851 Geologische Rundschau 78/3 I 851-8821

Stuttgart 1989

,Geochemistry of recent TOC-rich sediments from the Gulf of California and the Black Sea By HANS-]'. BRUMSACK,G&tingen*) With 13 figures and 8 tables

Zusammenfassung An rezenten Sedimentproben des Auftriebsgebietes des Golfs yon Kalifornien sowie Sapropelen des Schwarzen Meeres wurden sowohl Hauptelement-, als auch SpnrenmetallGehalte (Ag, As, Ba, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, St, V, Zn, u. a.) ermittelt und mit neueren Spurenmetall-Daten yon Meerwasser und marinem Plankton in Beziehung gesetzt. Im Chemismus der Sedimente des Golfs von Kalifornien spiegeln sich die in der Wassers~iule ablaufenden Regenerationsprozesse wider. Elemente (z. B. Cd), die sich im Meerwasser wie die ,,labilem~ N~hrstoffe (C, N, P) verhalten, gelangen nut in geringem Ausmag (< 10%) in die Sediments~ule, im Vergleich zu solchen Elementen (z. B. Ba), deren Verhalten im Meerwasser eher dem yon ,,resistenterem~ N~ihrstoff-Elementen (Si) entspricht. Eine Reihe yon Spurenmetallen, die vergleichsweise hohe Konzentrationen im Meerwasser aufweisen (As, Mo, U, V) und redox-sensibel sind und/oder stabile Sulfide zu bilden verm6gen, werden friihdiagenetisch im Sediment fixiert. Das friihdiagenetische Verhalten von Ba ist eng mit der bakteriellen Sulfat-Reduktion verkniipft. Die Bildung yon Baryt-Konretionen wird diskutiert. Anoxische Bedingungen in der Wassers~ule wirken als ideale ,,Fallen, fiir viele redox-sensible und/oder stabile Sulfide bildende Etemente. Mit Hilfe yon Element-Bilanzen kann nachgewiesen werden, daft der Chemismus der Sapropele des Schwarzen Meeres yon der Element-Zufuhr durch Flute- und Mittelmeerwasser sowie die Sedimentationsrate gesteuert wird.

Abstract Major and minor dements (incl. Ag, As, Ba, Cd, Co, Cr, Cn, Mn, Mo, Ni, Pb, Sr, V, Zn) have been determined in recent sediments from the Gulf of California upwelling area and Black Sea sapropels in order to reinterpret their chemical composition in view of reliable seawater and plankton data. The chemistry of the Gulf of California sediments reflects regeneration processes which occur in the water column; i.e. only a small fraction (< 10%) of elements like Cd, which in seawater are coupled to the *labile, nutrients (C, N, P), is buried in the sedimentary column. In contrast, elements like *) Author's address: Dr. H@ BRUMSACK,Geochemisches Institut der Universitiit G6ttingen, Goldschmidtstr. 1, D-3400 G6ttingen, ER. Germany.

the more resistant nutrients (Si) undergo a deeper regeneration cycle (Ba). Several trace metals which are present in comparatively higher concentrations in seawater (As, Mo, U, V) and at the same time are reactive under reducing conditions and/or are abte to form stable sulfides, are fixed in the sediments during early diagenesis. The early diagenetic behavior of Ba is closely related to bacterial sulfate reduction. The formation of barite concretions is discussed. Anoxic conditions in the water column act as ideal traps for a number of redox sensitive and/or stable sulfide forming elements. A simple trace metal balance calculation shows that the chemical composition of Black Sea sapropels is con trolled by fluvial and Mediterranean seawater element input and the accumulation rate of terrigenous detrital material. R6sum6 Des dosages d'616ments majeurs et en trace (notamment: Ag, As, Ba, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sr, u Zn) ont &6 effectu& clans des s6diments r&ents provenant des r6gions ~ courants ascendants (upwelling) du Golfe de Californie, ainsi que clans des saprop~tes de la Mer Noire, dans le but de rechercher les relations entre leur composition chimique, et celles de l'eau de mer et du plancton. Le chimisme des s~diments du Golfe de Californie refl&e les processus de r6g& n&ation qui se d&oulent dans ta colonne d'eau. En l'occurrence, les 6t6ments (tels le Cd) qui, dans l'eau de met, sont associ& aux nutrients ,labiles,, (C, N, P) ne passent qu'en faible quantit6 (<10%) dans la colonne s~dimentaire. L'inverse se pr&ente pour les 616ments (Ba, p.ex.) dont le comportement dans l'eau correspond ~ celui des nutrients ~,r&istants,, (Si). Certains m&aux en trace, qui existent en proportion relativement ~tev~e dans l'eau de mer (As, Mo, U, V) et qui en m~me temps sont sensibles au potentiel redox et/ou peuvent former des sulfures stables, sont fix& dans les s6diments au d6but de la diagen&e. Le comportement diag6n&ique hatif du Ba est &roitement li6 ~ la r6duction du sulfate bact& rien. L'auteur discute la formation de concr&ions de baryte. Des conditions anoxiques dans la colonne d'eau agissent comme des pi~ges id&ux pour un certain hombre d'616ments qui sont sensibles au potentiel redox et/ou qui forment des sulfures stables. Un calcul simple du bilan des 616ments en trace montre que la composition chimique des saprop61es de la Mer Noire est r6gie par l'apport des fleuves et de la M6diterrann& ainsi que par le taux d'accumulation des mat&iaux d&ritiques terrig~nes.

852

H.-J. BRUMSACK Kpa'rKoe co,~epxam~e

B peIIenTnbix npo6ax ce~nMettTOB B pernoHe Bocxo~I~nX Teqen~ Kanndpopn~ficKoro 3aanBa Hcanponesmfi qepnoro Mop~ orrpe~eanan ocnoBm,m rl pacceannue 3~eMenTbI (Ag, As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, St, V, Zn etc.) ~I conocTaBHnI~I c HOBeiTimnMn~aitni)iMn o cocraBe MOpCKOft BO~bI H uopcxoro nnanxwona. XnMn3M ce~nMeHTOBKan~qbopnnficKoro 3aJmBa 3aBHcnTOTnpo~eceoa pereHepaxlnH, rlpoTeKaiOi~laX Ha pa3anqnofi rny6nHe. ~eMeHTt,I, Hanp. : Ka~MI4ft,KOWOpt,IeBe~yT ce6~I B MopcKOI~IBo~e, KaK <>npo~yKTI,I nnTahu4~i,T.e.C., N, P, nonanamT B Bo~nnofi cwosI6 ToJnaKo B He3HatIHTeYlbHOMKOJIHqeCTBe,T.e. MeHee 10 %, BIIpOTI,IBOpO.IIO:aKHOCTI, noBe~enmo TaKIIX3.rleMeHTOB,KaK rlanp.: 6apnfi, KOTOpbleBe~yTce6a, KaK <~yCTOfiqrlBble>>npo~yKTLIiirlTaitngl, T.e. KpeMHHI~I. P ~ MrlKpOa,rleMeHTOB, KOTOpble nO~IBXDIIOTC~IB MOpCKOfIBoNe B cpaBanTeJIbHO BbICOKHX KonUeHwpan~I~Px (As, Mo, U, V), qyBCTBnTeat,HO pearnpy~oT na pe~oKC -- nowen~nan cpe~B~ n MOryT o6pa3oBb~BaTh CTa6nnb~bIe cynbqbaT~L KOWOpBm OKa3I,IBa~OTC~ CB~3aImBIMJJBce~nMenTax y)Ke na pammx cTa~nnx ~narene3a, Pa~ine~nareneTi~iecxoe noBe~eni~ie 6apnn TecHo CB~I3aHoC BOCCTaHOBJIen~IeMcyJI~,qbaTa6aKwepnnuI~. ]~ICKyTI4pytoTC~ ycaoBnu o6paaoBann~ 6apnwoBt,IX KOHKpe~Ifi. B e c x n c n o p o ~ m ycnoB~s cpe~I B BO~HOM CTOa6e OKa3BIBaIOTC~Ilei~eadlhliot~<> JIYl~IMHOFW'X.~..vleMenTos, npoaa~IalOnmX '-IyBCTBHTem~aOCTbK pe~oKc-noTenlInazy cpe~t, n o6paaylOT cTa6nm,nr~ie cym,qbaTl~i. C nOMOlar~m 6aaaanca DJIeMeHTOB,MO~KHO~OKa3aTb, *-/TO XHMH3Mcanponeaeft B t'IepnoM Mope 3aBnCHT OT KOJIHtIeCTBa 3YleMeHTOB,npl,tHOCI,IMbIXpeqHhlMn 1/1cpejIH3eMHOMOpCKI,1MHBO~aMt'I, a TaK)Ke OT CKOpOCTFIoCa~KOnaKOn.rleHH~. 1. I n t r o d u c t i o n

Recent and ancient sediments with high T O C (total organic carbon) contents often are enriched in specific trace metals, like Ag, Cu, Mo, Ni, V, Zn, etc. (BRUMSACK, 1980; [DEAN et al., 1984; DEAN 8~ ARTHUR, 1986; BRUMSACK & THUROW, 1986). For this reason the pioneers of analytical geochemistry were interested in this sediment type (GOLDSCHMIDT, 1954). If these metal enrichments are of syngenetic origin, a relation between the paleoenvironment of deposition, flora and fauna, tectonic position, and oceanographic parameters should exist (VINE • TOURTELOT, 1970). In principle two different paleoenvironments for the deposition of TOC-rich sediments may be distinguished, which are characterized by distinct chemical, oceanographic, and biological parameters. The most important requirement for the deposition of such sediments is that a significant fraction of the organic material which is produced in the photic zone survives the transit through the water column and the benthic boundary layer. After burial in the sedimentary col-

umn the organic material is much better preserved and protected against rapid destruction (oxidation). This may be achieved by decreasing the residence time of the organic matter in the oxic water column or at the sediment surface, or by a drastic reduction or complete absence of oxygen within the water column. The first case may be realized in areas with high organic primary productivity, the so called >>upwelling<~ regions. Here the supply of nutrient-rich waters from different water depths induces a strong plankton production. An oxygen-minimum-zone develops in the water column below such areas; the oxygen content in a few hundred meters water depth approaches zero (< 0.1 ml/1 O2), but ~,free,, hydrogen-sulfide is not yet present. Due to the high production of organic material and the concomitant rapid burial of labile organic compounds, a comparably large fraction of the T O C is preserved. Different paleoenvironmental conditions, which favor the deposition of TOC-rich sediments, are realized in anoxic basins, like the recent Black Sea (DEGENS & ROSS, 1974). In this case the circulation of oxygen supplying waters is restricted due to the presence of a shallow sill at less than 50 m water depthl Oxygen became depleted in the deep waters and finally hydrogen sulfide could diffuse from the sediments into the overlying waters, which turned anoxic (DEUSER, 1970). Furthermore, hydrogen sulfide is generated within the anoxic water column by the action of sulfate reducing bacteria (SWEENEY 8~ KAPLAN, 1980). High preservation rates of organic material and high T O C contents of the sediments deposited under such conditions (sapropels) may result even when the productivity is comparably low (GLENN 8~ ARTHUR, 1985). Sapropels therefore reflect organic matter preservation and not necessarily plankton productivity. Since the advancement of analytical techniques around 1970, a large number of even less abundant elements could be determined quantitatively with relatively little effort. Besides terrestrial geochemists, marine scientists have also benefited from this development and, through progress made in preventing contamination during sampling and analysis, the first reliable and >>oceanographically consistent<, trace metal data for seawater (BOYLE et al., 1976 & 1977, BRULAND et al., 1978) and marine plankton (MARTIN 8~ KNAUER, 1973) have been generated. In view of these new results, a reinterpretation of the genesis of recent TOC-rich sediments is worthwhile. The better understanding of the trace metal chemistry of recent sediments then may provide the tools to extract information regarding the genesis and paleoenvironment of fossil black shales.

