The Ponto-Caspian basin as a final trap for southeastern Scandinavian Ice-Sheet meltwater

This paper provides new data on the evolution of the Caspian Sea and Black Sea from the Last Glacial Maximum until ca. 12 cal kyr BP. We present new analyses (clay mineralogy, grain-size, Nd isotopes and pollen) applied to sediments from the river terraces in the lower Volga, from the middle Caspian Sea and from the western part of the Black Sea. The results show that during the last deglaciation, the Ponto-Caspian basin collected meltwater and fine-grained sediment from the southern margin of the Scandinavian Ice Sheet (SIS) via the Dniepr and Volga Rivers. It induced the deposition of characteristic red-brownish/chocolate-coloured illite-rich sediments (Red Layers in the Black Sea and Chocolate Clays in the Caspian Sea) that originated from the Baltic Shield area according to Nd data. This general evolution, common to both seas was nevertheless differentiated over time due to the specificities of their catchment areas and due to the movement of the southern margin of the SIS. Our results indicate that in the eastern part of the East European Plain, the meltwater from the SIS margin supplied the Caspian Sea during the deglaciation until ∼13.8 cal kyr BP, and possibly from the LGM. That led to the Early Khvalynian transgressive stage(s) and Chocolate Clays deposition in the now-emerged northern flat part of the Caspian Sea (river terraces in the modern lower Volga) and in its middle basin. In the western part of the East European Plain, our results confirm the release of meltwater from the SIS margin into the Black Sea that occurred between 17.2 and 15.7 cal kyr BP, as previously proposed. Indeed, recent findings concerning the evolution of the southern margin of the SIS and the Black Sea, show that during the last deglaciation, occurred a westward release of meltwater into the North Atlantic (between ca. 20 and 16.7 cal kyr BP), and a southward one into the Black Sea (between 17.2 and 15.7 cal kyr BP). After the Red Layers/Chocolate Clays deposition in both seas and until 12 cal kyr BP, smectite became the dominant clay mineral. The East European Plain is clearly identified as the source for smectite in the Caspian Sea sediments. In the Black Sea, smectite originated either from the East European Plain or from the Danube River catchment. Previous studies consider smectite as being only of Anatolian origin. However, our results highlight both, the European source for smectite and the impact of this source on the depositional environment of the Black Sea during considered period

The evolution of the Caspian Sea over the last 20,000 years: mineralogical data

International audienc

30,000 Years of the southwestern Lake Urmia (Iran) paleoenvironmental evolution inferred from mineralogical indicators from lake and watershed sediments

International audienceIn order to understand the pattern and trends of the environmental evolution of Lake Urmia (Iran), one of the largest terminal lakes in Western Asia before its level drop over the past two decades, two sediment cores (Golman 6, 8.0 m; Golman 7, 12.5 m) were collected from the recently dried-out southwestern part of the lake. These sediment cores represent a continuous sedimentary sequence, composite core, that was extensively studied for grain size, total mineralogy including clay minerals, carbonates and their crystallinities, in comparison with the basin geological formations and within a reliable AMS-14C timescale. Lake Urmia deposits cover the time-span from 30 to ca 2 cal kyr BP. Grain-size of the siliclastic fractions from the lower part of the composite core consists of fine-silt and clay particles likely representing lacustrine deposits while the top sediments are characterized by variable composition of sand and silt. At about 30 cal kyr BP, our proxies indicate a low lake stand and even drying out at the coring site, which was followed by water level rise and the establishment of lacustrine conditions between 29.9 and 20.2 cal kyr BP. Since then, all our data suggest lake's highly unstable conditions. Subsequently, clearly low lake levels to sometimes the drying out was recorded during the 20.2-15.3 cal kyr BP, 13.3-11.8 cal kyr BP and 5.6-4.1 cal kyr BP intervals. In contrast, lacustrine conditions were re-established between 15.3 and 13.3 cal kyr BP, between 11.8 and 5.6 cal kyr BP and between 4 0.1 and 2.3 cal kyr BP. High water level recorded between 15.3 and 13.3 cal kyr BP can be attributed to the Bölling/Alleröd warming, and the following regressive phase during the 13.3-11.8 cal kyr BP period corresponds to the Younger Dryas period. In the Early-Mid Holocene, the lacustrine environment from 11.8 to 5.6 cal kyr BP was characterized by high aragonite and salt contents, highlighting evaporative environment as like during the 29.9-20.2 cal kyr BP period. Our results allowed the Late Quaternary climate reconstruction at Lake Urmia basin scale and record the past climate change at a larger Western Asia scale

Sediment flux and early diagenesis inferred from high-resolution XRF-CS data and iron and arsenic sulfides during the last 30 kyr in Lake Urmia, Iran: Implications for studies of hypersaline lakes

