Isotopic Composition of Biogenic Carbonates and Holocene Paleogeographic Reconstructions of the Western Caspian Seashore

摘要

The Caspian Sea is remarkable for multiple strong sea level fluctuations during its geological history. Alternating transgressions and regressions stimulated the formation of several different-aged marine terraces along the coast that reflect the geomorphological development of the sea. The New Caspian transgression, which began approximately 10 ka ago and reached the level of-20 to -22 m, was the latest large transgression. Reconstruction of paleogeographic conditions is needed for adequate interpretation of the nature of Caspian Sea level fluctuations. We attempted to reconstruct one of the stages in the New Caspian transgression based on the study of stable oxygen and hydrogen isotopes, as well as some metals in shells of bivalve mol-lusks. The study of samples collected from growth layers of shells revealed seasonal dynamics of their isoto-pic and chemical compositions. We were also able to calculate seawater temperature and salinity for the studied period. No such studies were ever performed for the Caspian coast.