Magnetostratigraphic dating and paleoenvironmental assesment of the major sea level variations in the Early Pleistocene of the South Caspian Basin.

The Early Pleistocene development of the Pontocaspian region is strongly depended on climatic oscillations, which are characterised by alternations of glacial and interglacial intervals. These regular alternations are expressed as changes in a water budget of basins, which in turn resulted in fluctuations of the Black Sea and the Caspian Sea water level and connection/disconnection between them. This is registered in the outcrop, and our best option to understand past paleoenvironmental changes. For the Caspian Sea, the most representative record is provided by marginal basins like the Kura Basin in Azerbaijan. At the same time, strong tectonic activity along the Caucasian orogeny system caused regional landscape restructuring and acts as another active control on depositional environments. As a result, it creates preconditions for diachroneity of regional transgression/regression events, which together with fauna content define the boundaries of regional stages. To identify synchronous base level changes, we conducted paleomagnetic research on two continuous sections – Hajigabul and Goychay, that cover time intervals 2.7 – 0.5 Ma and 2.5 – 1.2 Ma respectively (Akchagylian, Apsheronian and Bakunian regional stages). These sections are situated in the northern, north-eastern interior of the Kura Basin (Azerbaijan) and represent a wide range of coastal environments. At the Goychay section, 142 levels are drilled in around 2000 m section, of which 78 samples are thermally demagnetized. In the Hajigabul section, we sampled 197 levels within 2000 m section thickness, among which 140 samples are thermally demagnetized. Our primary magnetostratigraphic results supported by facies analysis and observations on mollusks suggest the onset of the Akchagylian transgression at 2.7 Ma that preserved deepwater environments in both localities until 2.1 Ma. At the level of 2.1 Ma in both sections, we registered a basin level drop, which might be a sign of the Black Sea – Caspian Sea disconnection. Since this time, the facies in the Hajiqabul section show alternation between littoral, deltaic and floodplain depositional environments while in the Goychay section we observed a gradual transition from littoral to completely terrestrial environments. In the Hajiqabul section, the Bakunian transgression with a bloom of Didacna mollusks took place at 1 – 0.98 Ma. The ongoing micro-, paleontological analysis will further help to make a biostratigraphic division and correlate the sections to the regional stratigraphic time scale. The multidisciplinary approach of our study aims at deeper understanding of how the Pontocaspian ecosystems and depositional environments responded to the Caspian Sea level fluctuations in the Past.