Geochemistry of recent TOC-rich sediments from the Gulf of California and the Black Sea

853

2. Trace metals in seawater

3. Upwelling sediments from the Gulf of California

In order to understand the following sections, a brief summary of the distribution and abundance of trace metals in modern seawater seems necessary. Until a few years ago, essentially nothing was known about the behavior of trace metals in the marine environment. It is now known that many trace metals are much less abundant in seawater than previously thought, and do not behave like the ,,conservative,, major ions (BRULAND, 1983). By contrast, it could be demonstrated that many metals are strongly coupled to nutrient elements and involved in biG-cycling. Therefore regeneration processes within the water column, i.e., uptake of certain trace metals (Cd, Cu, Ni, Zn, etc.) by marine plankton and successive release from plankton remains when they settle through the oxic water column, are very important for the distribution of trace metals in surface waters and at depth. Principally three groups of trace metals may be distinguished: 1. elements which are considerably depleted in surface waters (due to the uptake by marine biota) and enriched in deeper waters (through regeneration processes), like Ba, Cd, Cu, Ni, Zn, etc. (see summary by BRULAND, 1983). 2. elements which are very reactive and not to the same extent involved in nutrient cycling processes, and therefore depleted in deep waters, like Co, Mn, Pb, Sn, etc. 3. elements which behave essentially ,,conservative~ in seawater, i.e., they are present in a more or less constant ratio to the major ions, like Mo or T1.

The Gulf of California, a long marginal sea of the Pacific Ocean covering an area of 25" 104 km 2, is characterized by an exceptionally high organic primary productivity (ZEITSCHEL, 1969). Laminated diatomaceous sediments are mainly found on the continental shelf of the central and southern Gulf (VAN ANDEL & SHOR, 1964; SCHRADER et al., 1980) in water depths ranging from 400 to 800 m, where the upwelling-induced oxygen minimum zone impinges on the sediment/seawater interface (CALVERT, 1966). The laminae reflect the seasonal input of predominantly terrigenous detrital material during the wet summer season and the deposition of mostly oceanic diatom remains during the dry winter season with prevailing NW winds and corresponding upwelling at the mainland side (DONEGAN & SCHRADER, 1982). Since bioturbation is virtually absent, these sediments not only are ideal for studying paleoclimate but also for investigating early diagenetic processes under suboxic conditions. Sediment samples have been obtained from box and kasten cores during cruise BAM-80 of the Oregon State University (R/V ,~Mariano Matamoros<,). The samples represent the ,~squeezed cakes,, from a previous porewater study (BRUMSACK & GIESKES, 1983). Sampling locations, coordinates and water depths are shown in Fig. 1. Sampling area E is located in the vicinity of DSDP Sites 479 and 480, where drilling has been performed in 1978/79 (SCHRADER et al., 1980). Analytical methods used and chemical data of the individual samples are listed in the appendix. Element ratios used in the text, tables and figures are weight ratios.

This simplified description of the behavior of metals in the marine environment in reality is much more complex, especially when scavenging processes, diffusion from the sediments (e.g., Cu; BOYLE et al., 1977) or anthropogenic influence (e.g., Pb; SCHAULE& PATTERSON, 1981) are considered. In contrast to the large body of information available on the behavior of metals under oxic water column conditions, comparably little is known from anoxic, hydrogen sulfide bearing waters. Many trace metals, especially the so called >>class-B<< metal ions (STUMM & MORGAN, 1981), tend to form insoluble sulfides. This could be demonstrated by JACOBS et al. (1985 & 1987), who could prove that, e.g., Cd undergoes a dramatic solubility decrease at the O2/H2S boundary of anoxic basins like the Cariaco Trench. The metals which are removed from the water column by this process finally are accumulating in the sediments, where they may produce an >>authigenic<< trace metal signal when ..sedimentation rates are low enough.

3.1 M a j o r

elements

The major element chemistry of sediments from the Gulf of California in principal reflects a mixture of two endmembers: terrigenous detritus with a composition like ,~average shale,, (WEDEPOHL, 1970) and biogenous material (plankton remains, mostly diatoms). Since the major element composition of the individual samples shows relatively little variation, with the exception of core G-32 from the southern Gulf, the following discussion is based on mean values of 50 samples (see Tab. 1) taken from 4 cores (E-5, E-9, E-13, and E-17). It was assumed that the >>detrital terrigenous<, fraction of the sediments is represented by the A1 content and that the major element/A1 ratios of this fraction are identical to those of ,>averageshale<<.Besides A1 (per definition) the Ti and K contents are also exclusively of terrigenous origin. The comparably low Fe content

854

H.-J. BRUMSACK

111~ w

28"

w

J

|

g

110~ l

i

!

~

i

I

~ASO~.E-[?x~~ ~,Guaymas - "L.~J'-'--..~ o-.---E -9 " ~ "'--E-5 ~ Yaqui

28"

m~E-13

,s r

~

2?*

Core # E-5 E-g E-13 E-17 .G-32

J

Guaymas

, 9

.w,

~

A

~

e

I

~

~

.

2'/0

111=

location water depth remarks 27~ 111"23.2'W 800 m homogeneous 27"4g.8'N 111~ 650 m laminated 27"54.7'N 111~ 630 m laminated 27"55,2'N 111"36,6'W 620 m laminated 23"54.7'N 107~ 415 m homogeneous

Fig. 1. Sampling localities for the Gulf of California upwelling area (Mexico).

indicates the suboxic environment of deposition; Fe may be mobilized under reducing conditions as long as hydrogen sulfide is absent at the sediment/seawater interface. Enhanced Fe concentrations in porewaters from the core tops have been reported for these sediments (BRUMSACK& GIESKES, 1983). This seems to be in agreement with enhanced Fe concentrations reported for intermediate waters of the North Pacific oxygen-minimum zone (GORDON et al., 1982; LANDING & BRULAND, 1987) and also high Fe/A1 ratios of particulates from within the oxygen-minimum of the Guaymas Basin, which is explained by supply from the suboxic shelf (CAMI'BELL,1985). On the other hand, a general Fe depletion of the terrigenous detritus cannot be excluded. Higher Mg and Na contents reflect the presence of smectites and albite (DONEGAN & SCHRADER, 1982). The elevated carbonate and Ca content is due to the presence of foraminifera tests in the core tops. Below 20 cm depth biogenic carbonate is absent in the laminated cores (dissolution). Enrichments in Si, TOC, and P are of biogenous origin. The proportion of terrigenous

detrital to biogenous input stays around 1:1, except for samples from core G-32, which are similar in chemical composition to ,>average shale,,. For characterizing the major element composition of the sediments, the individual data are shown in a triangular plot (SiO 2 - A120 395 - CaO-2, see Fig. 2). This kind of presentation is based on the assumption that marine sediments may be regarded as mixtures of three components: i. alumosilicates (represented by the A1203 and SiO 2 content of ,,average shale,,) 2. biogenic silica (partly represented by the SiO 2 content) 3. biogenic carbonate (largely represented by the CaO content) For comparison, the data point for ,average shaIe~, (WEDEPOHL, 1970) is also shown. From Fig. 2 it seems evident, that all samples from the Guaymas shelf represent mixtures of terrigenous detrital material with the chemical composition of ,,average shale,< and biogenic silica. A slight carbonate component is apparent as well. By contrast, the core

Geochemistry of recent TOC-rich sediments from the Gulf of California and the Black Sea Major elements1/ SiO2 TiO2

64.0 0.39 8.88 2.09 1.34 0.02 1.53 t.45 1.38 1.64 0.24 0.74 4.28 11.1

A1203 Fe203 FeS2 MnO MgO CaO ]~qa20 K20 })205 (202 TOC LO}

855

Trace metals0

Trace metals2)

RE elements3)

As Ba Bi Cd Co Cr Cu Mn Mo Ni Pb Se Sr T1 V

Ag Cs Hf Rb Sb Sc Ta Th U

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Zn

6.9 566 0.2 2.5 6.6 44 27 192 11.9 38 17 2.2 167 0.43 101 88

0.2 8 2.3 71 4 7.6 0.45 7.7 5.7

17 33 3.8 15.5 2.8 0.6 2.85 0.4 2.1 0.46 1.24 0.18 1.2 0.17

llMean values of 50 samples, determined by XRF, AA, and ICP-OES 2)Composite sample core E-17, determined by INAA, Ag by AA 3)Composite sample core E-17, determined by INAA, ICP-OES, ICP-MS. Major element concentrations in weight %, trace metals in ppm. Tab. 1. Chemical composition (mean values) of upwelling sediments from the Gulf of California, Mexico. G - 3 2 samples plot close to the >>average shale,< data point. 3.2 T r a c e

metal

chemistry

The following discussion of the trace metal chemistry of sediments from the Guaymas shelf is largely based o n mean values (Tab. 1), since systematic

trends in concentration with increasing core depth are not discernible for most elements. The behavior of Ba, Mo, and V during early diagenesis will be discussed later. Like the major elements, the chemistry of most minor elements may be explained by mixing of two components: terrigenous detrital and biogenous []

core

E-5

core

E-9

AI20 3 - 5

x

core

average ~

E-I 3 +

co, r e

E-I ,9 [] i~

core

..-~.-~

u-,_n! <>

SiO 2

Gulf of California

C c l O 92

Fig. 2. Major components of upwelling sediments from the Gulf of California in the system SiO 2 - A1203-5 - CaO'2 (weight ratios).

856

H.-J. BRUMSACK

material. But, in contrast to most major elements, many trace metals are involved in regeneration processes which take place in the water column. Therefore, a discussion of the trace metal accumulation in such sediments has to consider the metal regeneration occurring within the oxic water column. In Fig. 3 the element/A1 ratios of upwelling sediments from the Gulf of California (diatomaceous muds = DIAT) are plotted versus data for >>average shale<<. If all trace metals are of detrital terrigenous origin exclusively, they should plot on a 45 o straight line which runs through the A1203 data point. This seems to be the case for elements like Co, Cr, and the rare earth elements (REE). Their concentration in the diatomaceous oozes is easily explained by the mineral compound alone. From all elements under investigation, Mn is the only one where substantial mobilization under snboxic conditions seems evident. The following consideration supports this assumption: According to DONEGAN 8C SCHRADER(1982) the average sedimentation rate of sediments from the Guaymas slope equals 185 cm/ka. Then roughly 40 g/cm2/ka sediment are deposited (assuming a wet bulk density of 1.11 g/cm 3 and a water content of 84%). If the terrigenous detrital

material orginally had Mn and A120 ~ contents like ,,average shale<< (850 ppm Mn and 16.7% A1203; WEDEPOHL, 1970), the diatomaceous muds (8.88% A1203) should have a hypothetical Mn content of 452 ppm. The actually determined average Mn concentration equals 192 ppm (see Tab. 1). This is equivalent to a Mn depletion of about 260 ppm, equivalent to a loss rate of 10.4 mg/cm2/ka (1.9 Mol/m2/ka). A similar result was obtained by CAMPBELLet al. (1988) who calculated a diffusive Mn flux from the Guaymas Basin slope sediments of 1.3_+0.6 Mol/cm2/ka based on porewater gradients reported by BRUMSACK &: GIESKES(1983). This Mn flux rate is about a factor of 10 higher than the one calculated by HEGGIE et al. (1987) for the continental shelf of the Bering Sea (0.18 Mol/m2/ka), but comparable to the Mn porewater flux from the Hatteras Continental Rise sediments (1.6 Mol/m2/ka; HEGGIE & LEWIS, 1984). This Mn mobilization at or close to the sediment/seawater interface does not exclude substantial reductive leaching of MnO x phases in the oxygen-minimum zone of the overlying waters (LANDING &: BRULAND, 1980). The reductive destruction of Mn oxide phases may also be an important process mobilizing other trace metals like Co, Cr, Cu, and Ni. The behavior of Co

6

1:1 rat ~ 9 / / S i .'/AI- normalized M p y : [ K -K

4 I-0

3

"~ O o /

~

"~ 3 2

Mn

Z

CuNi~,.,~.~Cr MO

I

Cd

--4

0

9 cs?/_'% ~ ' L n

S~ U,," ~"~'=---~ u e_ ..'AS'LO "Se e / ' ~ . H , ' S m ./1-Vb/E,',

-

-./T~x~ "

TI

-I ~ ' L u -2

Ce

PbT/..~',..

