- Email: [email protected]
Biostratigraphy of the Caspian Pleistocene
546
Abstracts / Quaternary International 279-280 (2012) 462–565
dunes, located in the semi-arid zone of eastern Inner Mongolia, northern China) as example, we are studying the initiation and variations of the dune landscape in the eastern part of the desert belt in northern China. Our field work was carried out mainly along three N-S transects in this sandy land, ca. 21000 square kilometers in area. We are trying to decipher signals of environmental changes from aeolian sequences which are sometimes intercalated by lacustrine deposits and often by paleosols. On the basis of physical and chemical features of the sediments and OSL ages of aeolian sands (quartz and feldspar grains) and radiocarbon dates from paleosols and lacustrine deposits (organic carbon), we here argue that the dune system in the middle latitudes of eastern Asia is much younger than previously reported and it reacts sensitively to the climate changes during late Quaternary and to human impacts in more recent centenaries. The epochs of reworking or stabilization of the dunes are broadly consistent with the weakening or enhancement of the east Asian monsoons, demonstrating that dune systems are important repositories of information for understanding climate changes also. WARM-SEASON PRECIPITATION AS THE DOMINANT CONTROL ON C3/C4 PLANT VARIATIONS IN NORTHERN CHINA: EVIDENCE FROM CARBON AND OXYGEN ISOTOPE COMPOSITION OF PEDOGENIC CARBONATE Shiling Yang. Key Laboratory of Cenozoic Geology and Environment, China E-mail address: [email protected]
Plants use two principal biosynthetic pathways to fix carbon, the C3 and C4 cycles. C3 plants have d13C values ranging from -22& to -30&, and C4 plants from –10& to -14&. Generally, lower atmospheric pCO2, higher temperature and enhanced summer precipitation favor C4 over C3 plants. Evaluating how future climate changes may impact C3/C4 biomass in East Asia depends largely on the understanding of the relationship between past C3/C4 variations and monsoon circulation. Here we present isotopic results of soil carbonate from northern China, for the Holocene, the last and penultimate interglacial periods. Comparison of the observed and predicted d 18O values of modern soil carbonate suggests that pedogenic carbonate forms mainly in warm, rainy season. Carbonate nodules from Chinese loess all demonstrate a distinct negative d 18O- d 13C relationship, i.e. the lower d 18O values the higher C4 component, both spatially and temporally. d 18O of meteoric precipitation from summer monsoon domain exhibits a trough (low d 18O values) in rainy season. This trough damps inland with weakened monsoonal influence, and thus a distinctive characteristic of summer monsoon precipitation. In this context, the negative d 18O- d 13C relationship can be fully explained by the following mechanism: increased summer precipitation would have resulted in low d 18O values of soil water and simultaneously favored C4 over C3 plants. This mechanism promises a rapid increase in C4 biomass under projected increase in summer precipitation due to global warming. ORIGIN AND ENVIRONMENTAL IMPLICATIONS OF LOESS SEDIMENTS IN THE EASTERN TIBETAN PLATEAU Shengli Yang. Nanjing Normal University, China E-mail address: [email protected]
The loess-like sediments, widely preserved in the eastern Tibetan Plateau and its adjacent regions, have been regarded as a combined result of the uplift of the Tibetan Plateau and its related or coupled alterations of air circulation and climate environment. To reveal the formation and the timing of these deposits is of great importance to understand the impacts of the Tibetan uplift on climatic environmental changes. Geomorphic, sedimentologic/pedogenic, grain size distributions and quartz oxygen isotopic evidence collectively demonstrates the aeolian origin of these sediments and its main source area on the Tibetan Plateau. Detailed paleomagnetism dating demonstrates that the Ganzi loess has an oldest age of ca. 1.13 Ma, while that at Huagai (Sichuan Basin) has an age of ca. 0.8 Ma. The onset and climatic proxy records of these loess in the eastern Tibetan Plateau exhibit a similar drying trend toward the present and three remarkable drying event at w1.13 Ma, w0.8 Ma and w0.5 Ma. This suggests the establishment of a circulation system similar to the present one in conjunction with rapid uplift of the Tibetan Plateau at that time.
INVESTIGATION OF THE ULTRASTRUCTURAL CHARACTERISTICS OF FOXTAIL AND BROOMCORN MILLET DURING CARBONIZATION AND ITS APPLICATION IN ARCHAEOBOTANY Qing Yang. Institute of Earth Environment, Chinese Academy of, China E-mail address: [email protected]
Fossilized caryopses (or grains) of foxtail millet (Setaria italica) and broomcorn millet (Panicum miliaceum) are important archaeobotanical materials for the study of early human agricultural activities. The morphology and ultrastructural characteristics of carbonized modern millet caryopses treated in a drying oven and burning in a field were investigated at different temperatures to study how fossilized millets are formed. The caryopses shrank gradually at temperatures below 200 C, and starch granules in the endosperm retained their crystalline structure. At 250 C the foxtail millet caryopses expanded, whereas the broomcorn millet caryopses were greatly deformed. At this temperature, the structure of the starch granules of both millets became amorphous. At 300 C the caryopses partially turned to ash and became porous, and the ultrastructure of the starch granules was transformed into alveolate cavities. Fossil caryopses from the prehistoric storage cellar at the Beiniu Site retained their crystalline structure and were formed by the dehydrating effect of carbonization, indicating that water molecules were not involved in the starch crystallization. The results of a field burning experiment demonstrated that the ultrastructure of carbonized caryopses placed on the ground under the fire was amorphous. The amorphous ultrastructure of the carbonized caryopses recovered from the archaeological layers is consistent with the expected structure of caryopses that have been carbonized at 250 C. Therefore, we suggest that the recovered caryopses were formed at about 250 C by baking rather than by burning in an open fire. BIODIVERSITY OF THE CASPIAN SEA MOLLUSKS: NATURAL AND ANTHROPOGENIC IMPACT Tamara Yanina. Moscow State University, Russian Federation E-mail address: [email protected]
The modern biodiversity of the Caspian Sea simply reflects a complicated history of paleo-Caspian transgressions and regressions, desalinisation and salinization and, recently, human activity. The Caspian history during the last 10 ky includes the end of the Late Khvalynian transgression, Mangyshlak regression and several stages of the New Caspian transgression. The Late Khvalynian basin emerged 11-9 thousand years ago under climate conditions, which were more humid and colder than the present one. The maximum level of the Late Khvalynian transgression was close to the 0 m. The Mangyshlak basin formed about 9-8 thousand years ago. It emerged in the period of postglacial warming and climate aridity. Its waters used to cover only depressions of the Middle and Southern Caspian. The level of Mangyshlak Lake was – 80 m. The New Caspian transgression maximum emerged approximately 5-6 thousand years ago. The sea level was -19 – -20 m. In the 20th century it has been fluctuating within the range of almost four meters, approximately from -25 m in the beginning of the century to -29 m in 1977. In the end of the 20th century, the sea level soared, and in the beginning of the 21st century began to drop again. The influence of the Caspian Sea level change on the mollusk biodiversity we trace on two different areas: Turali (Dagestan, Middle Caspian) and Volga Delta (Northern Caspian). The modern Caspian ecosystem is the result of the long-term biological evolution. For a long time, all levels of biodiversity formed and interacted naturally without human influence. The development of the human civilization resulted in strong anthropogenic impact, which interferes with the natural course of events. The humankind has become a powerful external factor destabilizing the processes of the Caspian ecosystem. BIOSTRATIGRAPHY OF THE CASPIAN PLEISTOCENE Tamara Yanina. Moscow State University, Russian Federation E-mail address: [email protected]
Stratification of marine Pleistocene deposits is based on the vertical succession of fossil molluscan assemblages mainly belonging to Didacna Eichwald genus. N.I.Andrusov was the first to apply this approach at the
Abstracts / Quaternary International 279-280 (2012) 462–565
547
