Seminar

A vast shallow epicontinental sea extended across Eurasia during the Cretaceous and Palaeogene from Europe to central Asia, before it retreated westward and became isolated as the Paratethys Sea. Stratigraphic assemblage showed that the last transgression and retreat cycle occurred in the late Eocene. To date, very limited evidence, for instance, planktonic foraminifer found in the MR section (SE Tarim Basin) and marine-pattern long-chain alkenones (LCAs) detected in the DHG section (NE Qaidam Baisn) in Miocene strata, suggests a possible Miocene seawater incursion, but is highly debated. It is inferred that during the Mid-Miocene the Altun Shan at the northern margin of the Tibetan Plateau was topographically subdued and that the SE Tarim Basin and Qaidam Basin was close to sea level during the Mid-Miocene. To further address this, 181 mudstone samples (~5-18Ma) were collected from KC-1 well in the Qaidam Basin, and biomarkers including n-alkanes, C37 and C38 saturated ketones, β-carotane and gammacerane were analyzed by using GC and GC-MS in this study. Preliminary results indeed suggest a likely seawater incursion that occurred during the Mid-Miocene Climate Optimum (MMCO), perhaps linked to the global sea level rise.