The Depositional Environments and Shallow Subsurface Architecture of the Northeastern Caspian Sea

The Caspian Sea is often used to study the effects of sea-level change on coasts (Kroonenberg et al. 2000, Overeem et al. 2003, and Hoogendoorn et al. 2005). The results of these studies are of great importance to study the effect of eustatic sea-level change and analogue studies for hydrocarbon reservoirs. Relatively less research has been done in the Northeastern Caspian Sea, which is the flattest and shallowest part of the sea. The subsurface architecture and processes that lay down sediments in this area are relatively unknown. Therefore the objective of this study is to increase the knowledge of the depositional environments and shallow subsurface architecture of the Northeastern Caspian Sea. The results of this study can be used for the development of North Caspian offshore-petroleum-production facilities, as an analogue for reservoirs deposited in similar conditions and to study the effects of sea-level change on low gradient coasts. For this project 6 new offshore cores have been drilled to a depth of 10m in the Northeastern Caspian Sea. In addition, a large amount of shallow subsurface data has been gathered from cores, cone penetration tests and seismics, during the development of offshore hydrocarbon-fields in the area. Sedimentological descriptions of the new cores were made, samples were dated with radiocarbon techniques and a biostratigraphical analysis was performed. The depositional environments for the different lithofacies were determined and a sequence stratigraphical framework was developed. With the available data a 3D-subsurface model was build with Petrel software to visualize the spatial sediment distribution and test the developed concepts. Four lithofacies, deposited in different depositional environments were found in the cores. The oldest deposits are dated before 48.000y BP, they have been deposited as aeolian dunes during a lowstand and were reworked during a transgression by coastal processes. On top, lagoonal sediments are deposited between at least 48.000y BP and 42.000y BP during multiple centennial to millennial or less frequent sea-level cycles. These deposits are overlain by transgressive barrier-like sands which have been radiocarbon dated around 27.000y BP. The sediments in the top of the cores have been deposited after the Mangyshlak or Derbent regression in an environment with a low sediment influx and frequent sea-level changes. The study shows that the depositional environment in a low gradient environment with frequent sea-level changes mainly depends on the relative position to the coast, the supply of sediments and the speed of sea-level change. It increases our knowledge of the depositional environments and subsurface architecture of the Northeastern Caspian Sea.Applied Earth SciencesCivil Engineering and Geoscience