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Evolution of the Sefidrud Delta (South West Caspian Sea) During the Last Millennia

Abstract

The Sefidrud River has developed a large delta in the south west of the Caspian Sea. This delta is characterized by very rapid sedimentation rates in a steep slope setting, which can be used as a model for oil-bearing reservoirs. The Caspian Sea Level (CSL) has undergone significant changes over time with major impacts on the surrounding coasts. During the last millennium, the CSL has experienced two major fluctuations, a low-stand during the Medieval Climate Anomaly (MCA: AD 950–1250) and a high-stand during the Little Ice Age (LIA: AD 1300–1850). This study aims 1) to explain the evolution of the Sefidrud delta in the last millennia and to propose a mechanism for delta building; and 2) to detect the impact of sea level changes on sedimentation by a multiproxy analysis in different wetlands and lagoons. For this purpose, the Sefidrud Delta has been investigated using a large number of short cores (up to 3 m) and long cores (up to 13 m) taken onland and ofshore. Also, Ground Penetrating Radar (GPR) transects were obtained onland and seismic profiles offshore. The interpretation of the results from both methods were checked by cores taken on the geophysical profiles. The objectives of geophysical studies was to image the internal structure of sediments and consequently, to reconstruct the history of delta development. In addition lagoons and wetlands at various distances form the coast were cored. This study confirms that the Caspian Sea experienced a high stand during LIA following a low-stand during MCA and CSL was 5 m above the present sea level. Although previous studies in the southern coast of the CS have detected a high-stand during the LIA period, it is the first time that this high-stand has been reconstructed so far in land in a sedimentary sequence and at such a high altitude. Beside this, the internal sediment distribution patterns in the lagoons and along river distributaries were obtained using the correlation of cores and development of different lagoons and their evolutions under different situation were discussed. The highly dynamic sedimentation in the delta has been confirmed by radiocarbon and radionuclide dating.