International audienceWe analyzed by high resolution X-ray fluorescence core scanning (XRF-CS) the elemental composition of a 12.5 m long composite sediment core extracted from the hypersaline Lake Urmia (NW Iran). The main objective of the study was to reconstruct on a high temporal scale, the changes in sediment origin/inflow and water levels of Lake Urmia over the last 30,000 years. Combined with previously obtained results on 14C accelerated mass spectrometry (AMS) chronology, grain size and distribution of major minerals, albeit with a much lower temporal resolution than the XRF-CS data, this multi-proxy approach allowed recognition of specific hydrological changes and associated sedimentary processes in the Lake Urmia basin, including physical and chemical weathering, depositional fluxes and carbonate crystallization processes in lake water, and early diagenesis in anoxic bottom sediments. The high natural logarithm ratios (ln-ratios) of K/Ti, Ca/Ti and Sr/Ca, and low ln-ratios of Rb/Sr reveal increasing chemical weathering in the catchment area in conjunction with increasing authigenic carbonate precipitation in the lake. These findings reflect wet conditions, high lake levels and less saline water during the following intervals (i) 29.8-20.2, (ii) 15.2-13.3, (iii) 11.8-5.6 and (iv) 4.1-2.3 cal kBP.. In contrast, the increasing ln-ratios of Rb/Sr associated with decreasing ln-ratios of K/Ti, Ca/Ti and Sr/Ca indicate enhanced erosion in the catchment area linked to drier conditions, lower lake levels and more saline conditions predominating at around 30-29.8 cal kBP, 20.2-15.2, 13.3-11.8, and 5.6-4.1 cal kBP.. Based on the As-XRF-CS pattern and magnetic parameters we identified iron and naturally-occurring arsenic sulfides rarely reported from saline lakes, acting as specific indicators of anoxic conditions in the lake bottom environment. Moreover, XRF-CS data revealed short-lived periods with increasing chemical weathering in the catchment area at (i) 28.6-28.3, (ii) 27.3-27.1, (iii) 4.1-3.6 and (iv) 3.4-3.3 cal kBP, as well as increasing erosion at (i) 27.0-26.8, (ii) 26.3-26.0, (iii) 25.6-25.3 and (iv) 24.6-24.4 cal kBP.. Overall, this study confirms the previously reported findings concerning the sediments of Lake Urmia as well as completing these, both by providing more details on the environment for the periods already identified and by highlighting events of short duration. In particular, the results reported here permit better definition of the processes of chemical weathering versus erosion in the catchment area, and of the oxygenation levels of the lake bottom. The close correlation of these long- and short-term changes with the North Atlantic climate system clearly indicates that the Lake Urmia area has been affected mainly by this system during the last 30 cal kBP. Over and above their value with regard to Lake Urmia, these new data fill an important gap in eastern Mediterranean/western Asia paleoclimate records as a whole, providing unique and continuous 30 cal kBP information on the possible driving mechanisms of the observed changes. These can be compared to existing data on paleoenvironmental and climatic changes on regional and global scales and can also be used in global circulation models

Late Quaternary environmental changes of Lake Urmia basin (NW Iran) inferred from sedimentological and magnetic records.

International audienceThe ongoing changes affecting Lake Urmia (NW Iran) are revealed by the lake water level decrease (~7 m in the last 20 yr) that was attributed to natural and anthropogenic causes but the exact impact of these factors on the state of the lake is still not identified. Indeed, lack of detailed record of environmental evolution of the lake in the past limits the understanding of actual and future processes. Our project aims to obtain a high-temporal resolution record of environmental changes in the lake area for the last ~30 kyrs. Sediment cores have been obtained from the recently dried out part of the lake near Urmia City, and surface and ground waters have been measured for electric conductivity. This paper presents results of water and sediments analyses. Six 14 C AMS dating on organic fractions provide a chronological framework and indicate that the record covers the last ~30 cal kyr BP. During this period, evaporitic conditions were prevailing in the lake. The electric conductivity of brines from the sediment highlights changes in the lake water salinity. The data indicate a lake-level low stand at ~30 cal kyr BP that was followed by a water level rise and establishment of lacustrine conditions for the next ~9 kyr, this phase representing the highest lake level recorded since that time to date. From the LGM, the lake experienced several fluctuations of the water level. The relatively long-term lacustrine condition established during the Early Holocene before the water level decrease between ~5.5-4.9 cal kyr BP. Sediments from the two dry events at ~30 cal kyr BP and at 5.5-4.9 cal kyr BP are characterized by the presence of greigite, which indicates anaerobic early diagenetic conditions in the sediment