Published September 2010
Depositional History of the Productive Series in the South Caspian, with Consideration of the Basin Subsidence (part I)
Riley GregoryThis series of articles is an attempt of describing unique geology, stratigraphy and development of, as well as processes taking place in the South Caspian Basin. This article is dedicated to sedimentation and study of reservoirs in Pliocene of the South Caspian Basin. In the last 15 years, hydrocarbon exploration has intensified in the offshore part of the South Caspian Basin. New data allowed detailing regional distribution of reservoir beds and facies architecture of the Productive Series. Un the South Caspian Basin, there are more than 20 km thickness of Mesozoic and Tertiary sediments that have deposits on the oceanic or thinned continental crust. Much of this succession (6 km) is composed of fluvial and lacustrine deltaic sediments of the Pliocene Productive and Red Series, which are unconformly lie over the marine complex of Miocene age. It forms main hydrocarbon bearing reservoirs in the basin. The Productive Series (and its equivalent Red Series) in the South Caspian basin is distinguished by a much lower base level as compared to Miocene shelf margins that existed earlier. The Productive Series is divided into four stages. Differences between those stages indicate changes in balance between supply of sediments and water and alterations of the basin morphology. The basin morphology inherited from previous sedimentation phases significantly influenced depositions of sediments within the Productive Series. The fall of base level of deposition, which was approximately contemporary with the Messinian crisis, has resulted in isolation of the Caspian Sea from the global oceans. Reconstruction of the basin profile for the period immediately after this event shows lowering of the depositions base level bu 1.5 km in the South Caspian Basin. The drainage systems in combination with this strongly lowered depositions base level caused supply of large volumes of sediments and water from the Russian Platform, Caucasion Mountains, and Kopetdag to the South Caspian basin, fluvial and lacustrine facies accumulated in the topographic depressions, forming infill of the lower part of the Productive Series. Infill of topographic paleo depressions by deposits of the lower part of the Productive Series resulted in lower gradient over the majority of the South Caspian Basin. The middle part of the Productive Series deposited on this low gradient in the form of fluvial, deltaic, and lacustrine facies. Reconstructed profiles of the basin demonstrate lowering of gradient as a result of the filling accommodation space.
