Gilles Lericolais

Constraints on Black Sea outflow to the Sea of Marmara during the last glacial-interglacial transition

New cores from the upper continental slope off Romania in the western Black Sea provide a continuous, high-resolution record of sedimentation rates, clay mineralogy, calcium carbonate content, and stable isotopes of oxygen and carbon over the last 20 000 yr in the western Black Sea. These records all indicate major changes occurring at 15 000, 12 800, 8400, and 7100 yr before present. These results are interpreted to reflect an evolving balance between water supplied by melting glacial ice and other river runoff and water removed by evaporation and outflow. The marked retreat of the Fennoscandian and Alpine ice between 15 000 and 14 000 yr is recorded by an increase in clays indicative of northern provenance in Black Sea sediments. A short return toward glacial values in all the measured series occurs during the Younger Dryas cold period. The timing of the first marine inflow to the Black Sea is dependent on the sill depths of the Bosporus and Dardanelles channels. The depth of the latter is known to be −80±5 m, which is consistent with first evidence of marine inundation in the Sea of Marmara around 12 000 yr. The bedrock gorge of the Bosporus reaches depths in excess of −100 m (relative to present sea level), though it is now filled with sediments to depths as shallow as −32 m. Two scenarios are developed for the connection of the Black Sea with the Sea of Marmara. One is based on a deep Bosporus sill depth (effectively equivalent to the Dardanelles), and the other is based on a shallow Bosporus sill (less than −35 m). In the deep sill scenario the Black Sea’s surface rises in tandem with the Sea of Marmara once the latter connected with the Aegean Sea, and Black Sea outflow remains continuous with inflowing marine water gradually displacing the freshwater in the deep basin. The increase in the δ 18 O of mollusk shells at 12 800 yr and the simultaneous appearance of inorganic calcite with low δ 18 O is compatible with such an early marine water influx causing periodic weak stratification of the water column. In the shallow sill scenario the Black Sea level is decoupled from world sea level and experiences rise and fall depending on the regional water budget until water from the rising Sea of Marmara breaches the shallow sill. In this case the oxygen isotope trend and the inorganic calcite precipitation is caused by increased evaporation in the basin, and the other changes in sediment properties reflect climate-driven river runoff variations within the Black Sea watershed. The presence of saline ponds on the Black Sea shelf circa 9600 yr support such evaporative drawdown, but a sensitive geochemical indicator of marine water, one that is not subject to temperature, salinity, or biological fractionation, is required to resolve whether the sill was deep or shallow.

Pleistocene forced regressions and tidal sand ridges in the East China Sea

Abstract Tidal sand ridges are common features on modern shelves but only few examples of such preserved sand bodies are described in Pleistocene deposits. In the stratigraphic record, some sand bodies encased in shales, previously interpreted as sand ridges, have been reinterpreted as shoreface deposits. More than 5000 km of high-resolution seismic data from the East China Sea, correlated to geotechnical boreholes and shallow cores, demonstrate the potential of sand ridge preservation and allow reconstruction of the depositional history of Pleistocene fourth order (100-kyr) depositional sequences. A high subsidence rate of about 300 m/Myr allows the preservation of three elementary sedimentary facies, constitutive of a ‘motif’ which was repeated during glacio-eustatic cycles. They consist of (1) regressive marine prodeltaic prograding wedges, (2) estuarine and continental (deltaic) facies, and (3) transgressive sand ridges, similar in shape and orientation to modern sand ridges. Major discontinuities, traceable over the entire outer continental shelf along distances of hundreds of kilometers, are transgressive and regressive surfaces of marine erosion, whereas sequence boundaries formed by fluvial erosion are difficult to identify on this low-gradient shelf. Because of the asymmetry of the Pleistocene glacio-eustatic cycles, most of the preserved sedimentary record (with the exception of sand ridges) corresponds to forced regressive deposits (deposits that formed during a seaward shift of the shoreline due to relative sea-level lowering).

Morphology, Internal Structure, and Reversal of Asymmetry of Large Subtidal Dunes in the Entrance to Gironde Estuary (France)

ABSTRACT The Gironde is a macrotidal estuary characterized by important changes in tidal-current velocity and river discharge. Two surveys were made in the lower estuary in June 1987 and October 1989 in an area with large dunes. The symmetry of these dunes (1.5-6.7 m high) changes from flood-dominated (in upstream areas) to ebb-dominated (in downstream areas). A transition zone consists of symmetrical dunes with a very low vertical form index. The internal structure of the dunes, revealed by seismic records, shows a hierarchy of bounding surfaces related to fluctuations in movement speed and asymmetry of the dunes. The lowest part of symmetrical dunes consists of ebb-oriented reflectors, while the upper part has flood-oriented reflectors. The same profile lines run in 1989 show that each large dune can be identified, despite an upstream shift of the transition zone of about 1000 m. Comparison of seismic records shows that some lower reflectors are preserved between the two surveys, and that the dunes moved downstream a mean distance of 30 m. In 1989 the internal structure of symmetrical dunes was reversed, with flood-oriented reflectors in the lower part overlain by ebb-oriented reflectors. Both seasonal changes in river discharge and fortnightly oscillations of the tidal range control the magnitude and orientation of the net bed-load transport in the study area. Because the response time of the large dunes is longer than that of the superimposed small dunes, the reversal of asymmetry of the large dunes requires a long-period process, while fortnightly oscillation or even semi iurnal reversal of the tidal current (during spring tides) could cause reversal of small dunes.

Multiple bottom-simulating reflections in the Black Sea: Potential proxies of past climate conditions

Abstract A previously unknown pattern of multiple bottom-simulating reflections (BSRs) occurs on high-resolution reflection seismic data in the Danube deep-sea fan, associated with acoustic features indicating free gas. Our study provides evidence that this pattern is developed in relation with the architecture of distinct channel–levee systems of the Danube fan. Channel–levee systems hosting multiple BSRs act as relatively sealed gas-bearing systems whose top is situated above the base of the gas hydrate stability zone (BGHSZ). Inside these systems, free gas accumulates below the BGHSZ under a combined lithological, structural and stratigraphical control. The uppermost BSR marks the current equilibrium BGHSZ, for a gas composition of more than 99% methane. Model-derived depths of the BGHSZ for different gas compositions and pressure–temperature conditions show that multiple BSRs would correspond to the BGHSZ either for (1) layers of gas hydrates with high contents of heavy hydrocarbons or hydrogen sulphide, or (2) stable climatic episodes with temperatures between glacial values and the present-day conditions. As the gas hydrate compositions required by hypothesis (1) are in sharp contradiction with the general background of the gas composition in the study area, we suggest that multiple BSRs are most probably relics of former positions of the BGHSZ, corresponding to successive steps of climate warming. In this case, they can provide sea-bottom paleotemperature values for these episodes, and hence they are potential new proxies for deciphering past climate conditions.

Abrupt drainage cycles of the Fennoscandian Ice Sheet

Continental ice sheets are a key component of the Earth’s climate system, but their internal dynamics need to be further studied. Since the last deglaciation, the northern Eurasian Fennoscandian Ice Sheet (FIS) has been connected to the Black Sea (BS) watershed, making this basin a suitable location to investigate former ice-sheet dynamics. Here, from a core retrieved in the BS, we combine the use of neodymium isotopes, high-resolution elemental analysis, and biomarkers to trace changes in sediment provenance and river runoff. We reveal cyclic releases of meltwater originating from Lake Disna, a proglacial lake linked to the FIS during Heinrich Stadial 1. Regional interactions within the climate–lake–FIS system, linked to changes in the availability of subglacial water, led to abrupt drainage cycles of the FIS into the BS watershed. This phenomenon raised the BS water level by ∼100 m until the sill of the Bosphorus Strait was reached, flooding the vast northwestern BS shelf and deeply affecting the hydrology and circulation of the BS and, probably, of the Marmara and Aegean Seas.

Water-level fluctuations in the Black Sea since the Last Glacial Maximum

Preface Introduction Victor R. Baker List of contributors. General 1. Oxic, suboxic, and anoxic conditions in the Black Sea James W. Murray, Keith Stewart, Steven Kassakian, Marta Krynytzky, and Doug DiJulio 2. Molluscan paleoecology in the reconstruction of coastal changes Daniela Basso and Cesare Corselli 3. Climate modeling results for the Circum-Pontic Region from the late Pleistocene to the mid-Holocene Alexander V. Kislov and Pavel M. Toropov Principal Flood Scenarios 4. Status of the Black Sea flood hypothesis William B.F. Ryan 5. The Marmara Sea Gateway since ~16 ky BP: non-catastrophic causes of paleoceanographic events in the Black Sea at 8.4 and 7.15 ky BP Richard N. Hiscott, Ali E. Aksu, Peta J. Mudie, Michael A. Kaminski, Teofilo Abrajano, Dogan Yasar, and Andre Rochon 6. The late glacial great flood in the Ponto-Caspian basin Andrei L. Chepalyga 7. Controversy over Noahs Flood in the Black Sea: geological and foraminiferal evidence from the shelf Valentina V. Yanko-Hombach Research in the Northern Sector 8. On the post-glacial changes in the level of the Black Sea Pavel N. Kuprin and Valentin M. Sorokin 9. The post-glacial transgression of the Black Sea Valery I. Shmuratko 10. Climate dynamics, sea-level change, and shoreline migration in the Ukrainian sector of the Circum-Pontic Region Yuri Shuisky 11. The Middle Paleolithic and early Upper Paleolithic in the northern Black Sea region Viktor P. Chabai 12. Environment, sea-level changes, and human migrations in the northern Pontic area during late Pleistocene and Holocene times Pavel M. Dolukhanov and Konstantin K. Shilik 13. HoloceneMediterranization of the southern Crimean vegetation: paleoecological records, regional climate change, and possible non-climatic influences Carlos E. Cordova 14. Pontic-Caspian Mesolithic and Early Neolithic societies at the time of the Black Sea flood: a small audience and small effects David W. Anthony 15. Fluctuations in the level of the Black Sea and Mesolithic settlement of the northern Pontic area Vladimir N. Stanko Research in the Western Sector 16. The northwestern Black Sea: climatic and sea-level changes in the Late Quaternary Nicolae Panin and Irina Popescu 17. Sea-level fluctuations and coastline migration in the northwestern Black Sea area over the last 18 ky based on high-resolution lithological-genetic analysis of sediment architecture Evgeny G. Konikov 18 Water-level fluctuations in the Black Sea since the Last Glacial Maximum Gilles Lericolais, Irina Popescu, Francois Guichard, Speranta-Maria Popescu, and Laurence Manolakakis 19. Archaeological and paleontological evidence of climate dynamics, sea-level change, and coastline migration in the Bulgarian sector of the Circum-Pontic Region Mariana Filipova-Marinova 20. Dendrochronology of submerged Bulgarian sites Peter I. Kuniholm, Maryanne W. Newton, and Bernd Kromer 21. The Neolithization of the north Pontic area and the Balkans in the context of the Black Sea floods Valentin Dergachev and Pavel M. Dolukhanov 22. Holocene changes in the level of the Black Sea: consequences at a human scale Douglass W. Bailey Research in the Southern Sector 23. Morphotectonic development of the southern Black Sea region and the Bosphorus channel Yucel Yilmaz 24. Sea-level changes modified the Quaternary coastlines in the Marmara region,

The interplay between tectonics, sediment dynamics and gateways evolution in the Danube system from the Pannonian Basin to the western Black Sea.

Understanding the natural evolution of a river-delta-sea system is important to develop a strong scientific basis for efficient integrated management plans. The distribution of sediment fluxes is linked with the natural connection between sediment source areas situated in uplifting mountain chains and deposition in plains, deltas and, ultimately, in the capturing oceans and seas. The Danube River-western Black Sea is one of the most active European systems in terms of sediment re-distribution that poses significant societal challenges. We aim to derive the tectonic and sedimentological background of human-induced changes in this system and discuss their interplay. This is obtained by analysing the tectonic and associated vertical movements, the evolution of relevant basins and the key events affecting sediment routing and deposition. The analysis of the main source and sink areas is focused in particular on the Miocene evolution of the Carpatho-Balkanides, Dinarides and their sedimentary basins including the western Black Sea. The vertical movements of mountains chains created the main moments of basin connectivity observed in the Danube system. Their timing and effects are observed in sediments deposited in the vicinity of gateways, such as the transition between the Pannonian/Transylvanian and Dacian basins and between the Dacian Basin and western Black Sea. The results demonstrate the importance of understanding threshold conditions driving rapid basins connectivity changes superposed over the longer time scale of tectonic-induced vertical movements associated with background erosion and sedimentation. The spatial and temporal scale of such processes is contrastingly different and challenging. The long-term patterns interact with recent or anthropogenic induced modifications in the natural system and may result in rapid changes at threshold conditions that can be quantified and predicted. Their understanding is critical because of frequent occurrence during orogenic evolution, as commonly observed in the Mediterranean area and discussed elsewhere.

