Journal of Conference Abstracts

Session B07:2B

B07 : 2B/22 : G5

Coccolith Sr/Ca as an Indicator of Marine Paleoproductivity

Heather Stoll (heather.stoll@asturias.geol.uniovi.es)¹ &

Schrag Daniel (schrag@eps.harvard.edu)²

¹ Dept. de Geologia, Univ. de Oviedo, c/ Arias de Velasco, 33005 Oviedo, Asturias, SPAIN

² Dept. of Earth and Planetary Sciences, Harvard Univ., 20 Oxford St., Cambridge, MA 02138, USA

We present evidence supporting the utility of Sr/Ca of coccolith carbonate as a new index of changes in marine productivity in carbonate sequences. Sr/Ca of mixed coccolith assemblages from core tops covaries with productivity across modern productivity gradients in the Equatorial Pacific. In downcore records from the same region for the last 150 ky, coccolith Sr/Ca covaries with other paleoproductivity indices such as Ba and barite accumulation rates and opal accumulation rates. Because coccolith carbonate comprises the majority of carbonate in many deep sea settings, the Sr/Ca of bulk carbonate approximates the coccolith Sr/Ca ratio, and bulk carbonate analysis may be used for more indurated sediments. Bulk carbonate Sr/Ca from the Upper Albian to Lower Santonian of Gubbio, Italy, covaries with changes in trophic conditions inferred from the life strategy of the predominant planktonic foraminiferal populations (% r-selectors and intermediate forms; Premoli-Silva and Sliter, 1994). Bulk carbonate Sr/Ca from the Upper Campanian to Lower Maastrichtian of South Atlantic and Southern Indian Ocean deep sea sites (DSDP 516F, 762C) also covary with the %r+i index in Gubbio sections, implying global productivity changes. The mechanism for variation in coccolith Sr/Ca with productivity has not been documented, but we hypothesize that productivity increases coccolithophore growth rate and calcite precipitation rate, which has been shown to influence Sr partitioning in inorganic calcites (Lorens, 1981; Tesoriero and Pankow, 1996).

Tesoriero, AJ & Pankow JF, GCA, 60, 1053-1063, (1996).

Lorens, RB, GCA, 45, 553-561, (1981).

Premoli-Silva, I & Sliter, WV, Paleontographia Italica, 82, 1-89, (1994).

B07 : 2B/23 : G5

Palaeoenvironmental and Palaeoclimatic Interpretation of Pleistocene Seagrass-Bank Deposits Using Modern Sediments and Foraminiferal Analogues

Trudi Semeniuk

21 Glenmere Rd., Warwick, WA 6024, Australia

A combination of stratigraphic, sedimentological, foraminiferal ecological and biogeochemical techniques were used to reconstruct palaeoenvironments of Pleistocene marine units of the Perth Basin, Western Australia. Small-scale sedimentary structures, grain-size distribution and biogenic components from modern seagrass environments compare favourably with fossiliferous parts of the Pleistocene limestones suggesting the depositional environments of these units were seagrass banks. Sedimentological studies from modern settings show that palaeoenvironmental interpretation may be complicated by geomorphic setting (cuspate foreland vs. open coast settings) and reworking of relict material. A study of living and death foraminiferal assemblages from modern seagrass environments identified indicator species for seagrass-bank deposits. The presence of these epiphytic species in the Pleistocene units corroborates the palaeoenvironmental interpretation based on sedimentological data. Foraminiferal ecological studies show that assemblages from different climatic settings along the Western Australian coast are distinct. Assemblage features which are linked to sea-temperature include: abundance of porcellaneous foraminifera; the number of species with tropical affinity; and the number of species of larger foraminifera. These features may be used to infer palaeoclimate. More detailed studies found that most species have sporadic distributions, hence living foraminifera only in part reflect the climate gradient along the coast; they also reflect micro- to meso-scale biotic factors. These biotic factors vary on a seasonal to annual basis, generating temporal as well as spatial changes in foraminiferal assemblages. Hence, palaeoclimatic interpretation of foraminiferal assemblages may be equivocal, i.e., confused with differences in productivity, if based on species that are regulated by non-climatic factors at the regional scale. Comparison of modern living, death and fossil foraminiferal assemblages show that many descriptive criteria are sensitive to post-depositional processes and may be less reliable indicators of environment or productivity; e.g., diversity and total foraminiferal density. Isotopic composition of modern foraminiferal material was found to vary seasonally to annually in relation to productivity and population dynamics in addition to temperature. Isotopic data were only used to infer palaeotemperature in conjunction with supporting ecological information and independent corroboration from biological evidence, such as the presence of larger foraminifera. Thus, sedimentological and foraminiferal assemblage data provided reliable methods of interpreting depositional environment. Only some foraminiferal species and assemblage features could reliably be used as palaeoclimatic indicators.

B07 : 2B/24 : G5

Coastal Shifting Documented by Diatoms and Inorganic-Geochemical Data in Holocene Sequences (NW Germany)

Frank Watermann (frank.watermann@icbm.terramare.de)¹,

Olaf Dellwig

(dellwig@geo.icbm.uni-oldenburg.de)²,

Hans-Jürgen Brumsack¹ &

Gisela Gerdes²

¹ ICBM-Marine Station, Schleusenstr. 1, 26382 Wilhelmshaven, Germany

² ICBM,Carl von Ossietzky University, P.O. Box 2503, 26111 Oldenburg, Germany

Holocene depositional sequences in the coastal zone of the North Sea reflect past sea level changes resulting from climatic developments. These have led to lateral interfingering of marine, brackish, lagoonal and limnic sediments as well as peat layers. This succession is reflected in an 18 m sediment core drilled in the marsh lands of the river Weser and spanning the entire Holocene. The core was analyzed at high stratigraphic resolution for diatom inventaries and inorganic parameters, e.g., Si/Al-, Ca/Sr-ratios. Most units of the core contain well preserved diatoms. Changes of species dominance and life forms are tools to reconstruct coastal shifting, paleosalinity, paleotransport and paleohydrodynamics. Coastal shifting causing facies changes is documented in detail by a changing ratio between two salinity groups (polyhaline and oligohaline diatoms). At the base of the core, limnic conditions predominate. In the overlying sediments, polyhaline species increase as a result of the sea-level rise. In the upper part of the core, the increase of oligohaline diatoms verifies the influence of the river Weser. Besides the reconstruction of paleosalinity, the ratio between pelagic and littoral diatoms was used for interpretations of paleotransport, and reconstructions of paleohydrodynamic conditions. Particularly in sediments of the lower and upper part of the core, high abundance of pelagic diatoms indicates transport processes. In the lower part, the dominance of marine pelagic species underlines the rising sea-level, while changes towards brackish pelagic species in the upper part indicate increasing influence of the river Weser. The central part of the Holocene sequence indicates calm depositional conditions because of the relatively high abundance of littoral diatoms. The inorganic-geochemical data sets are also tools to reconstruct coastal shifting and paleohydrodynamics. Furthermore, inorganic analyses identified the provenance of deposited materials. Inorganic-chemical parameters, e.g., Si/Al-, Ca/Sr-ratios, and TOC contents correlate with depositional factors such as wave-energy and lithofacies changes, which allow a detailed reconstruction of the paleoenvironment. The correlation of diatom analyses and inorganic-geochemical data sets allow a detailed reconstruction of the paleoenvironment of Holocene sequences.

B07 : 2B/25 : G5

Climatic and Environmental Change During the mid Pliocene: Inferences from Laser Ablation ICP-MS Analysis of Cardita Senilis from the Coralline Crag of England

Gregory D. Price (g.price@plymouth.ac.uk)¹,

Nicholas J. G. Pearce² &

Brian M. Funnell³

¹ Department of Geological Sciences, The University of Plymouth, Plymouth, PL4 8AA, UK

² Institute of Geography and Earth Sciences, University of Wales, Aberystwyth, Llandinam Building, Aberystwyth, SY23 3DB, Wales, UK

³ School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK

The climate of the mid Pliocene has been considered to be notably warmer than today, with twice the carbon dioxide level. Substantial evidence for this warmth has been derived from faunal and isotopic analysis of ostracods, foraminifera and molluscs from numerous sites across the North Atlantic region, the most easterly being the Coralline Crag deposits of eastern England. The fauna from the Coralline Crag has been interpreted in terms of cool-temperate conditions, whilst others have suggested significantly warmer conditions with a reduced seasonality of temperature. Shells of the aragonitic bivalve Cardita senilis have been obtained from these mid Pliocene Coralline Crag deposits and analysed by Laser Ablation Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) for a suite of elements (Mg, Sr, Mn and Ba). The preservation of the bivalves has been assessed through the application of chemical analyses, X-ray diffraction and Scanning Electron Microscopy. Between 80-120 analytical points were placed along each shell transect crossing the growth lines and parallel to the axis of maximum growth. Barium and Strontium variation in the shells of C. senilis appear to be influenced by cyclic phytoplanktonic blooms possibly linked to upwelling of nutrient rich waters. The apparent cyclicity is interpreted to be controlled by tidal cycles, consistent with previous hypotheses regarding the deposition of the Coralline Crag. The incorporation of magnesium into C. senilis appears to be influenced in a predictable manner by seawater temperature which is in turn controlled by tidally influenced upwelling. The data support previous ideas that the mid Pliocene was more equable than at present.

B07 : 2B/26 : G5

Reconstruction of Paleoenvironmental Conditions from Comparative Studies of Foraminifera in Holocene and Modern Coastal Sediments

Anja Carlmeyer,

Gisela Gerdes (g.gerdes@icbm.terramare.de) &

Frank Watermann

ICBM-Marine Station, Schleusenstrasse 1, 26882 Wilhelmshaven, Germany

Holocene sequences from the southern North Sea area, composed of clastic sediments and intercalated bog deposits, indicate fluctuations of the Holocene sea level rise. The lithology is characterized by marine and semi-terrestrial features including littoral, brackish lagoonal and fluvial-limnic conditions. The microfossil record reveals a variety of foraminifera. Comparative studies in modern coastal areas indicate similar species compositions in both the fossil record and the modern environments studied. Species are common that live in intertidal flats and salt marshes at the southern North Sea coast. The species composition includes both agglutinating and calcifying benthic foraminifera. In the modern settings studied, the abundance of agglutinating species generally are of relatively lower abundance than the calcifying foraminifera which usually are dominated by Nonion depressulum and Elphidium selseyense. Comparing species composition, absolute abundance and faunal diversity of the calcifying foraminifera, there is a correlation possible between the modern study areas and the fossil assemblages. However, at specific depths of the Holocene coastal sequences mainly revealing lithofacies characteristic of regressive or stagnational stages of sea level rise, there is no simple correlation possible. In these cases, agglutinated foraminifera (e.g. Trochammina inflata) dominate the microfossil record. It seems therefore possible to derive a signal of lagoonal perimarine environments that may have existed during the Holocene in a more or less wider distance from the sea. Unhindered by dykes, sea water may have invaded the hinterland on the occasion of storm events, and fed shallow areas behind barriers and coastal dunes that became impoverished by marine sedimentation. In the present, dykes effectively hinder the sea water to reach the hinterland areas, thus, similar paralic systems and brackish shallow water habitats more or less are lacking at the southern North Sea coast. Such man-made environmental changes may have caused a faunal change.

B07 : 2B/29 : G5

Geochemical and Microfacial Indicators of Changing Paleoenvironmental Conditions in Holocene Near-Coastal Deposits (NW Germany)

Olaf Dellwig

(dellwig@geo.icbm.uni-oldenburg.de)¹,

Frank Watermann (frank.watermann@icnm.terramare.terramare.de)²,

Hans-Jürgen Brumsack (H.Brumsack@geo.icbm.uni-oldenburg.de)¹ &

Giesela Gerdes (gerdes@icbm.terramare.de)²

¹ Institute of Chemistry and Biology of the Marine Environment, University of Oldenburg, Carl-von-Ossietzky-Strasse 9-11, D-26129 Oldenburg, Germany

² Institute of Chemistry and Biology of the Marine Environment, Marine Station, Schleusenstrasse 1, D-26382 Wilhelmshaven, Germany

As part of the special research program "Bio-geochemical changes over the last 15,000 years - continental sediments as an expression of changing environmental conditions" funded by the German Science Foundation several cores were drilled in the NW German coastal area. The cores, which cover the entire Holocene were examined at high resolution by geochemical and microfacial methods for a detailed paleoenvironmental reconstruction. During the Holocene sea-level rise numerous lithological facies, e.g., tidal flat sediments, brackish water sediments, and peat layers were formed. Geochemical parameters, in particular Si/Al-, Zr/Al-, and Ca/Sr-ratios as well as bulk parameters, correlate with depositional factors like wave-energy and lithofacies changes. Furthermore these parameters reveal information about type and origin of the deposited material, e.g., loess-like material from eolian input. In combination with diatom inventories, which are, amongst others, a useful tool for the reconstruction of paleosalinity, these analyses allow a detailed description of the paleoenvironment.Early diagenetic effects of pyrite formation are evident in TOC-rich peat layers. Besides semi-terrestrial reed peats intercalated between clastic sediments, pure bog peats occur especially in the basal parts of the investigated cores. Most of these peats are affected by sulphate reduction and resulting pyrite formation. Furthermore enrichments of redox-sensitive trace metals occur. The highest enrichments can be observed for As, Mo, Re, and U indicating sea water as the main trace metal and sulphate source. Unusually high amounts of about 58% pyrite are found in some basal bog peat samples. Thin sections of these intervals reveal thin clayey layers (1 to 3 mm) with completely pyritized interfaces. The clayey layers are presumably caused by short-term transgressive events which led to a splitting of the peat and allow the input of clastic material. Afterwards the peat/clay interface may act as an aquifer for waters of higher salinity. The marine origin of the clastic material is documented by marine pelagic diatoms. Bulk sediment S-isotope data of peat samples provide information on sulphate availability during pyrite formation. S-isotope ratios are compatible with both, open and closed system conditions depending on exposition to sea water and coastline, respectively.

