Subsidence and Sedimentation in the South Caspian Basin

Tim Green¹, Nazim Abdullayev¹, Greg Riley¹, and Alan Roberts^2
1BP, Sunbury on Thames, United Kingdom
²Badley Geoscience Ltd, Hundleby, Spilsby, Lincs, United Kingdom

The South Caspian Basin is believed to contain more than 20 km of Mesozoic and Tertiary sediments deposited on oceanic or thinned continental crust. Mesozoic, Paleogene and Oligo-Miocene sediments have not been penetrated within the South Caspian Basin itself but are exposed onshore in the basin margins. The Pliocene to Recent sequence has been mapped on a regionally extensive grid of 2D seismic data and penetrated by recently drilled exploration wells and is over 7 km thick. Most of this sequence (6 km) is formed of fluvial-lacustrine deltaic sediments of the Pliocene Productive Series that are deposited unconformably above a marine Miocene shale sequence and form the principal HC reservoirs in the basin. The Productive Series is overlain by about 1 km of Late Pliocene to Recent marine sediments
The thickness of the Pliocene sedimentary sequence implies that relatively rapid, late Tertiary subsidence occurred in the South Caspian Basin; however there is no geological evidence of a tectonic event capable of generating major thermal subsidence at this time. Modelling presented in this paper suggests that it is possible to account for the observed pattern of subsidence and sedimentation in the South Caspian Basin by a process of sediment loading and compaction on a thermally-subsiding, late Mesozoic crust without the need for additional Tertiary subsidence mechanisms. Crucially this model interprets the Pliocene Productive Series to have been deposited in a topographic depression, isolated from the global oceanic system, in which base-level was controlled by local factors rather than by global sea-level.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece