The South Caspian Sea occupies the central part of a large intermontane downwarp in the Alpine fold belt. It formed at the site of an earlier deep-water depression, which was part of Tethys. The stratigraphic section of the pre-Pliocene rocks consists of an upper complex of Paleogene-Miocene age, a middle complex of Mesozoic age, and a lower complex of assumed Paleozoic and Precambrian age. Geophysical surveys show the consolidated basement to be heterogeneous, consisting of sectors with and without granitic crust and cut into blocks by deep faults. Depth to basement is 15-20 km and more. Three large downwarps are recognized on the base of the sedimentary cover. One is located south of Zhiloy Island, and the other two are in the Iranian part of the basin.
Two structural stages are recognized in the sedimentary cover. The upper is Neogene-Quaternary but includes also shallow-water deposits of the upper Paleogene (Maykop). The lower structural stage is largely Mesozoic but includes also rocks of the Paleocene and Eocene. The Mesozoic section appears to be marine and to have been deposited largely on oceanic crust that was under tension. The Mesozoic is composed probably of thin, well stratified clastic- carbonate, carbonate, and siliceous clays as well as volcanics. Its thickness is maximum at 7-8 km in the western part of the zone of the Apsheron Shallows (north margin of basin).
In the North Apsheron region and in the area of Neftyanyye Kamni (offshore Baku) the Mesozoic is near the surface - with corresponding decrease in thickness of the Cenozoic. Onshore in Turkmenistan the Mesozoic is 4-5 km thick. In some places the Mesozoic drapes basement highs. In others it is folded to form highs; these are associated with greater thickness of the Mesozoic. These folds developed during times of compression as a result of subduction at the end of the Mesozoic and in later times. Igneous intrusions were prominent in the structural development of the Mesozoic.
The Oligocene-Miocene (Maykop) consists of clastics 4-6 km and more thick as well as some volcanics. These are overlain by 1 km of marine clastics. On the whole the Paleogene-Miocene consists of weakly altered sand-clay rock. These rocks in many ways determined the structure of the Pliocene-Quaternary complex, composing the cores of diapirs, mud-volcano stocks, and occurring as normal anticlines in lower horizons.
In the east in the region of the West Kopet Dag thickness of the Paleogene-Miocene is 2 km, decreasing westward toward the sea to 200 m. On the west in the Kura depression of Azerbayjan the Paleogene-Miocene is represented by 4-5 km of clastics, increasing offshore. In the south in the Cis-Elbrus downwarp this thickness is 4-5 km. Maximum thicknesses are found in the north in the Apsheron- Balkhan zone at 6 km and in the inner parts of the depression at 6-8 km.
Depth to the top of the pre-Pliocene is greatest in the central part of the basin at 10-11 km. This region is characterized by a mosaic of small depression. Then to the east this surface rises to 7 km depth in the Turkmenistan coastal zone, and to the west to 8 km depth in the Apsheron zone.
The middle Pliocene clastics, which are host to the oil of the region, inherited their structure in general from the pre-Pliocene rocks.
Taken from Chernov, 1990; digested in Petroleum Geology, vol. 30,
no. 4, p. 350-357, three cross sections and one structure map on
base of middle Pliocene at scale of 1:500,000.
Copyright 2001 James Clarke. You are encouraged to print out this
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