Novel interpretation of the crustal structure and hydrocarbon evolution within the South Caspian and Kura sedimentary basins, Azerbaijan

Abstract

The South Caspian Basin, Lower and Middle Kura Basins, onshore Azerbaijan, and Georgia Upper Kura Basin are a genetically linked basin system created in a Mesozoic extensional setting with a complex Cenozoic sediment fill history. Delineating these basins shed new light on understanding the complex geodynamic history of the region between the Black Sea and the Caspian Sea and elucidate the petroleum prospectivity of the region. Key data used for basin analysis were a series of regional isopach maps, temperature measurements from over 150 onshore and offshore boreholes in Azerbaijan, derived geothermal gradient data, and published surface heat flow data. Taken together, they allowed us to put some constraints on the crustal structure of an area where accurate temperature measurements are limited. An integrated set of offshore and onshore regional isopach maps for the key stratigraphic units from Jurassic to Pleistocene were created. The depth to basement and the crustal thickness across four seismic cross-sectionswere estimated and validatedvia interpretation of isopach maps and gravity and magnetic modeling. The results encompass the area from the onshore Kura Basin in eastern Georgia to the offshore South Caspian. Several specific regions were differentiated, including a «cold» region in the South Caspian Basin. A reasonable correlation was established between basement depth, crustal thicknesses, and geothermal gradients. The tectonic boundary between these two basins controls the geothermal gradient change and therefore the hydrocarbon potential. The western margin of the South Caspian Basin represents a long-standing crustal boundary between the South Caspian Basin oceanic crust of the South Caspian Basin and the thicker crust of the Kura basin of the island-arc origin. The Mesozoic evolution of these basins started as a result of an island arc extension in Mesozoic, followed by Cenozoic flexural overprint with rapid burial and significant sediment flux, thus creating suitable conditions for the development of a dynamic petroleum systems in the South Caspian Basin.