Precaspian and South Caspian Basins: Subsidence Evolution of Two Superdeep Basins
Marie-Françoise Brunet, Andrei V. Ershov, Yury A. Volozh, Maxim V. Korotaev, Mikhail P. Antipov, Jean-Paul Cadet, 2007. "Precaspian and South Caspian Basins: Subsidence Evolution of Two Superdeep Basins", Oil and Gas of the Greater Caspian Area, Pinar O. Yilmaz, Gary H. Isaksen
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The Precaspian and South Caspian basins are two superdeep basins whose modeling has been undertaken in the frame of the international Peritethys Program that was sponsored by 13 companies or institutions.
The Precaspian Basin is situated to the north of the Caspian Sea mainly on land and has been trapped at the border of the east European Platform with the closure of the Urals Ocean during the Carboniferous. It is also influenced by the repercussions of Tethys closure during the Cenozoic, with the Caucasus compression to the southwest.
The Precaspian Basin contains about 20 km (12 mi) of clastic and carbonate sediments deposited since a time perhaps as old as the Riphean. It comprises a 4-km (2.5-mi) salt layer of Kungurian age (Lower Permian). Salt movements produce numerous salt structures that prevent a precise analysis of the post-salt subsidence.
The basement of the central Precaspian depression (central part of the Precaspian Basin) is characterized by a thin crust (around 10 km [6 mi]) where a low-velocity layer is absent. Its origin is still controversial; it could be either thinned continental or oceanic crust. At the base of the crust, a 8–10-km (4.9–6-mi) layer of velocity 8–8.1km/s (4.9–5mi/s) is recognized by seismic and gravity observations: anomalously high velocities at the base of the crust coincide in place with intense gravitational maxima. Analysis of some peculiarities of the structure, gravitational field, and composition of the crust leads us to suppose that this layer may be interpreted as eclogite. The problem remains on the way of implementation of full analysis.
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Throughout time, the greater Caspian area has maintained its position as one of the major petroleum provinces in the world. Its early history as a prolific producer of oil is well known. Caspian region exploration dates to the seventh century B.C., during the time of the Median Kingdom in today's southern Azerbaijan. Oil played an important role in the everyday lives of these ancient tribes of the region, and it is still a very important commodity today. The past two decades have seen many important advances in our knowledge of the geological evolution of hydrocarbon-bearing sedimentary basins. The success of modern exploration is, to a large extent, based on new advances in both deep and 3-D seismic imaging, as well as improved pressure-prediction and pre-drill oil and gas quality predictive methodologies, to mention just a few. Nevertheless, large areas of the greater Caspian region have remained unexplored due to a variety of factors such as deep-water conditions and zones with high pore-pressures in the South Caspian Sea and The Black Sea, and vast shallow-water regions with harsh winter ice conditions in the North Caspian Sea. This publication contains 12 extended abstracts and 6 full-length papers that discuss technology development, challenges in estimating proven and potential reserves, outcrop-based studies of potential reservoirs, regional tectonics and geodynamic evolution, and source rock and stratigraphic analyses of the greater Caspian area.