on the African continent (SEIDNER and MILLER. 1968): i.e., the sediments were dominated by felsir weathering products. Another factor which influenced the sedimentation process is the ocean water circulation. By the Santonian (-78 My) the Angola Basin was in an euxinic condition, which is reflected in the sediment characteristics. As the gap between South America and West Africa widened and the WaIvis Ridge subsided, water circulation in the Angola Basin improved progressively, leading to more homogeneous sedimentation. At this stage the sediments would reflect the source rock characteristics which covered a much larger area, CONCLUSIONS

The sedimentary history is closely linked to the evolution of the South Atlantic Ocean. The change of the Eu anomaly in REE patterns and the changes of the La/Th, Th/Yb, FeOfA1203. Ti/A1203, and Hf/AIzO; ratios all suggest a source change from mafic to a more felsic character, i.e., from an average source composition similar to andesite during the Albian-Santonian

I. Ce correlates better with SC, Ti, Fe. Ht, and ‘I a than other REE in carbonate oozes, suggesting that the Ce+4 is more preferentially coprecipitated with SC. Ti. Hf, Ta, and Fe oxyhydroxides than the other REE in an oxidizing condition. 2. The REE are adsorbed mainly onto carbonate mineral surface and onto rich Fe-Mn Bocs coating carbonate ooze and limestone. 3. The Ce anomaly of the REE pattern m carbonate

Deep sea sediment REE geochemistry

sediments can be used as a bottom seawater redox indicator. The change from normal to Ce-depleted REE patterns found at both Site 525A on the Walvis Ridge and Site 530A in the Angola Basin around 54 My refleets the change of bottom seawater redox condition from reducing in the Cretaceous to oxidizing during early Eocene which is close to the modem seawater redox condition. 4. The REE pattern ofthe OSAB and YSAB suggests a basaltic and aranodioritic origin. resoectivelv. The possible sources of the OSAB were erosion of the Kaoko basalt in South Africa and the basaltic Walvis Ridge. The changes of the Eu anomaly and the ratios (Sm/ Eu, La/Th, Th/Yb, Ti/A120,, FeO/A1203, and Hf/ Al*O,) suggest a change in the average source rock composition from andesite to granodiorite during the Campanian to Paleocene (78-54 My). 5. The REE abundances and patterns of YSAB very likely represent the average REE distribution of the exposed African continental crust. The strong resemblance of REE distributions of the YSAB, NASC, PAAS, and ES suggests the thoroughness of REE mixing from different sources and the uniformity of the average comoosition of different continents: North America, Australia, and Europe. Acknowledgements-This

work was supported by the Radiation Center, Oregon State University, Dr. C. H. Wang, Director. During this study, two of the authors, Wang and Liu, were supported by the Ministry of Education of China and their institutions, Chengdu Geological College and the Institute of Atomic Energy. China, respectively. We wish to thank S. S. Hughes for valuable help and discussion. We also acknowledge the assistance of T. V. Anderson and W. T. Carpenter in the neutron activations. Very helpful comments by S. R. Taylor, S. M. McLennan, T. R. Wildeman and an anonymous reviewer improved the manuscript considerably.

Editorial handling: S. R. Taylor

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BOLLIH. M., RYANW. B. F. and Shipboard Scientific Party (1978) Angola continental margin-Sites 364-365. Init. Repts. DSDP 40, 357-390.

BONATTIE. and CRANE K. (1984) Oceanic fracture zones. Scienlific American 250, 36-47.

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1341

DEAN W. E. and PARDUHNN. L. (1984) Inorganic geochem-

istry of sediments and rocks recovered from the southern Angola Basin and adjacent Walvis Ridge. Site 530 and 532, Deep Sea Drilling Project Leg 75. Inif. Repfs. DSDP 75, 93X95R DEBAARH. J. W., BACONM. P.. BREWERP. G. and BRULAND K. W. (1985) Rare earth elements in the Pacific and Atlantic

Oceans. Geochim. Cosmochim. Acta 49. 1943-1959. DYMONDJ., CORLISSJ. B. and STILLINGERR. (1976) Chemical composition and metal accumulation rates of metalliferous sediments from Sites 3 19. 320. and 32 1. Init. Reors. DSDP 34.575-588.

DYPVIKH. and BRUNFELTA. 0. (1976) Rare-earth elements in lower Paleozoic epicontinental and eugeosynclinal sediments from the Oslo and Tronheim regions. Sedimenlolug) 23, 363-378.

FLANAGANF. J. (1976) Descripticns and analyses of eight new USGS rock standards. U.S. Geol. Sure. Prc$ Pap. 840. FLEET A. J. (1984) Aqueous and sedimentary geochimistry of the rare earth elements. In Rare Earth Elemenf Geochimislry. Developments in Geochemistry 2. (ed. P. HENDERSON),pp. 343-373. Elsevier. FTLEET A. J., HENDERSONP. and KEMPED. R. C. ( 1976) The rare earth element and related chemistry of some drilled southern Indian Ocean basalts and Volcanogenic sediments. J. Geophys. Res. 81, 4257-4268. GOLDBERGE. D. ( I96 1) Chemistry in the oceans. In Oceanography. American Association,for the Advancement q/Sriences. pp. 583-597. Washington, D.C.

GOLDBERGE. D.. KOIDE M., SCHMITTR. A. and SMITH R. H. (1963) Rare-earth distributions in the marine environment. J. Geophys. Res. 68,4209-42 17. GROMETL. P., DYMEK R. F., HASKINL. A. and KOROTEV R. L. (1984) The “North American Shale Composite”: Its compilation, major and trace element characteristics. Geochim. Cosmochim. Acta 48. 2469-2482.

HASKINM. A. and HASKINL. A. (1966) Rare earths in European shales: a redetermination. Science 154, 507-509. HASKIN L. A. and PASTERT. P. (1979) Geochemistry and mineralogy of the rare earths. In Handbook on Physics and Chemistry of Rare Earths (eds. K. A. GSCHNEIDER,JR. and L. EYRING) Vol. 3, Chap. 21, pp. I-80. North-Holland Publishing Comoanv. HASKIN L.-A., WILD~MAN T. R.. FREY F. A., COLLINS K. A., KEEDY C. R. and HASKINM. A. (1966) Rare earths in sediments. J. Geophys. Res. 71, 6091-6105. HOCDAHL0. T.. MELSONS. and BOWENV. (1968) Neutron activation analysis of lanthanide elements in seawater. Adv. Chem. Ser. 73, 308-325.

HUGHESS. S.. WANG Y. L.. SCHMITTR. A.. FODOR R. V., CORW~NC. and ROISENBERG A. ( 1983) Parana Basin lavas: chemical and petrographic characteristics. Lunar Planef. Sci. XII’, 337-338. KENNEL J. ( 1982) Paleoceanographic and sediment history of the ocean basins. In Marine Geology, Chap. 18, pp. 652695. Prentice Hall.

LARSONR. L. and LADDJ. W. (1973) Evidence for the opening of the South Atlantic in the Early Cretaceous. Nufure 246, 209-2 12. LAUL J. C. (1979) Neutron activation analysis of geological materials. Atomic Energy Rev. 17, 603-695. LIU Y.-G. ( 1982) Chemical element profiles by instrumental neutron activation analysis in: I. Two species of wheat bunt spores. Tilletia caries (DC.) Tul. and Tilletia controversa Kuhn: and 2. Representative sediment and basalt samples taken from a DSDP 678 m core, Site 525A. Leg 74, Walvis Ridge. M.Sc. thesis. Oregon State University. LIU Y.-G. and SCHMITTR. A. (1984) Chemical profiles in sediment and basalt samples from Deep Sea Drilling Project Leg 74. Hole 525A, Walvis Ridge. Inil. Reprs. DSDP 74, 7 13-730.

MAILLOT H. and ROBERT C. (1984) Paleoenvironmental evolution of the Walvis Ridge deduced from inorganic geo-

1348

Y. L. Wang. Y.-G. 1.iu and R. A. Schmitt

chemical and clay mineralogical data, Deep Sea Drilling Project Le;g 74, Southeast Atlantic. Init. Rep& DSDP 74, 663-683. MCCOY F. W. and ZIMMERMANH. B. (1977) A history of sediment litbofacies in the South Atlantic Ocean. Inif.Reprs. DSDP39, 1047-1079. MCGREGOR V. R. and MASON B. (1977) Petrogenesis and geochemistry of met&asaltic and me~men~ enclaves in the Amitsoq gneisses, West Greenland. Amer. Mineral, 62,887-904. MCLENNANS. M., FRYER B. J. and YOUNG C. M. (19791 Rare earth elements in Huronian (Lower Proterozoic) sedimentary rocks composition and evolution of the postKenoran upper crust. Geochim. Cosmachim. ACKU 43,375 388. M~LENNANS. M., NANCE W. B. and TAYLOR S. R. ( 1980) Rare earth element-thorium correlations in sedimentary rocks, and the composition of the continental crust. Geechim. Cosmachim. Acta 44, 1833- 1839. NANCE W. B. and TAYLORS. R. (1976) Rare earth element patterns and crustal evolution--I. Australian post-Archean sedimentary rocks. Geochim. Cosmochim. Acta 40, 1S39l551. NANCE W. B. and TAYLORS. R. (1977) Rare earth element patterns and crustal evolution-II. Archean sedimentary rocks from Kalgoorlie, Australia. Geochim. Cosmnchim Acta 41,225-231. NATLUND1. G. (1978) Composition, provenance, and diagenesis of Cretaceous elastic sediments drilled on the Arlantic continental rise off South Africa, DSDP Site 36 lirnpl~~tio~ for the early circulation of the South Atlantic. Init. Rep& DSDP 40, IOZS- 1060. PALMERM. R. (1985) Rare earth elements in foraminifera tests. Earth Planet Sci. Lett. 73.285-298. PIPER D. Z. (1974) Rare earth elements in the sedimentar); cycle: a summary. Chem. Geol. 14,28S-304. RYAN W. B. F., BOLLIH. M., Foss G. N., NATLANDJ. H.. HOGAN W. E. and FORESMANJ. B. f 1978) Objectives. principal tesuits, operations and explanation notes of Leg 40, South Atlantic. Mr. Rep&. DSDP 40, 5-28. SALBUB., PAPPASA. C. and STTINNESE. ( 1979) Elemental composition of Norwegian Rivers. Nordic Hydrology, 10, 115-140. SCHOFIELDA. and HA~K~NL. ( 1964) Rare earth distribution patterns in eight terrestrial materials. Geuchim. Cosmochim Acta B3,437-446.

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b.

a.

:::*

8.3 120

57 g36 5i) ____

50 1100 :;K:

15.2 24.6 18 0:62 3 1

0.44

1.44 3.3 0.29

1.3 80 0.43

3.7 4.3 60

::&

7.0 122

47 57 :i4 ____

&I 2.3 1000

12.8 23.0

0.34

2.3 1.27 0.19

1.0 70 0.33

:I’: 58

Calculated

S102(I)

l-2.

l

and 7-l

:*(: 8i

:45 0.17

;::9 0.14

0.21

0:33 :O9

9.1 15.1

:;oo 09 340

2363 ____

2

33 17.2 116 148

36

ooze

3:: 2.5

170 3.6 0.97

I%

::: 5.6

4298

29.7 61

118 108 5.9 520 33.2

:;’

all

110 1.9 0.49 6.0

23; 4.7 0.81 0.61 3.9 I.8 0.32 :!6 1.12 0.81 4.8

;102 1.19

32 16.9 123 148 14 JO 84 130 350 6.8 450

;::7

others

160

150 3.6 1.03 10.7 2.9 19

I

:8(: 1:16 13.5 2.0 1.6

are taken from WA.

:;I3

z9 10.9

;::1

27

:: 6.6 1.23 0.89 4.7 2.6 0.44

34.7

s918 700

26 22.5 152 155 20 100 105 178

I?::4 170 4.4 1.24 13.8 2.5 0.8

180 5.3 1.11 13.4 2.7 1.2

z29 1.38 1.13 6.3

38.6 90

Mud

:! 8 11; 146 22 70 ____ 181 110 9.5 530

;:t4

:::3

i.436 0:99 4.7

34.4 82 32

474:

153 28 100 130 155 210

ii6

::622

::434 160 4.6 1.21 12.3

0:44 :*s 120 4.3 1.12 11.9

::9 1.35 0.84 5.3

34.8 81

34.9 ::: 5.1 1.31 0.87

:;o”

; 120 145 110

24 70 ____ 144 80 :(;c:

:4’ 4 10; 148

z9

%6 97 139

GJ

::t5

0.180 3.1

8::s 2.01

8.: 2:16

z 1:98 3.3 0.75

;:; 1.98

tg0 0:82 2.28

0.58 17.2 8.2

Gl

;$; 7.9

Z38

347 63.4

347 64.8

326 66.0 0.64 16.3 7.4 0.056

310 64.7 0.90 17.0

288 63.5 0.80 17.0 7.9 0.045

54.8 0.51 13.0

:;

:::

1 X-l

252

57

id ____ 136

21.2

30 17.0 108 140

i.0” o:s9

d? 530

41 10.0

:::o

:9:1 1.65

za 2:z 10.4

13.3

2:

::: 0.046

232

197 30.8 0.45

;: 10 40 57 71 800 3.9 470

are from HPC 5308;

130 1.6 0.48 6.0 2.8 56

:: 3.9 0.67 0.48 3.2 1.8 0.30

19.1

GO 4.2 480

64;

:;f ____

::;3

::gs3

6’i4 69 7.7

::431

ii44 l.i3

;::55

180 67.3 0.69 14.8 6.1 0.035 2.2

160

27.8 0.29 6.7

A P P E N0 of Sediment Samples In Cores 530 A and 530@

100 - (T102 + A1203 + Fe * IhO + M90 + CaC03 + Na20 + K20 + Cl)

4-2.

Nannofossll

0:44 13J

1.55 0.6 1.57

2.41

3.02

?5

f.59 0:044 45.7 1.8

9.4 0.10

24

4.6 i-23 0”:0033 D:D51 :;:2 33.8 1.3

14

24.5 0.32

2

26.7 0.22

Core sections

LIHwlOQy

Sub-bottom Depth (n)

Element Concentrations

358

-

160 4.8 1.14 12.0 2.6 1.5

3::2

:29 5.2 1.21 0.96 7.9

32.8

:? 660

:; --a_ 143

::.4 137 134

:::1

:::

yj75 .

0.74 15.6 7.6

66.2

385

:::

150 4.3 1.07 12.5

l%

:1: 6.3 1.24 0.79 5.7

33.9

t; 100 8.0 570

:? 80

17 22.6 105

64.5 0.93 16.4 8.1

397

140 4.0 1.16 10.6 1.7 1.1

8::’

29.1 71 27 5.12 1.12

18.6 116 122

67.8 0.77 15.7 6.5

150 4.4 1.21 13.4 2.9 1.6

:::9

i58 1.23 0.95 5.1

35.3 80

x;:

::.1 107 155 39 110 360 165 47

;::2

::“9 0.44 200 5.3 1.18 11.9 2.3 1.2

160 4.3 1.24 12.7 2.6 1.2

!! 5.9 1.07 0.82

31.2

:“9 520

13 18.4 103 130 15 50 83 147

:::o

Zl 0.42

:: 4.8 1.12 0.86

33.6

:;;

:2” 5 loi, 152 24 70 ___161 140

i:%o

* !::3

;:s 2.14 0”:: 2.22

438 68.2 0.82 14.8 6.4 ;.;40

418 66.1 0.85 16.0 6.8 0.052

404 65.2 0.79 16.6 7.0 0.046

I50 3.9 1.22 12.8 1.9 ?.4

Zr Hf la Th U(Ppm! CaC03(%

k: Sm

:,u OY Yb LU

;42 540

15 21.7 141 126 22 60 93 158

37.0 89 45 6.6 1.21 0.89 6.2 2.8 0.42

La

:"b Sr CS 8a

V Cr co Ni

;J(PPmi

:R%,

---

1.23 13.2 i.6 !.P

35.2 75. 29 6.6 1.28 0.91 4.8 3.1 0.45

::.8 115 139 18 70 130 160 210 7.6 710

:::72 2.2 0.6 2.07 3.3 0.52

451

64.6 0.92 16.6

442

65.4 0.71 15.8 7.8 0.046 3.2 0.8 1.94 3.2 0.48

Depth (m)

Al 03 8 k0 w Cd0 Na20

34-3 -_-%--L 35-2

CO& Sub-bottom dn.Y ction 1

27 16.4 79 109

:: 95 113 210 5.4 850

40.4 72

Es 1.62 1.18 7.7

10 2.8 89 22 3.2 10 ---17 330 0.87 770

11.7 19.+

29.1 0.38 0.27 2.3 1.1 0.17

-T---

E49 0.19 1.5 1.5 86

170 2.8 1.08 lo.! I.(! !:

Z

62.1 0.97 12.6 6.9 0.065 5.6 3.4 1.92 2.7 1.06

150 3.3 1.32 9.e 1.1 6.:

E 5.1 1.01 0.72 4.5 2.3 0.32

25.1

31 19. J 102 149 24 90 120 136 140 7.0 1120

488

56.1 0.73 11.3 5.3 0.113 4.6 9.6 1.82 2.1 0.85

478

485

39-l

38-2

Early Eocene

8.5 0.12 1.8 0.7 0.186 1.1 48.4 0.45 0.46 0.31

38-l

Late Oligoce 49n.y. 24 H.y.

Geok$ca' Sediaentatiop Rate

15.7 24.3 15 2.7 0.61 0.50 3.1 1.5 0.22

:400 2.0 1610

18 5.e 34 44 6.4 30 __ __

31.8 0.25 4.0 1.9 0.094 2.0 32.1 1.05 0.89 0.68

496

39-2

35 6.4 1.40 1.05 6.7 3.0 0.38

6%

37.2

:: 6.9 440

22 19.5 li9 190 17 80 _ __ _

::;41 4.1 1.2 2.45 3.3 0.68

65.7 0.69 13.6

502

40-2

54M.Y.

50 1.1 0.43 3.7 0.7 69 --

cy; 212 1.1 0.14

12.2 23. 15 2.4

680 2.5 180

27 29 6 24 ::

.~

15 0.30 0.10 i.7 0.33 95

ly; 114 0.67 0.09

7.4 12.0 8 1.1

170

E2

1.4 4 _ 11 ___

F2

5.0 1.4

504 0.9 0.08 1.1 0.34 0.060 0.7 53.4 0.32 0.30 0.17

503 20.0 0.32 4.6 2.4 0.036 1.9 38.5 0.74 1.0 0.27 ::2’

40- _

_..

30 0.51 0.22 i.87 0.39 86

0.34 0.22 1.7 0.86 0.1:

$4e 12' 1.6

550 1.1 210

23 19 3.0 20 23 ____

3.2 7.4

8.2 0.14 2.4 0.90 0.040 0.9 48.2 0.52 0.57 0.27

506

40-48

::: !.4 2.9

:Ms

41.0 81 40 7.8 1.68 1.34 9.2 3.6 0.50

?4 360

23 16.1 93 107 17 60 _ _ __ 112

67.5 0.84 13.3 4.8 0.085 4.9 1.6 1.87 3.0 0.84

507

41-1

jMudl

Tertiary

510

..--

0.68 6.2 0.5 s5

I06

Is2 0.59 3.5 1.7 0.24

21.0 44 21

ZO 4.5 490

9.4 9.3 63 62 11 40 __ __

------

0.46 4.3 0.3 69

47 1.1

:1’9 0.59 0.41 2.9 1.5 0.20

36

17.5

:&I 2.9 530

:0 __ _ _

9.0 6.5 34 41

20.4 0.27 4.8 1.8 0.047 1.4 38.6 0.92 1.21 0.31

509 29.2 0.38 7.2 2.6 0.052 1.9 30.9 1.20 2.0 0.31

541-28

41-2

I(_

98

1.1

L&2 0.07 0.65

E 0.18

::; 0.22 70 2.4 0.94 8.7 I.1

82* 1.6 0.31 0.24

11.3

:70 0.26 110

1.8 1.3 5 8.0 1.8 5 - _- -

E9 0.6 54.8 0.20 0.16 0.14

514 0.3 0.02 0.53

z! 3.9 0.83 0.73

22.2

8.8 11.9 63 92 13 60 _ _ _113 560 6.0 530

z34 2.4 20.2 1.51 2.2 0.37

512 42.7 0.47 9.5

41-3 .- 42-1

Late Paleocene

of Sediment Samples rn Cores 530A and 5308

40-4A

Element Concentrations

0.93 8.2 1.2 87

::6 0.50 2.5 1.6 0.23

16.4 3+ 13

4.4 240

0.04 0.3 0.9 98

A::3 0.17 1.4 1.0 0.15

9.2 k7

;10 0.12 65

7.4 0.8 7 6 0.4 3

516 0.1 0.09 0.33 0.10 0.094 0.68 55.1 0.24 0.06 0.23

____ g

6.2 9.7 61 85 22 60

515 73.3 0.44 7.9 3.8 0.028 2.1 4.9 1.50 1.8 0.39

0.25 0.46 7.4 95

:::8 0.32 2.2 1.1 0.18

15.1 :09

320 5 0.17 120

0.64 4.9 !.1* ? ;

0:41 :O4 0.37 1.9 1.3 0.14

12.6 25.

60 82 4.2 230

:: 30

4.4 8.3 58

525 81.8 0.39 7.3 3.4 0.019 1.7 1.2 1.21 1.7 0.37

43-l

5449 7.8 20

12 7.6

4.4 1.6 58 14 0.58 2

528 _s&._ 23.6 4.0 0.31 0.09 6.5 0.7 2.7 0.28 0.092 0.054 1.6 0.7 34.9 52.4 1.04 0.29 1.4 0.20 0.47 0.14

43-2A 43~2

60 1.2 0.55 5.0 0.4 62

a3::5 0.57 4.0 1.2 0.18

18.9 44 19

670 71 3.5 430

?27 0.19 0.34 i.4 94

A:!5 0.22 1.9 0.75 0.17

11.0 17.5 10

:40 0.11 70

____ ____ ____ ____

:796 3

5.8 1.9 13

517 2.3 0.13 1.0 0.30 0.079 0.9 53.0 0.41 0.15 0.18

42-2 42-1A 42-18 ___~-

11thology

:: Th

Zr

h’

0.11 0.34

A620

::;

180 3.9 1.26 11.0

::: 0.36

A::7 0.10

;; Yb LU

:f* 5.8 1.06 0.81

:::3 0.18

:c:

28.7

6.7 10 6

;;it

:: 160 161 430

ii.4 122 172

::y 0‘53

43::

8:b3

62.5 0.85 13.1

La Ce Nd

660 0.14 60

:: 3.4 2 ____

El

0.26 0.120 0.8 62.7 0.35 0.10 0.28

iti4 0.52

Cl 0.23 0.75 1.0 88

8.9 16.0 6 1.6 0.37 0.24 1.7 0.72 0.11

11 250 0.50 100

:I? 1.6 1 __-_

6.6 2.9

k10 0.i2 0.31 0.21

ZO ok67

8.0 0.20

151507 0.05 0.15 0.7 99

?A 0144 0.08

::; 4.3 0.85 0.16

X6 20 ^___ 2 230 0.07 40

gl

0.13 0.051 0.8 56.4 0.19 0.05 0.16

LfJ 0.22

!i”

::f 11.3

160

0”:!9

X0

574 2.2

36.6 89

ZO

:: 5 16; 155 21 100 130 140 310

f:&

6”*‘: I:89

:: L6

58.4 0.80 12.8

k4

0807 0:07 0.1x

x2 0.08

‘k86 0.17 0.10

::;

:: 1.1 20 ____

::; 0.25 20 m--* 2 180 0.03 70

f?31 0.22 0.39 0.6 96

fK7 0:23 1.5 0.61 0.09

9.4 13.0 8

;40 0.12 30

::X

k&6

El 0.8 53.7 0.28 0.14 0.15

57.7 0.82 11.8 6.4 0.081 E 2:11 8:s

;I:!08 ::d 2.12 kf4

:;”

:::5 9.9

130

::: 0.35

:: 6.2 1.38 0.82

31.1

23:: 0.28

24:: 0.36 Z-d 0:42 180 3.9 1.39 10.2 1.3 13

::96

Y7 Los 0.63

P9 1:27 0.82

F2 1.34 0.79

::4”

:;’ t;”

Mudstone

130 3‘4 1.05 7.2

130 ::;o 8.5

13o x9 9.2

20.8 48

29.0 56

29.4 62

37.5 80 31 7.3 1.64 1.04 6.9

tf;:

:;

:: 540

:o” 120 123

: 120 139

:If 120 126 160 6.5 280

if 20 80 120 127 250

::F 0.33

::t

68.8 0.79 11.1 7.2 0.027

ii.6 176 107 25 90 ____ 101 240

ii.1

::9*

60.1 0.72 11.4 6.4 0.078 3.7 7.3 1.77

:3 247

if.6 a3 80

:: 0 loi 110

56.6 1.00 12.8

:69 2 116 128

k&

::; 1.66

54.2 0.78 12.5

1.4 0.16 0.82

E4

to4 0.25 0.11 0.057 0.4 56.4 0‘19 0.05 0.14

Element Concentrations of Sediment Samples in Cores 530A and 530@

I?52

::6 0.81 0.54 3.9

17.5 37

:: .,-.... 59 170 2.5 llwf

::

::!I

Z8

54.6 0.57 7.0 3.8 0.070 2.7 15.6 1.29

Mudstone

LIISEstone

!

FO 0.66 4.8 0.6 35

::8 0.83 0.48 3.1 1.6 0.23

19.0 37

:: 270 2.9 220

:8

9.7 IO. 1 65 50

z

G49 2.2 19.6 1.14

48.4 0.54 6.8

:723 0.16 0.21 0.5 96

;70 0.06 30

:: 1.2 8 ____

::5’

P7 O.il 0.09 0.09

0:53 0.36 0.070

8%

Zr Hf Ta Th U(wm; CaC53j: __.-..

:t: DY Yb Lu

k: Sm

La

Br(wm) SC Y Cr co Ni Zn Rb Sr cs Ba

50 1.8 0.69 4.4 0.6 42 _ _.._

I% 0.63 3.4 1.6 0.23

21.0 42 22

2'; 2io

63

4": 13 40 ____

!X

:;:5 1.07 2.0 0.25

42.0 0.39 6.9 3.5 0.052

56 k%k!t ion Sub-bottom Depth (m) __.__650

Sedimentation Rate

55.1 0.69 8.6

-

56.1 0.65 9.8 4.5 0.044 2.7 12.2 1.45 2.6 0.35

a.4 10.8 88

12.2 0.68 9.8 6.4 0.026 3.2 1.7 1.60 2.7 0.37

8.6 14.R 121 100 14 60 ___112 ia0 5.5 230

19.6

;:: :.? j.ir _~_..

120 2.7

::: 3.8 2.2 0.25

:; 3.0

:02 1.0 5.7 1.5 zi

:63 0:71 0.51 3.6

i2a o:l36 0.64 4.7 2.1 0.26

25 ._~..

90 2.8 0.74 5.4 D 8

A:623

16.4 33

:: ____ 64 250 2.8 200

10 11.0 94 77

23.5 43

254;

:: 40 ____ 92 250

688

Z7O 2.6 13.7 1.57 2.1 0.43

38 60-2a

1

58-i

658

668

57-

ii

90

2.8 ._ _.

o”:aOa ____ ____ “... “_.

17.6 28 ____

2.6 ____

-__-

70 ____

a.5 10.6 91 75 ____ __._

57.9 0.73 a.3 4.4 0.067 2.5 12.3 1.64 2.1 0.38

688

60-2b

Campanian - Maastrichtian

64-la

90 2.1 0.77 4.0 0.6 36

:: 3.3 0.85 0.55 3.8 1.6 0.21

la.3

::0 2.1 220

7,2 a.8 76 39 12 40 ____

47.7 0.66 6.8 4.0 0.124 1.9 20.1 1.10 I.6 0.21

,,,

160 3.8 1.5 6.9 ll.f( :;

:: 4.4 1.15 0.73 3.9 1.7 0.25

20.8

7.0 17.7 125 74 19 60 __-_ 94 200 3.7 560

63.8 0.86 10.2 7.2 0.045 2.9 6.0 1.65 2.4 0.27

712 __~725

62-3

,,

130 3.8 1.43 6.8 0. 4 ;2 ._

:‘a 1:15 0.68 3.7 1.8 0.27

21.6 49.

:: 96 190 3.6 560

7.4 17.9 133 76 21

E 1.74 2.4 0.29

62.4 0.93 10.4 7.2 0.047

725.

64-lb

1.3 IR

90 2.5 i.03 4.4

g59 1:13 0.67 4.1 1.9 0.24

24.2 48.

:;o’

::0

:A 49

a.5 11.8 102 69

::: 0.092 1.9 10.2 1.22 1.7 0.25

64.1 0.77

762_

1168-l

1.30

170 3.5 1.70 5.9 0.6 b 4

260 5.8 2.8 3.3 1). 5

,/,,

,,, ,, ,,,,

3. 8

::‘: 0.27

:‘6 2:36 1.00

31.4 63

10.1 29.6 275 435 73 130 a5 17 230 0.6 120

52.3 3.1 14.0 12.1 0.087 7.7 2.7 5.2 0.4 0.31

120 3.0 0.91 3.6 0 5 3! ._

:“9 1:19 0.69 6.0 1.8 0.25

i24 110s 0.56 ::; 0.23

22.9 44

Eo 1.8 710

79 170 3.2 300 22.4 47

:a” 10 3o 47

9.7 14.0

1.4 0.23

53.6 0.75 6.3 3.9 0.248 1.8 17.1

.- 782

6.4 13.8 109 62 25 60 ____

LE3

::!a

71.8 0.87 a.7 6.5 0.045 2.1

772 __.-

794

78 M.Y. 69-l -_7o-271_.--_.__--_._~.

Campanian

Late Cretaceous

Element Concentrations of Sediment Samples in Cores 530A and 530@

73-6 20

::: Z.? 9.6 13

200

;::4

38.7 a7 42 9.8 2.91 1.33 a.3

9.2 20.3 243 130 28 70 ____ 23 260 0.4 90

52.1 3.4 14.1 a. 7 0.094 3.8 7.3 3.11 1.3 0.37

818

,,,, ,,

25:: 2.9 !I 5 i4

260

::; 0.2(i

:45 2.32 0.94

30.3 65

10.1 25.0 261 99 42 90 33 9 280 0.2 60

53.1 2.6 12.3 11.3 0.197 4.2 13.2 2.23 0.3 0.31

,

I.0 ;.i

240 5.0 2.1 12 -:

64.9 136 49 9.23 2.08 1.15 7.1 3.0 0.4i

9.0 21.7 127 93 17 50 ____ 150 240 7.0 590

79.4 1.10 12.7 7.6 0.044 1.7 0.63 1.72 2.6 0.30

75-3 a35

74-2 820 ___

Santonian

360 9.3 6.8 6.5 1.6 2.0

:::6 0.10

:03 2.39 0.77

70.2 142

LY7 23; 211 20 60 ____ 2.9 470 0.13 1500

64. a 4.31 la.8 4.7 0.096 2.6 1.1 2.36 0.04 0.25

838___.

76-l

7?3

160 3.9 1.20 4.5 0.2 32

:: 4.6 1.11 0.61 3.2 2.0 0.30

22.6

48; 56 80 ai 63 240 2.5 270

6.6 14.4

47.9 0.76 7.3 6.9 0.226 2.2 la.0 1.12 1.3 0.20

a51

I

a2 M.Y.

Sub-bottom Depth (m)

::: 13

;:;

:::

150 4.0 1.40

::;: 0.28

z4 0.59

15.6 37 24

Z*

E2

:::

tz

200 4.1 1.31 6.4 :;”

Y;”

;::*

;::3

z4 150 4.4 1,42 7.2

if7 1.38 0.73 4.3

.?6 1.18 0.69 3.5

230 6.1

25.2 65

EO 3.3 310

ZO

::

5.4 13.5 107

E

915

;:2” 0.238 6.0 13.1 1.19

12.1 29

:6:

;: 119 380

6.2 16.7 142 105 18

GO

711 1.64

y:i51

E 6.2 1.53 0.92 5.2

31.1

;:0 3.2. 560

:: 60 -_-_

;04

ZO 126 310 6.0 340

10 14.2 147

9.7 17.5 149

El

3’45 1:42

260

53.9 84 36 7.9 2.43 1.01 5.1 1.8 0.26

E 830

:P

5.0 16.8 243 374 39 110

;:: 2.64 0.6 0.23

:::86

:;rt 7.7 0.052 2.5 5.0 2.11 3.1 0.32

915 57.8 0.82

909 61.2 1.05 11.4

891

60.1

070

58.6 0.82 10.6

858

53.6 3.1 14.4 8.0 0.064

35.0

924

z

931

941

971

976

Element Concentrations of Sediment Samples in Cores 53OA and 53OE@

998

1000

1020

1045

9 1045

Y. 1.. Wang Y.-G. Liu and R. A. Schmitt

1354

Element ioncentrati~ns of Sed,ment iamples I" Cores 530A and 530&,

tion Rate wM.Y.) Core-Section Sub-bottom

i

uNp[R':;h-.

‘3-..

101-5 iao-1--m-.-

--

104-3

~.

__ 105-4 1100

108-I

1120

43.0 1.74 !5.9 9.3 0.179 8.2 i0.4 2.95 0.18 3.02

43 : i.54 16 4 Q' 23;

6 38.9 308 125 55 50

>: 37.6 309 9. 4% a0

0 260 0.03 110

O.iO 180

13.: 33 13 4.4 i.58 0.95 5.0 3.5 0.54

Ii.! .“ 16 4.3 49 0.89 5.2 2.9 0.43

120 3.3 i.30 I.4 0.7 ____

220 30 i.42 14 06

'3

APPENDIX 2 Ce oxidation in river water and seawaler Quantitative calculations on the Ce oxidation states in river water and seawater have been published (LIu, 1982) and given below for completeness. Some ofthese calculations have been presented in a slightly different approach by DEBAAR et al ( 1985). The major oceanic source of the REE is considered to be rivers which transport weathering products of rocks and sediments from continents to the oceans. The soluble content Ce is 0.06 &L at pH = 6.8 in river water. Eh = 0.4 (SALBI' etal.. 1979). Assuming that the chloride complexed Ce ions in river water are negligible the E” for uncomplexed Ce ions in HCIO, is

108-Z

1115

‘1

6 6 13.6 3.21 0 32 ' 02

‘x

I

For the Ce oxidation reaction in seawater (Cl - 0.6 Pi 1. Ce+’ = Ce+4 + e-;

E” = 1.28 V in I N I-lCl.

The average redox potential of seawater is Eh = 0.38 V at pH 8.1 (BAAS BECKING et a/., 1960). The Ce concentration in seawaterisl.2 X lO*ppm (COLDBERG~V~~., 1963;Hoc~~~r ef al., 1968). The temperature of seawater is assumed to be IO’C. If the concentration of Cee3 and Ce+’ are in equilibrium in seawater, Eh = E” + 0.056 log[Ce+‘]/[Ce”]:

and

Ce+‘/Ce+) = 8.5 X IO-”

Assuming that all observed Ce in seawater IS tnvalent and that r(Ce”‘) - 0.01 and y(Ce”) - 0. I, we obtain that the For the reaction, concentration ratio Ce+*/Ce+’ - lo-“. Therefore the concentration of Ce+’ is -7 X 10e2’ mol/L. Ce+3 = Ce+4 + Ed: E” =. 1.70 V m HCIO,. It appears that the equilibrium concentration of Ce’& rn seawater is very low. However, we note that the solubility of At 10°C equilibrium Ce(OH), is very low and within a few magnitudes of other Eh = E” + 0.056 log[Ce”]/[Ce “1; tetravalent ions like Ti, Zr, Hf and Th. If the Ce+* exceeds that allowed by the solubihty product of Ce(OH),, equilibrium and is reestablished by precipitation of Ce(OH),, thereby shifting [Ce’4]/[Ce’3] = 6.3 )( IO-? the Ceq3-Ce+’ oxidation reaction to the right and leading to Assuming the activity coefficients for both Ce+4 and Ce” a considerable fraction of quadrivalent Ce precipitation as are unity, [Ce”] = 2.7 X IO-” mol/L. From the I&, of Ce(OH),. From the REE concentration pattern in seawater Ce(OH),, the allowed [Ce’4] concentration is - 1.9 x 10m2’ and oceanic sediments, it is evident that about 80 percent of mol/L. Because the Ce+’ equilibrium concentration is much the total Ce entering the oceans has been lost as Ce(OH), and lower by - I3 magnitudes than that allowed by the I& of that about 20 percent remains in seawater as trivalent Ce. Ce(OH), we conclude that no appreciable Ce oxidation occurs For seawater at pE’ = 13.7 (I 3°C) (CULBERSON and PYTin the river water. KOWICZ, 1973) pH = 8. I and Ce+’ - 7 X 1O-29as calculated Used.

1355

Deep sea sediment REE geochemistry above. the calculated solubility product of Ce(OH), at 10°C is K,(Ce(OH),) = h+, . a&- - 3 X IO-“. This value is consistent with the reported K,,, of 2 X IO-” at 25°C (STEVENSON and NERVIK, 1961) if we assume that the Km is expected to decrease with decreasing temperature. The Km (Ce(OH),) value at 10°C might be checked in a related way. At 25°C Ce+3 = Ce+4 + e-; AG, = nfE”

E0 = 1.28 V in 1 N HCl

This calculaied value of 0.15 js close to the assumed 0.1 for Ce+3 and to the interpolated (between La and Pr data) fraction of 0.27 for free Ce+’ in seawater (TURNERet al., 1981). Another REE which may exist in an oxidation state other than trivalent is divalent Eu. For the reaction Eu+* = Eu’~ + e-;

E” = -0.43 V in 0.1 F HCOOH.

In present seawater at 10°C we find that Eu+~/Eu+~ - 3 X 1014.Obviously Eu+~is predominantly trivalent in seawater.

likewise it can be shown that in river water Eu is also trivalent.

= 29524 cal/mol

Ce+4 + 40H- = Ce(OH)4. APPENDIX The equilibrium constant K = [Ce(OH),]/[Cef4][OH-]4. Assuming the activity of [Ce(OH),] = I, it follows that

3

Correlation coefficients (r) for pairs of REE and other elements in carbonate oozes (1) and limestones (2)

K = l/K, = 1/[2 X 10-4*] = 5 X 104’ and Ce

Nd

h

Eu

Tb

Dy

'(b

Lu

1 .44 2 .52

.70 .67

.39 .78

.52 .6D

.38 .64

.36 .64

.40 .64

.41 .27

.50 .21

TiO2

1 .3a 2 .29

.67 .46

.31 .37

.4¶ .3a

.39 .50

.33 .34

.43 .34

.40 -.07

.55 -.08

Fe0

1 .56 2 .lO

.67 .3D

.46 .46

.64 .23

.55 .33

.52 .27

.52 .34

.56 -.20

.63 -.22

SC

1 2

.67 .71

.83 .79

.57 .90

.79 .79

.64 .86

.64 .78

.65 .75

.70 .41

.63 .38

Hf

1 2

.56 .51

.73 .72

.53 .75

.61 .62

.42 .70

.42 .63

.40 .63

.4D .I4

.44 .13

Ta

I 2

.55 .50

.71 .72

.58 .67

.47 .61

.45 .76

.45 .5¶

.41 .I5

.3a .51

.26 .O¶

Th

1 2

.59 .I5

.52 .21

.51 .30

.61 .I6

.60 .08

.58 .23

.65 -.2¶

.48 .21

.37 .lO

La

AGr = -RT In K = -6506 1 cal/mol. Al$j

Therefore, Ce+3 + 40H- = Ce(OH), + eAGo = AGP + AG$ = -35537 cal/mol, and

E" = - 1.544 V.

At lO”C,

Eh = E" + 0.056 log[Ce(OH),]/[Ce’3][OH-]4. For pH = 8.1 in seawater, CeC3 = 1.3 X lo-‘* mol/L. Since (I = yC, y(Ce+3) - 0.15.