-1

0

!

I

i

1

2

3

i

4

5

6

Log ppm s h a l e Fig. 3. Comparison of the element/A1 ratio of DIAT (diatomaceous muds from the Gulf of California) with the element/Al ratio of >>averageshale<<.

Geochemistry of recent TOC-rich sediments from the Gulf of California and the Black Sea

857

in seawater strongly parallels that of Mn (KNAUER et P b / A I . 10-4 al. 1982; BRULAND,1983), but data which could prove the mobilization of this element within the oxygen2 3 4 5 minimum zone are not yet available. On the other I I i I 9 9 =J hand, porewater data suggest that Co gets mobilized in ~r a suboxic sedimentary column and is fixed at the oxic sediment surface (HEGGIE & LEWIS, 1984; GENDRON 10 et al. 1986). But in the Gulf of California the suboxic zone extends into the water column and therefore Co may diffuse out of the sediments along with Mn. | Seawater profiles of Cu indicate an involvement of 20 -5 this element in biocycling processes. But the eintermediate- and deep-water distribution of Cu may eonly be understood when scavenging processes in the K 30 water column and diffusive supply from the seafloor are considered (BOYLE et al. 1977; MOORE, 1978; BRULAND, 1980). On the other hand Cu (and Ag) u 40, minima are reported from seawater with high Mn con- E centration; these data indicate that both metals are fixed as sulfides in slope sediments (MARTIN & KNAUER, 1984). A similar fixation process may be ac50, tive for Cd (GENDRON et al., 1986). Because higher O concentrations in the oxygen-minimum zone are > neither reported for Cu nor for Co or Ni, it has to be O 60 assumed that these elements are present in lower concentrations in the terrigenous detritus. Therefore, in 9 core E - 5 the following section the available data from the southern Gulf (core G-32) have been used to calculate 9 core G-32 the ,,excess,, metal concentrations of Co, Cr, Cu, and 9 laminated cores Ni in the diatomaceous muds. In contrast to the elements discussed before, the Fig. 4. Anthropogenic increase of the Pb/A1 ratio in surface distribution of Pb in the surface sediments of the Gulf sediments from the Gulf of California. of California (Fig. 4) is governed by anthropogenic activity. But while the Pb/A1 ratio of core G - 3 2 samples GOLDBERG, 1977). For all other trace metals under inapproaches the ,average shale~ value, the diatomaceous vestigation a significant anthropogenic input is not apmuds show a slightly higher Pb/A1 ratio which might parent. indicate a small biogenic Pb enrichment in the diatomaceous muds. 3.3 B i o g e n o u s metal accumulation The anthropogenic Pb contribution may be in upwelling sediments estimated as follows: The Pb mean value for 26 surface A number of elements seems to be slightly but samples from the Gulf (0-30 cm depth) equals 19.3 ppm (9.02% A1203), whereas 10 samples of >150 cm significantly enriched in the diatomaceous muds from depth (core E-17) have a mean Pb value of 14.4 ppm the Gulf of California compared to ~,average shale,, (see (9.14% A1203). Then surface sediments should have a Fig. 3). These elements comprise the trace metals Cd, non-anthropogenic Pb concentration of 14.2 ppm (AI- Mo, Ag, Sb, Se, and, less pronounced, Ba, U, V, and Zn, corrected). The difference of 5.1 ppm Pb represents the besides the major nutrients (C, Si, P). The aim of this anthropogenic Pb contribution. Based on a sediment section is to explain these metal enrichments in view accumulation rate of 40 g/cm2/ka the anthropogenic of more recent plankton and seawater data. Reliable plankton trace metal data like for seawater Pb flux into the sediments is about 0.2 mg/cm2/ka. This value seems comparable to the one from San have only been available for a few years (MARTIN & Clemente Basin (0.04 mg/cm2/ka), where only a KNAUER, 1973, MARTIN et al. 1976, COLLIER & EDminor anthropogenic input is evident. By contrast, the MOND, 1984). Many of the previously published data much more polluted inner California borderland are unrealistically high due to sample contamination basins show Pb fluxes of 1.6 mg/cm2/ka (BERTINE & or analytical difficulties.

858

Element

H.q. BRUMSACK

Literature data

Mean values

Ag As

0.67 a) 4 c)

0.08 d) 10 f)

Ba Bi Cd Co Cr Cu Mo Ni Pb Sb Se T1

55b) 2-8?*) 226) 1.8c) 1.0c) 13.5b) 2e) 12b) 5.4d) 0.5*) 2.7~) 0.1g)

147d) 0.04g) 12d) 1e) 4.9a) 7d) 20 6.4d) 6e)

V Zn

3 e) 131 b)

P Si C

7600h) 36000h) 310000i)

0.2 e) 4 k)

0.1 5

38e) 3.2e) 0.9~) 6c)

17e)

6.6c)

5.2e)

8.1a)

0.2-0.8.) 30 47 d)

80 0.1 12 1 1 10 2 8 6 0.5 1 0.1 3 80

44 c)

7600 36000 310000

a) FOWLER(1977), mikroplankton b) COLLIER& EDMOND(1984), Pacific c) TREFRY& PRESLEY(1976), their Tab. 3.7 without Missisippi el) MARTINet al. (1976), their Tab. 7 - 3 e) MARTIN& KNAUER(1973), their Tab. 6, mean values 0 EISLER(1981)

g) BOWEN(1979), value for fish ~) BROECKER& PENG(1982) i) calculated from ,,Redfield-ratio<< k) STOEPPLER& NErRNBERG(1979) All values in ppm (dry matter).

Tab. 2. Chemical composition of marine plankton.

Despite the large range of reported data, ,,realistict, average trace metal data for a number of elements may be used for the following discussion. These data are listed in Tab. 2. At a first glance marine plankton seems to be significantly enriched in Cd, an element which belongs to the more rare ones in crustal rocks (HEINRICHS et al. 1980). Comparably low concentrations are reported for Mo and V, elements which often are found enriched in TOC-rich sediments, like black shales (VINE & TOURTELOT, 1970). Based on the average chemical composition of diatomaceous sediments from the Gulf of California (DIAT, Tab. 1) the non-detritic element fraction (DIATxs) has been calculated (Tab. 3). It was assumed that, according to the A1 content of DIAT, a certain fraction of the trace metal content is attributed to the detrital terrigenous fraction (represented by ,,average shale<0 exclusively. The following formula was used: Mexs = MeDIAT --

Me h~le 9 AtDIAT Alsh~ie

(where Me = metal concentration, xs = excess, shale = ,,average shale% DIAT = diatomaceous muds from the Gulf of California).

The excess metal concentration determined this way then should represent the specific biogenic element fraction of the sediments from the Gulf of California. In Fig. 5 the excess concentrations calculated for the upwelling sediments from the Gulf of California (Tab. 3) have been plotted versus the plankton data from Tab. 2. A n explicit relation between the bio-fraction of DIAT and the chemistry of marine plankton does not seem to be evident at a first glance. But a more detailed look offers systematic trends for two different groups of elements. O n the one hand, the major nutrients C and P, as well as the trace metal Cd fall onto a straight line. The same seems to be true for the major element Si and the trace metals Ba and Zn. Cd belongs to those elements, which are rapidly regenerated in the water column, like the ,,labile<
Geochemistry of recent TOC-rich sediments from the Gulf of California and the Black Sea Element Ag As Ba Bi Cd Co Cr Cu Mo Ni Pb Sb Se T1 U V Zn P TOC Si A1

Average shale 1) 0.07 10 580 0.1 0.13 10.2" 80* 28* 2.6 43* 22 1 0.1 0.5 3 130 115 700 2000 275000 88500

DIAT 2) 0.2 6.9 566 0.2 2.5 6.6 44 27 11.9 38 17 4 2.2 0.43 5.7 101 88 1050 42800 299000 47000

6

DIAT~3) 0.16 1.6 258 0.15 2.4 1.2 1.5 12 10.5 15 5 4 2.1 0.16 4 32 27 680 41700 153000

1) WEDEPOHL(1970), HEINRICHSet al. (1980); values marked by* are from core G - 3 2 and are normalized to an Al-content like >,average shale<~ 23Average chemical composition of upwelling sediments from the Gulf of California (see Tab. 1) 3) ,,Biogenic<,element fraction of upwelling sediments from the Gulf of California All values in ppm. Tab. 3. Calculation of the *biogenic<< element fraction (DIATx,) of sediments from the Gulf of California.

A number of the other elements which have been analyzed fail between both lines. The special behaviour of Mo, U, and V will be discussed in the next section. To demonstrate the consistency of the sediment chemistry with actual seawater data, the fraction of the bioproduction that is finally buried in the sediments was calculated for some elements (see Tab. 4). Based on an average organic productivity of 0.38 g C / m 2 / d for the Gulf, which is higher by a factor of 3 in the highly productive areas (ZEITSCHEL, 1969), and an average T O C content of 31% for marine plankton (calculated :from an average P content of 0.76% and a C / P ratio corresponding to the >~Redfield-ratio<<(REDFIELD et al. 1963)), 135 mg/cm2/a plankton are produced annually in the surface waters. From this primary production less than 10% of the C and P finally are buried in the ,;ediments, whereas more than 90% of the Si survives t:he transit through the water column. The same is true for trace metals, where less than 10% of the Cd but

859 /

TOC 0 / 5

/~ISi

9 3

I -1

U Mo

"

A~Bi Tt

log ppm DIATxs Fig. 5. Comparison of the ~>biogemc,
of Mo and diagnesis

V

Mo and V are among those elements whose concentration in upwelling sediments cannot exclusively be explained by deposition of terrigenous detrital material or plankton remains alone. Both elements are often significantly enriched in recent and ancient TOC-rich sediments.

P, C d ~ ~,/~1

I

plankton production

I

'

1

Si, Bcl

I

j sediment bor'o'io I Fig. 6. Schematicdiagramof regenerationprocessesoccurring in the water column.

