petrology of organic matter in modern and late quaternary deposits of the equatorial atlantic:...

Ž .International Journal of Coal Geology 39 1999 155–184

Petrology of organic matter in modern and lateQuaternary deposits of the Equatorial Atlantic:

climatic and oceanographic links

Thomas Wagner )

Fachbereich 5-Geowissenschaften, UniÕersitat Bremen, Postfach 330440, 28334 Bremen, Germany¨

Abstract

Organic petrologic and geochemical analyses were performed on modern and Quaternaryorganic carbon-poor deep sea sediments from the Equatorial Atlantic. The study area covers

Ž .depositional settings from the West African margin ODP Site 959 through the EquatorialŽ . Ž .Divergence ODP Site 663 to the pelagic Equatorial Atlantic. Response of organic matter OM

deposition to Quaternary climatic cycles is discussed for ODP Sites 959 and 663. The results arewfinally compared to a concept established for fossil deep sea environments Littke, R., Sachsen-

hofer, R.F., 1994. Organic petrology of deep sea sediments: a compilation of results from thexOcean Drilling Program and the Deep Sea Drilling Project, Energy and Fuels 8, 1498–1512. .

Organic geochemical results obtained from Equatorial Atlantic deep sea deposits provide newaspects on the distribution of sedimentary OM in response to continental distance, atmosphericand oceanographic circulation, and depositional processes controlling sedimentation under modernand past glacial–interglacial conditions. The inventory of macerals in deep sea deposits is limiteddue to mechanical breakdown of particles, degree of oxidation, and selective remineralization of

Ž .labile mostly marine OM. Nevertheless, organic petrology has a great potential for paleoenviron-mental studies, especially as a proxy to assess quantitative information on the relative abundanceof marine vs. terrigenous OM. Discrepancies between quantitative data obtained from microscopic

Ž 13 .and isotopic d C analyses were observed depending on the stratigraphic level and deposi-org

tional setting. Strongest offset between both records was found close to the continent and duringglacial periods, suggesting a coupling with wind-born terrigenous OM from central Africa. SinceAfrican dust source areas are covered by C4 grass plants, supply of isotopically heavy OM isassumed to have caused the difference between microscopic and isotopic records. q 1999 ElsevierScience B.V. All rights reserved.

Keywords: organic facies; modern deep sea deposits; Quaternary deep sea deposits; organic carbon isotopes;C4 plants; paleoclimate; paleoceanography; Equatorial Atlantic

) Tel.: q49-421-218-7137; Fax: q49-421-218-7431; E-mail: [email protected]

0166-5162r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.Ž .PII: S0166-5162 98 00044-5

( )T. Wagnerr International Journal of Coal Geology 39 1999 155–184156

1. Introduction

Petrology of sedimentary OM fundamentally evolved during the last decades with itsŽapplication to fossil and recent organic-rich, marine sediments Tissot and Welte, 1984;

.Teichmuller, 1987; Tyson, 1995; Littke et al., 1997; Taylor et al., 1998 . Since then,¨petrology has become an integrated part of organic geochemical processing especially to

Žassess and evaluate the petroleum potential of hydrocarbon source rocks Demaison and.Moore, 1980 . Like litho- and biofacies models, combined organic geochemical and

petrologic approaches were used to establish comprehensive organic- and palynofaciesŽ .concepts Jones, 1987; Tyson, 1995 . These concepts have been successfully employed

and further developed to evaluate ancient and recent depositional settings of the marineŽenvironment e.g., Jones, 1983, 1987; Rullkotter et al., 1982; Stein et al., 1986;¨

Summerhayes, 1987; Stein and Littke, 1990; Wiesner et al., 1990; Littke, 1993; Littke.and Sachsenhofer, 1994; Wagner and Henrich, 1994; Littke et al., 1997 . A recent

compilation of organic petrologic data from Triassic to Holocene deep sea sediments,mainly derived from studies related to the Deep Sea Drilling Project and the Ocean

Ž .Drilling Program, was presented by Littke and Sachsenhofer 1994 . They recognizedseveral factors which determine changes in relative amounts of terrigenous and marineOM, such as continental distance, pelagic vs. turbidity deposition, paleoproductivity,activity of oxidizing agents, as well as direction and velocity of paleocurrents. Theinfluence and interaction of these different controls are discussed with respect to globalplate tectonic settings and paleoceanographic environments. Despite the progress of thisconcept, it can neither be simply applied to ‘typical’ past deep sea settings nor to

Ž . Ž .modern surface deposits. This relates to the fact 1 that total organic carbon TOC -poorŽ .deep sea sediments are underrepresented by most organic petrologic studies, and 2 that

OM in surface deposits has not yet completely undergone diagenetic processes andtherefore not necessarily is represented by concepts developed on fossil deposits.

Few studies discuss the organic character of marine surface sediments using com-Žbined organic petrology and geochemistry Wiesner et al., 1990; Stein, 1991; Littke,

1993; Wagner and Henrich, 1994; Wagner and Wiesner, 1994; Wagner and Dupont, in.press , although the benefit of such approaches is considered to be multi-fold for modern

Ženvironmental studies McArthur et al., 1992; Littke and Sachsenhofer, 1994; Tyson,.1995 . In this study, results from organic petrologic and geochemical analyses are

presented for surface and late Quaternary deposits of the Equatorial Atlantic. SampleŽ .locations follow an east–west transect from the West African margin ODP Site 959

Ž .through the central Equatorial Divergence ODP Site 663 to the Equatorial Atlantic atŽ .298W Fig. 1 . This transect allows to assess spatial gradients in organic characteristics

Fig. 1. Generalized map of the Equatorial Atlantic showing main coastal and oceanic upwelling areasŽ .Voituriez and Herbland, 1982; van Bennekom and Berger, 1984; van Leeuwen, 1989; Verstraete, 1992 ,major African vegetation zones, and approximate boreal winter positions of source and corresponding

Ž .depositional areas for atmospheric dust Semmelhack, 1943; Schutz, 1980; Pokras and Mix, 1985 . Black¨Ž .arrows indicate surface trade winds; open arrows show the mid-level African Easterly Jet AEJ and the

ŽSaharan Air Layer. Sample positions are displayed in an insert map circles mark locations of surface.sediments, stars of surface sediments and late Quaternary sections .

( )T. Wagnerr International Journal of Coal Geology 39 1999 155–184 157


along a continuum of marine settings. General sedimentological and bulk organicŽgeochemical frameworks of the study area are discussed elsewhere Westerhausen et al.,

1993; deMenocal et al., 1993; Verardo and McIntyre, 1994; Verardo and Ruddiman,.1996; Ruddiman, 1997; Wagner, in press; Wagner and Dupont, in press . The present

contribution focuses on the inventory and relative abundance of dispersed organicŽ .particles macerals in these immature deep sea sediments. In addition, implications for

Ž 13 .the interpretation of bulk organic carbon isotopic data d C as a quantitative proxyorg

to estimate marine vs. terrigenous OM are discussed. Results from the EquatorialAtlantic are compared to organic petrologic characteristics reported from hemipelagic

Ž .settings of the Norwegian Sea Wagner, 1993; Wagner and Wiesner, 1994 and shallowŽ .water areas of the North Sea Shelf Wiesner et al., 1990 . Information on changes in the

deposition and preservation of OM during past glacialrinterglacial conditions arepresented for the last 2.2 Ma from ODP Site 959 and for a single glacial–interglacialcycle covering the time interval between 0.4 to 0.48 Ma from ODP Site 663.