Late Pleistocene to Recent ostracod assemblages from the western Black Sea

During the last glacial phase the Black Sea basin was isolated from the worlds oceans due to the lowering of global sea-levels. As sea-levels rose during the latest glacial and early Holocene period, the Black Sea was once again connected to the eastern Mediterranean via the Dardanelles–Marmara–Bosporus seaway. In recent years, trace element and stable isotope analyses of ostracod assemblages have yielded important details regarding the hydrological evolution of the Black Sea during these events. Despite this focus on the geochemical signatures of the ostracods, little if any attention has been paid to the taxonomic composition of the ostracod assemblages themselves and there are notably few publications on the sub-littoral fauna of this important water body. We present a summary of the most abundant ostracod taxa of the Black Sea during the late glacial to early Holocene phase (dominated by the Candonidae, Leptocytheridae and Loxoconchidae) and chart their response to the subsequent environmental changes in the early Holocene with the pre-connection, low salinity ‘lacustrine’ fauna being replaced by one with a more Mediterranean aspect. Many of these taxa are illustrated using SEM for the first time, providing an important initial step in establishing taxonomic stability within Black Sea ostracod studies and noting faunal similarities with neighbouring areas, such as the Caspian Sea.

Magnetic minerals as indicators of major environmental change in holocene black sea sediments: preliminary results

Four of the 38 sediment cores, collected from the northwestern part of the Black Sea (French–Romanian BLASON Programme, 1998), were analysed in order to study the major hydrological and environmental change of the sea during the Holocene. This change was caused by the inflow of the marine Mediterranean waters into the freshwater basin of the Black Sea. Two cores from the northwestern shelf and two from the deep part of the sea, representing distinct sedimentary environments along the same profile, were chosen. Lacustrine sediments from deep-water cores and uppermost marine sediments in all studied cores are characterised by the presence of pyrite (FeS2), which indicates anoxic, sulphate reducing conditions in sediment and in water column (as it is observed nowin the Black Sea). Pyrite formation in this anoxic environment takes place belowthe oxic/anoxic limit, by reduction and sulphidation of iron. The transition from freshwater to marine conditions is marked in all studied cores by the presence of ferrimagnetic iron sulphide––greigite (Fe3S4). Greigite is an intermediate mineral in the pyritisation reactions during early diagenesis, which can be preserved in the sediment if pyritisation cannot be accomplished, due to a high Fe/S ratio. In shallow water cores from the shelf, where marine transgression is marked by a discontinuity, greigite is present below and above it. This suggests that the anoxic, sulphate reducing conditions, allowing preservation of greigite, started in the sediment after marine transgression. In cores from the deep part of the sea, the transgression is represented by a level of sediments with high organic matter content (sapropel). The greigite is present only in the lower part of this level and its formation is related to the arrival of marine water. The presence of pyrite in the upper part of the lacustrine sediments indicates that anoxic conditions probably prevailed here during marine transgression. These results showthe sensitivity of magnetic parameters to major environmental change in the Black Sea, and allowa correlation between cores from different depths, by recognition of greigite in the sediments marking the marine transgression. � 2002 Elsevier Science Ltd. All rights reserved.

Variations in 14C Reservoir Ages of Black Sea Waters and Sedimentary Organic Carbon during Anoxic Periods: Influence of Photosynthetic Versus Chemoautotrophic Production

Radiocarbon activity of dissolved inorganic carbon has been measured in the northwestern Black Sea. Both continental shelf and open-sea profiles show that surface waters are in equilibrium with the atmosphere. The observed distribution of 14C activity shows a weak contribution of the deep 14C-depleted CO2 to the photic zone. Such a distribution of 14C within the water column is unable to explain the aging of sedimentary organic matter and reservoir ages greater than 500 yr. A contribution of production by chemoautotrophic bacteria feeding on 14C-depleted methane at the boundary of the oxic and anoxic zones is a realistic hypothesis. Also, a contribution to sedimentary organic carbon estimated at <15% of the photosynthetic primary production could explain 14C reservoir ages greater than 1300 yr.