860

H.-J. BRUMSaCK

Element

DIATxJ)

P TOC Cd Zn Cu Ni

680 41700 2.4 27 12 15

Si Ba

153000 258

Mo U V

Plankton2)

PPR 3)

BEAR4)

7600 310000 12 80 10 8

1026 41850 1.6 10.8 1.35 1.08

27 1668 0.096 1.08 0.48 0.60

3 4 6 10 36 56

50000 80

6750 10.8

6120 10.3

91 96

10.5 4 32

2 0.5 3

0.27 0.07 0.41

% BEAR5)

0.42 0.16 1.28

> 100 > 100 > 100

1) Non-detrital terrigenous element fraction of the sediments from the Gulf of California, see Tab. 3 (in ppm) Chemical composition of marine plankton, see Tab. 2 (in ppm) 3) Plankton produktion rate in the water column in mg/cm2/ka (average production was multiplied by 3 = 42 mg/cm2/ka C for highly productive coastal waters) 41Biogenic element accumulation rate im mg/cm2/ka s) Percent element fraction of biogenic plankton production which survives transit through the water column and is finally buried in the sediments 2)

Tab. 4. Calculation of the biogenic element fraction accumulating in the sediments from the Gulf of California. Concentration versus depth profiles for both elements in sediments from the Gulf of California display an increase in concentration with increasing depth (Fig. 7). This increase in concentration is independent from the T O C content and must result from an early diagenetic process. The mobility and availability of Mo and V could be demonstrated by porewater analyses (BRUMSACK& GIESKES, 1983). Mo is correlated with the S content (Fig. 8) which indicates the presence of a Mo sulfide mineral or the coprecipita-

tion of Mo with Fe sulfides (COLLIER, 1985). In any case, the fixation of Mo occurs within the sedimentary column close to the sediment/sewater interface. The source for Mo is seawater (Mo is the transition metal with the highest concentration in seawater, averaging more than 10 ppb). It is trapped as a sulfide, perhaps after being bound to organic matter. In seawater, Mo is present as molybdate (Mo w) which becomes easily adsorbed on organic matter (e.g., humic substances) after reduction to Mo v (SZILAGYI, 1967). This fixation

V/AI-10-4

M o / A I . 1 0 -4 ! 0,.,~+ <

10,.C ~L G,I 'lD

E u

+ +

2

3

4

5

I

I

I

Q DX

10

[] x []

X

20[ O+

+

.C z

~'~

lid "O

• []

BO

E u

+x []

40

• [] + D

X

22

2q

2&

28

X XH Q X •

BO

[] X

40

• Core E - 1 3

+

H

+

5O [] Core E - 5

20

20

+

50

18

0

X

D

§ Core E - 1 7

Fig. 7. Early diagenetic increase of the Mo/Al and V/AI ratios in surface sediments from the Gulf of California.

Geochemistry of recent TOC-rich sediments from the Gulf of California and the Black Sea 20 r

Both Mo and V, therefore, belong to the key elements for interpreting ancient, TOGrich sediments. Their accumulation reflects redox-conditions within the water column and/or the underlying sediment. Under suboxic conditions, like presently occurring in the Gulf of California, the incorporation of both elements is limited by diffusion. Significant in~ corporation of both elements into TOC-rich sediments will occur only when accumulation rates are low. Maximum Mo concentrations are probably limited by coprecipitation with Fe sulfides, while V is limited by the amount and kind of organic matter.

= o/

= 0.85

[n

271

15 m

.2

!

O

10

9

3.5 T h e 0

1

2

3

4

861

5

behavior o f Ba early diagenesis

during

Ba belongs to those elements that enter the sediments as plankton remains. In seawater Ba is M0 / At x 10 - 4 strongly correlated with Si (CHAN et al. 1977). This Fig. 8. Correlation of the Mo/A1 and S/A1 ratios in surface relationship does not imply that Ba is very abundant sediments from the Gulf of California. in opaline silica, but suggests that a Ba-rich phase may of Mo by organic phases induces a concentration gra- exist which displays dissolution characteristics in dient towards seawater, which forces Mo to diffuse into seawater comparable to Si (BISHOP, 1988). The results of MARTIN & KNAUER (1973) and COLLIER &; EDthe sediment. This early diagenetic fixation process for Mo is im- MOND (1984) oppose the assumption of high Ba conportant, because it is limited by diffusion. If sedimen- centrations in opaline silica. Only a small fraction of tation rates are low, higher concentrations of Mo in the the Ba content of marine plankton is bound to a labile sediments may result. If the opposite is true, Mo incor- organic carrier phase. On the other hand, DEHAIRS et poration would be limited because diffusion is a slow al. (1980 & 1987) could confirm the presence of small process compared to sedimentation. Therefore, high barite crystals of possibly biogenic origin in the water Mo-concentrations of TOC-rich, marine sediments in- column. Since seawater is only slightly undersaturated with respect to barite (CHURCH & WOLGEMUTH, dicate low sedimentation rates. V is an element with a redox chemistry that seems 1972), a significant fraction of this phase may accomparable to that of Mo. In seawater, V is present as cumulate in the sediments, especially in highly producthe metavanadate anion (VO3-). After reduction to tive areas like the Gulf of California. the vanadyl cation (VO 2+) it is easily sorbed by In Fig. 9 the concentrations of Ba and sulfate as well organic matter (SZALAY & SZILAGYI, 1967). In sea- as the sulfur isotopic composition of sulfate in water, V is slightly involved in biological regeneration porewaters are plotted versus depth for core E-17. The cycles. The V concentration in seawater is about 1.7 non-terrigenous Ba fraction of the sediments (Bax) is ppb. The relatively minor V depletion in surface also shown. waters which, however, correlates with P (COLLIER, Except for samples from the core top, where the 1984), explains the comparably low V content of mobilization of labile, probably organically bound Ba seems evident, the porewater Ba concentrations are marine plankton. In porewaters from the Gulf of California, V exhibits determined by barite solubility. The porewater sulfate a strong correlation with ~yellow substance,~ (BRUM- depletion due to the action of sulfate-reducing bacteria SACK& GIESKES, 1983), an indication for the ability of (with parallel heavier sulfur isotopic composition of "V' to form metallo-organic complexes. Besides Ni, V the remaining porewater sulfate) corresponds with inbelongs to those elements which are found enriched in creasing Ba porewater concentrations (BRUMSACK geoporphyrins (SIMONEIT,1978). The increase of the GIESKES, 1983). The very high Ba porewater data V/A1 ratio with increasing burial depth (Fig. 7), below the sulfate reduction zone (> 3 m core depth) intherefore, seems to document the early diagenetic in- dicate dissolution of a Ba-rich phase, possibly barite. In the depth range of very low porewater sulfate concorporation of V into TOC-rich sediments. Since V does not form stable sulfides, the association with centrations barite seems to precipitate. This hypothesis is supported by the increase in the Ba/_Al-ratio of the organic matter seems most likely.

862

H.-J. BRUMSACK Core BAM E - 17 0

10

20

,

,

.

30

solids

, 9 m Mot SOl. = PW

0

2

/.

6

8

,

=

,

=

, = ppm

BOpw

ppm Bo e x c e s s

200 400 i ,';" ,:z i i i

9t';~, "ii." ;,:~ %'

SO/-"

PW

=. .= 6345

/

*20

*30 A

PW

Bapw

*40

.50

~ 3&S PWsulfot e

*60 (ret. C D T )

Fig. 9. Early diagenetic behavior of Ba and sulfate in porewaters and solids in core E-17 from the Gulf of California. solids in this depth interval (BRUMSACK, 1986). Whereas Ba diffuses upwards from deeper sediment layers, porewater sulfate diffuses into the sediments from the sediment/seawater interface. A zone of barite formation and dissolution develops, which moves as a ,,barite front~, through the sedimentary column, keeping a more or less constant distance to the sediment surface, as long as the sedimentation rate does not change significantly. The barites formed by this process then should be isotopically heavy, since only the porewater sulfate reservoir depleted in 32S is available for barite formation. When sedimentation rates or sulfate reduction rates drastically change, the ,,barite front, may stay at a certain depth interval and barite concretions may form. Such concretions have been described from the Japan

Sea (SAKAI, 1971) and off the California coast (GOLDBERG et al., 1969). The heavy sulfur isotopic composition of these concretions (+54 to +78%o rel. CDT) makes an early diagenetic origin of these nodules very likely, since such heavy sulfur isotope values are only reported from the residual porewater sulfate reservoir of TOC-rich sediments. A hydrothermal origin, like postulated by SAKAI(1971), would require very special conditions during formation of these concretions and seems not to be realized in nature. It should be mentioned, that such barite concretions with a heavy sulfur isotope composition are not only reported from recent but also from old, e.g., Mesozoic sediments. They have been frequently recovered at several DSDP sites (DEAN & SCHREIBER, 1978). Our

Geochemistry of recent TOC-rich sediments from the Gulf of California and the Black Sea analysis of barite concretions in Cenomanian/Turonian sediments from the Gibraltar arch area yielded Sisotope values of +50 to +70%0 (rel. CDT). An early diagenetic origin according to the above mentioned process seems very likely, especially since these barites are intercalated with black shales.

4. Comparison of the chemical composition of

863

In any case, bioaccumulation of trace metals by marine plankton does not seem to be a process which exclusively is responsible for the extreme metal content of ancient black shales, e.g., the Permian ,,Kupferschiefer,,, like proposed by BRONGERSMASANDERS (1965). This example rather documents, that TOC-rich sediments are ideal traps for metal-rich solutions which migrate into or through them during later diagenesis (WEDEPOHL, 1971).

sediments from the Gulf of California with other upwelling localities Besides the Gulf of California diatomaceous muds, the upwelling sediments from off the Namibian coast (CALVERT & PRICE, 1970; CALVERT, 1976; BRONGERSMA-SANDERSet al. 1980) and the California borderland basins (BRULAND et al. 1974; BERT1NE & GOLDBERG, 1977) are very well studied. From all these investigations it seems evident that, except for some elements (like Mo, U), high trace metal contents are not reported from such biogenous sediments. In view of the chemistry of marine plankton (Tab. 2) and the behavior of trace metals in seawater (regeneration processes), this result is not surprising. A comparison of the chemical composition of upwelling sediments from different localities is given in Tab. 5. For the majority of elements presented in this table a biogenic metal enrichment in the same order of magnitude is noticeable. Element Gulf of SW Africa California St. Barbara California1) shelf2) borderland3) Basin4) Ag Ba Cd Co Cr Cu Mn Mo Ni Pb Se V Zn

0.2 566 2.5 6.6 44 27 192 11.9 38 17 2.2 101 88

-.1.4 280 650- 8306 (32?) 2 5.2 -.123 103 18-129 s) 38 124 360 15 3 76 50 3 -32 s) 10 (11.6?) -.139 49 113

<0.5 575 1.3 10.4 88 -.305 6 -.-.-.-.108

1) This work, Tab. 1 2) BRONGERSMA-SANDERSet al. (1980) 3) BRULANDet a]. (1974) 4) BRUMSACK(1988) s) CALVERT& PRICE(1970) 6) NG & PATTERSON(1982) All values in ppm. Tab. 5. Trace metal chemistry of recent upwelling sediments.