beginning of this century. His investigations were continued by others scientists. Exact classification of the Caspian deposits was realizes. But the existent geological bodies are determined as different grades, diverse stratigraphical and nomenclature position in the scales of different investigators. We work out the groups of Didacna molluscs with diverse taxonomic composition and grade: fauna, assemblage, subassemblage, association, which correspond to paleogeographical events of diverse grade (transgression, stage of transgression, phase, etc). They form a kind of a «framework» for biostratigraphical subdivision of the Neopleistocene marine deposits in the Caspian Sea Region. The highest rank in the regional Neopleistocene stratigraphic scale of the area is represented by the Caspian group corresponding to the biozone of Didacna Eichward genus. This zone covers the whole Neopleistocene (0.780 mln yrs). By Didacna groups several horizons, subhorizons and layers are distinguished in the Caspian Neopleistocene. Thus, the Baku, Urundzhik, Lower Khazarian, Upper Khazarian, Khvalinian and New Caspian horizons are distinguished on the base of different Didacna faunas (subzones). The assemblages of mollusks (interval-zones) serve as the basis for subdivision of the horizons into the subhorizons. More detailed subdivision of the Caspian Neopleistocene into layers is based on the succession of fossil Didacna subassemblages. The index-fossils are defined for horizons and subhorisons. The stratotypical sections are distinguished for all biostratigraphic units. The mollusks associations reflect the diversity of palaeohydrological and palaeoecological conditions of Caspian basins, they demonstrate facial manifoldness of horizons, subhorizons and layers.
processes. Additional processes considered include the effects of orographic precipitation, partial degree day mass balance, snow avalanching, basal ice super-freezing, and a basal water buoyancy feedback in large overdeepenings. The effects of climate on landscape denudation are explored by varying the temperature at the lowest elevation of each simulation from -4oC to 15oC during glacial periods. Each climate scenario maintains a 6oC amplitude in temperature variation over a period of either 100 or 40 ky. Rock-uplift rate is varied between 0.4 and 2.5 mm/yr. We generate a steady-state landscape with fluvial and hillslope processes. Next, we allow glaciers to grow and track erosion rates for 4 million years following the onset of glaciation. Results indicate that an increase or decrease in denudation rates relative to preglacial rates depends on the local sea-level climate as well as the initial topographic relief, which is set by the tectonic rate of rock-uplift and erosional parameters. The model also predicts large temporal variation and pulses in glacial denudation over various timescales. We discuss these predictions in the context of natural glaciated landscapes located at various latitudes. The results of the model are consistent with measurements of long-term erosional histories constrained with thermochronology and resolves discrepancies between spatial and temporal denudation histories in glaciated landscapes across the world.
EVOLUTION OF THE VOLGA RIVER DELTA DURING HOLOCENE
Valentina Yanko-Hombach. Odessa I.I. Mechnikov National University, Ukraine
Tamara Yanina. Moscow State University, Russian Federation
E-mail address: [email protected]
E-mail address: [email protected]
During the maximum Late Khvalynian sea-level highstand the river discharge was restricted to the two main branches – the modern Volga River valley and Sarpinsko-Davanskaya depression. Distinct fan-shaped groups of hollows oriented towards the sea evidence former location of the Caspian shoreline. They do not reach the modern shoreline and either end in the dry limans or flatten out. These are “incised” deltas formed under abrupt sea-level fall. During the Mangyshlak regression the Caspian Sea level decreased down to –70 m, and the Volga River delta was located in the latitude of the Agrakhan spit. Two wide channels were formed in the central and eastern parts of the Volga-Akhtuba valley which served as pathways for river discharge. Delta sediment sequence gives evidence for several stages in its formation during the New Caspian epoch. The Caspian sea-level fall interrupted by episodic rises up to -23 - -24 m reached -29 m by 1977. The above- and underwater parts of the delta were filled with riverine sediments, thus causing considerable seaward advance of the delta. The northern part of submarine delta became exposed and turned into a low insular floodplain, while its frontal part, the avandelta, occupied the shallow Northern Caspian shelf. During the period between 1918 and 1980 the delta front penetrated seaward by 10-50 km, and the number of big branches decreased from 320 to 260. During certain periods (19271939) the rate of delta advance reached 1 km per year. On the exposed patches grasslands replaced hydrophite vegetation, and accumulation of specific organogenic deposits of avandelta terminated. Since the onset of the new Caspian sea-level rise in 1978 (up to -27.5 m by the end of 1992) no evident changes in the natural processes within the delta have been observed. These processes are undoubtedly latent, and their manifestation is simply the matter of time. GLOBAL CLIMATE CONTROLS ON THE DENUDATION OF GLACIATED MOUNTAIN Brian Yanites. University of Michigan, United States
LARGE SCALE GEOLOGICAL SURVEY OF THE NW BLACK SEA SHELF AND CONTINENTAL SLOPE DENIES RAPID TRANSGRESSION OF THE BASIN IN THE EARLY HOLOCENE
Based on seven low-resolution cores about 1.25 m long and 350 km of seismic profiles collected within a fairly restricted area of the Black Sea's NW shelf during a single mission in 1993, Ryan et al. (1997) proposed that the freshwater Neoeuxinian Lake (the Black Sea's lacustrine phase) was rapidly and catastrophically flooded by Mediterranean seawater at 7.2 ka BP. This flooding impacted early society in coastal areas, formed the basis for Great Flood legends, and accelerated the spread of agriculture into Europe. This hypothesis was supported by some but sharply criticized by many. Ryan et al. (2003) then pushed the date of the flooding back to 8.4 ka BP, and instead of a single inundation, two lowstands (–120 m at 13.4–11.0 ka BP; and –95 m at 10.0–8.4 ka BP) and two rapid floods (sea-level rise from –120 to –30 m at 11.0–10.0 ka BP; and from –95 to –30 m at 8.4 ka BP) were proposed. Since the early 80s, a large-scale (1:200,000, and in certain areas 1:50,000) geological survey of the NW Black Sea shelf and continental slope has been carried out to prepare the sea bottom for industrial exploration. This survey has led to a massive database (described in many publications and summarised in Yanko-Hombach et al. 2007) that has enabled us to reconstruct (1) the salinity of the Neoeuxinian Lake, which was brackish, not freshwater, and (2) the level of the Neoeuxinian Lake, which was neither –120 mbsl nor –95 mbsl, but instead was –37 and –20 mbsl, respectively, meaning that the amplitude and rapidity of sea-level rise could not have been as great as was originally proposed by Ryan et al. Exposed shelf along the coastline was mostly swampy and prone to salinisation, not favourable for arboriculture, agriculture, or animal husbandry, as is evident from geologic, archaeological, and palynological evidence. We also intend to show that comparative analysis of 14C dates obtained by the “Bulk” and AMS methods for the interval in question shows their similarity. AN OVERVIEW OF THE IGCP 521-INQUA 501 PROJECT “CASPIAN-BLACK SEA-MEDITERRANEAN CORRIDOR DURING THE LAST 30 KY: SEA LEVEL CHANGE AND HUMAN ADAPTIVE STRATEGIES”
E-mail address: [email protected]
Late Cenozoic cooling produced repeated glacial and periglacial conditions in previously ice-free landscapes. Such changes are hypothesized to increase denudation and limit mountain elevations. We test this hypothesis by exploring a range of climatic and tectonic scenarios in a landscape evolution model to compare pre- and post-glacial denudation rates. Specifically, we use an orogen-scale coupled precipitation and landscape evolution model that incorporates fluvial, hillslopes, and glacial
Valentina Yanko-Hombach. Odessa I.I. Mechnikov National University, Ukraine E-mail address: [email protected]
IGCP 521-INQUA 501 began in April 2005 to correlate scientific data obtained by diverse research projects dealing with climate change, sea-level fluctuations, coastline migration, and human adaptation within the Caspian-Black Sea-Mediterranean Corridor. Lately, this region has been the
Abstracts / Quaternary International 279-280 (2012) 462–565