2. Depositional setting

It is well-documented for the Quaternary Tropical Atlantic that orbital-forced changesin deposition of carbonate and organic carbon are closely coupled to glacial–interglacialvariations in global atmospheric and oceanic circulation and lateral displacements of

Žmajor bottom currents Verardo and McIntyre, 1994; Bickert and Wefer, 1996; Mix and.Morey, 1996 . Due to complex feedback mechanisms between low latitude wind

systems and northern hemisphere glaciations, intensities of the African Trade-, andŽHarmattan-winds were enhanced preferentially during cold climatic periods Sarnthein et

.al., 1982; deMenocal et al., 1993; Tiedemann et al., 1989, 1994; Ruddiman, 1997 .Glacially enforced wind systems triggered upwelling of nutrient-rich intermediate

Žwaters or lateral cold-water advection which, in turn, caused higher productivity Muller¨.et al., 1983; Mix, 1989; Berger and Herguera, 1992 . These winds, on the other hand,

Ž .determine the eolian supply of terrigenous dust to the Atlantic Ocean Fig. 1 . Duringboreal summer, dust from the NW-African continent reaches as far west as the

Ž .Caribbean Sea Semmelhack, 1943; Schutz, 1980 , although atmospheric release is¨Žstrongest in the eastern Atlantic Sarnthein et al., 1982; Ruddiman and Janecek, 1989;

.Tiedemann et al., 1989; deMenocal et al., 1993; Moulin et al., 1997; Ruddiman, 1997 .Ž .In response to the seasonal displacement of the Intertropical Convergence Zone ITCZ ,

the dust plume gradually migrates and approaches its southernmost position duringboreal winter. At that time, eolian material is deposited over a broad area covering theentire Equatorial Atlantic between West Africa and Brazil, again revealing a strongeast–west asymmetry with regard to total amounts of dust fall-out. Fig. 1 shows that thestudy area is affected by dust supply during the boreal winter season. Westerhausen et

Ž .al. 1993 estimated from n-alkanes in surface sediments off West Africa that terrestrialOM is almost entirely derived from eolian transport. Mineralogical and palynologicaldata localize source areas for eolian dust recovered in Equatorial Atlantic deposits in

Žarid to semiarid zones of central Africa Pokras and Mix, 1985; Sarnthein et al., 1982;.Bonifay and Giresse, 1992; Fredoux, 1994 .´


Ž .Continental dust comprises minor amounts of terrestrial OM Romankevich, 1984 .Plant debris is admixed to lithogenic dust either as highly resistant organic particles oras macromolecular compounds of plant biomass depending on the composition anddensity of the vegetation and its stage of biogeochemical degradation. Studies discussingthe supply of terrigenous OM to the Tropical Atlantic are based on biomarker evidenceŽ .Simoneit, 1977; Chesselet et al., 1981; Poynter et al., 1989; ten Haven et al., 1989 ,

Žabundances of freshwater diatoms Pokras and Mix, 1985; Pokras and Ruddiman, 1989;. ŽdeMenocal et al., 1993 and palynomorphs Maley, 1982; Turon, 1984; Lezine and´

.Hooghiemstra, 1990; Dupont and Agwu, 1991; Lezine, 1991; Fredoux, 1994 , terrige-´ ´Ž .nous macerals Stein et al., 1989; Wagner, in press; Wagner and Dupont, in press , or

Ž .other potential terrigenous markers charcoal sensu latu; Verardo and Ruddiman, 1996 .Source area for most of these highly resistant plant fragments is the shrub and grass

Žsavannah of the Sahel and Sahara zones Prospero, 1981; Ruddiman and Janecek, 1989;.Bonifay and Giresse, 1992; Pokras and Mix, 1985; Fig. 1 . Mixing of eolian and riverine

OM is restricted to areas off-shore the main West African rivers, e.g., the Congo andŽ .Niger Jansen et al., 1984; Westerhausen et al., 1993; Muller et al., 1994 . Influence of¨

long-range lateral advection of river-born or resuspended OM by bottom or midwatercurrents is not indicated by siliceous microfossil assemblages, studied in sediment trap

Žmaterial from multi-year deployments in the pelagic Equatorial Atlantic Lange et al.,.1994 .

3. Material and methods

Equatorial Atlantic surface sediments were recovered during Meteor cruises 9-4Ž . Ž .Wefer et al., 1989 and 29-3 Schulz et al., 1995 . Late Quaternary sections of ODP

Ž .Site 959 were drilled during ODP Leg 159 Mascle et al., 1996 . Samples were takenshipboard and maintained deep frozen until further processing in the shore-based

Ž .laboratories. Samples from ODP Site 663 deMenocal et al., 1993 were resampled atŽ .the ODP Core Repository USA and stored refrigerated at 28C immediately after arrival

at Bremen University.Organic and inorganic carbon were measured on homogenized samples using a Leco

CS-300 elemental analyzer. For organic carbon determination, inorganic carbon wasremoved by repetitive addition of 0.25 N HCl. Carbonate contents were calculated

Ž .following CaCO s C yC =8.33. Rock–Eval pyrolysis was performed using the3 tot orgŽ .analytical cycle described by Espitalie et al. 1977 . For the thermally immature organic´

character of unconsolidated marine deposits, hydrocarbons detected in the S1 windowŽ . Žwere added to the S2 yield before hydrogen indices HI were calculated Tissot and

. ŽWelte, 1984 using TOC values obtained from Leco analysis for analytical details, see.Liebezeit and Wiesner, 1989; Wagner and Dupont, in press .

Quantitative information on the relative proportions of marine and terrigenous OMŽ . Žwere deduced using two different approaches: 1 quantitative organic petrology maceral

. Ž . Ž 13 . Ž . 13analyses and 2 isotopic data d C published by Fischer et al. 1998 . d Corg org

records of modern and Quaternary marine deposits are commonly used to evaluatemarine and terrigenous fractions of organic carbon using two-component mixing equa-


Žtions Muller et al., 1983; Jasper and Gagosian, 1990; Stein, 1991; Westerhausen et al.,¨1993; Muller et al., 1994; Ruhlemann et al., 1996; Schneider et al., 1996; Schneider et¨ ¨

.al., 1997; Schlunz et al., in press . However, various other factors, such as changes in¨surface water CO concentrations or C4 plant supply, may have an additional effect on2

Žthe bulk isotopic signal of marine deposits Stein, 1991; Muller et al., 1994; see Tyson,¨.1995 for review . Terrestrial C4 plants include many grasses which exhibit optimum

photosynthesis at temperatures about 108 higher than vascular C3 plants and are thuscommon in warm tropical and dry to arid climates, such as the African Sahel andSahara. Typically, d

13C signatures of C4 plants range from y9 to y19‰ with anorg

average of y12‰. From their isotopic signal, they are clearly distinguished fromvascular C3 plants which reveal average d

13C values of y27‰. In this study,org

estimation of marine vs. terrigenous organic carbon based on d13C was calculatedorg

using the two endmembers of y18‰ and y27‰ for marine and terrigenous OM,Žrespectively for the discussion on factors influencing the marine or terrigenous end-

member values, see Westerhausen et al., 1993; Tyson, 1995; Wagner and Dupont, in.press . Since the definition of the isotopic endmember value controls the sensitivity of

the mixing model, one should be aware that a 1‰ shift of the marine endmembertowards more negative values amounts to an increase of the terrigenous fraction byapproximately 11%.

Application of quantitative organic petrology to modern TOC-poor deep sea sedi-ments offers a new approach which has just recently been introduced for the study areaŽ .Wagner, in press; Wagner and Dupont, in press . Organic petrologic analyses wereperformed on bulk sediment samples using a Zeiss Axiophot equipped with incidentwhite and reflected ultraviolet light. Bulk sediment samples were embedded in alow-viscosity resin, then stored for at least 48 h before grinding and polishing. Organicparticle identification was conducted at 500- and 1000-fold magnification using both,

Ž .normal and ultraviolet light mode. Individual macerals 250 were counted as grainpercentages of the whole maceral composition following the standard nomenclature of

Ž . Ž .Stach et al. 1982 see following chapter for modifications . The reproducibility ofmicroscopic results, based on duplicate countings, was better than 95%.

4. Results

4.1. ObserÕations on the petrographic inÕentory of sedimentary OM in modern and lateQuaternary marine deposits

Ž .The inventory of dispersed organic particles macerals in organic-poor marinesediments is limited compared to the one of organic rich black shales or coals. This isrelated to a number of climatic and oceanographic factors controlling the sources,dispersion, deposition and selective degradation of organic particles in the various

Žmarine environments through time Stein, 1991; Littke, 1993; Littke et al., 1997;.Wagner and Dupont, in press . Classification of individual macerals following the

Ž .standard nomenclature of Stach et al. 1982 therefore needs to be adapted to unconsoli-dated marine sediments in order to obtain a useful nomenclature.


Fig. 2 compares typical petrologic inventories of organic constituents in coal and oilŽ .shale as introduced by Stach et al. 1982 with those of recent shallow to deep water

Žsediments as observed in this and other related studies from the literature ten Haven et.al., 1989; Wiesner et al., 1990; Stein, 1991; Littke, 1993; Wagner, 1993 . Generalized

Fig. 2. Petrographic classification of organic constituents in coal or oil shales and in modern shelf and deep seasediments. Generalized trends in frequency of individual macerals and clasts, their relative occurrence inshallow to deep water environments, as well as their potential to be of reworked-fossil origin is indicated.


trends in frequency of individual macerals and clasts, their relative occurrence inshallow to deep water environments, as well as their potential to be of reworked-fossilorigin is indicated. Typical macerals observed in modern and Quaternary deposits of theEquatorial Atlantic are shown for the marine fraction in Fig. 3 and for the terrigenousfraction in Fig. 4. Marine macerals rarely occur as strongly fluorescing algal bodies of

Ž .different shape and size Fig. 3a,b , but more frequently as pale yellow–green fluoresc-Ž .ing, fragile structures of dinoflagellate cysts Fig. 3c . Detrital fragments of these marine

Ž .macerals liptodetrinite overall dominate the autochthonous spectrum and are recogniz-Ž .able as thin, pale fluorescing filaments embedded in the mineral groundmass Fig. 3d .