B07 : 2B/30 : G5

High-Resolution Geochemical Record of a 1.5 m Long Core from the Gotland Basin: Indication of Changing Salt Water Inflow Patterns and Surface Productivity

Helmar Kunzendorf (helmar.kunzendorf@risoe.dk)¹,

Birger Larsen (bil@geus.dk)²,

Aarno Kotilainen (aarno.kotilainen@gsf.fi)³ &

Thomas Andrén (thomas.andren@geo.su.se)⁴

¹ Plant Biology and Biogeochemistry Department, Risø National Laboratory, P.O. Box 49, DK-4000 Roskilde, Denmark

² The Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen NV, Denmark

³ Geological Survey of Finland, Betonimiehenkuja 4, FIN-02150 Espoo, Finland

⁴ Department of Quaternary Research, Stockholm University, S-10691 Stockholm, Sweden

As part of the EU MAST3 project BASYS, subproject 7 (partly funded by the EU), the upper 1.5 m obtained by combining a Niemistö-type surface sediment core (0.5 m length) and the section 0.5 to 1.5 m of a large box core from the central part of the Gotland Basin (water depth ~240 m) were cut into 1-cm sections. The freeze-dried sediment was analysed by non-destructive energy-dispersive X-ray fluorescence for a number of major and trace elements. Sediments were also dated by ²¹⁰Pb (Kunzendorf et al., 1998), ¹⁴C, and by paleomagnetic measurements. The geochemical profiles display a characteristic element distribution pattern superimposed on the visible fine lamination of the sediment The geochemical signal can be traced to normal sedimentation processes that occurred during the past about 3000 years: terrestrial material transport, primary productivity in the surface waters, and current-transported material interacting at the sediment-water interface or in its close vicinity.

The distinct geochemical geochemical profiles of Ca and Mn covarying perfectly along the core sections suggest that the mineral rhodochrosite is produced at the sediment-seawater interface. Saline water from the North Atlantic moves at depth during prevailing northwesterly storm periods via the Skagerrak, Kattegat into the Gotland Basin. Ca-enriched North Sea water and diagenetically supplied Mn combine to rhodochrosite (Ca-Mn carbonate) during such periods. The signal prevails during burial. Alternating low- and high Ca-Mn periods of durations of several hundreds of years are displayed by the geochemical record.

A distinct pattern is observed for the trace metal Mo. Along the 1.5 m section, contents are rather high, above 150 mg/kg, in the upper 15 cm and between 55 and 115 cm of the core. Earlier investigations (Halberg, 1974) used Mo as an indicator of anoxicity in spite of the rather high values actually requiring a special source and hence, a provenance explanation. Being one of the seven known micronutrients, Mo is probably involved in the biological productivity in the surface waters in that it may be participating in the nitrogen fixing by cyanobacteria (blue-green algae). If this is the case, high Mo in the sediment may reflect algal blooming periods and Mo may be a sensitive paleoenvironmental indicator in the Baltic Sea.

Halberg O, Havforskningsinst. Skr, 238, 3-16, (1974).

Kunzendorf H, Emeis K-C, Christiansen C, Danish J, Geography, 98, 1-9, (1998).

B07 : 2B/31 : G5

Palaeoenvironmental Changes During the Last 330 kyr in the Tropical Indian Ocean

Frauke Rostek (rostek@cerege.fr),

Sonja Schulte (schulte@cerege.fr) &

Edouard Bard (bard@cerege.fr)

CEREGE, Europole de l'Arbois BP 80, 13545 Aix-en-Provence cdx 4, France

Analyses of the deep-sea core MD900963 (05°04'N, 73°53'E; 2450 m water depth) were extended to reconstruct the paleoenvironment of the tropical Indian Ocean during the past 330 kyr (SST, productivity, redox-conditions). We measured organic geochemical proxies (organic carbon and specific biomarkers) which can be compared to trace metals concentrations (Pailler et al. 1998) and micropaleontological counts (Beaufort et al., 1997; Cayre et al. in press) obtained on the same sediments. Alkenone SSTs fluctuate by about 4°C, between 23.5 and 27.5°C with highest temperatures during stage 5.5 (the Last Interglacial). A broad SST minimum of about 23-24°C is observed for isotope stages 4 and 3.3. SST changes roughly follow the ¹⁸O variations measured in planktonic foraminifera. The concentrations of organic carbon (TOC) and C37 alkenones are strongly correlated with each other and are used as qualitative proxies of the primary productivity (Rostek et al, 1997). This interpretation is strengthened by the high correlation of these parameters with two paleoproductivity records based on statistical transfer functions using coccoliths and foraminiferal distributions (Beaufort et al., 1997). Our results show that the primary productivity was enhanced during glacial stages and substages but was lower during the interglacials and interstadials. All productivity related proxies are dominated by a clear 23 kyr cyclicity related to the insolation variations driven by the precession cycle. The n-alkanes were detected in a carbon number range from C17 to C37 showing an odd over even predominance with carbon preference indices (CPI) between 1.3 and 4.8 and variations in total concentration between 0.5 and 5.4 mg/g dry sediment. Frequency analyses performed on the n-alkanes time series exhibit the same cyclicity as for the productivity related parameters. This, together with the relatively low CPI values suggests a marine source for the n-alkanes as proposed by Zegouah et al. (1998) in contrast with the more classical view that these compounds only belong to the detrital component of terrestrial organic matter. In order to reconstruct past changes of redox-conditions, we measured the C35/C31-n-alkane ratio, which has been shown to be enriched under suboxic conditions (Schulte et al. 1998). This ratio never reaches values typical for suboxic or anoxic conditions (i.e. > 0.6) which indicates that deep waters remained well oxygenated during the last 330 kyr. This contrasts with the conclusion by Sarkar et al. (1993) that during the last glacial period deep waters were fully anoxic in this part of the Indian Ocean. The observed slight changes of the C35/C31 ratios could be explained by changes of redox-conditions within the upper sediment column due to enhanced productivity. This conclusion would be compatible with a companion study of authigenic trace metals (U, Mo, Cd) in the same core (Pailler et al., 1998).

Beaufort L, Lancelot Y, Camberlin P, Cayre O, Vincent E, Bassinot F, Labeyrie L, Science, 278, 1451-1454, (1997).

Pailler D, Rostek F, Bard E, van Geen A, Mortlock R, Zheng Y, Mineralogical Magazine, 62A, 1122-1123, (1998).

Rostek F, Bard E, Beaufort L, Sonzogni C, Ganssen G, Deep Sea Research II, 44, 1461-1480, (1997).

Sarkar A, Bhattacharta SK, Sarin MM, Geochimica et Cosmochimica Acta, 57, 1009-1016, (1993).

Schulte S, Rostek F, Bard E, Mineralogical Magazine, 62A, 1356-1357, (1998).

Zeghouagh Y, Derenne S, Largeau C, Bardoux G, Mariotti A, Organic Geochemistry, 28, 571-583, (1998).

B07 : 2B/32 : G5

Calibration and Application of Planktic Foraminiferal Proxies for Paleoproductivity in a Seasonal Upwelling System (NW Indian Ocean)

Gerald Ganssen (gang@geo.vu.nl) &

Jan van Hinte (hinj@geo.vu.nl)

Fac. of Earth Sciences, Free University Amsterdam, De Boelelaan 1085, Amsterdam, the Netherlands

Within the framework of the Netherland Indian Ocean Programme (NIOP) and as part of its project "Tracing a seasonal upwelling" the reconstruction of paleoproductivity is one of the main objectives. Our approach was to numerically calibrate the foraminiferal skeletal record to in situ determined hydrographic and biologic parameters to finally reconstruct Late Quaternary monsoon history. We collected foraminifera from the watercolumn and the sediment during the SW Monsoon upwelling season of 1992 and the NE Monsoon non-upwelling season of 1993 and employed two sediment trap moorings covering both seasons from May 1992 till February1993.

The water and trap samples show large seasonal variation in species composition, relative as well as absolute abundances and fluxes. Generally, shell absolute abundances and fluxes decreased by an order of magnitude when coastal upwelling ceased and basin-wide stratification set in. With Globigerina bulloides dominant the SW monsoon accounted for close to 90% of the annual shell flux whereas Globigerinoides ruber dominated the highly diverse NE monsoon fauna. Consequently the ratio of these two species reflects the relative importance of the two seasons in the modern environment. The left coiling Neogloboquadrina pachyderma is nearly restricted to the upwelling season.

Our stable oxygen isotope data from both seasons show that the eight analyzed species are in equilibrium with the measured temperature and isotopic composition of the ambient water. The difference in the stable carbon isotopic composition of two planktic foraminiferal species proved to vary significantly with the intensity of productivity: While the tests of Globigerina bulloides get enriched, those of Neogloboquadrina dutertrei get depleted in the light isotope ¹²C.

Various proxies have been applied on two piston cores one from the Somalia continental slope and one from the Gulf of Aden. The stratigraphy of the cores is based on ¹⁴C AMS datings combined with the stable oxygen isotopic composition of three planktic foraminifera.

Our different productivity proxies show ambiguous patterns for the past 30 ka which will be discussed in relation to the complex dynamics of the rapidly changing upwelling and productivity processes. Nevertheless, very typical for both cores are the high-frequency fluctuations in all studied faunal and isotope parameters, reflecting short-term variations in monsoon intensity over the past 30 ka. These changes are taking place with a frequency between 1000 and 2000 years.

B07 : 2B/33 : G5

Reconstruction of Late Quaternary Palaeoenvironment in the Eastern Arctic Ocean Continental Margin Area: Implications from Major and Minor Element Distribution in Marine Sediments

Frank Schoster (fschoster@awi-bremerhaven.de),

Monika Wahsner &

Ruediger Stein (rstein@awi-bremerhaven.de)

Alfred Wegener Institute for Polar and Marine Research, Columbusstr., 27570 Bremerhaven, Germany

The chemical composition of marine sediments and its change in space and time can be used for reconstruction of terrigenous sediment supply from different source areas, paleoceanic circulation patterns, and paleoenvironment. In our study, more than 200 surface sediment samples and several sediment cores obtained from the Kara and Laptev seas as well as the adjacent Arctic Ocean continental margin were analyzed by XRF for major and minor elements.

The Arctic Ocean and especially the Laptev and Kara seas are strongly influenced by the input of terrigenous material of the major Siberian rivers. The source areas of these rivers are different. Khatanga and Yenisei rivers draining into the western Laptev and the Kara Sea, respectively, transport the weathered material of the Putoran Mountains built-up by large trapp basalt and tuff sequences. The source area of the Lena River draining into the eastern Laptev Sea, is dominated by granitic and gneissic rocks. The chemical signature of weathered basaltic material from the Putoran Mountains is clearly indicated in the Kara Sea and western Laptev Sea surface sediments by higher Fe/Al-, Mg/Al-, Ni/Al-, Cr/Al- and Ti/Al-ratios. Furthermore, the distribution of these elements indicates that the Vilkitzky Strait connecting the Kara and Laptev seas, is an important pathway for modern sediment transport. The eastern Laptev Sea surface sediments, on the other hand, display high Rb/Al-ratios caused by the Lena River discharge. The changes in the chemical composition determined in sediment cores from the eastern Arctic Ocean continental margin are related to glacial/interglacial-variations and interpreted as climate-induced changes in sediment sources and circulation patterns. At the last glacial/interglacial transition, for example, Ni/Al-ratios increase and Rb/Al-ratios decrease in the western Laptev Sea cores, indicating a higher supply of material from the Kara Sea into the Laptev Sea in the Holocene. Thus, we suggest that the Vilkitzky Strait was not opened during the last glacial maximum, but developped during postglacial/Holocene times due to sea-level rise.

B07 : 2B/34 : G5

Reconstruction of Late Quaternary Paleoenvironment in the Laptev Sea (Arctic Ocean): An Organic-Geochemical and Micropaleontological Approach

Bettina Boucsein (bboucsein@awi-bremerhaven.de),

Kirsten Fahl (kfahl@awi-bremerhaven.de),

Martina Kunz-Pirrung (mpirrung@awi-bremerhaven.de),

Jens Matthiessen (jmatthiessen@awi-bremerhaven.de) &

Ruediger Stein (rstein@awi-bremerhaven.de)

Alfred Wegener Institute, Columbusstrasse, 27568 Bremerhaven, Germany

Organic carbon data in marine sediments can be used for the reconstruction of the depositional environment, terrigenous supply from the hinterland, and surface-water productivity. For this purpose, however, more detailed information about the composition of the organic matter (i.e., its marine and terrigenous proportions) are needed. In coastal, high latitudes like the Laptev Sea, the interpretation of single organic-carbon-source indicators (e.g., biomarker data) is much more complicated and less definitive in comparison to similar data sets from low-latitude open-ocean environments (Fahl et al., 1998). This is mainly caused by the complexity of the Arctic Ocean system, which is characterized by a high seasonality of sea-ice cover and primary productivity, sea-ice sediment transport and a high fluvial supply of freshwater (aquatic) organic matter. A combination of organic geochemical, organic petrographic and micropaleontological data used in this study, may yield to a more precise identification of organic-carbon sources for these complex systems. Based on organic geochemical bulk parameters (total organic carbon content, C/N ratios, hydrogen indices), specific biomarkers (n-alkanes, fatty acids, sterols), maceral composition, and palynomorph assemblages, distinct spatial and temporal variations in organic carbon supply originated from marine, freshwater (aquatic), and terrigenous higher-plant sources, were determined in sediments from the Laptev Sea continental margin. Data from sediment Core PS2458-4 (continental slope, water depth 980 m) allow the reconstruction of the paleoenvironmental conditions during the last about 15,000 years BP. The variations in flux and origin of organic matter are related to changes in sea level, river discharge, surface-water productivity, and Atlantic Water inflow along the Eurasian continental margin.

Fahl K and Stein R, Marine Chemistry, 63, 293-309, (1998).

Session B07:3A

B07 : 3A/01 : G5

Trace Element Signatures of Eastern Mediterranean Sapropels: Implications for the Sapropel Formation Scenario

Birgit Warning

(Warning@geo.icbm.uni-oldenburg.de),

Rolf Wehausen

(Wehausen@geo.icbm.uni-oldenburg.de) &

Hans-Jürgen Brumsack (H.Brumsack@geo.icbm.uni-oldenburg.de)

Institute of Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University Oldenburg, P.O. Box 2503, F.R. Germany

Sapropels and homogenous sediments of Pliocene to Holocene age recovered during ODP Leg 160 from different drill sites across the eastern Mediterranean were analysed by XRF for major and minor elements and selected samples by ICP-MS for rare trace metals.

Eastern Mediterranean sapropels are characterized by high contents of redox-sensitive and sulphide-forming trace elements. Enrichment factors relative to "average shale" for highly accumulated elements (Ba, Co, Cr, Ni, V) as well as for rarer trace metals (Cd, Mo, Sb, Tl) are comparable to those found in Cretaceous black shales. The Re content is extremely high in sapropels with maximum values up to 1000 ng/g. Re/Mo-ratios close to the sea water value and high trace metal enrichments clearly indicate anoxic conditions during sapropel formation. Additionally elevated Ba concentrations reflect an enhanced bioproductivity which promotes sapropel deposition.

Pliocene sapropels are characterized by elevated contents of trace metals compared to Pleistocene ones. Higher trace metal concentrations, correlating with higher TOC contents in the older sapropels, possibly document that different paleoceanographic conditions persisted during the Pliocene compared to the Pleistocene. The reason for this difference must be related to the gradual climatic change observed during this time period.

A more humid climate and a higher fluvial runoff during times of sapropel formation alternating with a more arid climate and a higher eolian contribution during deposition of the light intervals is revealed by cyclic variations in Si/Al, Ti/Al, Mg/Al, K/Al and Zr/Al ratios of the sediments. At Eratosthenes Seamount the enhanced Nile discharge during sapropel formation is reflected by minima in the Si/Al, Ti/Al, Mg/Al, K/Al and Zr/Al ratio record corresponding to the maxima in the 65°N summer insolation curve.

On a transect across the eastern Mediterranean trace metal enrichment is most pronounced in the Ionian Basin and on the Mediterranean Ridge, whereas trace element contents are significantly lower on top of Eratosthenes Seamount and south of Cyprus. At the northern slope of Eratosthenes Seamount intermediate concentrations are found. Increasing trace element enrichment probably is not only a result of increasing water depth but also depends on the location of the site in the eastern Mediterranean. Metal contents seem to be lower at the eastern compared to the western sites.

Assuming a reversal of the Mediterranean circulation from anti-estuarine to estuarine during periods of sapropel formation the westernmost sites were possibly influenced to a larger extent by the inflowing trace metal and nutrient enriched western Mediterranean intermediate waters and consequently are showing higher trace element enrichments. Budget calculations demonstrate that not enough trace metals are supplied to the eastern Mediterranean to account for the sapropel metal signal if water exchange was totally restricted.

B07 : 3A/02 : G5

Sr Isotope Evolution of the Eastern Mediterranean Prior to the Messinian Salinity Crisis and its Implications for Palaeoceanography

Rachel Flecker (rf211@esc.cam.ac.uk)¹ &

Rob Ellam (rob.ellam@surrc.gla.ac.uk)²

¹ Department of Earth Sciences, Downing Street, Cambridge, UK

² Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow, UK

The evolution of oceanic ⁸⁷Sr/⁸⁶Sr through the Tertiary has been sufficiently well documented to provide a useful stratigraphic tool for carbonate-rich marine sediments which were deposited in basins connected to the global oceans. In isolated basins however, seawater ⁸⁷Sr/⁸⁶Sr will diverge from coeval oceanic values towards a value influenced strongly by the weighted average ⁸⁷Sr/⁸⁶Sr of rocks in the drainage hinterland. If the time of initial divergence can be dated then the geochemical signature can constrain the period of isolation. While not all models for salt deposition in the Mediterranean during the Messinian involve isolation, those that do have assumed that isolation either coincided with the last occurrence of open marine fauna or immediately preceded salt precipitation. This is in accord with the current negative hydrological balance of the Mediterranean which suggests that if the connection to the Atlantic were severed today, the Mediterranean would desiccate within 1500 years. However, ⁸⁷Sr/⁸⁶Sr data from southern Turkey challenge this assumption and can be interpreted as indicating a protracted period of isolation prior to the Messinian salinity crisis (c. 3 myr), during which time marine conditions prevailed. This interpretation has profound implications for our understanding of the hydrology and climatic evolution of the Mediterranean and other marginal basins. New data from Cyprus will be presented as a first step to ascertaining the local or regional nature of this phenomenon in the Eastern Mediterranean.

B07 : 3A/03 : G5

Paleoceanographic Changes in the Neogene Mediterranean: Geochemical and Micropaleontological Evidence

Mario Sprovieri (rspr@unipa.it)¹,

Adriana Bellanca (bellanca@unipa.it)²,

Angelo Bonanno (bonanno@unipa.it)³,

Salvatore Mazzola (mazzola@itpp.pa.cnr.it)¹,

Rodolfo Neri (neri@unipa.it)²,

Bernardo Patti (bpatti@itpp.pa.cnr.it)¹,

Daniela Salvagio Manta (salvagio@cfta.math.unipa.it)²,

Juan Jose Pueyo (juanj@natura.geo.ub.es)⁴ &

Conxita Taberner Pujol (ctaberner@ija.csic.es)⁵

¹ Istituto di Ricerche sulle Risorse Marine e Ambiente, CNR, Mazara del Vallo (TP), Italy, Via Vaccara, 61, 91026 Mazara del Vallo (TP), Italy

² Dipartimento di Chimica e Fisica della Terra e Applicazioni delle Georisorse e ai Rischi Ambientali, Palermo, Italy, Via Archirafi, 36, 90123 Palermo, Italy

³ Dipartimento di Energetica e Applicazioni della Fisica, Palermo, Italy, Viale delle Scienze, 90100 Palermo, Italy

⁴ Departament de Geoquimica, Petrologia y Propspecio Geologica, Barcelona, Spain, Zona Universitaria de Pedralbes, 08071 Barcelona, Spain

⁵ Institut of Earth Sciences Jaume Almera, CSIC, Barcelona, Spain, Luis Sole i sabaris s/n, 08028 Barcelona, Spain

An integrated geochemical and micropaleontological study of two central Mediterranean land sections (Gibliscemi and Punta Piccola, Sicily), of two central Mediterranean ODP Leg 160 Sites (963 and 964) and of the Tyrrhenian ODP Leg 107 Site 653 has been carried out to obtain paleoceanographic information for the last 15 MA. Samples were collected at a mean 70 k.y time interval, enabling us to analyse long term paleoceanographic trends in the Mediterranean from the Langhian to the Holocene. Based on SEM observations, all the analysed samples showed good preservation. The geochemical results were compared with relative abundance fluctuations of planktonic and benthonic foraminifera. Ba/Ca and Sr/Ca ratios were measured in specimens of planktonic foraminifera. Oxygen and carbon isotope compositions were determined in selected species of planktonic and benthonic foraminifera. Ba/Ca ratios measured on planktonic foraminifera tests define a generally monotonous trend from the base of the Pliocene up to the Holocene, with values of about 1 µmol/mol. Relatively higher Ba/Ca ratios (up to 7 µmol/mol), associated to low values of O, during the Tortonian-Messinian indicate strong continental influxes in the central-eastern Mediterranean. Variations in the benthonic assemblage and in oxygen isotopic values of Cibicidoides pachyderma indicate periodic alternation of Atlantic and Mediterranean bottom waters in the Eastern basin, suggesting an unstable 3D circulation system in this part of the basin at the end of the Miocene.The Sr/Ca record shows a decreasing trend from the base of the Tortonian up to the base of the Pliocene, followed by a regular increase of the ratio during the latest Neogene. This pattern is comparable with that reported for the Atlantic ocean suggesting a good continuous communication between the two basins during the late Neogene. A decreasing trend in the C-isotope composition of Cibicidoides pachyderma, associated with an abundance reduction of the benthonic assemblages, is consistent with a sluggish 3D circulation system during the latest Tortonian and the early Messinian in the eastern Mediterranean. Superimposed to long trends, a high frequency sedimentary cyclicity has been recorded in the studied sedimentary sequences. In particular, the alternation of homogeneous and anoxic sapropelitic sediments is interpreted as driven by precession astronomic periodicity. Relative high percentage of oligotrophic planktonic species associated to low values of O and high values of Ba/Ca in the sapropelitic layers indicate periodic continental influxes that cyclically inhibited the deep water formation in the eastern Mediterranean basin.

B07 : 3A/04 : G5

Paleoceanographic Reconstruction at the Western Slope of the Yermak Plateau: Implications from Organic Carbon Flux and Biomarker Records

Kirsten Fahl (kfahl@awi-bremerhaven.de)¹,

Daniel Birgel (dbirgel@awi-bremerhaven.de)¹,

Pieter M. Grootes

(pgrootes@leibniz.uni-Kiel.de)² &

Ruediger Stein (rstein@awi-bremerhaven.de)¹

¹ Columbusstrasse 2, Bremerhaven, 27568, Germany

² Max-Eyth-Strasse 11-13, Kiel, 24118, Germany

Major goals of our detailed sedimentological and organic-geochemical study of a sediment core from the western slope of the Yermak Plateau (PS2837-5; 81°13.99 N, 02°22.85 E; water depth 1042 m) are twofold:(1) Data on flux and composition of organic carbon are used for the reconstruction of the paleoceanographic and paleoclimatic conditions and their change during upper oxygen isotope stages (OIS) V to I (i.e., the last about 100,000 years BP). The organic geochemical results will be compared with micropaleontological data. (2) Due to low abundances of mircofossils needed for AMS ¹⁴C datings, restricted diversity of microfossil species, and local melt-water overprint of the ¹⁸O signal, the dating of sedimentary records from high-latitide areas like the Arctic Ocean is often very difficult and causes major problems. Thus, we established a chronological framework based on AMS¹⁴C dating of specific biomarkers.

Total organic carbon (TOC) and carbonate contents, hydrogen index values (HI), and biomarkers (n-alkanes, fatty acids, sterols, and alkenones) as well as the amount of ice-rafted debris (IRD) display distinct variations throughout the entire core, which can be related to glacial/interglacial variations. Minimum TOC values occur duirng OIS 4 and OIS 2. Hydrogen index values and biomarker composition indicate the dominance of terrigenous organic matter with minor but significant amounts of marine-derived organic material being preserved in the sediments. At the OIS 1/2 boundary, flux of organic carbon distinctly increases. The variations in accumulation of terrigenous and marine organic matter at the Yermak Plateau are interpreted in terms of changes in sea-ice cover influencing surface-water productivity as well as supply of IRD, and changes in Atlantic water inflow.

B07 : 3A/05 : G5

Reconstructing Palaeoclimate Conditions Using the Mercury Record of an Ombrotrophic Peat Bog, Xistral Mountains, NW Spain

Antonio Martínez Cortizas,

Xabier Pontevedra-Pombal,

Eduardo García-Rodeja &

William Shotyk (shotyk@geo.unibe.ch)

¹ Geologisches Institut, Universitat Bern, Baltzerstrasse 1, Switzerland

Mercury was analyzed in a peat profile of an ombrotrophic bog located in the Xistral Mountains, NW Spain. The base of the core has a radiocarbon age of 4,000 ¹⁴C yr BP (Martinez-Cortizas et al., 1997). Mercury was measured in wet (HgT) and dry samples (samples dried at 30°C and 105°C for two weeks, Hg30° and Hg105°) using a LECO-ALTEC AMA-254 mercury analyzer. It was found that Hg accumulation and thermal lability reflected a profound control by palaeoclimate conditions occurred at the time of deposition: cold climates promoted and enhanced accumulation and the preservation of low establity Hg while warm climates were characterized by a lower accumulation and the predominance of high to moderate stability Hg. After reviewing the available palaeoclimatic information (Font Tullot, 1996; Martin-Vide & Barriendos, 1995; Ramil et al., 1996; Perez Antelo, 1996), each peat sample was assigned to a climate period and the following classes were defined: cold, cold to-mild, mild-dry, warm-dry and warm-humid. Using these classes as the grouping variable and the Hg stability forms as predicting variables a discriminant analysis was performed, resulting that two canonical functions explained 96.5% of the total variance and the overall percentage of correctly classify cases was 94%. The first function (F1) primarily represent temperature variations and the second function (F2) mainly humidity variations. The reconstructed palaeoclimate conditions for the last 4,000 years reveal many of the dramatic climate events of the late Holocene, including the Little Ice age, the Roman Warm Period, the Medieval Warm Period and the Neoglacial Period.

Martinez-Cortizas A, Pontevedra-Pombal, X, Novoa-Munoz JC & Garcia-Rodeja E, Water Air & Soil Pollut, 100, 387-403, (1997).

Font Tullot I, Historia del Clima de Espana, Cambios Climaticos y Sus Causas. Instituto Nacional de Meteorologia, (1988).

Martin-Vide J, Barriendos M, Climatic Change, 30, 201-221, (1995).

Ramil P, Fervedes, 3, 33-53, (1996).

Perez-Antelo, Fervedes, 3, 151-161, (1996).

B07 : 3A/06 : G5

Hauterivian Carbon Isotope Record of the Vocontian Basin and its Paleo-Environmental Implications for the Northern Tethys

Bas van de Schootbrugge

(bas.vandeschootbrugge@geol.unine.ch)¹,

Luc G. Bulot (reef@newsup.univ-mrs.fr)²,

Stephen J. Burns (stephen.burns@geo.unibe.ch)³ &

Karl B. Föllmi (karl.follmi@geol.unine.ch)¹

¹ Institut de Géologie, Rue Emile-Argand, 11, CH-2007, Neuchâtel, Switzerland

² ESA CNRS 6019, Centre de Sédimentologie/ Paléontologie, Université de Provence, Marseille, France

³ Universität Bern, Geologisches Institut, Baltzerstrasse, 1, CH-3012, Bern, Switzerland

Three sections consisting of hemipelagic limestone-marl alternations, forming together a composite section spanning the whole Hauterivian stage, were investigated for their carbon and oxygen stable isotopic signature. The Vocontian Basin was chosen, because of the possibility to calibrate the isotope record against a high resolution ammonite biostratigraphy (Bulot et al, 1995). Therefore, the here presented isotope record could serve in the future as a reference to sections with less detailed biostratigraphy, like often encountered in carbonate platform settings.

Analyses were performed on bulk rock samples. Unlike the oxygen isotope signal, the carbon isotope signal is less affected by diagenesis. For the Lower Hauterivian a gradual decrease of 1‰ for the ¹³C_cc values with a minimum (+0.59) around the Lower/Upper Hauterivian boundary is observed. The Upper Hauterivian shows a gradual increase of 1‰ up to the boundary with the Barremian (+1.65).

Variations in the carbonate carbon isotope record are thought to reflect the efficiency of removal of organic carbon into the sediment with respect to carbonate carbon burial. High ¹³C_cc values indicate high burial rates for organic carbon and/or low burial rates for carbonate carbon in association, for example, with carbonate platform drowning and oceanic anoxia. The early late Valanginian may have been a period with a high organic carbon to carbonate carbon burial ratio as is evidenced by a positive ¹³C_cc excursion (e.g., Weissert et al., 1998). This period has been identified as a phase of widespread carbonate platform drowning.

In the late early and late Hauterivian, two further phases of platform drowning have been identified in the northern Helvetic Alps of central Europe, which are less well imaged by the preliminary ¹³C_cc curve. This may suggest that links between the mode of carbon burial, sea-level and environmental change, and platform drowning may have been different from what is known from the Valanginian and Aptian (e.g., Föllmi et al., 1994). Our goal is, therefore, to explore possible changes in feedback links between the carbon cycle and environmental change through the early Cretaceous.

Bulot, LG, Thieuloy, J-P, Arnaud, H & Delanoy, G, ''Lower Cretaceous Cephalopod biostratigraphy of the Western Tethys'', Bulot, LG, Argot, M & Arnaud, H Eds, Geologie Alpine, Grenoble, Mem., 20, 383-400, (1995).

Föllmi, KB, Weissert, H, Bisping, M & Funk, H, Geol. of Soc. Am. Bull, 106, 729-746, (1994).

Weissert, H, Lini, A, Föllmi, KB & Khun, O, Pal., Pal., Pal., 137, 189-203, (1998).

B07 : 3A/09 : G5

Calpionellids and Calcareous Dinoflagellates Versus Sea Level Fluctuations Recorded in the West Carpathian [Late Jurassic/Early Cretaceous] Pelagic Environments

Daniela Rehakova (geolreha@savba.savba.sk) &

Jozef Michalik (geolmich@savba.savba.sk)

¹ Geological Institute SAS, Dubravska cesta 9, 842 26 Bratislava, Slovakia

Bio-events are mostly connected with a facies changes. The phyletic evolution of planktonic microorganisms studied includes a number of events very favourable for detailed interregional and intercontinental correlation of the carbonate deposits of pelagic origin, mainly in regions such as Western Carpathians are, where cephalopod remains (ammonites, belemnite rostra, aptychi) are very rare. The authors tried to obtain authentic, detailed and integrated data on the vertical distribution of planktonic associations above mentioned by co-sampling of same levels at same sections; to select characteristic bioevents, mainly first and last occurence data, within the parallel successions of these microfossil groups; to evaluate the biostratigraphic potencial of the selected bioevents for refining and enhancing the resolution of Lower Cretaceous zonal schemes, as well as to investigate the changes in evolution and distribution of calcareous microplankton components in interaction with the changes of the paleo-ceanographic and paleoclimatic regime. The quantitative study and bio-events recorded in calpionellid and calcareous dinoflagellate associations became currently used tool of stratigraphy and paleobiogeography. Despite of their global occurrence in ancient tropical seas, variations in their distribution were influenced by local environmental factors. Mass abundance of these microfossils was closely connected with elevated zones and shallow intrashelf basins opened to nutrients bringing currents. Evolution of these groups of calcareous microplankton reflected global climatic changes influencing directly the salinity and the water temperature. Several stagnation and radiation phases have been identified during the quantification of their remnants. It seems that these phases coincide with movements of the sea level. Thus, both, calpionellids and calcareous dinoflagellates can serve as useful indicators of the sea level fluctuation.

B07 : 3A/10 : G5

Belemnite Rostra: Fossils or Pseudomorphs?

Paola Iacumin (labgeois@univ.trieste.it),

Michele Ramigni &

Antonio Longinelli

University of Trieste, Department of Geological Sciences, Via E. Weiss, 6, 34127 Trieste, Italy

Isotopic measurements of the calcium carbonate of Belemnite rostra have been widely carried out between about 1955 and 1970, with the main purpose of obtaining palaeoclimatological and palaeoenvironmental information on Mesozoic oceans. For several reasons these fossil were considered a well preserved material yielding reliable isotopic data equal or very close to their pristine values. Longinelli and Longinelli and Nuti, after measuring the oxygen isotopic composition of Belemnite carbonate (1969) and Belemnite phosphate (1968) questioned the reliability of these fossils for palaeoenvironmental reconstructions. However, no further relevant data were published to help to clear up this matter. Recently, we started a geochemical study of Belemnite rostra to obtain further information on these fossils which, by the way, have been considered recrystallized fossils by authors from the former USSR, their suggested pristine mineralogical composition being aragonite. Several specimens from continental Europe, of both Jurassic and Cretaceous age, showed secondary, pervasive quartz structures filling microcracks, covering the external surface of the rostra and the walls of the apical canal. The oxygen isotopic values obtained from carbonate, dispersed phosphate and pervasive quartz structures, were generally far from equilibrium conditions showing that each mineralogical component could be related to aqueous solutions with different isotopic values and/or to different temperatures of precipitation. According to the isotopic values obtained, to the existence of well developed pervasive secondary quartz structure, to the volumetric distribution of phosphorous and silicon atoms determined by electron microprobe and to other various considerations, the possibility of considering the studied samples as pseudomorphs instead of real fossils is suggested. If so, most of the palaeoceanographic and palaeoclimatological conclusions drawn in a number of previous studies carried out on Belemnites should be crytically reconsidered.

3713

B07 : 3A/11 : G5

Reconstructing Aquatic Environments and Climate in the Maastrichtian-Danian of Bolivia by Combining Sedimentology, Palynology, and ¹⁸O of Vertebrates

Gilles Dromart (Gilles.Dromart@ens-lyon.fr)¹,

Christophe Lecuyer

(Christophe.Lecuyer@ens-lyon.fr)²,

Mireille Gayet (gayet@cismsun.univ-lyon1.fr)¹,

Patricia Grandjean³,

Henriette Meon

(henriette.meon@cismsun.univ-lyon1.fr)¹ &

Olga Otero (Olga.Otero@ens-lyon.fr)²

¹ Centre Sciences Terre, UMR 5565, Université de Lyon, F-69622 Villeurbanne

² Laboratoire Sciences Terre, UMR 8517, Ecole normale supérieure de Lyon, F-69364 Lyon Cedex 07

³ 304B rue Garibaldi, F-69007 Lyon

The El Molino Formation of central Bolivia is interpreted as having deposited in marginal marine environments through distinct lines of evidence: 1) depositional facies showing association of tidal, storm-influenced and fluvial fabrics; 2) palynofacies including marine fraction composed of either dinoflagellate cysts or foraminiferal linings and land-sourced sporomorph ; 3) assemblage of vertebrate fossils showing a mélange of pure marine fishes including selacians and pycnodonts, marine to brackish water fishes (semionotid Lepidotyle), and freshwater fishes (polypterids), amphibians and reptiles (chelonians and crocodilians).

Terrestrial arid climatic conditions can be inferred from the abundance of thick-wall sporomorphs throughout the section.

Oxygen isotope compositions of phosphate from vertebrate remains (teeth, scales and bones) are in close agreement with the environmental distribution of vertebrate fauna. ¹⁸O values range from 15.1-15.3‰ (freshwater faunal end-member) to 17.6-22.3‰ (brackish waters and ubiquitous fauna) to 23.0-24.2‰ (seawater faunal end-member). Calculated temperatures of the marine waters assuming a ¹⁸O value of -1‰ (ice-free world) vary from 4 to 8°C. These very low temperatures are definitely not consistent with the 21-23°S paleolatitude currently estimated for the area (Camoin et al., 1993), even if Maastrichtian-Danian times are marked by global cooling (Lecuyer et al., 1993). Slight oversaturation of seawater (up to 37-38 g/l) may have caused a +2‰ increment of the ¹⁸O composition conducing to a 13-17°C span of calculated temperatures. The interpretation in terms of higher salinities, and somewhat restricted conditions, is substantiated by the presence of anhydrite nodules in the immediately underlying unit (i.e. Chaunaca Fm), the occurrence of pollens of the Ephedra genus, the abundance of slightly erosive, short hummocky cross-beds, the extensive development of stromatolites, and the lack of the mollusk macrofauna. And yet, such an average value for seawaters temperature of about 15°C for a latitude of about 22°S implies that central Bolivia was probably either connected to the austral Atlantic seaway or influenced by a southeastern Pacific upwelling.

B07 : 3A/12 : G5

Stable Isotopes (C, N and O) in Upper Pleistocene and Holocene Herbivore and Human Skeletal Remains from Russia. Palaeoenvironmental Considerations

Paola Iacumin (labgeois@univ.trieste.it),

Laura Genoni,

Michele Ramigni &

Antonio Longinelli

University of Trieste, Department of Geological Sciences, Via E. Weiss, 6, 34127 Trieste, Italy

60 samples of woolly mammoth and reindeer skeletal remains of Upper Pleistocene and Early Holocene age (from 40,000 to 10,000 BP) and 32 samples of human and sheep bones of Holocene age (from 5,000 to 600 BP) from different locations in Russia were studied for the oxygen, carbon and nitrogen isotopic composition of their phosphate and collagen. According to the results obtained the following considerations can be made: 1) as regards the palaeoclimatological interpretation of the oxygen isotope measurements on phosphate and the evaluation of environmental palaeowaters the elephant and deer equations can be reasonably used in the case of fossil mammoth and reindeer skeletons respectively. It seems that the mean isotopic composition of atmospheric precipitation over Siberia during Upper Pleistocene was not much lighter than modern mean annual precipitation in the same area; 2) according to the nitrogen isotope measurements, there is a clear evidence of a trend towards decreasing aridity for the period between 25,000 and 13,000 BP in the central Russian plain and in Southern Siberia. The environmental conditions in the Yakutia region seem to be quite similar araund 10,000 and 40,000 BP; 3) the relatively enriched nitrogen isotope values measured in humans are, at least partially, due to the arid conditions of the studied area. The values are similar to or higher than the values measured in Egyptian population of about the same age; 4) all the isotope signals in sheep bones (O, C and N) suggest arid conditions in the Russian plain at least between 3,700 and 2,000 BP; 5) collagen carbon and nitrogen values in mammoth and reindeer living probably in the same habitat indicate a differece in the diet preferences or, alternatively, in their physiological processes.

Session B07:3P

B07 : 3P/01 : PO

Environmental Changes in the Benguela Upwelling for the Last 1.5 My (ODP Leg 175, Site 1082A)

Britta Jahn (bjahn@uni-bremen.de),

Barbara Donner,

Peter J. Mueller,

Ursula Roehl,

Ralph R. Schneider &

Gerold Wefer

Dept. of Geosciences, University Bremen, P.O.Box 330440, D-28334 Bremen, Germany

During Leg 175, a North-South transect of sediment cores was drilled west of the coast of SW-Africa. Site 1082 (21°5S, 11°49E, 1290 m) is located in the northern Walvis Basin. For this site, stable oxygen isotopes have been measured on planktonic foraminifera to obtain a chronology for the last 1.5 My. This age model is supported by the shipboard bio- and paleomagnetostratigraphy. To reconstruct environmental changes in the Benguela Current System and upwelling history for the last 1.5 My, we compared measurements of CaCO₃ and TOC with high resolution XRF core scanner records for elemental Ca and Fe. These records indicate that the Mid-Brunhes period (280-530 kyr BP) was characterized by increased carbonate accumulation and decreased TOC and Fe flux to the sediments, which may be a result of weakened upwelling and trade winds during this period. It is also indicated that productivity and winds from Namibia were stronger before 750 kyr BP. The TOC and Fe records further suggest that during oxygen isotope stage 7, the Namibian upwelling system changed its mode of climatic response. While prior to 200 kyr higher productivity and stronger trades prevailed during interglacials the opposite is indicated for the last 200 kyr, when glacial stages 6 and 2-4 are characterized by a high TOC MAR and Fe content.

B07 : 3P/02 : PO

High Resolution Planktonic Foraminiferal Records from the Southern Cape Basin - Evidence for Regional and Global Climate Change

Ruth Acheson (racheson@glg.ed.ac.uk)¹,

Ralph R. Schneider² &

Dick Kroon¹

¹ Department of Geology and Geophysics, University of Edinburgh, West Mains Road, Edinburgh, EH9 1BT, Scotland

² Fachbereich Geowissenschaften, Universität Bremen, 28334 Bremen, Germany

Planktonic foraminiferal abundance and benthic isotope data from the Southern Cape Basin (core GeoB 3603-2, 35° 0.7'S \ 17° 32.6' E, 2840 m water depth) enable reconstruction of palaeoceanographic change over the past 355, 000 years. Circulation in the Southern Benguela System is determined by a combination of meteorological, oceanographic and topographic factors. In contrast to the Northern Benguela System upwelling is seasonal and concentrated in the spring-summer period. Additionally, changes in the nature and extent of warm, saline, surface water transport from the Indian Ocean via the Agulhas Current are an important component of the circulation in this area. Interpretation of our foraminiferal data suggests that changes in the surface water masses reflect reflect both global climate change and variation in regional and basin scale circulation patterns in the South Atlantic ans southwest Indian Ocean.

The benthic foraminiferal (Cibicidoides wuellerstorfi) ¹⁸O record is correlated to the SPECMAP standard curve to chronologically constrain the proxy records. Glacial- interglacial transitions at Terminations I and II are marked by a decrease in cold water N. pachyderma (d), followed by an associated increase of Gr. inflata and tropical species. As observed in other marine records from the southern hemisphere, warming events preceed those of the northern hemisphere climate as recorded in the benthic ¹⁸O record by 2-3 kyr. Superimposed on variability explained by orbital frequencies there is also evidence for change on sub-Milankovitch scales. Glacial and interglacial periods are punctuated by abrupt climatic changes, indicating that interocean teleconnections and regional circulation interplay to produce significant changes in surface circulation in this region during the late Quaternary.

High-Resolution Paleomonsoon Record of the Past 30 ka in the Western Arabian Sea

Ekaterina Ivanova (ivae@geo.vu.nl)¹,

Gerald Ganssen (gang@geo.vu.nl)¹,

Simon Jung (jung@geo.vu.nl)¹,

Gert-Jan Reichart (reichart@geo.uu.nl)²,

Simon Troelstra (tros@geo.vu.nl)¹ &

Jan Van Hinte (hinj@geo.vu.nl)¹

¹ Institute of Earth Sciences,, Vrije Universiteit, De Boelelaan 1085, 1081HV, Amsterdam, The Netherlands

² Institute of Earth Sciences, Utrecht University, Budapestlaan 4, 3508TA, Utrecht, The Netherlands

Based on sections of two sediment cores from the Western Arabian Sea we reconstructed the upwelling history of the last 30 ka. Core 905P is located at the depth of 1586 m offshore Somalia. Core 929P is located at the depth of 2490 m between Socotra Island and the coast of Yemen. Both cores were densely sampled resulting in time resolution of 200 to 500 years. Offshore Somalia sedimentation rates reached up to 36 cm/ka during the Holocene and about 13 cm/ka during the LGM. In contrast to north off Socotra where sedimentation rates were lower during the Holocene (around 10 cm/ka) compared to those during the LGM (around 13 cm/ka). We use the relative abundance of the planktic foraminifera G. bulloides, the G. bulloides/ G. ruber ratio, the total flux of planktic foraminifera, the Ba/Al ratio, C_org-based primary productivity calculated according to Sarnthein et al. (1992) and the difference between carbon isotope values of G. bulloides and N. dutertrei (¹³C G. bulloides - N. dutertrei ) to reconstruct the paleoproductivity. All of the proxies indicate generally higher productivity offshore Somalia compared to the north off Socotra. In core 905P the SW-monsoon/upwelling productivity was higher during the Holocene, in particular, the early part. In core 929P productivity proxies are decoupled. The relative abundance of G. bulloides and G. bulloides/G. ruber ratio suggest higher productivity during the Holocene while primary paleoproductivity according to Sarnthein (1992) and the total flux of planktic foraminifera reached equally high values during the beginning of the Holocene and the LGM. This can be an effect of both NE-monsoon/winter productivity changes as well as different carbonate and carbon preservation during the last 30 ka.Indicators of the wind strength and the mixing in the upper part of the water column (Ti/Al ratio and relative abundance of the planktic foraminifera N. pachyderma sin and T. quinqueloba) are high both during the early Holocene and during the LGM. This indicates that the SW monsoon winds intensified during the Holocene, whereas the influence of the NE monsoon winds was stronger during the LGM. The high values of the proxies might be also partially linked the low sea-level stand during the LGM. The most characteristic features in both cores are the high-frequency fluctuations in all studied parameters, reflecting short-term variations in monsoon intensity over the past 30 ka. These changes are taking place with a frequency of approximately 1000-2000 years.

B07 : 3P/04 : PO

Facies Analysis of Selected Bays of Curaçao (Netherlands Antilles), with Special References to Benthic Foraminifera

Bogumila B. Klosowska (klob@geo.vu.nl)¹,

Simon R. Troelstra (tros@geo.vu.nl)¹,

Jan E. van Hinte (hinj@geo.vu.nl)¹,

Cees Laban (c.laban@nitg.tno.nl)² &

Gerard Klaver (g.klaver@nitg.tno.nl)²

¹ Department of Earth Sciences, Vrije Universiteit, De Boelelaan 1085, 1081HV Amsterdam, The Netherlands

² NITG TNO, Postbus 157, 2000AD Haarlem, The Netherlands

The climate of Curaçao (12°N 69°W) is semi-arid; hydrographic conditions are controlled mainly by constant east trade winds. A weak northwest current flows along the southwest coast. Facies analysis is carried out on 75 grab samples from two small and shallow (<25 m) bays of Curaçao: Spaanse Water and Schottegat. The bays are situated on the south coast of the island and have narrow channeled connections to the open sea.The distribution maps of various skeletal components (fraction >125 µm) in Spaanse Water reveal four facies: 1) the Halimeda facies in the western and perimeter areas of the bay; 2) a bivalves facies in the channel, central and eastern parts; 3) an ostracodes-echinoid spines facies in the south-eastern part; and 4) a gastropods-serpulids facies characterizing the inner-western part of the bay. Other components associated with these facies but occurring only locally and in small quantities are: coral debris, bryozoans, sponge spicules, coralline algae, pteropods and fish bones. Non-skeletal components include mainly lithoclasts, volcanic grains and faecal pellets.Foraminifera are more evenly distributed and make up to 20% of all components. In total approximately 130 species were identified in Spaanse Water. Common forms include Elphidium spp., Ammonia tepida (Cushman), Archaias angulatus (Fichtel and Moll), Textularia agglutinans d'Orbigny, Cyclorbiculina compressa (Silvestri), miliolids and peneroplids. Miliolids are in particular dominant in the channel and central inner area of the bay; an Elphidium facies occurs in perimeter areas and Ammonia spp. occur mostly in the eastern part. The distribution of peneroplids, Amphistegina lessoni d'Orbigny, Asterigerina carinata d'Orbigny and A. angulatus correlates with the Halimeda pattern i.e. restricted to the western and perimeter areas of the bay. The distribution pattern of foraminiferal assemblages appears to be related to salinity fluctuations, dissolved oxygen concentrations at the bottom, nature of the substrate but may be modified by hydrographic (energy) factors and redistribution of dead tests. The examined samples from Schottegat yield similar facies as in Spaanse Water but microfaunas, represented by foraminifera and ostracoda, are extremely impoverished. This is probably due to anthropogenic pollution since Schottegat sediments are greatly enriched in crude oil and heavy metals. A number of samples from Schottegat consist entirely of volcanic rock fragments (eastern and northern part of the bay). The present study is part of a PhD project by the first author entitled: "Late Holocene microfacies history of selected bays of Curaçao (Netherlands Antilles)".

B07 : 3P/05 : PO

Paleoclimate Changes Through the Last 2,000 Years in the Tropical Atlantic Derived from a Foraminiferal and Geochemical Record

Johan Nyberg (Johann@gvc.gu.se)¹,

Björn A Malmgren,

Antoon Kuijpers² &

Amos Winter³

¹ Dep. of Earth Sciences-Marine Geology, Göteborg university, SE-405 30 Göteborg, Sweden

² Geological Survey of Denmark and Greenland, Dep. of Geophysics and Marine Geology, DK-2400 Copenhagen, Denmark

³ Dep. of Marine Sciences, University of Puerto Rico, Mayaguez, Puerto Rico

We present a high resolution climate reconstruction of the northeastern Caribbean through the last 1865 ¹⁴C reservoir-corrected years. The data obtained are from a piston core retrieved at 17^o53.27' N, 66^o36.02' W (349 m water depth), south of Puerto Rico. Sea-surface temperatures (SST's) in this region are controlled by the El Niño-Southern Oscillation (ENSO) system, and mean annual precipitation is synchronous with variations in the North Atlantic Oscillation (NAO) (the system of westerly winds across the North Atlantic onto Europe) at least since 1914. Hence, longer, reconstructed records of SST and salinity derived from this site might provide a reflection of the variability of these two major climate phenomena. Sea-surface temperature and salinity fluctuations are derived from a continuous planktonic foraminifer record, together with associated oxygen isotope values of Globigerinoides ruber (white variety). The past SST's are predicted using Artificial Neural Networks (ANN), i.e. an approach using Artificial Intelligence, based on fluctuations in the relative abundance of 26 species of planktonic foraminifera. To determine the reliability of the ANN predictions, a comparison between estimated and instrumentally measured SST's was made on the basis of material from a ²¹⁰Pb dated box core, spanning the last 70 years, which was retrieved at the same location. As proxy indices of productivity changes we use carbon isotope values of G. ruber (white variety), the organic carbon content of the sediment, and the relative abundance of the coccilitophorid Gephyrocapsa oceanica. Winter and summer SST's increase at about 1400 ¹⁴C years BP, and are generally relatively high until about 500 ¹⁴C years BP, when an abrupt decrease, predominantly in the recorded winter SST, is observed. Distinctly lower values of salinity leads this SST depression, and higher values of organic carbon, ¹³C, and relative abundance of G. oceanica appeared. This event correlates with a rapid increase in meridional atmospheric circulation seen in annually dated ice cores from West Antarctica and central Greenland, which reflects the beginning of the Little Ice Age around 1400 AD (Kreutz et al., 1997). Enhanced seasonal variability appears to be a typical feature of the Little Ice Age, i.e. the time span from about 500 ¹⁴C years BP to the end of the last century.

Kreutz KJ, Mayewski PA, Meeker LD, Twickler MS, Whitlow SI & Pittalwala II, Science, 277, 1294-1296, (1997).

B07 : 3P/06 : PO

Paleoenvironmental Analysis of Pliocene Foraminiferal Faunules from Sarasota, Florida

Kusali R. Gamage (gkusali@bgnet.bgsu.edu)

Samples of fossil foraminifera were studied for their taxonomic composition. They were collected from Macasphalt Pit Mine, one of the best preserved Pliocene Pinecrest shell beds in Sarasota, Florida. Foraminifera are excellent paleoenvironment indicators due to their high sensitivity to environmental profiles, yet no studies have been published on these protozoans from these beds. The foraminiferal assemblage in the area is dominated by Hanzawaia concentrica, Ammonia beccarii and Elphidium discoidale. Sanders similarity index will be used to determine their similarities among the samples. Based on the taxonomic ratio and the shell-type ratio of the samples, information on the habitats of living representatives of the fauna will be used to infer the paleoenvironments of the fossil faunules. I will also examine whether foraminifera experienced a mass extinction like the mollusks during late Pliocene.

B07 : 3P/07 : PO

The Influence of Varying Climate on the Sediment Conditions Near the Tropic Seamount in the Subtropical Northeast-Atlantic Ocean

Steffen Richter (richters@rz.uni-greifswald.de),

Johann Mrazek &

Jürgen Eidam

University Greifswald, Friedrich-Ludwig-Jahn-Street 17a, D-17489 Greifswald, Germany

Two gravity cores from the south piedmont slope of Tropic Seamount in the northeastern subtropical North Atlantic Ocean at the border of North-African continental piedmont slope and Canary Basin were used to carried out detailed sedimentological, geochemical and stratigraphical investigations. The results can reveal details about sediment formations and influence of varying climate conditions on the palaeo-oceanographic development in this area. During the Holocene and Pleistocene clayey and strong clayey calcareous ooze were deposited predominant with high content of foraminiferals and nannofossils as pelagites and turbidites. The origin of the calcareous turbidites is the mountain slope and edge of mountain plateau of the Tropic Seamount. The oxygen isotopic studies show that during the interglacials the high bioproductivity in surface water produced aggradation of sediments on the top of the Seamount. Turbidity currents from edge of mountain plateau caused due to overloading of sediments. On the other hand, during the glacials submarine erosion and lower water level involved turbidity currents from mountain slope. Further on laminated, strong calcareos muddy ooze with a high content of organic substance were supplied by contour currents. The contourites occures only on SW-pidmont slope due to coriolis force and higher water depth of 150 m. A high content of organic carbon causes reducing conditions with green-oliv colourations and element mobilisations, e.g. manganese, in these laminated sediments. The recent influence of the contour current down the SW-pidmont slope towards north is very high. Each type of sediment facies - pelagites, turbidites and contourites - possesses a typical element composition with significant chemical differences. In the investigated area the changes of sediment conditions occure in type of symmetrical cyclotheme (ABCBA) with a lot of rhythmics. Geochemical investigations with high resolution show the changes from pelagic sediment conditions (A) with low Sr/Ca-ratios to contourites (C) with high Sr/Ca-ratios. Between pelagites and contourites occure turbidites with extremely low or strong changing Sr/Ca-ratios.

B07 : 3P/08 : PO

A Combined Geochemical and Micropaleontological Approach to the Coccolithophore Genus Gephyrocapsa

Hanno Kinkel (kinkel@nioz.nl)¹,

Joerg Bollmann (bolle@erdw.ethz.ch)²,

Christine Klaas (cklaas@erdw.ethz.ch)²,

Ian Probert (Billard@ibba.unicaen.fr)³,

Markus Geissen (marg@nhm.ac.uk)⁴,

Claudia Sprengel

(csprengel@mail.sedpal.uni-bremen.de)⁵ &

Patrizia Ziveri (zivp@geo.vu.nl)⁶

¹ Netherlands Institute for Sea Research, The Netherlands

² Geological Institute, Swiss Federal Institut of Technology, Switzerland

³ Laboratoire de Biologie et Biotechnologie Marines, Universitaet de Caen, France

⁴ Paleontology Department, Natural History Museum, London, England

⁵ Department of Geosciences, Universitaet Bremen, Germany

⁶ Center for Marine Geosciences, Vrije Universiteit Amsterdam, Netherlands

Coccolithophores are one of the most suitable phytoplankton groups to study past ocean surface water conditions, since they are preserved as both calcitic microfossils (coccoliths) and organic biomarkers (long-chain alkenones) in the geological archive. Since the discovery of long-chain alkenones and their use for reconstructing paleo SST's a lot of studies addressed to alkenone biosynthesis in Emiliania huxleyi, the dominant coccolithophore species in todays oceans. However relatively little is known about the relationship between alkenone synthesis in species of the genus Gephyrocapsa, which is closely related to Emiliania huxleyi (e.g. Volkmann et al. 1995). Species of the genus Gephyrocapsa dominated fossil assemblages during the late Pleistocene in a similar way as Emiliania huxleyi does since the last glacial interval (Bollmann et al. 1998). Therefore we foussed our investigations on this species, to improve both the micropaleontological and organic geochemical approaches in studying fossil assemblages predating the dominance interval of Emiliania huxleyi. The dominance interval of Gephyrocapsa notably differs from that of Emiliania huxleyi, and it is therefore unlikely, that everything that is known about Emiliania huxleyi can be applied to Gephyrocapsa. Our approach includes the investigation of lipid biomarkers and morphometric meassurements in different strains of Gephyrocapsa oceanica cultured at various temperature conditions. We present the intraspecific variabillity of biomarker indices as well as the variation in morphometric features. In addition, we investigate a set of plankton and sediment trap samples from areas where species of Gephyroapsa are abundant in the living assemblages. We carried out quantitative meassurements of cell numbers, coccolith and long-chain alkenone production in order to asses a combined method for reconstructing the productivity of coccolithphores in the past.

Volkman JK, Barrett SM, Blackburn SI & Sikes EL, Geochimica et Cosmochimica Acta, 59, 513-520, (1995).

Bollmann J, Baumann KH & Thierstein HR, Paleoceanography, 13, 517-529

B07 : 3P/09 : PO

Spicules Analysis ­ The Possible Perspectives of its use for Paleoecological Studies of Bottom Sediments in Lake Baikal

Eckert Carsten (eckert@awi-potsdam.de)¹,

Elena Weinberg (root@lin.irkutsk.su)²,

Johannes Mueller (jmueller@awi-potsdam.de)¹ &

Dorte Mehl³

¹ Alfred-Wegener-Institut für Polar- und Meeresforschung FS Potsdam, Telegrafenberg A 43, 14473 Potsdam, Germany

² Limnological Institute Irkutsk, Sibirian Branch of the Russian Academy of Sciences PO Box 4199, Irkutsk 664033, Russia

³ Freie Universität Berlin, Institut für Paläontologie, Malteserstr. 74-100, Haus D, 12249 Berlin, Germany

Compared to most oft the today existing fresh water lakes is the uniquity of Lake Baikal also shown in its fossil fauna composition in the sediments. Spicules of the silicous sponges as well as diatom frustules are well preserved and found in great amounts. In the bottom sediments of Lake Baikal the biogenic silica content reaches weighting percent of 10 to 30%. The main part here are the diatoms, which are traditionally used for paleostratigraphic analysis.Sponges are because of their wide spatial distribution in geological time a further species for stratigraphy in Lake Baikal. For a sure identification of species of baikalian sponges it is necessary to know the architectonics of their skeletons and the form of their spicules. The difficulty: in Lake Baikal bottom sediments is that we have only isolated skeleton spicules. There fore to identify the spicules in the sediments we compared photos of skeleton architectonics in recent sponges, their spicules and spicules of the sediments. It has been found that some species of baikalian sponges can be easily identified by their typical morphological and morphometric pecularities of their spicules. The spicules of such species as (Baikalospongia intermedia, B. bacilifera, B. tenera, g. Lubomirskia) are more variable, therefore the identification of these species by spicules is done with less trustworthiness degree. Here, we present and discuss sponge spicules analysis data of gravity core STX3 GC in the light of possibility its use for paleoecological studies and also climate changes at Lake Baikal during the Holocene and Pleistocene. Sampling interval for the gravity core was every 10 cm, i.e. alltogether 48 samples were used for determination of the different sponge taxa over the core. The sponge analysis on gravity core STX3 GC gave 4 genus out of the family of Lubomirskidae, alltogether 9 species, as well as macro and micro scleres of the Spongilidae Spongilla sp. and Ephidatia sp. could be identified. Spicules quantity and their morphological diversity reach their maximum during warm climate periods. Cold periods coincide with the absence of Spongilla sp. and Swartschewskia papyracea spicules in the sediments, the number and diversity of other spicules significantly decreases. The occurence of specimen, which can not be classified with already known species, show, that still not all species of the Baikal sponge fauna have been found, yet. This can especially be said for the endemics out of the family of the Lubomirskidae. Fo further investigations on the deep drilling cores BDP-96 from Academician Ridge, which contains nearly 5 Ma, are those paleontological founds of special interest. Thus, even single spicules of new species can give us information about the evolution of the Lubomirskidae as well as about their probably spongiliidic roots.

B07 : 3P/10 : PO

Calcification Rate and High-Resolution Trace Element Distributions (ICP-MS and LA-ICP-MS) in the Caribbean Coralline Sponge Ceratoporella Nicholsoni

Claire Eugénie Lazareth (clazaret@vub.ac.be)¹,

Philippe Willenz (pwillenz@ulb.ac.be)²,

Frank Dehairs (fdehairs@vub.ac.be)¹ &

Luc Andre (lucandre@africamuseum.be)²

¹ Analytical Chemistry Department, Vrije Univeristeit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium

² Royal Belgian Institute of Natural Sciences, Department of Invertebrate Zoology, Vautier Street 29, B-1000 Brussels, Belgium

Coralline sponges (sclerosponges) are unique among invertebrates in the sense that they secrete simultaneously calcium carbonate and silica to form their skeleton. Their massive calcareous skeleton is an archaic feature that makes them survivors of the abundant Paleozoic and Mesozoic Eras reef-builders fossils such as stromatoporoids, chaetetids and sphinctozoans. In addition to the information provided on these reef-building fossils, their very low growth rate makes them potentially powerful paleoenvironmental recorders.

Growth rate was measured on Ceratoporella nicholsoni from North Jamaican reefs. Specimens growing in a dark tunnel at a depth of 28 m near Discovery Bay were stained in situ with calcein up to five times from 1984 to 1997. The growth rate of the skeleton, calculated from measurements of the linear extension between calcein stained lines along the growth axis, falls within a range of 170 to 290 µm per year with an average of 200 µm/y. Determination of the mean growth rate provides the essential time-scale for analysis and microanalysis of trace elements of the calcareous skeleton of coralline sponges.

Micro-drillings (~ 1 mm diameter) have been made along a profile of a C. nicholsoni specimen, allowing to go back in time until the end of the 17th century, with a sampling resolution of about 10 years. Trace element distributions, such as Sr, Mg, Ba, Pb and U, known to be related to environmental conditions, have been analysed by inductively coupled plasma mass spectrometry (ICP-MS). The Pb/Ca profile shows an important increase from 1921 (~45% between 1921 and 1935), most probably related to the industrial input of Pb into the atmosphere. The core of this specimen shows a more homogeneous composition. Preliminary laser ablation ICP-MS and ICP-MS comparative analyses of this part of the sponge reveal great potential for further use as a standard material for LA-ICP-MS measurements. Furthermore, a time resolution of less than 3 months can be achieved (40 µm craters) and thus a far more detailed record of trace element evolution is obtained.

B07 : 3P/11 : PO

Shell Chemistry of Modern Mytilus Edulis as a High Resolution Proxy of Environmental Conditions: Influence of Biological Parameters

Erika Vander Putten (evderput@vub.ac.be),

Frank Dehairs (fdehairs@vub.ac.be),

Eddy Keppens &

Willy Baeyens (wbaeyens@vub.ac.be)

V.U.B. / ANCH, Pleinlaan 2, 1050 Brussel, Belgium

The shell of Mytilus edulis (blue mussel), a fast growing bivalve with a wide geographical distribution and tolerance to a broad range of environmental conditions, is a potential high resolution recorder of (seasonally) varying environmental conditions. However, the influence of physiology on shell element and isotope chemistry can complicate the extraction of paleoenvironmental information. In the present study, the relative importance of a number of environmental and biological controls on the minor and trace element- and carbon isotopic composition of mussel shells is evaluated by combining a field experiment with a high resolution Infrared Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry analysis of shell (calcite) element chemistry and analysis of shell ¹³C.

Mussels of the same size were collected from a population in the Oosterschelde and were transplanted to the Westerschelde-estuary. For a period of one year, specimens were collected at regular time intervals and shell analyses were compared with simultaneously collected data on temperature, salinity and primary production. Mg/Ca, Mn/Ca, Sr/Ca, Pb/Ca and ¹³C show seasonal variations which are only in part related directly to environmental conditions. The shell ¹³C-profile shows no direct relation with variations in ¹³C of the dissolved inorganic carbon but can be explained by the seasonal cyclicity in the mussel's respiration rate: an increasing respiration rate during spring corresponds to a decreasing ¹³C and is followed by a decreasing respiration rate during summer, corresponding to an increasing ¹³C. The Mg/Ca- and Pb/Ca-profiles show a significant correlation with water temperature during spring; this is followed by a sudden decrease in element concentration which is not related to temperature. This decrease is localized around the ¹³C-minimum, suggesting the influence of metabolic processes on shell element chemistry. The Ba/Ca-profiles show one high, sharp peak and a number of smaller peaks. The highest peaks coincide approximately with the periods of highest phytoplankton production but there is no direct relation between shell Ba/Ca and chlorofyll a concentration, which is a measure of primary production. These results emphasise the fact that biological controls on shell chemistry should be taken into account when extracting paleoenvironmental information from bivalve skeletons.

B07 : 3P/12 : PO

Dinoflagellate Cysts, Chemostratigraphy and Sea-Level Change in the Late Cretaceous: New Data from the Banterwick Barn Chalk Borehole, Berkshire, UK

Martin Pearce (m.pearce@king.ac.uk)¹,

Ian Jarvis (i.jarvis@king.ac.uk)¹,

Andy Swan (swan@king.ac.uk)² &

Bruce Tocher (bruce@statoil.no)¹

¹ School of Geological Science, Kingston University, Kingston-upon-Thames, UK

² Head, Biostratigraphy, Forus N-4035, Stavanger, Norway

The dinoflagellate-cyst record from a cored borehole through the uppermost Cenomanian to upper Coniacian (Upper Cretaceous) Chalk at Banterwick Barn, Berkshire, UK is described. For the first time, quantitative dinocyst abundance and diversity trends are compared statistically to elemental geochemistry and stable-isotope chemostratigraphy. This study also examines dinocyst assemblages through the Chalk Rock and Top Rock hardgrounds in their type areas, the bases of which define the base of the Upper Chalk and Coniacian Stage in the UK, respectively.

Fifty-nine recognised species and subspecies, eight informal, and two unclassified species are recorded. An extremely impoverished assemblage of dinocysts in the high Cenomanian to lower Turonian is associated with sediments deposited during a global oceanic anoxic event (OAE 2) ~ 93.5 Ma. A sharp increase in diversity within the low Turonian corresponds with a change in lithology. The dinocyst abundance profile is characterised by eight 'bloom events' corresponding to sharp increases in a few species; the different proportion of species in these events may be of stratigraphic use. A progressive decrease in diversity is observed through the mid-Turonian to Upper Coniacian, associated with a gradual oceanic cooling established from the oxygen isotope record.

The study area was located on a structural high associated with the Anglo-Brabant Massif. Dinocyst assemblages and the condensed nature of the lithologies suggests a relatively shallow-water environment. Sea-level trends interpreted from dinoflagellate cyst ecological groups compare well to published sea-level curves and indicate relative highstands in the low Turonian and through the Coniacian. A minor transgression during the late Turonian may be the result of local subsidence. A proposed dinocyst depth stratification model suggests sea-level may be reconstructed from dinocyst absolute abundance data alone. The generally low abundance and diversity of cysts and the absence of high nutrient, deeper-water-associated palynomorphs, suggest upwelling was minimal and available nutrients were supplied by continental weathering. Statistical analysis of a wide range of geochemical data with the dinocyst record has produced three distinct species groups with characteristic geochemical associations: (1) high carbonate flux and low detrital supply; (2) increased detrital supply; (3) cooler water, independent of carbonate and detrital input.

Strong relationships between geochemical and palynological trends demonstrate the importance of palaeoenvironmental factors in controlling sediment and biotic compositions. The observed stratigraphic trends have great potential for inter-regional correlation.

B07 : 3P/13 : PO

Lower and Middle Pliocene Climate Deduced from Palynological Studies in the Chelif Basin

Mostefa Bessedik &

Sidi Mohamed Abdemalek

Laboratoire de Paléontologie stratigraphique et Environnement, Cité du Chercheur (ex. I.A.P.), Université d'Oran, BP 1524, Oran El M'Naouer, 31000 Oran (Algérie)

The Sidi Brahim section (Gl. margaritae, Gl. puncticulata, Gl. bononiensis, Gl. crassaformis) and the Arzew-1 off shore drilling. (Gl. margaritae, Gl. crassaformis, Gl. inflata, located in Chelif basin and dated from the Lower and Middle Pliocene age, give evidence of a rich pollen grain flora. These floristic data are new for the Southwest Mediterranean region. The vegetation was marked by a dry zone located on lowlands (Asteraceae, Poaceae, Amaranthaceae/Chenopodiaceae, ...) including the Lygeum cf. spartum species which lives nowadays in the semi arid regions and which is ruled by a subtropical to Mediterranean type-climate. Like today, this zone must be located in the North of a desertic (Saharan) zone which provides saharo-sindian elements (Nitraria, Calligonum, ...). This hypothesis does not exclude the presence of some small arid areas (saharo-sindian elements ) inside the Pliocene semiaride zone of lowlands.

According to modern floristic data, the presence of the semiaridLygeun cf. spartum species is an important paleogeographic and climatic witness which suggests, as today, a north-south latitudinal climatic zonation. The origine of this xeric zone could be explained by the evolution of the Aquitanian semiarid zone which was evidenced in the Mediterranean regions and upto Messinian times in the Oran area. Probably, the modern vegetation characteristics were yet emplaced since the Messinian age (Sahara emergence, Lygeum cf. spartum steppe)

In the upper part of the semi arid zone, we suggest an altitudinal vegetation, sclerophylous oak grove-type (Engelhardtia, Acer, Alnus, Juglans, Carya, Carpinus, ...) with Lauraceae containing some deciduous and conifer elements in its uppermost part. The Mediterranean-type elements (Olea, Phillyrea, ...) must constitute, like today, an ecotonal vegetation between temperate and arid to semiarid vegetations.

Climatically, the Oran area enjoyed a subtropical to mediterranean climate-type from arid to semiarid (Early Pliocene) suffering a progressive and general cooling at 3.5 Ma, then general warming at 3.1 Ma. These phases are similar to those evidenced in the Mediterranean and north-European regions.

B07 : 3P/14 : PO

Paleoceanography and Basin Evolution of A Miocene Section in the Monferrato Area (Northern Italy) Based on Benthic Foraminifera

Thomas Mühlstrasser (thomas.muehlstrasser@uni-tuebingen.de),

Gerhard Schmiedl

(gerhard.schmiedl@uni-tuebingen.de) &

Christoph Hemleben

(christoph.hemleben@uni-tuebingen.de)

University of Tübingen / Institute and Museum for Geology and Paleontology, Sigwartsrasse 10, D - 72076 Tübingen, Germany

The Monferrato area in Northern Italy is of special interest for micropaleontologists, because it owns a number of marine sedimentary sections that cover a wide stratigraphic range within the Tertiary. These sections provide the opportunity to study the paleoenvironmental and paleogeographical evolution of the Northern Mediterranean Tethys including the global climatic fluctuations of the Miocene and the regional paleoceanographic changes that are associated with the tectonic evolution of the Appennines and Alpine orogens. In this study we analyzed the benthic foraminiferal fauna in the >125 µm fraction of a profile extending from the upper Oligocene (about 24 mio years) to the middle Miocene (about 15 mio years). The benthic foraminifera were classified on the species level and grouped into different assemblages. Recent faunas from the Mediterranean and Atlantic oceans were used as modern equivalents to unravel the paleoecological significance of the fossil faunas. Variations in the dominance of infaunal genera like Uvigerina, Praeglobobulimina and Brizalina in contrast to epifaunal species like Cibicides, Cibicidoides and Hanzawaia indicate changes from an eutrophic environment with low oxygen contents in the bottom and pore water to oligotrophic and well ventilated conditions. This information can be interpreted in terms of changes in water depth, paleocirculation, and paleoclimate and contributes to distinguish global from regional climatic signals.

B07 : 3P/15 : PO

Lithium Isotope Composition of Carpatian Foraminifera from LKS- 1 Borehole (Southern Slovakian Basin)

Denisa Hammerschmidtova (denisah@hotmail.com)¹,

Jan Kosler (kosler@natur.cuni.cz)¹ &

Katarina Holcova (holcova@natur.cuni.cz)²

Petr Jakes (jakes@natur.cuni.cz)¹

¹ Department of Geochemistry, Charles University, Albertov 6, 128 43 Praha 2, Czech Republic

² Department of Paleontology, Charles University, Albertov 6, 128 43 Praha 2, Czech Republic

Ratio of lithium to calcium in the present day ocean is constant. The oceanic geochemistry of lithium is dominated by hydrotermal input (Holland, 1978) and the weathering of continental crust. Therefore, if these processes have varied over geologic time, the lithium content in the ocean may have changed significantly. Because of its relatively small ion radius ( rLi+ = 0.59 angstrom) lithium substitutes for Mg²⁺ in crystal-lattices (Heier and Billings, 1970). Its high ion potential induces a very strong hydration of the monovalent ion in aqueous systems. Foraminiferal shells could be a useful tracer of oceanic lithium (Hoefs et al., 1997). In this study, planktonic foraminifera were chosen to determine the effects of variations in Li-isotopes composition. We assume that dissolved lithium in the seawater is the only input to foraminiferal shells. Globigerina praebulloides is probably the most similar from ecological point of view to recent species which live mainly in moderate climate (Kennett, 1976). We are using the analogies of recent Globigerina bulloides to estimate the depth habitat (about 100 m) of Carpatian Globigerina ex gr. praebulloides. It corresponds with results of Bé, 1977 (50 - 100 m) and Hemleben and Spindler, 1983 (50 - 200 m). Analysed samples from LKS- 1 borehole, measured by ICP- MS, represent a typical foraminiferal development of the Central Paratethys (Early Miocene). If the changes in lithium isotope ratios observed in planktonic foraminifera are induced by variations in the global ocean water composition, then the correlations betwen the lithium isotope curve, production rates of sediments, phases of global plate reorganisations, and periods of intense mountain-building can be predicted.

Hoefs et al, Geochim. Cosmochim. Acta, 61, 2679-2690, (1997)

Heier and Billings, Lithium. In Handbook of Geochemistry (Ed. K. H. Wedepohl). Springer-Verlag, (1970)

Holland, The Chemistry of the Atmosphere and Oceans. John Wiley and Sons. 351, (1978)

Kennett, In Hedley, R. H. and Adams, C. G. (Eds.): Foraminifera 2. Academic Press, 111-170, (1976)

Bé, In Ramsay, A. T. S. (Ed.): Oceanic micropaleontology, Academic Press, 1, 1-100, (1977)

Hemleben and Spindler, Ultrech Micropaleont. Bull., 30, 141-170, (1983)

B07 : 3P/16 : PO

On Climatic Sensitivity to the Atmospheric Gas Composition Using Paleoclimatic Data

Irena Borzenkova (borzen@climate.shi.spb.ru)

Department of Climatology, State Hydrologycal Institute, St Petersberg, Russia

Comparison between geologicla data on past climates and the data on atmospheric gas composition has shown that global temperature changes over the Phanerozoic largely depended on atmospheric concentration of carbon dioxide, methane and other greenhouse gases (Budyko et al., 1995; Lorius et al., 1990, Sloan and Barron, 1992).

According to the estimates obtained by different GCMs, mean global air temperature increase with doubling CO₂ content in the atmosphere can range from 1.5 to 4.5°C. Paleoclimatic data used to assess the sensitivity of global temperature to doubling of atmospheric CO₂ concentration have allowed to narrow this range to 3±0.5°C (Budyko et al., 1985).

Later this result was confirmed by paleoclimatic data on seven time intervals (from the late Cretaceous to the Late Pleistocene) which are characterized by different levels of CO₂ content in the atmosphere (from 0.20-0.25% in the Cretaceous time to 0.02% during the cooling time of the late Pleistocene) (Borzenkova, 1992). Not long ago Hoffert and Covey (1992) obtained similar estimates of global climate sensitivity to doubling of atmospheric CO₂ concentration using paleoclimatic data.

The major difficulty in the use of paleoclimatic data for assessing global sensitivity arises from insufficient quantity of reliable empirical materials. Though independent empirical data on past climates become more numerous as epochs become close to modern time, it is rather difficult to recontruct the climates of the geological epochs closest to recent time. Primarily, it is characteristic of Pleistocene and Holocene due to relatively small departures of values of climate parameters from those of modern ones lying in the limits of the accuracy of recent methods.

Of special interest are climate reconstructions for comparatively distant geological epochs when CO₂ concentration in the atmosphere 6-10 times exceeded the modern one and global temperature was 5-8°C higher than now.

To determine global temperature, the author's maps-reconstructions have been used for four time slices of the late Cretaceous (Alb, Cenoman, Santon-Coniac and Maastricht), the Eocene optimum, the Middle Pliocene and the Wurm glacial maximum which are characterized by different levels of CO₂ content in the atmosphere.

The logarithmic correlation between the values of global temperature and CO₂ content in the atmosphere for different time intervals of the last 100 Ma allow us to assess the sensitivity of global temperature to doubling of CO₂ concentration equal ±3°C.

B07 : 3P/17 : PO

Black Shales and Limestone/Marlstone Rhythms in the Cenomanian -Turonian of the Northeastern Dolomites (Italy): Biotic Response and Paleoceanographic Implications

Valeria Luciani (lcv@dns.unife.it)¹ &

Miriam Cobianchi (miriam@unipv.it)²

¹ Dipartimento di Scienze Geologiche e Paleontologiche, Università degli Studi di Ferrara, Corso Ercole I° d'Este, 32, 44100 Ferrara, Italy

² Dipartimento di Scienze della Terra, Università degli Studi di Pavia, via Ferrata, 1, 27100 Pavia, Italy

A Cenomanian-Turonian succession, characterized by limestone-marl alternations and containing several black shales, is well exposed in the northeastern Dolomites, near Cortina d'Ampezzo (Southern Alps, northern Italy). Two formations have been recognized: the Scaglia Variegata and the Scaglia Rossa. The 1-m-thick black interval, separating the Scaglia Variegata from the overlying Scaglia Rossa, has been identified as the Bonarelli Level, considered to be the sedimentary expression of the global OAE2 (Oceanic Anoxic Event; Schlanger, Jenkyns, 1976). The continuous occurrences and high abundance of planktonic foraminifera and calcareous nannofossil assemblages throughout the section allowed a detailed integrated biostratigraphical analysis to be carried out. According to our data, the succession spans the foraminiferal Rotalipora brotzeni to the Helvetoglobotruncana helvetica Zones p. p. and the nannofossil CC9c Zone to the CC12 Zone p.p. The oldest black interval occurred in the Cenomanian Rotalipora greenhornensis Zone- CC9c Subzones, while the youngest time interval of anoxia is Turonian in age (H. helvetica- CC12 Zones). The Bonarelli Level is referable to the Whiteinella archaeocretacea- CC10a Zones. The crisis related to the Cenomanian Turonian Boundary Event is documented by the disappearance of rotaliporids below the Bonarelli Level. Biotic changes in the fossil assemblages related to the lithology can suggest implications for regional, palaeobiological and palaeoceanographic events. Unlike the Bonarelli Level, which is devoid of both planktonic and benthonic fauna, the accumulation of variable amounts of organic matter in the numerous black horizons did not affect planktonic assemblages, which are generally well preserved and diverse without any dominance of eutrophic indicators. On the contrary, an increase of oligotrophic forms among planktonic foraminifera (rotaliporids and marginotruncanids) is recorded in the black levels as well as in the marls. The eutrophic radiolaria and calcispheres are very rare throughout the section. The lowest percentages of oligotrophic forms accompanied by a relative increase of eutrophic/mesotrophic indicators (hedbergellids, heterohelicids, globigerinelloids), occur in the limestones. These data suggest that the limestones correspond to times of relative enhanced surface water productivity respect to deposition of marls and black levels and that bottom redox cycles probably prevailed over productivity cycles among the mechanisms leading to the formation of the Cenomanian-Turonian black shales of the section. The Total Organic Carbon (TOC) content reaches a high value only in the Bonarelli Level (5.85%) while the other black levels contain less than 1% in TOC. Benthonic foraminiferal fauna is absent in the deposits where the TOC ranges from 0.5 to 1%, suggesting anoxic conditions on the sea floor, where the TOC is less than 0.5%, benthonic forms are present and indicate dysaerobic conditions of variable intensity.

Schlanger SO, Jenkyns HC, Geol. Mijn, 55, 179-184, (1976).

B07 : 3P/18 : PO

Biotic and Geochemical Response to Anoxic Events: the Aptian Pelagic Succession of the Gargano Promontory (Southern Italy)

Valeria Luciani (lcv@dns.unife.it)¹,

Miriam Cobianchi (miriam@unipv.it)² &

Hugh Jenkyns (Hugh.Jenkyns@earth.ox.ac.uk)³

¹ Dipartimento di Scienze Geologiche e Paleontologiche, Università di Ferrara, Corso Ercole I° d'Este, 32, 44100 Ferrara, Italy

² Dipartimento di Scienze della Terra, Università di Pavia, via Ferrata, 1, 27100 Pavia, Italy

³ Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK

The Lower Cretaceous basinal succession of the Gargano Promontory (southern Italy) consists of two superimposed lithologic units: Maiolica and Scisti a Fucoidi, respectively. They crop out in the northeastern part of the promontory and were deposited adjacent to the Apulia Platform, a shallow-water carbonate bank subject to various exposures and drownings in respose to relative sea-level fluctuations. The Scisti a Fucoidi Formation typically consists of marl-limestone couplets, probably controlled by orbital (Milankovitich) parameters that influenced palaeoclimate and palaeoceanography, and contains three black shale horizons (anoxic episodes). The onset of deposition of the Scisti a Fucoidi in the basin (Early Aptian) is coeval with a drowning of the Apulia Platform margin, related to a transgression which was probably eustatically controlled (Luciani, Cobianchi, 1994; Bosellini et al., submitted).The planktonic foraminiferal and calcareous nannofossil data enable the oldest black shale to be attributed to the upper part of the Globigerinellodes blowi and Chiastozygus litterarius Zones of late Early Aptian age. The second black horizon can be referred to the Ticinella primula and Prediscosphaera columnata Zones of the Early Albian and the youngest black shale is referred to the Ticinella praeticinensis Subzone and Parhabdolithus achlyostaurion Zone of the Late Albian. The oldest black shale can be considered to be the equivalent of the Selli Level of Umbria-Marche and represents the sedimentary expression of the global Ocanic Anoxic Event 1a (OAE1a). A perturbation of the biotic signal occurs across the Selli Level: a crisis of globigerinelloids and nannoconids precedes and follows the anoxic episode, and a marked increase of the eutrophic indicators (hedbergellids, Zygodiscus erectus, Biscutum constans, radiolaria) has been observed. These critical conditions associated with the OAE1a are widely documented and generally related to a high fertility episode of surface water. However, with respect to the the Umbria-Marche Basin (Coccioni et al., 1992), the Selli Level from the Gargano is not completely barren of calcareous plankton, probably suggesting slightly less fertile conditions of the surface water or a shallower environment. Moreover, the occurrence of the benthonic genus Spirillina indicates local dysaerobic conditions versus complete anoxia of the sea floor. Relevant stable-isotope data will also be presented.

Bosellini A, Morsilli M, Neri C, submitted to J. Sed. Res.

Coccioni R, Erba E, Premoli Silva I, Cret. Res, 13, 517-537, (1992).

Luciani V, Cobianchi M, Mem. Sc. Geol, 46, 283-301, (1994).

B07 : 3P/19 : PO

Elemental Nomalies at the Permian - Triassic (P/T ) Boundary in the Idrijca Valley (W. Slovenia): Evidence of Changing Redox Conditions at the P/Tr Transition in the Western Tethys

Tadej Dolenec (tadej.dolenec@ntfgeo.uni-lj.si)¹,

Sonja Lojen²,

Anton Ramov¹ &

Matej Dolenec (matej.dolenec@s5.net)³

¹ Department of Geology, University of Ljubljana, Askerceva 12, Slovenia

² Department of Environmental Sciences, Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia

³ Geoexp d.o.o., Slap 21, 4290 Trzic, Slovenia

Geochemical evidence from the (P/Tr) boundary section in the Idrijca Valley (W. Slovenia) indicates an abrupt changes of redox conditions at the P/Tr transition in this part of the Western Tethys, which coincide with a drastic disappearance of typically Upper Permian marine fauna of algae, foraminifers and brachiopods.

In Western Slovenia the limestone sedimentation proceeded concordantly across the P/Tr boundary. The topmost part of the Upper Permian - Zazar Formation is characterized by a 25 - 30 cm thick layer of black algal packstone very rich in microfossil fragments which prove the Upper Permian age. The P/Tr boundary is sharp, not erosional, and is placed at the top of this black algal packstone layer, followed by a light grey well bedded Lower Scythian sparitic limestone containing, only some conical tube - like fragments of fossils, not known in the Upper Permian.

Our observations from the REE distribution in the boundary sequence and the shape of the Ce/Ce* curve suggest that oceanic anoxia was typical of the Upper Permian during sedimentation of the Zazar Formation, and that the transition to more oxygenated conditions occurred at the P/Tr boundary. This observation is also supported by an abrupt decrease in the boundary whole-rock Mo, V and U contents as well as by the depletion in C_org. and chalcophile elements such as Zn and Cu, which starts approximately 50 cm below the boundary. The shape of Ce/Ce* curve and the enrichment of the Lower Scythian limestone with C_org., as well as slightly higher concentrations of Mo, V, U, Zn and Cu 30 cm above the boundary indicate that redox environmental conditions changed drastically in the earliest Triassic, again resulting in oxygen deficient conditions.

The depletion of Mo, V, U and their irregular distribution in the remaining Lower Scythian beds as compared to the Zazar Formation indicates that environmental conditions in the Lower Triassic were probably less reducing and less steady than during the deposition of the majority of the Upper Permian beds.

The faunal composition displays a gradual impoverishment of Upper Permian taxa moving upward towards the boundary and an abrupt disappearance at the boundary.

B07 : 3P/20 : PO

Paleoclimatic Reconstructions for the Late Precambrian Sedimentary Successions on the Western Slope of the South Urals

Andrei V. Maslov (root@igg.e-burg.su)¹ &

Emir Z. Gareev (emik@bash.ac.ru)²

¹ Institute of Geology and Geochemistry, Urals Branch of RAS, Ekaterinburg, Russia

² Institute of Geology, Ufa Scientific Centre of RAS, Ufa, Russia

For sedimentary deposits of the Riphean stratotype and Vendian associations of Bashkirian anticlinorium were proposed various evolutionary models of the paleoclimatic conditions, but this problem is still contradict. We used as a paleoclimatic indicator CIA-index (Nesbitt, Young, 1982), which is usefull instrument for reconstruction of paleoclimatic conditions for not only Phanerozioc sedimentary deposits, but Proterozoic also. Fresh (unweathered) rocks is characterized by CIA ~ 50; in highly weathered rocks CIA is ca.100. It was established that the rocks with CIA~70 were formed in relatively cold climatic conditions.

There are three main groups of shales with different CIA values in the Upper Precambrian section of the Bashkirian anticlinorium. First group (CIA370) combines shales of the lower and middle levels of the Middle Riphean (Mashak, Zigalga and Zigazino-Komarovo Formations, ~ 1,34-1,2 Ga). These shales were formed probably from fine-grained silicoclastic material, which was derived from the zones of relatively warm humid climate. The predominance of quartz sandstones in the Mashak and Zigalga Formations is confirmed our supposition about intensive chemical weathering on the continent. The shales of the Lower Riphean Suran Formation (~1,4-1,3 Ga), the Middle Riphean Avzyan Fm. (~1,2-1,1 Ga), the Upper Riphean Bederysh Member and Katav Fm. (~1,0-0,9 Ga) and Lower Vendian Suirovo Fm. belong to the second group (CIA¾60). Based on the lithology and geochemical parameters and CIA values of the shales of the Bederysh Member (Zilmerdak Fm.) and the Katav Fm., it is possibly to consider it as the deposits, which were formed due to silicoclastic material from source zones with arid conditions. The CIA values in the shales of the Suirovo Fm. (Lower Vendian) are combined with glaciogenic Laplandian events, so the low CIA values reflect the cold climatic conditions on the continent. The third group (60<CIA<70) is represented by the argillitic rocks of the Lower Riphean Ai and Bakal Fms, Upper Riphean Inzer, Minyar and Uk Fms. and Upper Vendian deposits. It is highly probably, that all these deposits were formed under "temperate" climatic conditions.

So, the Late Precambrian climatic conditions on the territory under review were similar to semiarid. Only for the beginning and the middle part of the Middle Riphean (1,35-1,2 Ga) we may suppose warm climate. These humid and warm conditions led to formation of the petrochemically mature fine-grained silicoclastic deposits. The shales with the CIA¾50 are probably the deposits of the extraarid (the Bederysh Member of the Zilmerdak Fm.) and subglacial (the Suirovo Fm. of the Lower Vendian) environments.

The investigations on this theme were supported by RBRF (grant 97-05-65107).

Nesbitt HW, Young GM, Nature, 299, 715-717, (1982).

B07 : 3P/21 : PO

Oceanography and Productivity in the Sea of Okhotsk During the Last Approximately 300.000 Years

André Kaiser (akaiser@geomar.de)¹,

Dirk Nuernberg (dnuernberg@geomar.de)¹,

Ralf Tiedemann (rtiedemann@geomar.de)¹,

Nicole Biebow (nbiebow@geomar.de)¹ &

Gorbarenko Sergei (sgorbar%dan78@poi.marine.su)²

¹ GEOMAR, Wischhofstr. 1-3, D-24148 Kiel, Germany

² Pacific Oceanological Institute, Vladivostok, Russia

The subarctic Pacific and adjacent marginal seas like the Sea of Okhotsk are charcterized by their high biological production and are known to act as sinks for CO₂. However, the processes that control the timing and the fluctuations in paleoproductivity and deep water ventilation within these high latitude regions are poorly understood, although they are of outstanding importance to understand climate change. Sediment cores from the Sea of Okhotsk covering the last approximately 300.000 years have been studied to reconstruct temporal and spatial changes in paleoproductivity, to examine the formation of deep water and to investigate oceanographic changes that are related to climate variability.

Tephrachronology, bio- and lithostratigraphic information, stable isotope data, as well as cyclic changes in the magnetic susceptibility were combined to establish an age model for the sediment records. Typical changes from warm diatom-rich to cool terrigenous horizons are expressed in sharp lithological boundaries reflecting rapid and drastic environmental changes through time. Even short-term climatic rebound phases during Termination I are reflected in sedimentological, geophsyical and geochemical parameters.

Various geochemical proxies (TOC, CaCO₃, Ba_excess, biogenic silica, chlorines) indicate extremely enhanced marine productivity in hemipelagic areas off Kamchatka and Sakhalin, mainly driven by the strength of the inflowing Kamchatka Current, the contribution of Amur River water, and upwelling features. Sediment component and grain size analyses suggest the continuous deposition of ice-rafted debris (IRD) that is strongly enhanced during the glacials. The absence of large glacier systems ashore even during glacial stages suggests that (seasonal) sea ice is the dominant transport agent to distribute IRD basin-wide.

Widespread rhyolitic volcanic ashes are present in most sediment records and differ significantly in chemical composition as shown by TiO₂ vs. K₂O and total alkali vs. SiO₂ concentrations. Distinct ash layers are identified as KO (8.300 yrs. B.P.), TR (8.300 yrs. B.P.), and K2 (26.000 yrs B.P.) and are related to specific source areas. Several new Pleistocene ash layers previously unknown in the Sea of Okhotsk and still undated are found and serve for core correlation.

B07 : 3P/22 : PO

Sea Surface Temperatures in the Nordic Seas During the Last Glacial Maximum

Marius Mæland (marius.maeland@student.uib.no)

Department of Geology, Allégaten 41, 5007 BERGEN, NORWAY

Modelling of climate changes depends on the quality of datasets for ocean temperatures. Untilnow the CLIMAP-reconstruction is used for estimation of SST (Sea Surface Temperature) inthe LGM (Last Glacial Maximum). The CLIMAP-reconstruction used transfer functions, based on counting of planktonic foraminifera, to develop a global SST-map for LGM. In the light of their results, they concluded that great areas of the Nordic Seas were perennially ice covered in this period, based on T ¾0 ºC, low carbonate content, evidence of IRD, and generally low sedimentation rate. The transfer-function method they used, acts good in lower latitudes, where the diversity of species is good. The method is not accurate in polar and subpolar areas, because of low foraminiferal species diversity. New investigations indicate that there has been, at least seasonally, open water conditions. Accordingly, there are good reasons to revise the CLIMAP-reconstruction for the Nordic Seas.

New data sets for glacial SST has been developed by different authors. The temperature data is based on ¹⁸O-measurements, the modern technique analogue method (SIMMAX 26) of planktonic foraminifera, and transfer functions of diatoms. The purpose of my work will then be to compose these data together, by gridding/interpolation techniques, to make a new SST-map for LGM.

When an SST-map is made, ¹⁸O-data and salinity-data from the data sets will, together with the SST-data, be used to give a description and an interpretation of the surface water circulation during LGM. Potential areas for intermediate and deep water convection will be interpreted.

B07 : 3P/23 : PO

Northwest Pacific Marginal Basin Environment: The Kurile - Okhotsk Sea Marine Experiment (KOMEX)

Nicole Biebow (nbiebow@geomar.de)

KOMEX Participants

GEOMAR, Wischhofsstr.1-3, 24148 Kiel, Germany

The Sea of Okhotsk and its marginal regions represent a system of extraordinary plate tectonical, climatic and ecological conditions which affects the global climate considerably. The German-Russian joint project KOMEX focusses on the investigation of the mechanism of this system and its influence on environmental parameters such as the global biogeochemical cycle, surface and deep-ocean circulation, plate tectonics and the global climate. The main scientific aims of this joint project are:

(1) to quantify the geogene and biogene methane influx into the atmosphere; (2) to quantify the fluid influx from active vents and their reconstruction from authigene mineral precipitates; (3) to characterize the influence the magmatic systems of the Kurile Island Arc have on the distribution and circulation of organic matter; (4) to examine sedimentological primary production and its spin-off products as well as its effects on the global carbon cycle; particular attention will be payed to seasonal oscillation and the sensitivity of the various eco systems; (5) to evaluate the role the Sea of Okhotsk plays in water mass formation and ciculation in the north-western part of the Pacific Ocean palaeoceanographically; (6) to examine the seismic fazies and the character of the BSR in cold vent areas and along the bordering continental slope areas; (7) to understand the evolution of the Sea of Okhotsk and its geological and structural borders.

In 1998 two joint German/Russian ship expeditions to the Sea of Okhotsk took place. During these expeditions geophysical, geochemical, volcanological and paleooceanographical investigations were performed along the margin of E-Sakhalin, the Kurile Basin, and within central parts of the Sea of Okhotsk. The scientific highlights of these expedition were

1) The recovery of gas flares (several hundrets of meters high) along the continental slope of Sakhalin

2) t