5. The Black Sea The Black Sea exemplifies the type locality for stagnant conditions in the water column. It represents the largest anoxic basin in the world (423.000 km 2 areal extent, 543.000 km 3 volume; Ross et al. 1974) and, due to its interesting geological situation as well as chemical nature, already early found the attention of marine scientists (see, e.g., MURRAY, 1913). The Black Sea basin, with a maximum water depth of 2200 m, was a brackish lake before it was connected to the Mediterranean 5000 to 7000 years ago during Holocene sea level rise. The dense, saline Mediterranean water entering the Black Sea through the Bosporus, a shallow strait (averaging 36 m water depth), descended to the seafloor and created a welldefined pycnocline. Caused by the restricted circulation of oxygen containing water, anoxic bottom waters developed ca. 5 000 years ago, which gradually extended to the whole basin up to water depths of 100 to 200 m. Two different water masses may be distinguished in the present Black Sea; the deep water (22.5%0 salinity), consisting of a mixture of Mediterranean surface water (200 km3/a; 35%o salinity) and Black Sea surface water, and the Black Sea surface water (17.5%o salinity) which represents a mixture of river water (200 km3/a, corrected for evaporation) and Black Sea deep water. The halocline has an average water depth of 150 m. The exchange between both water masses is limited. Annually, 500 km 3 surface water (together with 200 km 3 Mediterranean water) are mixed into the Black Sea deep waters, whereas 700 km 3 deep water are mixed into the surface water (FONSELIUS, 1974). Therefore, annually only 1%o of the water masses are exchanged. The residence time of the water, therefore, is about 103 a (see 14C data by (~)STLUND, 1974); this time interval is equivalent to one mixing cycle of the whole oceans. For this investigation 22 sediment samples from 5 cores, taken during cruise 49 of R / V ~Atlantis II,~ (Woods Hole Oceanographic Institution), have been analyzed. A detailed description of the sampling loca-

864

H.-J. BRUMSACK

tions together with sedimentological, structural and oceanographic data are published in DEGENS ~x~ROSS (1974). Twelve of the samples under study (cores 1445, 1450, 1451, and 1462) are sapropels with TOC contents ranging from 1.2 to 14.7% and were sampled exclusively from the western part of the Black Sea (see Fig. 10). They represent part of a profile from the basin center (core 1464, 2186 m water depth) to the shelf (core 1451, 460 m water depth). Core 1474, by contrast, was recovered from the eastern Black Sea. Since the TOC values of this core average only 0.8% it seems like these samples are Neoeuxynian in age and do not belong to the sapropels. For this reason, these samples are of subordinate importance for the interpretation of the chemistry of Black Sea sapropels. 5.1 C h e m i s t r y of Black sediments

Sea

All analytical data are listed in the appendix, mean values are listed in Tab. 6. Regarding the major element composition of Black Sea sediments, they may be characterized as marls, since the carbonate content of all samples averages 25% (n=22). They represent a mixture of detrital clays and biogenic carbonate (coccoliths) with varying amounts of TOC. When the data 28 ~

30 ~

32 ~

are plotted into the SiO 2 - A1203"5 - CaO-2 triangle, all samples fall onto a dilution line connecting >>average shale,, with carbonate (Fig. 11). While the northwestern Black Sea receives considerable amounts of detrital clays (83' 106t/a) from the river Danube, terrigenous detritus is transported to the southeastern Black Sea by numerous small rivers from the Caucasus and Anatolia (SHIMKUS & TRIMONIS, 1974). Ultramafic rocks are present in the latter area (BRINKMANN,1974). This fact explains the enhanced Mg (as well as Cr and Ni) content of core 1474 samples, which reflects the higher abundances of montmorillonite and chlorite in the southern source area (MULLER &~ STOFFERS, 1974; HIRST, 1974). The higher than normal Na content is due to porewater salts; a salt correction could not be performed because of the small sample sizes. Furthermore, Black Sea sediments are characterized by higher TOC, S, and P contents. These elements reflect the euxinic environment of deposition and the high preservation rate for organic matter and associated nutrients. At a first glance, Black Sea sediments do not show abnormal trace metal concentrations (see Tab. 6), except for the element Mo. On the other hand, a number of trace metals are slightly but consistently enriched,

34 ~

36 ~

38 ~

t~O ~

42 ~

% \ 46 ~ 46 ~

Denau

44 ~

44 ~

1451 9

.----" 01450

.....

~%~%~

.-,-

--" 9

\~:

Black

~,~

SEE].

1462

1445

r'""

'~

\

""

.--,

,'

/ 1474

/

L

42 ~

~ -

!

28 ~

I00

200

I

I

!

/

i9

42 ~

300 l

m

30 ~

32 ~

Fig. 10. Sampling localities ~r Black Sea sediments.

34 ~

36 ~

38 ~

40 ~

Geochemistry of recent TOC-rich sediments from the Gulf of California and the Black Sea compared to ,,average shale<<. A m o n g these elements are Ag, As, Cd, CU, Ni, and V, but also z n . Many of these trace metals exhibit pronounced correlations with T O C , S, and P (see Fig. 12 and Tab. 7). While Mo, V, Cd, and Zn preferentially correlate with T O C , Co seems to be associated with S. Ag, As, and partly V correlate with both T O C and S, whereas Cu and N i are related to P as well. The terrigenous origin of Cr is demonstrated by the strong relationship to A1. Most of the Sr is hosted in the carbonate fraction. Similar results for several of these elements have already been reported by VOLKOV & FOMINA (1974). 5.2 D i s c u s s i o n

of

results

In the following section the chemical composition of Black Sea sediments will be discussed in view of more A

Major elements B

A

]7205 TOC S

30.2 0.41 9.7 4.54 0.08 2.12 13.2 3.39 1.88 0.17 6.47 1.28

42.4 0.67 12.8 6.46 0.15 4.19 10.0 2.59 2.17 0.15 0.80 0.77

CaCO3

25

32

16

TiO 2 A1203 Fe203 MnO MgO CaO Na20 K20

A Si/A1 Ti/AI Fe/A1 Mg/A1 Ca/A1 Na/A1 K/AI I?/AI TOC/A1 S/AI TOC/S TOC/P

2.86 0.053 0.65 0.31 1.96 0.43 0.29 0.013 0.80 0.20 3.4 50

recent results from marine Chemistry. The most relevant book about the largest anoxic basin of the world is <
C

35.7 0.53 11.1 5.41 0.11 3.06 11.7 3.03 2.01 0.16 3.89 1.05

SiO 2

Ag As Ba Cd Co Cr Cu Mn Mo Ni Pb Sr V Zn

Major element/A1 ratios B C 2.79 0.047 0.63 0.26 2.68 0.56 0.31 0.016 1.37 0.27 5.1 82

A = mean value all samples (n=22) B = mean value sapropels (n= 12) C = mean value core 1474 (n= 10)

1.3 12

0.11 21 478 0.67 27 117 71 888 45 118 16 449 158 82

A

2.94 0.060 0.67 0.38 1.10 0.28 0.26 0.010 0.11 0.11

865

Ag/A1 As/A1 Ba/A1 Cd/Al Co/AI Cr/Al Cu/A1 Mn/A1 Mo/A1 Ni/A1 Pb/A1 Sr/A1 V/AI Zn/A1

0.021 3.9 91 0.13 4.9 19 13 149 9.O 20.3 2.8 106 28.5 14.4

Trace metals B 0.15 25 624 1.04 27 70 87 594 80 96 17 597 173 83

C 0.06 16 304 0.23 27 174 52 1240 3 144 14 271 140 82

Trace metal/A1 ratios B 0.031 5.1 130 0.22 5.6 14 18 117 16.1 19.5 3.4 161 35.1 16.4

C

0.009 2.3 45 0.03 4.0 26 7.6 187 0.4 21.4 2.1 41 20.5 12.1

Major element concentrations in weight %, trace metals in ppm. Major element/Al-ratios expressed as weight ratios. Trace metai/Al-ratios expressed as weight ratios - 10-4.

Tab. 6. Chemical composition of sediments from the Black Sea (mean values).

866

H.-J. BRUMSACK H

core

1445

core

1458

A[203 9 5

•

average A

1451

core +

r-I.\

1462

core []

1474

core 0

Si0 2

BlackSea

CctO. 2

Fig. 11. Major components of sediments from the Black Sea in the system SiO2 - A1203"5 - CaO'2 (weight ratios). BREWER & SPENCER (1974). Compared to more recent results, the reported concentrations for several elements in Black Sea water seem to be too high; contamination problems during sampling and analysis of seawater had not yet been realized. The trace metal content of upwelling sediments seems to reflect the uptake of metals by marine plankton and regeneration processes within the water column, whereas this biogenic metal enrichment seems to be of subordinate importance for the Black Sea (VOLKOV& [FOMINA,1974). Of major importance is the metal input by rivers and Mediterranean seawater (ignoring aeolian input). Therefore, a simple model will be presented in the following section, which is based on mass balances of the potential metal sources and considers paleoenvironmental conditions leading to metal accumulations in sapropels.

5.3 S o m e considerations regarding the accumulation of heavy metals in Black Sea sediments According to 14C-measurements conducted by C)STLUND (1974), the average residence time of Black Sea waters is 935 a. Since the thickness of the anoxic water column is about 2000 m, roughly 2 m of water are exchanged annually. A similar calculation, based on the Mediterranean seawater input and the annual exchange between surface and deep water of 700 km 3

over an area of 423.000 km 2, leads to an average oscillation of the water masses through the redoxclyne of 1.7 m/a. The following considerations shall help to evaluate whether the fluctuation of the waters at the O2/H2S boundary is large enough to allow the trapping of sufficient quantities of trace metals in the anoxic zone to explain the metal signals in the sapropel layers. This mass balance is initially based on data for Mo and Cd, elements which exhibit comparably low concentrations in terrigenous detritus (mean values for ,,average shale,,: 2.6 ppm Mo and 0.13 ppm Cd). According to PILIPCHUK& VOLKOV(1974) the difference in Mo concentration between Black Sea surface and deep water is 2 ppb. Using the above mentioned water exchange rate of 1.7 m/a, about 3.4 mg Mo are annually removed per m 2. Since the average sedimentation rate is 20 cm/ka (MANHEIM & CHAN, 1974), about 40 g/m 2 of sediment are deposited anually, based on a porosity of 83% and a density of 1.2 g/cm 3 (KELLER, 1974). These 40 g sediment then should receive the 3.4 mg Mo removed in the anoxic zone of the water column. The hypothetical mean Mo content of recent Black Sea sediments then should be about 85 ppm. The actually determined average Mo content of 12 sapropel samples is 80+56 ppm, which is very close to the theoretical value. Therefore, it may be concluded at least for this element that the excess Mo concentration found in Black Sea sapropels originates from the overlying water column.

Geochemistry of recent TOC-rich sediments from the Gulf of California and the Black Sea 21-

"O U

I 5~

E Q,

9-, 6~

oq,ml

1 2"

9 r-0.78 (u-12)

3ie-= O

2

281918~

Z

=

16~

+

m

<

15~ 14~

N

13i~ o I

r-0.89 (n-22)

9 " r.O.68 ( u - ' 2) r-0.86 ( a - 2 2 )

. . . .

llJO

LS

S

7.S

le

12.S

15

t

17.S

2.S

S

W

E 8a_

188 168 148 128

0 0 0

x

12

x9

E Q.

t, o

9 8g.86,838

~ Q o+o

o tg

Q.

r-0.65 (mail) r-O.71 (a-22)

o

----~

?.S

10

12.S

15

17.5

% TOC

% TOC

Z724211B1512-

867

i

i

i

i

,S

I

l.S

2

0

9

88 68 40 28

~ ~176176 r-0.113( - . l l ) + r-0.79 (,,-22)

8 2.S

0 0

188

3

1

J

.S

1

%s

I.S

!

2.S

3

%s C o r e ~ 445

IBO ~

U

+ o

100~

o 9

b

U

~ ",

B0i L

218888168 140.

~

160 1401 120

[

60~

L

48 a

§

~

28 J 8.: . . . . e

r-0.86 (nai2) raO.Sl (ha22)

120

e~o ~ ~

l

180 8868

§

C o r e 1450 Core

1451

Core

1462

Core I 4 7 4

9 ~o

40-

r-0.98 (n-12) ruO.?2 (nu22)

9

28-

0 .~

,I

,IS

,2

,2S

.3

% P~O~

t

S

It

IS

2~

H

% AI20~

Fig. 12. Correlationsoft~ce metals with TOC andSinsedimentsfrom theBlackSea. The average Cd concentration in 12 Black Sea sapropel samples is 1.04+0.59 ppm. Using a sediment accumulation rate of 40 g/m2/a, about 0.04 mg/m2/a Cd must have been removed from the water column by sulfide precipitation. Based on the water exchange rate between the oxic and anoxic reservoir (1.7 m/a) this removal mechanism must reduce the Cd concentration in Black Sea waters by 0.024 mg/m 3 (24 ng/1). According to analyses performed by JAcoI3s et al. (1987) the

actual decrease in Cd concentration at the O2/H2S boundary amounts to 12 ng/1 in the Cariaco Trench and 38 ng/1 at the Framvaren Fjord, which agrees with the Cd removal required for the Black Sea. 5.4 A s i m p l e mass balance model for Black Sea sapropels Knowing the average chemical composition of Black Sea sapropels (Tab. 6) the non-terrigenous fraction of

868

Ag As Ba Cd Co Cr Cu Mn Mo Ni Pb Sr V Zn Zn/A1 TOC S

Ag As Ba Cd Co Cr Cu Mn Mo Ni Pb Sr V Zn Zn/A1 TOC

S

H.-J. BRUMSACK

TOC

S

0.64 0.73 0.20 0.78 0.44 0.02 0.88 0.12 0.75 0.77 0.21 - 0.39 0.79 0.36 0.68

0.65 0,65 -0.35 0.55 0.65 0.21 0.83 0.63 0.30 0.80 0.17 - 0.46 0.70 0.41 0.46 0.65

TOC

S

~ ~ 0.51 0.89 0.29 -0.68 0.87 -0.36 0.88 - 0.16 0.42 0.06 0.70 0.26 0.86

0.71 0.63 0.01 0,65 0.50 -0,38 0.79 0.14 0.50 0. I2 0.33 -0.13 0.61 0.31 0.58 0.69

Black Sea sapropels (n= 12) P A1 0.53 0.48 0.24 0.59 0.23 0.20 0.86 0.45 0.55 0.86 0.29 - 0.39 0.66 0.43 0.42 0.86 0,63

0.16 0.23 0.25 0.00 0.15 fl,9_8 0.22 0.26 0.20 0.47 0.87 - 0.72 0.22 0.88

All Black Sea samples (n=22) P A1 0.54 0.47 0.32 0.56 0.21 0.15 ~ 0.24 0.53 0.38 0.3 ! -0.23 0.65 0.35 0.42 0.74

- 0.23 - 0.02 - 0.11 -0,35 0.16 0.72 -0.03 0.39 - 0.26 0.63 0.50 -0.77 0.09 0.75

Fe

Ca

0.62 0.68 0.05 0.42 0.67 0.76 0.45 0.11 0.42 0.59 0.86 - 0.75 0.49 0.90

-0.48 - 0.63 -0.34 -0.45 -0.36 - 0.81 - 0.68 - 0.23 -0.64 -0.81 -0.84 fl_..8.3_ - 0.66 -0.93

Fe

Ca

- 0.06 0.19 - 0.32 -0.23 0.51 0if_9_ 0.02 0.38 - 0.25 ~ 0.34 -0.78 0.22 0.66

- 0.23 -0.46 - 0.17 -0.17 -0.38 -0.41 -0.52 -0.21 - 0.29 - 0.65 - 0.69 0.81 -0.59 -0.91

0.58

Underlined values are significant at the 99.9 % confidence level. Emphasized values are significant at the 99.0 % confidence level. Tab. 7. Correlation coefficients of major elements with trace metals in Black Sea sediments.

trace m e t a l s o r i g i n a t i n g f r o m t h e water c o l u m n trapp i n g m e c h a n i s m d e s c r i b e d above m a y be estimated. T h e s e c o n s i d e r a t i o n s are based o n t h e a s s u m p t i o n t h a t t h e detrital clay fraction is characterized b y e l e m e n t / A 1 ratios c o m p a r a b l e to ,,average shale,< (WEDEPOHL, 1970). Since t h e m e a n A1 c o n c e n t r a t i o n o f Black Sea sapropels is k n o w n , t h e excess trace m e t a l fraction, w h i c h m u s t originate f r o m t h e water c o l u m n , m a y be calculated. Tab. 8 lists t h e m e a n values as well as t h e terr i g e n o u s detrital a n d excess trace m e t a l c o n t e n t o f

e l e m e n t s , w h i c h m a y f o r m stable sulfides u n d e r seawater c o n d i t i o n s a n d / o r are reactive w i t h respect to c h a n g e s in t h e redox potential. F o r m o s t o f t h e s e e l e m e n t s s t r o n g c o r r e l a t i o n s w i t h T O C a n d / o r S are noticeable (see Fig. 12), illustrating t h e n o n - e x c l u s i v e t e r r i g e n o u s origin of m o s t metals. Based o n t h e already m e n t i o n e d s e d i m e n t a c c u m u l a t i o n rate o f 40 g / m 2 / a a n d a water e x c h a n g e rate o f 1.7 m / a , t h e e l e m e n t m a s s w h i c h h a s to be r e m o v e d f r o m t h e water c o l u m n at t h e O 2 / H 2 S interface for explain-

Geochemistry of recent TOC-rich sediments from the Gulf of California and the Black Sea ing the excess concentration in the sapropels has been calculate& This hypothetical ,,minimum,, element concentration required in surface waters is compared with the most likely surface water composition. Due to the lack of reliable data it was assumed that the Black Sea surface water represents a 1:1 mixture of seawater and river water (see Tab. 8). The minimum trace metal concentrations in Black Sea waters to explain the excess concentrations in the sapropels have been plotted against the available metal concentrations in surface waters in Fig. 13. A close relationship between the potential metal source (Black Sea surface water) and sink (sapropel layers) is evident. Considering the uncertainity of the water composition it seems remarkable that the trace metal balance is consistent within a factor of 3. It may be concluded that the excess metal concentrations of the sapropel layers indeed may originate from the water column. This demonstrates the efficiency of anoxic environments in trapping trace metals. From Fig. 13 it also seems evident, that the elements As, Mo, and U are not completely removed in the anoxic zone. These elements exhibit high concentrations in seawater and removal processes must include a reduction step.

6. Some considerations regarding the importance of upwelling sediments and sapropels in the present oceans Under present day oceanographic conditions TOCrich sediments are predominantly deposited at the western continental margins, in water depths ranging

B1 ack Sea. M o d e l

3.5

e

3

C

24

Cul/'m/U/

/ / _ _ . J c o,

"~,

1 -&5

0

,5

]

1.~

g

2.$

a

log ng/l required Fig. 13. Trace metal balance of the Black Sea.

a.$

4

869

from 200 to 1000 meters. This depth interval represents only 4% of today's area of the oceans (REID, 1974). According to an estimate by BATURIN(1983) upwelling areas have an areal extent of 0.5" 106 km 2, which is equivalent to only 0.14% of the ocean area or 3% of the area covering the depth interval from 200 to 1000 meters. This fact demonstrates, that the upwelling phenomenon is restricted to comparably small parts of the oceans. Enxinic, stagnant basins (Black Sea, Cariaco Trench, Norwegian fjords, etc.) cover a comparably small area of the present seas. This does not necessarily mean that both environments have the same relevance with respect to the deposition of TOC-rich sediments. Due to the high organic primary productivity upwelling areas are characterized by accumulation rates which are by about a factor of 20 higher than those of stagnant basins like the Black Sea. Therefore, in today's oceans about 20 times more upwelling sediments are deposited than sapropels. The depositional conditions prevailing in the present oceans are not directly transferable to the geological past. Depending upon climatic and tectonic parameters, suboxie or euxinic paleoenvironments may have persisted during certain time intervals in larger parts of the ancient oceans. These periods then should be documented in the sedimentary column.

7. Trace metal concentrations in Cretaceous black

shales from the Cenomanian/Turonian boundary event (CTBE) As has been mentioned in the introduction, many ancient TOC-rich sediments are characterized by high abundances of specific trace metals, including Cd, Ag, Mo, Zn, V, Cu, and As. In comparison to ,,average shale~, low in TOC (WEDEPOHL, 1970) these metals are often enriched by factors of 10 to 300 (BRUMSACK & THUROW, 1986). Frequently concentration levels are attained, which are rarely found in recent TOCrich sediments. Therefore it seems worthwhile to use trace metals as indicators of the environment of deposition of such sediments. From the preceeding chapters it seems evident, that recent sediments from high productivity environments (,,upwelling~ sediments) are not characterized by extremely high trace metal concentrations. This is due to the comparably low trace metal concentration of contemporaneous marine plankton, the intense nutrient and metal regeneration processes which take place in the water column, and the high accumulation rate of such strata. By contrasts, sediments which have been deposited under anoxic water column

870 element Ag As Cd Co Cr Cu Mo Ni Pb U V Zn A1

H.-J. BRUMSACK S

L

E

M

SW

RW

Mix

0.15 25.4 1.04 26.6 70 87 80 96 17.1 161) 173 83 9.74%

0.04 5.8 0.08 11 55 26 1.5 40 12.8 1.8 76 67 9.74%

0.11 19.6 0.96 15.6 15 61 78.5 56 4.3 14.2 97 16 0.00%

2.6 461 22.6 367 353 1435 1847 1318 101 334 2282 377

2.7 1700 78 1 210 250 10600 470 2 3000 1800 390

3 1700 20 200 1000 1500 500 500 100 240 1000 450

3 1700 49 100 605 875 5550 485 51 1620 1400 420

S) L) E) M)

Mean values of Black Sea sapropels from Tab. 6 (in ppm) Terrigenous detrital element fraction of S (in ppm), based on Al-corrected ,,average shale,, data Non-terrigenous detrital element fraction of S (=excess) Minimum element concentration in surface waters (in ng/kg), which has to be removed at the O2/H2S interface to explain the sapropel chemistry (based on a water exchange rate of 1.7 m/a and a sediment accumulation rate of 40 g/m2/a, see text) SW) Seawater concentrations in ng/kg based on data from BROECKER& PENG (1982), BRULAND(1983), MART~Net al. (1983), FLEGAL& PATTERSON(1983), COLLIER(1984 & 1985), JEANDELet al. (1987), STATHAMet al. (1987) RW) River water concentrations in ng/kg based on data from MARTIN& WHITFIELD(1983), SHILLER&; BOYLE(1985), IqEINRICHSet al. (1986b);non-anthropogenic Ag value estimated in analogy to Cd and Zn seawater/river water concentration ratio Mix) Assumed trace metal concentrations of Black Sea surface water; equivalent to a 1:1 mixture of seawater (SW) and river water (RW) 1) Mean vaule from DEGENSet al. (1977) Tab. 8. Trace metal balance of the Black Sea.

conditions (sapropels) seem to accumulate metals pro- SACK, 1988), based on today's fluvial runoff portional to the metal availability in surface waters. (HOLLAND, 1978) and river water composition (see High concentrations of elements like Cd, Ag, Zn, Tab. 8). and Cu, which are involved in regeneration processes, indicate enhanced preservation in the water column. Therefore TOC-rich sediments do not necessarily 8. Conclusions reflect high bio-productivity of the overlying water column. O n the other hand elements like Mo, V, As, 1. The chemical composition of recent upwelling sediments is affected by bio-accumulation and and U enter the sedimentary column predominantly following regeneration processes under oxic water during early diagenesis. Anoxic conditions within the column conditions. Trace metals which are coupled water column or at the sediment/seawater interface, to the ,,labile,~ nutrients, like Cd and Zn, are found combined with low sediment accumulation rates then less enriched in this sediment type than may be exare required to produce a significant authigenic trace pected from the chemical composition of marine metal signal. A n intensified oxygen-minimum zone plankton. (ARTHUR et al. 1984) or even an anoxic water column (BRUMSACK, 1980) therefore seems to be a likely 2. Several redox-sensitive and stable sulfide forming elements like As, Mo, U, V, which exhibit relatively paleoenvironment for many Cretaceous black shales. high concentrations in seawater (> 1 ppb), enter the Furthermore trace metals might provide a time sedimentary column predominantly during early frame for black shale deposition, if areal extent and diagenesis. The absolute concentrations of these chemical composition are known. By performing mass elements then depend upon the sedimentation rate. balance calculations it can be demonstrated, that at least 500,000 a are required for the deposition of CTBE 3. Barite concretions may form during early diagenesis in TOC-rich sediments in the depth black shales during an oceanic anoxic event (BRUM-