dunes, located in the semi-arid zone of eastern Inner Mongolia, northern China) as example, we are studying the initiation and variations of the dune landscape in the eastern part of the desert belt in northern China. Our field work was carried out mainly along three N-S transects in this sandy land, ca. 21000 square kilometers in area. We are trying to decipher signals of environmental changes from aeolian sequences which are sometimes intercalated by lacustrine deposits and often by paleosols. On the basis of physical and chemical features of the sediments and OSL ages of aeolian sands (quartz and feldspar grains) and radiocarbon dates from paleosols and lacustrine deposits (organic carbon), we here argue that the dune system in the middle latitudes of eastern Asia is much younger than previously reported and it reacts sensitively to the climate changes during late Quaternary and to human impacts in more recent centenaries. The epochs of reworking or stabilization of the dunes are broadly consistent with the weakening or enhancement of the east Asian monsoons, demonstrating that dune systems are important repositories of information for understanding climate changes also. WARM-SEASON PRECIPITATION AS THE DOMINANT CONTROL ON C3/C4 PLANT VARIATIONS IN NORTHERN CHINA: EVIDENCE FROM CARBON AND OXYGEN ISOTOPE COMPOSITION OF PEDOGENIC CARBONATE Shiling Yang. Key Laboratory of Cenozoic Geology and Environment, China E-mail address: [email protected]
Plants use two principal biosynthetic pathways to fix carbon, the C3 and C4 cycles. C3 plants have d13C values ranging from -22& to -30&, and C4 plants from –10& to -14&. Generally, lower atmospheric pCO2, higher temperature and enhanced summer precipitation favor C4 over C3 plants. Evaluating how future climate changes may impact C3/C4 biomass in East Asia depends largely on the understanding of the relationship between past C3/C4 variations and monsoon circulation. Here we present isotopic results of soil carbonate from northern China, for the Holocene, the last and penultimate interglacial periods. Comparison of the observed and predicted d 18O values of modern soil carbonate suggests that pedogenic carbonate forms mainly in warm, rainy season. Carbonate nodules from Chinese loess all demonstrate a distinct negative d 18O- d 13C relationship, i.e. the lower d 18O values the higher C4 component, both spatially and temporally. d 18O of meteoric precipitation from summer monsoon domain exhibits a trough (low d 18O values) in rainy season. This trough damps inland with weakened monsoonal influence, and thus a distinctive characteristic of summer monsoon precipitation. In this context, the negative d 18O- d 13C relationship can be fully explained by the following mechanism: increased summer precipitation would have resulted in low d 18O values of soil water and simultaneously favored C4 over C3 plants. This mechanism promises a rapid increase in C4 biomass under projected increase in summer precipitation due to global warming. ORIGIN AND ENVIRONMENTAL IMPLICATIONS OF LOESS SEDIMENTS IN THE EASTERN TIBETAN PLATEAU Shengli Yang. Nanjing Normal University, China E-mail address: [email protected]
The loess-like sediments, widely preserved in the eastern Tibetan Plateau and its adjacent regions, have been regarded as a combined result of the uplift of the Tibetan Plateau and its related or coupled alterations of air circulation and climate environment. To reveal the formation and the timing of these deposits is of great importance to understand the impacts of the Tibetan uplift on climatic environmental changes. Geomorphic, sedimentologic/pedogenic, grain size distributions and quartz oxygen isotopic evidence collectively demonstrates the aeolian origin of these sediments and its main source area on the Tibetan Plateau. Detailed paleomagnetism dating demonstrates that the Ganzi loess has an oldest age of ca. 1.13 Ma, while that at Huagai (Sichuan Basin) has an age of ca. 0.8 Ma. The onset and climatic proxy records of these loess in the eastern Tibetan Plateau exhibit a similar drying trend toward the present and three remarkable drying event at w1.13 Ma, w0.8 Ma and w0.5 Ma. This suggests the establishment of a circulation system similar to the present one in conjunction with rapid uplift of the Tibetan Plateau at that time.
INVESTIGATION OF THE ULTRASTRUCTURAL CHARACTERISTICS OF FOXTAIL AND BROOMCORN MILLET DURING CARBONIZATION AND ITS APPLICATION IN ARCHAEOBOTANY Qing Yang. Institute of Earth Environment, Chinese Academy of, China E-mail address: [email protected]
Fossilized caryopses (or grains) of foxtail millet (Setaria italica) and broomcorn millet (Panicum miliaceum) are important archaeobotanical materials for the study of early human agricultural activities. The morphology and ultrastructural characteristics of carbonized modern millet caryopses treated in a drying oven and burning in a field were investigated at different temperatures to study how fossilized millets are formed. The caryopses shrank gradually at temperatures below 200 C, and starch granules in the endosperm retained their crystalline structure. At 250 C the foxtail millet caryopses expanded, whereas the broomcorn millet caryopses were greatly deformed. At this temperature, the structure of the starch granules of both millets became amorphous. At 300 C the caryopses partially turned to ash and became porous, and the ultrastructure of the starch granules was transformed into alveolate cavities. Fossil caryopses from the prehistoric storage cellar at the Beiniu Site retained their crystalline structure and were formed by the dehydrating effect of carbonization, indicating that water molecules were not involved in the starch crystallization. The results of a field burning experiment demonstrated that the ultrastructure of carbonized caryopses placed on the ground under the fire was amorphous. The amorphous ultrastructure of the carbonized caryopses recovered from the archaeological layers is consistent with the expected structure of caryopses that have been carbonized at 250 C. Therefore, we suggest that the recovered caryopses were formed at about 250 C by baking rather than by burning in an open fire. BIODIVERSITY OF THE CASPIAN SEA MOLLUSKS: NATURAL AND ANTHROPOGENIC IMPACT Tamara Yanina. Moscow State University, Russian Federation E-mail address: [email protected]
The modern biodiversity of the Caspian Sea simply reflects a complicated history of paleo-Caspian transgressions and regressions, desalinisation and salinization and, recently, human activity. The Caspian history during the last 10 ky includes the end of the Late Khvalynian transgression, Mangyshlak regression and several stages of the New Caspian transgression. The Late Khvalynian basin emerged 11-9 thousand years ago under climate conditions, which were more humid and colder than the present one. The maximum level of the Late Khvalynian transgression was close to the 0 m. The Mangyshlak basin formed about 9-8 thousand years ago. It emerged in the period of postglacial warming and climate aridity. Its waters used to cover only depressions of the Middle and Southern Caspian. The level of Mangyshlak Lake was – 80 m. The New Caspian transgression maximum emerged approximately 5-6 thousand years ago. The sea level was -19 – -20 m. In the 20th century it has been fluctuating within the range of almost four meters, approximately from -25 m in the beginning of the century to -29 m in 1977. In the end of the 20th century, the sea level soared, and in the beginning of the 21st century began to drop again. The influence of the Caspian Sea level change on the mollusk biodiversity we trace on two different areas: Turali (Dagestan, Middle Caspian) and Volga Delta (Northern Caspian). The modern Caspian ecosystem is the result of the long-term biological evolution. For a long time, all levels of biodiversity formed and interacted naturally without human influence. The development of the human civilization resulted in strong anthropogenic impact, which interferes with the natural course of events. The humankind has become a powerful external factor destabilizing the processes of the Caspian ecosystem. BIOSTRATIGRAPHY OF THE CASPIAN PLEISTOCENE Tamara Yanina. Moscow State University, Russian Federation E-mail address: [email protected]
Stratification of marine Pleistocene deposits is based on the vertical succession of fossil molluscan assemblages mainly belonging to Didacna Eichwald genus. N.I.Andrusov was the first to apply this approach at the
Abstracts / Quaternary International 279-280 (2012) 462–565
547
beginning of this century. His investigations were continued by others scientists. Exact classification of the Caspian deposits was realizes. But the existent geological bodies are determined as different grades, diverse stratigraphical and nomenclature position in the scales of different investigators. We work out the groups of Didacna molluscs with diverse taxonomic composition and grade: fauna, assemblage, subassemblage, association, which correspond to paleogeographical events of diverse grade (transgression, stage of transgression, phase, etc). They form a kind of a «framework» for biostratigraphical subdivision of the Neopleistocene marine deposits in the Caspian Sea Region. The highest rank in the regional Neopleistocene stratigraphic scale of the area is represented by the Caspian group corresponding to the biozone of Didacna Eichward genus. This zone covers the whole Neopleistocene (0.780 mln yrs). By Didacna groups several horizons, subhorizons and layers are distinguished in the Caspian Neopleistocene. Thus, the Baku, Urundzhik, Lower Khazarian, Upper Khazarian, Khvalinian and New Caspian horizons are distinguished on the base of different Didacna faunas (subzones). The assemblages of mollusks (interval-zones) serve as the basis for subdivision of the horizons into the subhorizons. More detailed subdivision of the Caspian Neopleistocene into layers is based on the succession of fossil Didacna subassemblages. The index-fossils are defined for horizons and subhorisons. The stratotypical sections are distinguished for all biostratigraphic units. The mollusks associations reflect the diversity of palaeohydrological and palaeoecological conditions of Caspian basins, they demonstrate facial manifoldness of horizons, subhorizons and layers.
processes. Additional processes considered include the effects of orographic precipitation, partial degree day mass balance, snow avalanching, basal ice super-freezing, and a basal water buoyancy feedback in large overdeepenings. The effects of climate on landscape denudation are explored by varying the temperature at the lowest elevation of each simulation from -4oC to 15oC during glacial periods. Each climate scenario maintains a 6oC amplitude in temperature variation over a period of either 100 or 40 ky. Rock-uplift rate is varied between 0.4 and 2.5 mm/yr. We generate a steady-state landscape with fluvial and hillslope processes. Next, we allow glaciers to grow and track erosion rates for 4 million years following the onset of glaciation. Results indicate that an increase or decrease in denudation rates relative to preglacial rates depends on the local sea-level climate as well as the initial topographic relief, which is set by the tectonic rate of rock-uplift and erosional parameters. The model also predicts large temporal variation and pulses in glacial denudation over various timescales. We discuss these predictions in the context of natural glaciated landscapes located at various latitudes. The results of the model are consistent with measurements of long-term erosional histories constrained with thermochronology and resolves discrepancies between spatial and temporal denudation histories in glaciated landscapes across the world.
EVOLUTION OF THE VOLGA RIVER DELTA DURING HOLOCENE
Valentina Yanko-Hombach. Odessa I.I. Mechnikov National University, Ukraine
Tamara Yanina. Moscow State University, Russian Federation
E-mail address: [email protected]
E-mail address: [email protected]
During the maximum Late Khvalynian sea-level highstand the river discharge was restricted to the two main branches – the modern Volga River valley and Sarpinsko-Davanskaya depression. Distinct fan-shaped groups of hollows oriented towards the sea evidence former location of the Caspian shoreline. They do not reach the modern shoreline and either end in the dry limans or flatten out. These are “incised” deltas formed under abrupt sea-level fall. During the Mangyshlak regression the Caspian Sea level decreased down to –70 m, and the Volga River delta was located in the latitude of the Agrakhan spit. Two wide channels were formed in the central and eastern parts of the Volga-Akhtuba valley which served as pathways for river discharge. Delta sediment sequence gives evidence for several stages in its formation during the New Caspian epoch. The Caspian sea-level fall interrupted by episodic rises up to -23 - -24 m reached -29 m by 1977. The above- and underwater parts of the delta were filled with riverine sediments, thus causing considerable seaward advance of the delta. The northern part of submarine delta became exposed and turned into a low insular floodplain, while its frontal part, the avandelta, occupied the shallow Northern Caspian shelf. During the period between 1918 and 1980 the delta front penetrated seaward by 10-50 km, and the number of big branches decreased from 320 to 260. During certain periods (19271939) the rate of delta advance reached 1 km per year. On the exposed patches grasslands replaced hydrophite vegetation, and accumulation of specific organogenic deposits of avandelta terminated. Since the onset of the new Caspian sea-level rise in 1978 (up to -27.5 m by the end of 1992) no evident changes in the natural processes within the delta have been observed. These processes are undoubtedly latent, and their manifestation is simply the matter of time. GLOBAL CLIMATE CONTROLS ON THE DENUDATION OF GLACIATED MOUNTAIN Brian Yanites. University of Michigan, United States
LARGE SCALE GEOLOGICAL SURVEY OF THE NW BLACK SEA SHELF AND CONTINENTAL SLOPE DENIES RAPID TRANSGRESSION OF THE BASIN IN THE EARLY HOLOCENE
Based on seven low-resolution cores about 1.25 m long and 350 km of seismic profiles collected within a fairly restricted area of the Black Sea's NW shelf during a single mission in 1993, Ryan et al. (1997) proposed that the freshwater Neoeuxinian Lake (the Black Sea's lacustrine phase) was rapidly and catastrophically flooded by Mediterranean seawater at 7.2 ka BP. This flooding impacted early society in coastal areas, formed the basis for Great Flood legends, and accelerated the spread of agriculture into Europe. This hypothesis was supported by some but sharply criticized by many. Ryan et al. (2003) then pushed the date of the flooding back to 8.4 ka BP, and instead of a single inundation, two lowstands (–120 m at 13.4–11.0 ka BP; and –95 m at 10.0–8.4 ka BP) and two rapid floods (sea-level rise from –120 to –30 m at 11.0–10.0 ka BP; and from –95 to –30 m at 8.4 ka BP) were proposed. Since the early 80s, a large-scale (1:200,000, and in certain areas 1:50,000) geological survey of the NW Black Sea shelf and continental slope has been carried out to prepare the sea bottom for industrial exploration. This survey has led to a massive database (described in many publications and summarised in Yanko-Hombach et al. 2007) that has enabled us to reconstruct (1) the salinity of the Neoeuxinian Lake, which was brackish, not freshwater, and (2) the level of the Neoeuxinian Lake, which was neither –120 mbsl nor –95 mbsl, but instead was –37 and –20 mbsl, respectively, meaning that the amplitude and rapidity of sea-level rise could not have been as great as was originally proposed by Ryan et al. Exposed shelf along the coastline was mostly swampy and prone to salinisation, not favourable for arboriculture, agriculture, or animal husbandry, as is evident from geologic, archaeological, and palynological evidence. We also intend to show that comparative analysis of 14C dates obtained by the “Bulk” and AMS methods for the interval in question shows their similarity. AN OVERVIEW OF THE IGCP 521-INQUA 501 PROJECT “CASPIAN-BLACK SEA-MEDITERRANEAN CORRIDOR DURING THE LAST 30 KY: SEA LEVEL CHANGE AND HUMAN ADAPTIVE STRATEGIES”
E-mail address: [email protected]
Late Cenozoic cooling produced repeated glacial and periglacial conditions in previously ice-free landscapes. Such changes are hypothesized to increase denudation and limit mountain elevations. We test this hypothesis by exploring a range of climatic and tectonic scenarios in a landscape evolution model to compare pre- and post-glacial denudation rates. Specifically, we use an orogen-scale coupled precipitation and landscape evolution model that incorporates fluvial, hillslopes, and glacial
Valentina Yanko-Hombach. Odessa I.I. Mechnikov National University, Ukraine E-mail address: [email protected]
IGCP 521-INQUA 501 began in April 2005 to correlate scientific data obtained by diverse research projects dealing with climate change, sea-level fluctuations, coastline migration, and human adaptation within the Caspian-Black Sea-Mediterranean Corridor. Lately, this region has been the