Strongly degraded, amorphous-like OM probably of marine origin is scarcely observedŽ .in deep sea sediments Fig. 3e , but apparently dominates the bulk maceral associationŽ .in upwelling deposits ten Haven et al., 1989; Littke et al., 1997 . Terrigenous macerals

reveal typical features of plant tissues, showing internal structures of different shape andŽ . Ž .thickness Fig. 4a–f , or as detrital fragments thereof Fig. 4g–i . Internal structures

Ž .probably represent segments of cell lumina Fig. 4a–d or vascular systems, i.e.,Ž .tracheids showing elongated, thick-walled, or pitted structures Fig. 4e,f and k,l .

Ž .Fig. 3. Marine macerals in modern and late Quaternary sediments of the open pelagic ODP Site 663 andŽ . Ž .near-continental eastern ODP Site 959 Equatorial Atlantic. a,b Strongly fluorescing solid algae bodies ofŽ . Ž .different shape and size polished surface, UV-light excitation . c Pale fluorescing, fragile dinoflagellate cyst

Ž . Žwith typical filaments, and d detrital fragments thereof liptodetrinite, LD; polished surface, UV-light. Ž .excitation . e,f Intensively degraded OM probably of marine origin showing transitional stages to amorphous

Ž .OM, non-fluorescent polished surface, reflected white light .


Ž .Fig. 4. Terrigenous macerals in late Quaternary sediments of the open pelagic ODP Site 663 andŽ . Ž .near-continental eastern ODP Site 959 Equatorial Atlantic. a–d Thin or thick-walled vitrinite and inertinite

Ž . Ž .with entire or broken cell lumina of plant tissue. e,f Highly oxidized inertinite fusinite revealing elongated,Ž .thick-walled, often-pitted structures of vascular bundles tracheids . Severe oxidation may be caused by in situ

Ž .plant burning resulting in ‘charcoal-type’ OM. g–i Detrital fragments of inertinite and vitrinite frequentlyŽ .showing characteristic forms, such as ‘bogen-structures’. k,l Non-oxidized terrigenous organic particles

Ž . Ž . Ž .vitrinite probably documenting cross-sections through parts of plant vascular systems tracheids . mDegraded vitrinite showing marginal decomposed structures due to microbiological attac. All photographs are

Ž .taken at 200–1000-fold magnification on polished surfaces under white incident light oil .


Depending on the degree of carbonization, macerals change their chemical compositionŽwhich is reflected by a continuous increase in light reflectance dark gray—vitrinite;

.light gray to almost white—inertinite . Microbial-degraded vitrinite was rarely observedshowing strongly decomposed, sponge-like structures preferentially along the marginal

Ž .rims of the particle Fig. 4m .Ž .Littke 1993 concluded that more than 80% of the total OM in non-upwelling

depositional settings occurs in form of discrete, optically resolvable particles. Hence,petrologic data may provide important quantitative information on the composition of

Ž .sedimentary OM Senftle et al., 1993; Tyson, 1995 . Nevertheless, some principleconfinements have to be considered when quantitative microscopic data are discussed:

Size and average density of organic particles in open marine deposits change withŽ .increasing continental distance Stein, 1991; Littke, 1993, Littke et al., 1997 and the

type of vegetation covering continental source areas. It has to be mentioned, however,Žthat deposition of detrital, oxidized OM is typical organic facies D according to Jones,

.1987 but not restricted to remote oceanic settings and may also occur in specificŽshallow water environments Combaz et al., 1974; Wiesner et al., 1990; Anton et al.,

.1993 . If necessary, ‘weighing factors’ may compensate for the different particle sizesŽ .although their application may also produce some artifacts Stein, 1991 . Particulate OM

in modern and late Quaternary sediments of the Equatorial Atlantic is dominated by50% to 90% -10 mm particle sizes with an average content of about 80%. Applicationof weighing factors to correct for particle sizes was therefore not conducted in thisstudy.

Lateral advection of marine or terrigenous organic particles by currents and alonginner or bottom nepheloid layers is problematic to assess. Due to the small particle sizesin deep sea samples, distinguishing of autochthonous huminitervitrinite from recycled,higher-reflecting huminitervitrinite is often difficult or even impossible. Additionalproblems are reported for the separation of detrital high reflecting vitrinite fromlow-reflecting inertinite and of highly reflecting inertinite from small-sized mineral

Ž .grains Combaz et al., 1974; Wiesner et al., 1990; Wagner, 1993 . To resolve theseproblems and to standardize the nomenclature applied to deep sea sediments, Littke and

Ž .Sachsenhofer 1994 suggested estimating the relative proportions of reworked andautochthonous humic components according to reflectance histograms, if available.Where neither differentiation of recycled from autochthonous vitrinite nor determinationof representative numbers of reflectance values is possible, a standardized percentage ofvitrinite sensu latu should be regarded as recycled. In agreement with Littke and

Ž .Sachsenhofer 1994 , it is expected that percentages of autochthonous huminitervitrinitein remote oceanic settings are much lower than those for recycled vitrinite. It is thereforesuggested to use an average proportion of 75% of total huminitervitrinite as recycledvitrinite, if no other data are available.

Ž .Alginite sensu strictu Stach et al., 1982; Taylor et al., 1998 is rarely observed inrecent deep sea deposits. TOC-poor deep sea sediments almost exclusively reveal

Ždinoflagellate cysts and fragments of them -10 mm, liptodetrinite of marine origin,.Fig. 3c,d . Since this type of OM represents the best preserved indicators of past surface

production, it should be counted as marine alginite sensu latu. Inaccurate separation ofŽ . Ž .fluorescent marine alginite from terrestrial sporinite, cutinite debris of either au-


tochthonous or reworked origin may also influence results from maceral analyses,especially if the degree of fragmentation is high. Other organic particles of possiblemarine origin, e.g., bituminite, foraminiferal linings or fluorescent amorphous OM,

Ž .occur accessory in deep sea settings Holemann and Henrich, 1994; Fig. 3e,f . The¨fraction of amorphous OM, however, may rise up to 90% of the total OM in sediments

Ž .deposited below upwelling areas ten Haven et al., 1990 .Reworked, fossil OM, derived either from submarine outcrops along continental

margins or from terrestrial source areas, dilute the autochthonous organic signal and maycomprise a considerable fraction of the bulk OM in specific deep and shallow marinesettings. Fossil-reworked OM in modern and Quaternary marine deposits providesevidence of persistent basinward sediment transport either by currents or, more impor-tant in high latitude settings, by glaciomarine supply. This allochthonous fraction,bearing an inherited stratigraphic older and higher thermal maturity signature than theembedding sediment, overall dominates the organic character in marine deposits of high

Žlatitude northern basins, e.g., the Nordic Seas and the Arctic Ocean Holemann and¨Henrich, 1994; Stein et al., 1994; Wagner and Henrich, 1994; Wagner and Holemann,¨1995; Wagner et al., 1995; Stein and Schubert, 1996; Hebbeln et al., 1998; Henrich et

. Žal., 1997; Knies and Stein, 1998 , but may also occur in other shallow Combaz et al.,. Ž1974; Wiesner et al., 1990; Anton et al., 1993 and deep Jones, 1987; Wagner et al.,

.1995; Wagner and Dupont, in press marine settings.

4.2. Distribution of sedimentary OM in modern Equatorial Atlantic deposits

Lateral variations in water depth, content and composition of total organic carbon areŽ .displayed in Fig. 5 for sample locations, see Fig. 1 . A simple relation of water depth

and content or composition of TOC in surface samples is not observed. Elevated TOCcontents, recognized close to the continental margin off West Africa, are attributed toincreased terrestrial dilution via eolian supply or lateral advection of reworked OM.

Ž .Reworked material is expected at the deep position off West Africa ODP Site 962Žconsidering high T values of 4508C reported from Quaternary sections Wagner etmax

.al., 1995 . Microscopic data show a continuous increase of the marine and total detritalorganic fraction towards the central Equatorial Atlantic reaching up to 80% and 95%,

Ž .respectively Fig. 5d,e . Elevated HI around 150 mg HCrg TOC are observed betweenŽ .about 108 and 198W Fig. 5c probably documenting enhanced flux rates of marine OM

below the central Equatorial Divergence.Ž .In contrast to other shelf–ocean transects Littke et al., 1997 , no clear increase in the

Ž .ratio of inertinite vs. vitrinite is observed with increasing continental distance Fig. 5f .The scattering pattern may partly be attributed to the dominant detrital fraction of

Žterrigenous macerals range from 50% to 90%, average 83% of the bulk terrigenous.fraction , which in most cases excludes distinguishing autochthonous from reworked

vitriniterhuminite and the determination of vitrinite reflectance. Reflectance values fromQuaternary deposits of ODP Site 663 range from 0.83% R to 1.74% R , supportingm m

Ž .the assumption by Littke and Sachsenhofer 1994 that most of the terrestrial organicfraction in pelagic sediments is of reworked origin. Huminite, representing the au-


Ž . Ž .Fig. 6. Histograms of vitrinite reflectance obtained from a modern and and b–d late Quaternary deposits atODP Site 959 off Ivory CoastrGhana. Immature OM below 0.5% R probably represents autochthonousm

huminitervitrinite, whereas the occurrence of higher reflecting vitrinite exceeding 0.5% R in late Quaternarym

samples suggests enhanced deposition of recycled vitrinite and inertinite.

tochthonous terrigenous fraction, was exclusively identified close to the West AfricanŽ .margin at ODP Site 959 Fig. 6 . Here low-reflecting huminitervitrinite ranges from 0.2

to 0.6% R with a pronounced maximum at 0.3–0.4% R . Higher reflecting organicm m

components of either primary oxidized or reworked origin occur in underlying lateŽ .Quaternary sections of ODP Site 959 Fig. 6b–d . Nevertheless, with regard to the

Fig. 5. Compilation of organic geochemical and petrologic characteristics of modern deep sea sediments fromthe Equatorial Atlantic. Samples are located along an east–west transect from the West African continentalmargin through the Equatorial Divergence to the central Equatorial Atlantic. Quantitative estimates of marineOM are based on organic petrologic and isotopic data. Total detrital OM comprises marine and terrigenousmacerals -10 mm particle size. C4 plant concentrations are estimated from the difference in total marine OMas obtained from microscopic and isotopic analyses.


Fig. 7. Organic petrologic characteristics of surface sediments from three different depositional settings in theŽ .modern Atlantic Ocean according to Littke and Sachsenhofer, 1994 . Note the clear separation of Equatorial

Ž .Atlantic deposits compared to hemipelagic sediments from the Norwegian Sea Wagner, 1993 and the NorthŽ .Sea Shelf Wiesner et al., 1990 . For estimation of recycled vitrinite, see discussion in the text.

scarcity and heterogeneity of reflectance data available from Equatorial Atlantic andŽ .Norwegian Sea Wagner, 1993 deposits and for reasons of standardization, these data

were corrected as proposed above, i.e., 75% of total vitrinite is regarded to be reworked.Ž .No correction was performed on data reported from the North Sea Wiesner et al., 1990

Ž .because autochthonous terrigenous OM huminite was distinguished from recycled OMŽ .vitrinite plus inertinite .

Characterization of deep sea settings based on three main maceral classes wasŽ .recently introduced by Littke and Sachsenhofer 1994 . They distinguished: a ‘vitrinite

and terrigenous liptinite’ class including bituminite III or amorphous OM; an ‘inertiniteand recycled vitrinite’ class; and a ‘marine liptinite’ class comprising alginite, liptodetri-nite bituminite and amorphous bituminous matter. Fig. 7 shows a compilation of organic

Fig. 8. Correlation of terrigenous OM obtained from maceral analyses with estimated percentages of C4 plants.Ž 13 .C4 plant concentrations are derived from the difference between microscopic and isotopic d C data. Fororg

Ž . Ž .estimation of C4 plant material, see discussion in the text. a Modern Equatorial Atlantic deposits, bŽ .Quaternary deposits from near-continental ODP Site 959, and c past glacial–interglacial sediments from open

ocean ODP Site 663.


petrologic data from surface sediments obtained from different settings of the EquatorialŽ .and high-latitude Atlantic Wiesner et al., 1990; Wagner, 1993 . Distribution patterns

clearly separate equatorial from high latitude settings based on differences in the amountof marine OM. Maceral compositions observed in high latitude deposits broadly scatter,showing highest variability in shallowest areas, whereas equatorial samples are lined up,revealing a lateral trend from pelagic to near-continental environments. Higher concen-trations of marine OM in equatorial deposits is attributed to enhanced productivity inthis area, or related to more intense remineralization of labile OM due to the influence of

Ž .young, oxygen-rich North Atlantic Deep Water NADW formed in the Norwegian-Greenland Sea.

Regarding the interpretation of quantitative estimates of marine and terrigenous OMin deep sea deposits, it appears important to compare results derived from optical and

Ž .isotopic analyses. It is evident that both records reveal partly opposing trends Fig. 5d .13 Ž .Marine proportions calculated from d C persist at very high levels 90–100%org

suggesting that dilution by terrigenous OM can be disregarded in the eastern EquatorialAtlantic. Organic petrologic results, in contrast, show a different pattern. They matchwell with the isotopic record at the western end of the transect, but gradually divergewith decreasing continental distance reaching a maximum offset of about 40% off WestAfrica. This pattern was recently explained by eolian supply of C4 plant material from

Ž .grass-covered source areas in central Africa Wagner and Dupont, in press . Sincerelease of atmospheric dust is concentrated near continents, modification of bulk d

13Corg

towards heavier, more marine values is expected to be strongest at the eastern part of thestudy area. The C4 plant fraction always remains a minor component of the bulk organic

Ž .composition showing highest contents off West Africa 25% which gradually decreaseŽ .towards the central Equatorial Atlantic -10% . Comparison of maximum C4 plant

estimates with contents in vitrinite, inertinite and total terrestrial macerals reveal linearŽ .correlations of 0.25, 0.76, and 0.87, respectively Fig. 8a , suggesting that C4 plant

debris is composed of both, thermally altered and non-altered plant matter, showing bestfit for the bulk terrigenous organic fraction.

4.3. Glacial–interglacial records of sedimentary OM in near-continental and openpelagic settings of the eastern Equatorial Atlantic

Temporal variations in supply and composition of sedimentary OM were studied onŽ .Quaternary deposits from ODP Site 959 Figs. 9 and 10 and in a sediment section

Ž . Žcovering one single glacial–interglacial cycle 0.40–0.48 Ma from ODP Site 663 Fig..11 . Variations in TOC, distinguished as marine vs. terrigenous OM, and maceral

Ž .composition are shown for the past 2.1 Ma of ODP Site 959 Fig. 9 . Glacial–intergla-cial cycles in TOC, known from other parts of the eastern Equatorial Atlantic, are notclearly recognizable at ODP Site 959. This pattern together with a dominance of the

Fig. 9. Total organic carbon, distinguished as marine and terrigenous OM, and variations in maceralcomposition observed in Quaternary sections of near-continental ODP Site 959 off Ivory CoastrGhana.Interglacial isotopic stages of the past 1.0 Ma are indicated by gray bars. Note the persistent dominance ofterrigenous OM throughout the Quaternary.


Fig. 10. Compilation of organic geochemical and petrologic characteristics of Quaternary sediments fromŽ .near-continental ODP Site 959. TOC and Hydrogen Index records are taken from Wagner in press .

Quantitative estimates of marine OM are based on organic petrologic and isotopic data. Total detrital OMcomprises marine and terrigenous macerals -10 mm particle size. C4 plant concentrations are estimated fromthe difference in total marine OM as obtained from microscopic and isotopic analyses. Interglacial isotopicstages of the past 1.0 Ma are indicated by gray bars.


terrigenous organic fraction is attributed to intense continental dilution or, probablymore important, to climate-driven changes in bottom water intensities causing winnow-

Ž .ing effects at the exposed location of ODP Site 959 Wagner, in press . The marinefraction ranges from 35% to 55% of the bulk OM, showing enhanced proportionsassociated with interglacial conditions. Vitrinite overall parallels the marine record,whereas inertinite is negatively correlated, showing highest concentrations during glacialstages. Concentrations of detrital OM scatter around 80% of the bulk organic fractionŽ .Fig. 10 . A dominance of terrigenous OM is also indicated by HI below 150 mg HCrgTOC. Comparison of quantitative estimates based on organic petrologic and d

13Corg

reveal an offset ranging from 15% to 60%. This equals a maximum C4 plant fractionŽ .between 10% to 35% of total OM, with average proportions of about 25% Fig. 10 .

Correlation of maximum C4 plant estimates with contents in vitrinite, inertinite and totalterrestrial macerals reveal low linear regressions of 0.12, 0.24, and 0.52, respectivelyŽ .Fig. 8b . Compared to modern conditions, supply of C4 debris was enhanced between2.1 Ma to about 0.45 Ma, then shifted to more variable patterns with periods of higherand lower eolian release. Assuming that the degree of oxidation of terrigenous maceralsat Site 959 is mainly inherited from dust-source areas, the inertinite plus recycledvitrinite vs. vitrinite ratio documents variations in African paleoaridity on glacial–inter-

Ž .glacial time scales Fig. 10 . Peak values are mainly associated with glacial climaticŽ .conditions, supporting a scenario introduced by Pokras and Mix 1985 , which proposed

extended savannah fires on the African continent related to glacially enhanced drynessand wind intensities.

To test if similar observations are documented in late Quaternary sediments from theŽ . Žcentral Equatorial Atlantic ODP Site 663 , a single glacial–interglacial cycle 0.4 to

.0.48 Ma was chosen for further investigations. Fig. 11 shows a compilation of bulkgeochemical, isotopic and organic petrologic results. Levels in TOC and HI persist highduring glacial stage 12, reflecting periodically enhanced marine flux rates in response to

Ž .intensified paleoproductivity Wagner and Dupont, in press . Quantitative estimates ofmarine OM derived from maceral analyses parallel these fluctuations in TOC and HI,whereas the d

13C record does not follow these profiles. The detrital fraction oforg

particulate OM dominates the bulk maceral composition showing lower concentrationsduring glacial stage 12. Hence, larger organic particles of marine and terrigenous originwere preferentially supplied and preserved during glacial conditions when wind-intensi-ties were enforced. This assumption is supported by corresponding profiles of inertiniteplus recycled vitrinite vs. vitrinite and estimated maximum amounts of eolian C4 plantmaterial. Both records show enhanced, but fluctuating values during cold climaticconditions. As was anticipated for ODP Site 663, estimated maximum concentrations ofeolian C4 plant material are considerably lower compared to near-continental Site 959Ž .Fig. 10 , reflecting gradients in supply and release of atmospheric dust from shelf toopen ocean. The linear correlation between C4 plant estimates and contents in vitrinite,

Ž .inertinite and total terrestrial macerals is -0.1, 0.24, and 0.52, respectively Fig. 8c .Additional evidence for eolian supply of grass-type vegetation to the Equatorial Atlantic

Ž .is provided by phytoliths Pokras and Mix, 1985; deMenocal et al., 1993; Fig. 11 andŽ .grass pollen Jahns et al., in press; Wagner and Dupont, in press which typically show

increased accumulation rates during glacial periods.


Fig. 12. Pyrolytic, isotopic and organic geochemical characteristics of grain size fractions from glacial andinterglacial deposits of ODP Site 959. Note the general increase in d

13C and T with coarsening grainorg max

size suggesting enhanced proportions of isotopically heavy and thermally mature OM especially in the 20–63mm fraction. This organic geochemical signature may be explained by the occurrence of wind-blown C4 plantmaterial from central Africa.

To assess the proposed C4 plant fraction in more detail, a set of samples from glacialand interglacial sections of ODP Site 959 was selected for organic geochemical studies

Ž .on grain size fractions Fig. 12 . TOC contents and HI decrease with increasing grainsize fraction, documenting the affinity of labile OM to fine-grained sediment

Fig. 11. Compilation of organic geochemical and petrologic characteristics of glacial–interglacial sedimentsŽfrom open ocean ODP Site 663. TOC and Hydrogen Index records are taken from Wagner and Dupont in

.press . Quantitative estimates of marine OM are based on organic petrologic and isotopic data. Total detritalOM comprises marine and terrigenous macerals -10 mm particle size. C4 plant concentrations are estimatedfrom the difference in total marine OM as obtained from microscopic and isotopic analyses. Accumulation

Ž . Ž .rates AR of phytoliths according to deMenocal et al. 1993 . Glacial isotopic stages 12 and 10 are indicatedby gray bars.


Ž .Bordovskiy, 1965; Hedges and Keil, 1995 . Weight-balanced TOC values, however,reveal similar or even higher proportions in larger grain size fractions. With regard tothe isotopic and thermal maturity signature of individual size fractions, it is interesting tonote that d

13C and T records steadily increase with coarsening grain size, reachingorg max

peak values in the 20–60 mm or coarser fraction. T of the 20–63 mm fractionmaxŽ .indicate thermally mature OM T ranges420–4558C , whereas isotopic values reachmax

heaviest signatures. This pattern could be produced by thermally altered, isotopicallyheavy OM from C4 plant debris. Optical inspection of the 20–63 mm fraction reveals amixture of oxidized and non-oxidized terrestrial macerals, thus supporting the assump-tion.

Characterization of depositional environments based on results from maceral analysesare presented in Fig. 13 following the approach proposed by Littke and SachsenhoferŽ .1994 . Past glacial–interglacial sediments from central Equatorial Atlantic and near-continental settings off Ivory CoastrGhana separate mainly due to differences in therelative fraction of marine and oxidized or recycled OM. Distribution areas from bothsites overlap to a certain extent causing an almost linear trend between the twodepositional environments. The total extent of both areas may define endmembers of a

Fig. 13. Organic petrologic characteristics of Quaternary deposits from near-continental ODP Site 959 andŽ .open ocean ODP Site 663 ternary plot according to Littke and Sachsenhofer, 1994 . For estimation of

recycled vitrinite, see discussion in the text.


slope–basin transect through the modern and Quaternary ocean although more organicpetrologic data from other Quaternary deposits are required to verify or modify thismodel.

5. General discussion

Organic petrologic and geochemical analyses performed on modern and past glacial–interglacial sediments from the Equatorial Atlantic provide new aspects on the distribu-tion of marine and terrigenous OM in response to continental distance, atmospheric andoceanographic circulation, and depositional processes controlling marine sedimentation.Implications of petrologic data for the paleoenvironmental reconstruction of TOC-poormarine deep sea settings are multi-fold, since they provide detailed information on thenature and appearance of dispersed OM including thermal maturation levels, particlesizes, and degree of degradation. One of the most important aspect, however, relates tothe use of organic petrology as an alternative proxy to assess quantitative information onthe composition of sedimentary OM. Comparison of quantitative data obtained from

Ž 13 .microscopic and isotopic bulk d C studies indicate that similarities and discrepan-org

cies between both records depend on the stratigraphic level and depositional setting.Organic petrologic characteristics of surface sediments are in agreement with deposi-tional processes operating in the modern tropical Atlantic. Decreasing eolian supply of

Ž .terrigenous grass-type organic material with increasing continental distance, as sug-gested from divergent trends in quantitative estimates of terrigenous OM based onpetrologic and isotopic data, appears reasonable to expect. The proof of C4 plantmaterial in Equatorial Atlantic sediments still remains an open target for future workalthough results from individual grain size fractions suggest that this type of terrigenousOM is concentrated in the size fraction 20–60 mm. Response of eolian supply andpaleoproductivity to late Quaternary glacial–interglacial climate is recorded in ODP Site663 profiles supporting the model of a productivity driven sedimentation in theQuaternary Equatorial Atlantic.

Organic petrologic characteristics of modern and past glacial–interglacial sedimentsof the Equatorial Atlantic reveal some distinctions from the classification established for

Ž .fossil deep sea environments Littke and Sachsenhofer, 1994 . These differences inmaceral composition are attributed partly to the depositional environment of the tropicalAtlantic, but probably also reflect some modifications due to the immature, diageneti-cally fresh condition of sedimentary OM. A compilation of petrographic data derivedfrom three different modern settings of the low and high latitude Atlantic and from lateQuaternary sections of ODP Sites 959 and 663 is presented in Fig. 14. The broadspectrum of modern depositional settings apparently is not represented by the roughdifferentiation of ‘marine upwelling’ and ‘central ocean’ settings, as depicted from fossil

Ž .deep sea deposits Fig. 14a . Instead, maceral associations of three marine sub-environ-ments are recognized covering end-member settings between the shallow and deepmodern ocean. The present data, however, do not rule-out if the separation of the

Ž .Equatorial Atlantic from the Norwegian Sea Wagner and Henrich, 1994 and the NorthŽ .Sea Wiesner et al., 1990 is due to regional differences in marine upwelling, deposi-


tional processes which determine the dispersion of OM, or different intensities of oxicremineralization of OM related to lateral gradients in oxygen concentration of NADWon its way from northern to southern latitudes. The primary control would support the

Ž .classification pattern from Littke and Sachsenhofer 1994 , considering that most of theEquatorial Atlantic surface sediments are deposited below upwelling areas. Reduceddeposition of inertinite and recycled vitrinite to the Equatorial Atlantic compared to highlatitude settings is probably determined by eolian transport, whereas in high latitudes,dispersion of OM is mainly controlled by lateral advection of autochthonous andreworked terrestrial OM either by currents or glaciomarine supply. Decreasing supply ofinertinite and recycled vitrinite with increasing continental distance in the EquatorialAtlantic is opposite to reported depositional trends, whereupon an increasing transportdistance causes a greater degree of chemical degradation and, consequently, leads to

Ž .enhanced deposition of inertinite Stein et al., 1989; Littke, 1993 . This pattern may beexplained by sorting of organic components during eolian transport according to their

Ž .average density and grain size Littke, 1993 .

6. Conclusions

Organic petrologic and geochemical analyses were performed on modern and Quater-nary TOC-poor sediments from the Equatorial Atlantic. The study area is located alongan east–west transect covering depositional settings from the West African margin off

Ž . Ž .Ivory CoastrGhana ODP Site 959 through the Equatorial Divergence ODP Site 663to the pelagic Equatorial Atlantic at 298W. Information on factors controlling thedeposition of sedimentary OM in response to Quaternary climatic cycles are discussedfor the past 2.1 Ma at ODP Site 959 and for the time interval 0.4–0.48 Ma at ODP Site663.

Organic geochemical results provide new aspects on the distribution of sedimentaryOM in response to continental distance, atmospheric and oceanographic circulation, anddepositional processes which control marine sedimentation under modern and past

Ž .glacial–interglacial conditions. The inventory of dispersed OM macerals in TOC-poormarine deep sea is limited due to mechanical breakdown of particles, degree of

Ž .oxidation, and selective remineralization of labile mostly marine OM. Nevertheless,petrology of sedimentary OM bears a great potential for paleoenvironmental studiesespecially as an alternative proxy to assess quantitative information on the relativeabundance of marine vs. terrigenous OM. Comparison of quantitative data obtained frommicroscopic studies with results from bulk d

13C signatures of surface and Quaternaryorg

deposits show similarities and discrepancies which apparently depend on the strati-graphic level and depositional setting. Strongest offset between both records was

Fig. 14. Comparison of organic petrologic characteristics observed in fossil deep sea sediments from variousŽ .marine settings Littke and Sachsenhofer, 1994 with those of modern and Quaternary sediments from the

Ž . Ž .Equatorial Atlantic, the Norwegian Sea Wagner, 1993 and the North Sea Wiesner et al., 1990 .


observed close to the African continent and during glacial periods, suggesting a couplingmechanism with wind-born terrigenous OM from central African. Since these Africansource areas are dominantly covered by C4 grass plants, supply of isotopically heavyterrigenous OM is assumed to have caused the observed difference between microscopicand isotopic records.

Organic petrologic characteristics of modern and past glacial–interglacial sedimentsof the Equatorial Atlantic are compared to the classification pattern established for fossil

Ž .deep sea environments Littke and Sachsenhofer, 1994 . Differences in maceral compo-sition between modern and fossil deep sea sediments are attributed partly to the specificdepositional environment of the tropical Atlantic, but probably also reflect somemodifications due to the immature, diagenetically fresh condition of sedimentary OM.

Acknowledgements

I would like to thank R. Henrich, Jim Hower, and one unknown referee for criticaland instructive comments on a former version of the manuscript. Technical assistancewas performed by R. Henning, J. Kim, J. Funk, U. Langrock, and H. Orthey. This study

Žwas funded by the Deutsche Forschungsgemeinschaft Sonderforschungsbereich 261 at.Bremen University, Contribution 181 and Ocean Drilling Program grant ‘Wa 1036r3’.

References

Anton, K.K., Liebezeit, G., Rudolph, C., Wirth, H., 1993. Origin, distribution and accumulation of organiccarbon in the Skagerrak. Marine Geology 111, 287–297.

Berger, W.H., Herguera, J.C., 1992. Reading the sedimentary record of the ocean’s productivity. In:Ž .Falkowski, P.G., Woodhead, A.D. Eds. , Primary Productivity and Biogeochemical Cycles in the Sea.

Plenum, New York, pp. 455–486.Bickert, T., Wefer, G., 1996. Late Quaternary deep water circulation in the South Atlantic: reconstruction from

carbonate dissolution and benthic stable isotopes. In: Wefer, G., Berger, W.H., Siedler, G., Webb, D.Ž .Eds. , The South Atlantic: Present and Past Circulation. Springer, Berlin, pp. 599–620.

Bonifay, D., Giresse, P., 1992. Middle to Late Quaternary sediment flux and post-depositional processesbetween the continental slope off Gabon and the mid-Guinean margin. Marine Geology 106, 107–129.

Bordovskiy, O.K., 1965. Accumulation and transformation of organic substances in marine sediments. MarineGeology 3, 3–34, Parts I and II.

Chesselet, R., Fontugne, M., Buat-Menard, P., Ezat, U., Lambert, C.E., 1981. The origin of particulate organiccarbon in the marine atmosphere as indicated by its stable carbon isotopic composition. Geophys. Res.Lett. 8, 345–348.

´Combaz, A., Bellet, J., Poulain, D., Caratini, C., Tissot, C., 1974. Etude microscopique de la matiere`Ž .organique de sediments quaternaires de Mer de Norvege. In: Marines, C.d.G. Ed. , Orgon I Mer de´ `

Norvege. CNRS, Paris, pp. 81–139.`Demaison, G.J., Moore, G.T., 1980. Anoxic environments and oil source bed genesis. Org. Geochem. 2, 9–31.deMenocal, P.B., Ruddiman, W.F., Pokras, E.M., 1993. Influences of high- and low-latitude processes on

African terrestrial climate: Pleistocene eolian records from equatorial Atlantic Ocean Drilling Program SiteŽ .663. Paleoceanography 8 2 , 209–242.

Dupont, L.M., Agwu, C.O.C., 1991. Environmental control of pollen grain distribution patterns in the Gulf ofŽ .Guinea and offshore NW-Africa. Geol. Rundschau 80 3 , 567–589.


Espitalie, J., Laporte, J.L., Madec, M., Marquis, F., Leplat, P., Paulet, J., Boutefeu, A., 1977. Methode radide´ ´de characterisation des roches-mere, de leur potential petrolier et de leur degre d’evolution. Revue del´ ` ´Institut Francais Petrole 32, 23–42.

Fischer, G., Muller, P.J., Wefer, G., 1998. Latitudinal d13C variations in sinking matter and sediments from¨ org

the South Atlantic: effects from anthropogenic CO and implications for palaeo-pCO reconstructions.2 2

Journal of Marine Sciences 547.Fredoux, A., 1994. Pollen analysis of a deep-sea core in the Gulf of Guinea: vegetation and climatic changes´

during the last 225,000 years B.P. Palaeogeogr., Palaeoclimat., Palaeoecol. 109, 317–330.Hebbeln, D., Henrich, R., Baumann, K.-H., 1998. Paleoceanography of the last interglacialrglacial cycle in

the polar North Atlantic. Quaternary Science Review 17, 125–153.Hedges, J.I., Keil, R.G., 1995. Sedimentary organic matter preservation: an assessment and speculative

synthesis. Marine Chemistry 49, 81–115.Henrich, R., Baumann, K.-H., Wagner, T., 1997. Modern and Quaternary pelagic and glaciomarine deposi-

tional regimes in the Nordic Seas: response to climate forcing and ice sheet dynamics. Developments inMarine Geology 1, 1–37.

Holemann, J.A., Henrich, R., 1994. Allochthonous versus autochthonous OM in Cenozoic sediments of the¨Ž .Norwegian Sea: evidence for the onset of glaciations in the Northern Hemisphere. Mar. Geol. 121 1r2 ,

87–103.ŽJahns, S., Huls, M., Sarnthein, M., in press. Palynological results from a marine core off Liberia Site GIK¨

.16776 covering the last 4400,000 years, Rev. Palaeobot. Palynol.Jansen, J.H.F., van Weering, T.C.E., Gieles, R., van Iperen, J., 1984. Middle and late Quaternary oceanogra-

phy and climatology of the Zaire-Congo Fan and the adjacent eastern Angola Basin. Netherlands Journal ofŽ .Sea Research 17 2–4 , 201–249.

Jasper, J.P., Gagosian, R.B., 1990. The sources and deposition of OM in the Late Quaternary Pigmy BasinGulf of Mexico. Geochim. Cosmochim. Acta 54, 1117–1132.

Jones, R.W., 1983. Organic matter characteristics near the shelf–slope boundary. SEPM Special Publication33, 391–405.

Jones, R.W., 1987. Organic facies. Advances in Petroleum Geochemistry 2, 1–80.Knies, J., Stein, R., 1998. New aspects of organic carbon deposition and its paleoceanographic implications

Ž .along the northern Barents Sea margin during the last 30,000 years. Paleoceanography 13 4 , 384–394.Lange, C.B., Treppke, U., Fischer, G., 1994. Seasonal diatom fluxes in the Guinea Basin and their

Ž .relationships to trade winds, hydrography and upwelling events. Deep-Sea Research 41 5r6 , 859–878.Lezine, A.M., 1991. West African paleoclimates during the last climatic cycle inferred from an Atlantic´

deep-sea pollen record. Quat. Res. 35, 456–463.Lezine, A.M., Hooghiemstra, H., 1990. Land–sea comparison during the last glacial–interglacial transition:´

pollen records from the west tropical Africa. Palaeogeogr., Palaeoclimatol., Palaeoecol. 79, 313–331.Ž .Liebezeit, G., Wiesner, G., 1989. Pyroysis of recent marine sediments. Biopolymers. Org. Geochem. 16 4–6 ,

1179–1185, Part 1.Littke, R., 1993. Deposition, diagenesis, and weathering of OM-rich sediments. Lecture Notes in Earth

Sciences 47, 0–216.Littke, R., Baker, D.R., Rullkotter, J., 1997. Deposition of petroleum source rocks. In: Welte, D.H., Horsfield¨

Ž .B., Baker, D.R. Eds. , Petroleum and Basin Evolution. Springer, Berlin, pp. 271–334.Littke, R., Sachsenhofer, R.F., 1994. Organic petrology of deep sea sediments: a compilation of results from

the Ocean Drilling Program and the Deep Sea Drilling Project. Energy and Fuels 8, 1498–1512.Maley, J., 1982. Dust, clouds, rain types, and climatic variations in the Tropical North Africa. Quat. Res. 18,

1–16.Mascle, J., Lohmann, G.P., Clift, P.D., Shipboard Party, 1996. Proceedings of the Ocean Drilling Program,

Initial Reports 159. ODP, Texas.McArthur, J.M., Tyson, R.V., Thomson, J., Mattey, D., 1992. Early diagenesis of marine OM: alteration of the

carbon isotopic composition. Marine Geology 105, 51–61.Mix, A.C.,1989. Pleistocene paleoproductivity: evidence from organic carbon and foraminiferal species. In:

Ž .Berger, W.H., Smetacek, V.S., Wefer, G. Eds. , Productivity of the Ocean. Wiley, Chichester, pp.313–340.

Mix, A.C., Morey, A.E., 1996. Climate feetback and Pleistocene variations in the Atlantic South Equatorial


Ž .Current. In: Wefer, G., Berger, W.H., Siedler, G., Webb, D. Eds. , The South Atlantic: Present and PastCirculation. Springer, Berlin, pp. 503–525.

Moulin, C., Lambert, C.E., Dulac, F., Dayan, U., 1997. Control of atmospheric export of dust from NorthAfrica by the North Atlantic Oscillation. Nature 387, 691–694.

Muller, P.J., Erlenkeuser, H., Von Grafenstein, R., 1983. Glacial–interglacial cycles in oceanic productivity¨inferred from organic carbon contents in Eastern North Atlantic sediment cores. In: Thiede, J., Suess, E.Ž .Eds. , Coastal Upwelling: Its Sedimentary Record, Part B. Plenum, NY, pp. 365–393.

Muller, P.J., Schneider, R., Ruhland, G., 1994. Late Quaternary pCO variations in the Angola Current:¨ 213 Ž .evidence from organic carbon d C alkenone temperatures. In: Zahn, R. et al. Eds. , Carbon Cycling in

the Glacial Ocean: Constraints on the Ocean’s Role in Global Change. Springer, Berlin, pp. 343–366.Pokras, E.M., Mix, A.C., 1985. Eolian evidence for spatial variability of Late Quaternary climates in tropical

Africa. Quat. Res. 24, 137–149.Pokras, E.M., Ruddiman, W.F., 1989. Evolution of south SaharanrSahelian aridity based on freshwater

Ž .diatoms genus Melosira and opal pytholiths: sites 657–661. In: Ruddiman, W.F., Sarnthein, M. et al.Ž .Eds. , Proceedings of the Ocean Drilling Program, Scientific Results 108. ODP, Texas, pp. 143–148.

Poynter, J.G., Farrimond, P., Robinson, N., Eglinton, G., 1989. Aeolian-derived higher plant lipids in theŽ .marine sedimentary record: links with Paleoclimate. In: Leinen M., Sarnthein, M. Eds. , Paleoclimatology

and Paleometeorology: Modern and Past Patterns of Global Atmospheric Transport. Kluwer AcademicPublishers, Dodrecht, pp. 435–462.

Prospero, J.M., 1981. Arid regions as sources of mineral aerosols in the marine environment. In: Pewe, T.L.,Ž .Ed. , Desert Dust: Origins, Characteristics, and Effects on Man, Geol. Soc. Am., Spec. Paper, 186, 71–86.

Romankevich, E.A., 1984. Geochemistry of Organic matter in the Ocean. Springer, Berlin.Ruddiman, W.F., 1997. Tropical terrigenous fluxes since 25,000 yrs B.P. Marine Geology 136, 189–207.Ruddiman, W.F., Janecek, T.R., 1989. Pliocene–Pleistocene biogenic and terrigenous fluxes at equatorial

Ž .Atlantic Sites 662, 663 and 664. In: Ruddiman, W.F., Sarnthein, M., et al. Eds. , Proceedings of theOcean Drilling Program, Scientific Results 108. ODP, Texas, pp. 221–240.

Ruhlemann, C., Frank, M., Hale, W., Mangini, A., Mulitza, S., Muller, P.J., Wefer, G., 1996. Late Quaternary¨ ¨productivity changes in the western equatorial Atlantic from 230 Th-normalized carbonate and organiccarbon accumulation rates. Marine Geology 135, 127–152.

Rullkotter, J., Cornford, C., Welte, D.H., 1982. Geochemistry and petrography of OM in northwest african¨continental margin sediments: quantity, provenance, depositional environment and temperature history. In:

Ž .von Rad, U., Hinz, K., Sarntheim, M., Seibold, E. Eds. , Geology of the Northwest African ContinentalMargin. Springer, Berlin, pp. 686–703.

Sarnthein, M., Thiede, J., Pflaumann, U., Erlenkeuser, H., Futterer, D., Koopmann, B., Lange, H., Seibold, E.,¨1982. Atmospheric and oceanic circulation patterns off Northwest Africa during the past 25 million years.

Ž .In: von Rad, U., Hinz, K., et al. Eds. , Geology of the Northwest African Continental Margin. Springer,Berlin, pp. 545–604.

Schlunz, B., Schneider, R.R., Muller, P.J., Showers, W.J., in press. Terrestrial organic carbon accumulation on¨ ¨the Amazon Deep Sea Fan during the last glacial sea level low stand, Chemical Geology.

Schneider, R.R., Muller, P.J., Ruhland, G., Meinecke, G., Schmidt, H., Wefer, G., 1996. Late Quaternary¨surface temperatures and productivity in the East-Equatorial South Atlantic: response to changes intradermonsoon wind forcing and surface water advection. In: Wefer, G., Berger, W.H., Siedler, G. Webb,

Ž .D. Eds. , The South Atlantic: Present and Past Circulation, Springer, Berlin, pp. 527–551.Schneider, R.R., Muller, P.J., Schlunz, B., Segel, M., Showers, W.J., Wefer, G., 1997. Late Quaternary¨ ¨

Western Atlantic paleoceanography and terrigenous sedimentation on the Amazon Fan: a view from d18 O

and d13C of planktonic foraminifera and bulk OM d

13C. In: Flood, R., Piper, D., Klaus, A., Peterson, L.L.Ž .Eds. , Proceedings of the Ocean Drilling Program, Scientific Results Leg 155. ODP, Texas, pp. 319–333.

Schulz, H., Bleil, U., Henrich, R., Segel, M., 1995. Meteor-Berichte, 95-2, Geo Bremen South Atlantic, CruiseNo. 29. Leitstelle Meteor, Hamburg.

Schutz, L., 1980. Long-range transport of desert dust with special emphasis on the Sahara. In: Kneip, T.J.,¨Ž .Lioy, P.J. Eds. , Annals of the New York Academy of Sciences, Vol. 338. The New York Academy of

Sciences, NY, pp. 515–532.Semmelhack, W., 1943. Die Staubfalle im nordwest-afrikanischen Gebiet des Atlantischen Ozeans. Ann.¨

Hydrogr. Marit. Meteor. 62, 273–277.


Senftle, J.T., Landis, C.R., McLaughlin, R.L. 1993. Organic petrographic approach to kerogen characterisa-Ž .tion. In: Engel, M.H., Macko, S.A. Eds. , Organic Geochemistry: Principles and Applications. Plenum,

New York, pp. 355–374.Simoneit, B.R.T., 1977. Organic matter in eolian dusts over the Atlantic Ocean. Mar. Chem. 5, 443–464.Stach, E., Mackowsky, M.-T., Teichmuller, M., Taylor, G. H., Chandra, D., Teichmuller, R., 1982. Stach’s¨ ¨

Textbook of Coal Petrology. Borntrager, Berlin.¨Stein, R., 1991. Accumulation of Organic Carbon in Marine Sediments. Lecture Notes in Earth Sciences 34,

1–216.Stein, R., Littke, R., 1990. Organic-carbon-rich sediments and paleoenvironment: results from Baffin Bay

Ž . Ž . Ž .ODP Leg 105 and the upwelling area off Northwest Africa ODP Leg 108 . In: Huc, A.Y. Ed. ,Deposition of Organic Facies, American Association of Petroleum Geologists, Studies in Geology 30,41–56.

Stein, R., Schubert, C., 1996. Organischer Kohlenstoffeintrag im zentralen Arktischen Ozean wahrend des¨Ž .Spatquartars. Geowissenschaften 14 9 , 370–375.¨ ¨

Stein, R., Rullkotter, J., Welte, D.H., 1986. Accumulation of organic-carbon-rich sediments in the Late¨Jurassic and Cretaceous Atlantic Ocean—a synthesis. Chemical Geology 56, 1–32.

Stein, R., ten Haven, H.L., Littke, R., Rullkotter, J., Welte, D.H., 1989. Accumulation of marine and¨terrigenous organic carbon at upwelling Site 658 and nonupwelling Sites 657 and 659: implications for thereconstruction of paleoenvironments in the eastern subtropical Atlantic through late Cenozoic times. In:

Ž .Ruddiman, W.F., Sarnthein, M., et al. Eds. , Proceedings of the Ocean Drilling Program, ScientificResults 108. ODP, Texas, pp. 361–386.

Stein, R., Grobe, H., Wahsner, M., 1994. Organic carbon, carbonate, and clay mineral distributions in theeastern central Arctic Ocean surface sediments. Marine Geology 119, 269–285.

Summerhayes, C.P., 1987. Organic-rich Cretaceous sediments from the North Atlantic. In: Brooks, J., Fleet,Ž .A.J. Eds. , Marine Petroleum Source Rocks, Geol. Soc. London, Spec. Publ. No. 26. Blackwell Scientific,

Oxford, pp. 301–316.Taylor, G.H., Teichmuller, M., Davis, A., Dissel, C.F.K., Littke, R., Robert, P., 1998. Organic Petrology.¨

Schweitzerbart, Stuttgart.Teichmuller, M., 1987. Recent advances in coalification studies and their application to geology. In: Scott,¨

Ž .A.C. Ed. , Coal and Coal-bearing Strata: Recent Advances, Geological Society Special Publications No.32. London, pp. 127–169.

Tissot, B.P., Welte D.H., 1984. Petroleum Formation and Occurrence. Springer, Berlin.ten Haven, H.L., Rullkotter, J., Stein, R., 1989. Preliminary analysis of extractable lipids in sediments from the¨

Ž . Ž .eastern North Atlantic Leg 108 : comparison of a coastal upwelling area Site 658 with a nonupwellingŽ . Ž .area Site 659 . In: Ruddiman, W.F., Sarnthein, M., et al. Eds. , Proceedings of the Ocean Drilling

Program, Scientific Results 108. ODP, Texas, pp. 351–360.ten Haven, H.L., Littke, R., Rullkotter, J., Stein, R., Welte, D.H., 1990. Accumulation rates and composition¨

of organic matter in Late Cenozoic sediments underlying the active upwelling area off Peru. In: Suess, E.,Ž .von Huene, R., et al. Eds. , Proceedings of the Ocean Drilling Program, Scientific Results 112. ODP,

Texas, pp 591–605.Tiedemann, R., Sarnthein, M., Stein, R., 1989. Climatic changes in the western Sahara: aeolo-marine sediment

Ž . Ž .record of the last 8 million years, Sites 657–661 . In: Ruddiman, W.F., Sarnthein, M., et al. Eds. ,Proceedings of the Ocean Drilling Program, Scientific Results 108. ODP, Texas, pp. 241–277.

Tiedemann, R., Sarnthein, M., Shackleton, N.J., 1994. Astronomic time scale for the Pliocene Atlantic d18 O

Ž .and dust flux records of Ocean Drilling Program Site 959. Paleoceanography 9 4 , 619–638.Turon, J.L., 1984. Direct landrsea correlations in the last interglacial complex. Nature 309, 673–676.Tyson, R.V., 1995. Sedimentary organic matter: organic facies and palynofacies. Chapman and Hall, London.Verardo, D.J., McIntyre, A., 1994. Production and destruction: control of biogenous sedimentation in the

Ž .tropical Atlantic 0–300,000 years B.P. Paleoceanography 9 1 , 63–86.Verardo, D.J., Ruddiman, W.F., 1996. Late Pleistocene charcoal in tropical Atlantic deep-sea sediments:

Ž .climatic and geochemical significance. Geology 24 9 , 855–857.van Bennekom, A.J., Berger, G.W., 1984. Hydrography and silica budget of the Angola Basin. Netherlands

Ž .Journal of Sea Research 17 2–4 , 149–200.


van Leeuwen, R.J.W., 1989. Sea-floor distribution and Late Quaternary faunal patterns of planktonic andbenthic foraminifers in the Angola Basin. Utrecht Micropaleontol. Bull. 38, 1–287.

Verstraete, J.M., 1992. The seasonal upwellings in the Gulf of Guinea. Progr. Oceanogr. 29, 1–60.Voituriez, B., Herbland, A., 1982. Comparison des systemes productifs de l’Atlantique Tropical Est: domes` ˆ

thermiques, upwellings cotier et upwelling equatorial. Rapp. P.-V. Reun. Cons. Int. Explor. Mer. 180,ˆ ´ ´114–130.

Wagner, T., 1993. Organisches Material in pelagisches Sedimenten: glazialerinterglaziale Variationen imEuropaischen Nordmeer, Ber. Sonderforschungsbereich 313, Univ. Kiel 42, 1–138.¨

ŽWagner, T., in press. Pliocene–Pleistocene carbonate and organic carbon fluxes off Ivory CoastrGhana ODP.Site 959 : paleoenvironmental implications for the eastern Equatorial Atlantic. In: Mascle, J., Lohmann,

Ž .G.P., Clift, P. Eds. , Proceedings of the Ocean Drilling Program, Scientific Results 159, College Station,Texas.

Wagner, T., Henrich, R., 1994. Organo- and lithofacies of glacial–interglacial deposits of the Norwegian-Greenland Sea: responses to paleoceanographic and paleoclimatic changes. Mar. Geol. 120, 335–364.

Wagner, T., Wiesner, M.G., 1994. Application of the concept of macerals to recent sediments, 207th ACSNational Meeting, March 13–17, San Diego, CA, Abstracts of Papers, Part 1.

Wagner, T., Holemann, J.A., 1995. Deposition of organic matter in the Norwegian-Greenland Sea during the¨past 2.7 million years. Quat. Res. 44, 255–266.

Ž .Wagner, T., Holemann, J., Wiesner, M.G., 1995. The Rock–Eval maturity record T of Late Pleistocene to¨ maxŽ .Quaternary deposits ODP Legs 104 and 159 —a tool for identification of reworked, thermal mature

organic matter, 5th International Conference on Paleoceanography. Halifax, p. 67.Wagner, T., Dupont, L., in press. Terrestrial organic matter in marine sediments: analytical approaches and

Ž .eolian-marine records of the central Equatorial Atlantic. In: Fischer, G., Wefer, G. Eds. , The use ofProxies in Paleoceanography: Examples from the South Atlantic. Springer, Berlin.

Wefer, G., Bleil, U., Schulz, H., 1989. Meteor Cruise Report No. 9-4, Berichte aus dem FB Geowis-senschaften, Univeritat Bremen, 7, pp. 1–103.¨

Westerhausen, L., Poynter, J., Eglinton, G., Erlenkeuser, H., Sarnthein, M., 1993. Marine and terrigenousorigin of OM in modern sediments of the equatorial East Atlantic: the d

13C and molecular record.Ž .Deep-Sea Research 40 5 , 1087–1121.

Wiesner, M.G., Haake, B., Wirth, H., 1990. Organic facies of surface sediments in the North Sea. Org.Ž .Geochem. 15 4 , 419–432.

petrology of organic matter in modern and late quaternary deposits of the equatorial atlantic:...

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