Geochemistry of recent TOC-rich sediments from the Gulf of California and the Black Sea range where porewater sulfate concentrations approximate a value of zero. These barites are characterized by very ,,heavy,, sulfur isotope ratios. 4. Anoxic water column conditions like those presently occurring in the Black Sea, are ideal traps for many redox-sensitive and stable sulfide forming elements. The trace metal composition of sapropels results from fluvial and marine metal input and the accumulation rate of terrigenous detrital material. !5. In the modern oceans more TOC-rich sediments are deposited in areas of high organic productivity than in euxinic basins. 6. Trace metal concentrations of Cretaceous black shale sequences provide informations about the paleoenvironment of deposition of such strata. These conditions must have been very different from those found in today's oceans. Cretaceous black shale layers seem to represent periods of enhanced preservation of organic matter rather

871

than high bioproductivity. Euxinic conditions must have persisted in large parts (expanded oxygen m i n i m u m zone) or even the whole water column. Acknowledgements I would very much like to thank J. M. Gieskes (La Jolla, U.S.A.), H. Schrader (Corvallis, U.S.A., now Bergen, Norway), and K. H. Wedepohl (G&tingen, ER.G.) for their scientific and logistic support during this study. Thanks also to captain and crew of the Mexican R/V ,,Mariano Matamoros,,. The Black Sea samples were made available through T. Bralower. REE determinations were kindly carried out by B. Schnetger. I am very much obliged to A. C. Campbell and J. Rullk&ter, who kindly reviewed the manuscript. This publication forms part of a Habilitation Thesis submitted to the Geoscience Department of the University of G&tingen (F.R. Germany). Financial assistance by the German Science Foundation (DFG) is gratefully acknowledged.

Appendix (analytical methods, precision and accuracy) The analytical methods used during this investigation are listed in the following Table.

Ref.:

XRF

ICP-OES

AES flame

AAS flame

AAS flameless

Coulometry

SiO2 TiO2 A1203 Fe203 MnO MgO CaO P205

A1 Ba Ca Co Cr Mo Ni Sr V REE

Na K

Cd Cu Fe Mn Zn

Ag As Bi Cd Co Cr Cu Mo Ni Pb Sb Se T1 V

C

b, c

c, d

c

c, e

f, g

a

It= SCHULZ-DOBRICK(1975) b=WALSH & Howm (1980) c=HEINmCHS et al. (1985)

d = HERRMANN(1975) e = HEINRICHS& KELTSCH(1982)

S

f= HERRMANN& KNAKE(1973) g = LANGE& BRUMSACK(1977)

Acid digests of the samples (100 mg sample, 3 ml HF, 3 ml HC10,, 1 ml HNO 3, kept at 180~ for 5 h, evaporated to dryness, residue dissolved in 1 ml HNO3, filled up to 50 ml volume with deionized water, solutions stored in precleaned PE-bottles) have been performed in contamination-free teflon autoclaves (HEINRICHSet al.,1986a). XRF-analyses have been made on Li-metaborate fused glasses (Sr for internal standardization). If enough material was available, all analyses were carried out in duplicate. The precision of the methods used is better than 3 % (rel.) for major elements and in the 5 to 10 % (tel.) range for trace metals. Close to the detection limit a larger error (up to 30 % rel.) is possible. For flameless AA determinations matrix modifiers (0.1% La-nitrate or ammonium-phosphate solutions) have been applied. The accuracy of the methods has been checked by analyzing international reference materials (SGR-1, G-2, W-l).

872

H.-J. BRUMSACK Appendix (Gulf of California data) sample #

ppmAs

ppmBa

ppmBi

p~mCd

ppmCo

ppmCr

ppmCu

E-5 E-5 E-5 E-5 E-5 E-5 E-5 E-5 E-5 E-5 E-5

2.0 4.5 7.5 i0.5 13.5 16.5 22.5 28.5 37.5 49.5 54.0

3.8 4.6 5.5 6.7 7.0 7.1 7.4 9.2 7.2 6.0 6.6

627 611 584 552 550 562 564 584 524 592 568

0.34 0.19 0.16 0.14 0.13 0. i0 0.12 0. ll 0.ii 0. i0 0. i0

3.5 2.9 2.8 3.2 2.8 3.0 2 99 3.0 2.7 3 91 2 .4

8.2 7.8 8.2 8.3 7.8 7.7 7.2 6.8 5.7 5.8 6.8

51 48 48 45 43 45 47 45 40 42 50

33 31 31 27 26 25 26 25 24 26 27

E-9 E-9 E-9 E-9 E-9 E-9 E-9 E-9 E-9

1.5 4.5 7.5 10.5 13.5 19.5 25.5 34 .5 48.5

7.2 6.4 6.3 15.3 12.4 7.5 5.5 4 .1 6.6

598 595 596 482 548 479 502 586 556

0.21 0.18 0.23 n.d. 0.19 0.15 0.16 0.12 0.19

3.0 3.0 3.2 2.9 2.9 1.7 2.5 I. 9 3.5

7.7 7.8 7.8 6.2 6.7 6.3 6.3 5.7 5.0

45 42 45 36 39 34 38 39 42

30 30 30 27 31 24 24 24 24

E-13 E-13 E-13 E-13 E-13 E-13 E-13 E-13 E-13

1.5 4.5 7.5 10.5 13.5 19.5 25.5 34.5 45.5

4.5 3.8 4.9 4.0 4.6 6.9 5.1 3.6 6.9

515 486 513 496 444 502 540 498 572

0.19 0.18 0.20 0.18 0.18 n.d. n.d. n.d. n.d.

2.0 1.7 1.6 1.8 I. 9 2.2 2.5 2.0 2.7

5.7 6.7 7.3 5.7 6.2 6.3 5.2 5.2 6.2

41 42 41 41 39 40 39 41 47

31 31 30 29 29 28 27 26 28

E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17

2.5 7.5 13.5 22.5 33.5 46.5 61.5 78.5 97.5 118.5 141.5 166.5 193.5 222.5 253.5 286.5 321.5 358.5 397.5 421.5 448.5

6.5 6.9 9.0 6.1 4.1 5.8 6.4 6.5 6.6 6.0 6.5 6.8 7.0 5.7 4,7 5.6 4.9 4.4 4,4 6.9 6.4

511 503 528 512 502 523 497 581 606 585 625 554 595 609 684 632 680 811 794 617 537

n.d. 0.21 0.20 0.13 0.13 0.23 0.15 0.15 0.13 0.16 0.17 0.18 0.13 0.14 0.17 0.14 0.18 0.16 0.12 0.13 0.24

1.9 2.6 2.0 2.3 1.9 2.4 2.1 3.3 3.1 2.4 3.2 3.2 2.6 2.6 2.3 2.8 2.7 2.6 2.3 2.2 2.2

6.7 7.7 7.7 6.7 5.2 5.7 6.2 5.7 5.7 6.3 6.7 5.6 6.7 6.8 6.1 6.2 8.2 6.7 6,2 8.2 5.7

55 47 47 38 40 41 46 46 48 48 56 44 46 45 45 43 47 44 44 49 46

28 28 32 24 24 24 25 25 23 26 26 26 25 26 28 26 27 25 25 27 25

9

.

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w

~

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,.~,l~

,

W

~ ~ 0 0 . . . .

W

~

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9

W

0 0 o o 0 0 o 0 o

~

~0 -.I 0

0

W

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

~

9

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t.--,'.O 0

~

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9

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W

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~

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O 0 0 % tk) 0 , ~ ,

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Ol

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"

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~

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9

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9

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874

H.-J. BRUMSACK

Apoend/x (Gulf of California data) sample #

ppm V

ppm Zn

% SiO 2

% TiO 2

% A12ch

Fe2o3

E-5 E~5 E-5 E-5 E-5 E-5 E-5 E-5 E-5 E-5 E-5

2.0 4.5 7.5 I0.5 13.5 16.5 22.5 28.5 37.5 49.5 54.0

112 108 I01 99 102 105 iii i00 89 93 90

108 104 103 98 93 93 88 89 78 84 95

55.1 57.3 54.1 57.7 59.3 57.8 61.7 61.7 61.9 64.4 58.5

0.47 0.45 0.45 0.42 0.40 0.40 0.41 0.42 0.36 0.34 0.44

ii. 3 10.6 10.7 10.1 9.3 9.4 9.4 9.1 8.2 7.9 10.4

3.60 3.46 3.55 3.57 3.35 3.46 3.33 3.48 2.93 2.88 3.44

2.03 1.96 1.88 1.74 i. 65 1.69 1.80 1.93 1.86 1.52 1.86

E-9 E-9 E-9 E-9 E-9 E-9 E-9 E-9 E-9

1.5 4.5 7.5 10.5 13.5 19.5 25.5 34.5 48.5

103 108 113 83 i00 80 94 108 99

108 98 109 83 98 73 78 82 78

55.8 62.0 60.7 65.5 63.2 65.6 66.7 64.7 66.2

0.43 0.40 0.46 0.34 0.38 0.33 0.35 0.37 0.31

8.6 9.3 8.6 8.1 9.2 7.8 8.3 8.9 6.9

3.68 3 909 3.36 3.28 3.53 2.95 2.78 2.78 2.48

1.78 i. 65 1.64 1.28 1.52 1.30 1.40 1.45 1.21

E-13 E-13 E-13 E-13 E-13 E-13 E-13 E-13 E-13

1.5 4.5 7.5 10.5 13.5 19.5 25.5 34.5 45.5

82 92 89 87 85 93 102 99 113

87 93 88 84 83 84 83 78 94

55.3 59.0 65.3 65.7 65.6 64.0 63.4 65.1 63.1

0.37 0.40 0.38 0.36 0.34 0.37 0.36 0.35 0.40

8.6 9.3 8.6 8.1 7.9 8.4 8.6 8.3 9.3

3.00 3.09 2.88 2.61 2.78 2.97 2.92 2.75 2.95

i. 62 i. 66 i. 63 1.49 1.43 1.49 1.51 1.45 1.59

E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17 E-17

2.5 7.5 13.5 22.5 33.5 46.5 61.5 78.5 97 .5 i18.5 141.5 166.5 193.5 222.5 253.5 286.5 321.5 358.5 397.5 421.5 448.5

93 91 89 90 99 88 94 103 105 lll 133 103 105 106 112 108 118 119 103 112 112

88 87 92 78 73 72 77 82 82 90 87 77 82 83 92 87 87 88 88 102 93

56.8 59.8 62.1 63.3 66.5 66.8 66.2 63.5 65.2 63.0 64.7 66.9 65.3 65.0 63.2 66.1 64.4 63.9 65.9 60.4 65.0

0.38 0.40 0.41 0.33 0.32 0.33 0.38 0.37 0.37 0.41 0.38 0.35 0.42 0.40 0.39 0.37 0.42 0.41 0.40 0.46 0.38

8.8 9.2 9.7 7.6 7.3 7.5 8.5 8.9 8.7 9.9 9.0 7.7 9.2 8.9 9.3 8.5 9.5 9.0 9.4 10.8 9.0

3.22 3. ii 3.29 2.70 2.50 2.66 2.92 2.95 2.76 3.19 2.80 2.72 3.01 2.95 2.92 2.74 3.21 3.16 2.97 3.75 2.93

1.50 1.54 1.59 1.37 1.33 1.29 1.66 1.44 1.42 i. 65 I. 54 1.32 1.53 1.48 1.56 1.48 1.71 1.58 1.59 1.96 I. 57

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~

01

~

O. tnO~

9

0

~

~

~

~

O

~

M

~

O

0

0

0 0 0 0 0 0 0 0 0 0 0 , , - e o e , e . o e

e e a l o o e e 6 a t

~

0 0 0 0 0 0 0 0 0 0 0

~ ~

Otn

9

9 0

0

"6

v

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I-'-

0

u.

m-

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5~

o

c

m-"

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876

H.-J. BRUMSACK

Apperdix sample # G-32 G-32 G-32 G-32 G-32 G-32 G-32 G-32 G-32

2.5 5.5 8.5 11.5 14.5 20.5 26.5 32.5 40.5

sample # G-32 G-32 G-32 G-32 G-32 G-32 C--32 G-32 G-32

2.5 5.5 8.5 11.5 14.5 20.5 26.5 32.5 40.5

sa~le G-32 G-32 G-32 G-32 G-32 G-32 G-32 G-32 G-32

~le G-32 C--32 G-32 G-32 C--32 G-32 C--32 G-32 G-32

#

2.5 5.5 8.5 ii. 5 14.5 20.5 26.5 32.5 40.5

# 2.5 5.5 8.5 11.5 14.5 20.5 26.5 32.5 40.5

ppmAs

ppmBa

6.9 8.7 7.1 7.1 8.1 8.5 n.d. 7.3 10.4

487 506 513 514 511 537 529 533 498

ppmMn 395 381 386 366 373 372 392 386 398

ppm V ii0 120 112 124 128 128 117 121 119

(Gulf of California data) ppmCd

ppmCo

ppmCr

ppmCu

n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.

1.9 2.8 1.9 2.3 2.0 3.2 1.3 2.6 3.4

8.1 8.3 9.7 8.7 8.7 9.3 9.7 10.7 8.9

66 70 68 69 74 76 69 76 72

24 26 24 24 26 26 25 25 25

ppmMo

ppmNi

ppml~

ppmSe

ppmSr

ppmTl

3.7 4.7 4.3 6.3 6.2 6.5 4.1 5.6 6.0

33 35 38 40 43 42 39 39 38

28.4 30.2 31.5 29.5 25.6 23.8 20.4 19.3 18.9

2.2 2.6 2.6 3.3 3.1 2.7 1.8 2.5 2.6

274 237 201 199 201 156 201 200 190

0.39 0.51 0.58 0.53 0.50 0.52 0.46 0.45 0.64

ppm Zn 127 130 127 122 123 119 117 117 121

% CaO

% Na20

5.4 4.4 3.3 3.5 2.9 2.3 3.1 3.0 3.2

1.72 1.74 1.80 1.86 1.87 1.89 1.91 1.93 2.16

ppmBi

% SiO 2

% TiO 2

48.1 48.8 50.6 49.5 50.2 51.4 51.7 52.1 50.4

0.57 0.56 0.59 0.57 0.57 0.59 0.59 0.59 0.59

14.4 14.6 15.5 14.8 15.1 15.1 15.0 14.9 14.6

4.59 4.50 4.66 4.42 4.46 4.55 4.55 4.53 4.48

% 1:'205

% CO2

% TOC

% K20 2.54 2.64 2.72 2.70 2.71 2.77 2.77 2.76 2.80

0.28 0.28 0.27 0.28 0.30 0.29 0.25 0.26 0.28

% AI203

3.8 2.6 2.1 2.1 2.0 0.5 1.4 2.0 1.5

% Fe203

4.89 5.12 4.70 5.51 5.37 5.49 4.85 5.08 5.37

% Mc30 1.92 1.95 2.00 i. 97 2.02 1.97 2.04 2.11 2.08

%S 0.21 0.18 0.21 0.27 0.25 0.20 0.26 0.24 0.29

Geochemistry of recent TOC-rich sediments from the Gulf of California and the Black Sea

877

A p p e n l i x ( B l a c k Sea data) sample #

ppmAg

ppmAs

ppmBa

ppmCd

ppmCo

ppmCr

ppmCu

BS BS BS BS BS BS BS BS BS BS BS BS

1445/20 1445/40 1445/52 1450/20 1450/40 1450/50 1451/19 1451/33 1451/48 1462/20 1462/38 1462/58

0.26 0.27 0.24 0.II 0.13 0.15 0.13 0.16 0.07 0.05 0.05 0.16

42.0 48.0 49.0 13.0 16.0 35.0 12.0 25.0 14.0 i1.5 18.0 21.0

355 360 790 845 1240 995 535 1090 370 300 345 265

2.10 1.40 2.00 0.94 1.20 1.36 0.61 0.75 0.53 0.46 0.30 0.82

47.5 51.1 35.8 22.1 19.2 25.2 17.0 25.9 10.5 21.8 18.2 24.5

62 83 60 49 83 75 35 100 60 34 105 95

ll0 114 175 59 82 112 45 75 48 30 41 150

BS BS BS BS BS BS BS BS BS BS

1474/29 1474/38 1474/49 1474/59 1474/70 1474/80 1474/89 1474/111 1474/120 1474/130

0.07 0.05 0.05 0.i0 0.05 0.07 0.07 0.05 0.07 0.05

29.0 12.5 7.0 21.0 ii.0 20.0 17.0 15.0 15.0 ii.0

355 265 270 320 310 290 290 290 315 330

0.24 0.24 0.25 0.33 0.25 0.24 0.21 0.15 0.19 0.16

30.5 29.0 28.3 24.5 28.1 25.7 24.2 24.7 26.4 26.4

163 170 168 170 188 180 185 175 170 169

80 53 53 54 59 51 45 40 38 50

ppmMn

ppmMo

ppmNi

ppmPb

ppmSr

ppmV

ppmZn

sample # BS BS BS BS BS BS BS BS BS BS BS BS

1445/20 1445/40 1445/52 1450/20 1450/40 1450/50 1451/19 1451/33 1451/48 1462/20 1462/38 1462/58

420 530 230 415 390 590 395 400 245 350 630 2530

50.0 140.0 185.0 50.0 i00.0 130.0 50.0 i00.0 75.0 12.0 20.0 48.0

115 115 125 70 I00 125 50 103 80 50 68 150

18.0 22.0 16.5 14.5 22.5 19.5 12.0 23.0 13.5 7.8 18.5 17.0

520 315 175 970 275 255 1140 225 1625 1120 230 315

210 250 415 I00 150 145 73 150 130 71 135 245

94 105 88 63 i00 93 46 108 64 42 92 95

BS BS BS BS BS BS BS BS BS BS

1474/29 1474/38 1474/49 1474/59 1474/70 1474/80 1474/89 1474/111 1474/120 1474/130

590 1145 1530 1235 1520 1210 1360 1470 1350 990

I0.0 4.0 2.2 2.5 2.2 2.2 2.5 1.8 1.3 1.2

130 160 160 135 155 145 140 130 135 150

17.0 16.5 16.0 13.5 15.0 13.5 12.5 11.5 12.5 14.0

112 230 240 315 310 310 330 300 305 255

175 150 145 115 160 125 115 135 120 155

108 90 85 78 80 78 74 70 73 83

878

H.q. BRUMSACK

Appendix (Black Sea data) sample #

% SiO 2

% TiO 2 % AI203

% Fe203

%~O

%SgO

%CaO

BS 1462/20 BS 1462/38 BS 1462/58

26.9 34.5 24.6 22.1 36.9 31.0 18.4 43.1 26.4 17.3 47.9 33.2

0.38 0.51 0.35 0.28 0.53 0.43 0.20 0.61 0.34 0.17 0.67 0.47

9.3 11.8 8.1 6.9 12.5 i0.1 5.3 14.4 8.1 4.5 14.5 11.5

5.68 7.37 4.59 2.94 5.06 4.66 2.62 5.55 3.28 2.35 5.75 4.62

0.06 0.07 0.04 0.05 0.06 0.08 0.05 0.06 0.03 0 904 0 908 0.32

2.01 2.45 2.23 1.42 2.37 2.28 1.23 2.67 2.16 1.15 2.26 3.25

13.2 6.3 2.2 25.8 5.9 3.8 31.9 4.9 18.0 32.5 7.7 6.8

BS BS BS BS BS BS BS BS BS BS

46.8 43.0 42.1 42.0 43.9 41.8 40.7 40.6 40.9 41.8

0.72 0.70 0.69 0.65 0.67 0.66 0.64 0.66 0.67 0.67

15.8 13.8 13.4 12.5 13.5 12.3 11.8 ii. 2 ii. 0 13.0

7.42 6.87 5.98 6.16 7.20 6.42 6.40 5.64 6.13 6.42

0.09 0.15 0.19 0.15 0.19 0.15 0.17 0.18 0.16 0.13

3.94 4.62 4.54 4.25 4.46 4.04 3.96 3.92 3.78 4.41

0.8 7.7 8.9 ll.9 8.8 i1.3 13.0 13o 6 13.2 I0.6

% P205

% TOC

BS 1445/20

Bs 1445/40 BS BS BS BS BS BS

1445/52 1450/20 1450/40 1450/50 1451/19 1451/33

Bs 1451/48

1474/29 1474/38 1474/49 1474/59 1474/70 1474/80 1474/89 1474/111 1474/120 1474/130

sample #

% Na20

% K20

%S

~caa%

BS BS BS BS BS BS BS BS BS HS BS BS

1445/20 1445/40 1445/52 1450/20 1450/40 1450/50 1451/19 1451/33 1451/48 1462/20 1462/38 1462/58

3.53 3.69 5.01 3.29 3.49 4.11 3.24 2.62 3.22 3.11 2.26 3.09

1.74 2.17 1.72 1.36 2.26 2.02 i. 00 2.87 1.64 0.92 2.66 2.22

0.19 0.14 0.23 0.15 0.17 0.22 0.15 0.18 0.17 0.ii 0.ii 0.24

8.44 6.52 14.74 3.62 5.86 11.36 3.24 4.60 5.98 3.44 1.21 8.57

1.76 1.94 1.82 0.78 0.87 1.48 0.71 0.80 0.72 1.18 0.80 2.50

29 17 37 45 26 3O 52 16 44 54 12 19

BS BS HS BS BS BS BS BS HS BS

1474/29 1474/38 1474/49 1474/59 1474/70 1474/80 1474/89 1474/Iii 1474/120 1474/130

3.07 2 .68 2 .45 2 .49 2.62 2.48 2 .24 2.37 2.31 3.22

2.96 2.41 2 .26 2 .03 2.26 1.79 1 .89 1.86 1.98 2.25

0.15 0.14 0.16 0.15 0.17 0.15 0.16 0.16 0.17 0.15

2.04 0.67 0 .61 0.64 0.85 0.64 0 .84 0.53 0.53 0.60

0.61 1.20 0.94 I. 04 0.67 i. 18 0.90 0.27 0.70 0.23

4 ii 13 17 16 22 2O 23 20 17

Geochemistry of recent TOC-rich sediments from the Gulf of California and the Black Sea

879

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-

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