In order to increase our understanding of the tectonic evolution and hydrocarbon potential of West Central Asia, a detailed structural analysis of the Aral-Caspian Sea region of West Kazakhstan was conducted utilizing approximately 7,000 km of reflection seismic data along with seismic refraction data, surface geological maps, and well data from appropriate locations. The Aral-Caspian Sea region of West Kazakhstan can be divided into several distinct sedimentary basins, including: (1) the Pri-Caspian Basin, (2) the Northwestern Pri-Aral Basin, (3) the North Ustyurt Basin and the Buzachi Peninsula, (4) the South Ustyurt Basin, and (5) the Mangyshlak Basin. The Mangyshlak and South Ustyurt Basins in the south are separated from the Buzachi region and the North Ustyurt Basin to the north by the west-northwest-trending Karatau (Mangyshlak) Uplift, a complex structural system which has undergone tectonic reactivation several times since the late Paleozoic. The North Ustyurt Basin is separated from the Pri-Caspian Basin by the South Emba Uplift, a northeast-southwest trending structural high of Late Triassic-Jurassic age. The Central Aral Fault Zone, a north-south trending strike-slip fault system which can be traced northward into the southern Ural Mountains, defines the eastern boundary of the Northwestern Pri-Aral region and the North Ustyurt Basin. Our research indicates that the Aral-Caspian Sea region of West Kazakhstan has undergone several phases of deformation since the middle paleozoic, beginnning with early to middle Carboniferous subduction of the Pri-Caspian Basin beneath the North Ustyurt block and the development of a north-vergent accretionary wedge along the North Ustyurt-Pri-Caspian boundary. Extensional deformation characterized the Late Permian through Triassic of West Kazakhstan, during which time the North Ustyurt and Mangyshlak Basins developed as southward-deepening half grabens while the Buzachi region developed as a full graben structure and north-south oriented pull-apart basins developed within the Northwestern Pri-Aral region. Compressional deformation during the Late Triassic-Early Jurassic resulted in the reactivation and tectonic inversion of the South Emba and Karatau fault systems and the development of hangingwall anticlines within the North Ustyurt and Buzachi regions. Limited tectonic warping at the Jurassic-Cretaceous boundary was followed by general tectonic sagging across West Kazakhstan during the Cretaceous and Paleogene. Finally, West Kazakhstan has been dominated by transpressional to strike-slip tectonics during the Neogene, with the Karatau Uplift developing as a transpressional structure along a restraining bend within the Karatau (Mangyshlak)-Samarkand wrench-fault system.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah