Plate Tectonic Development of North Caspian Depression
Internet Geology News Letter No. 38, March 27, 2000
The North Caspian depression is in the southeast part of the East European craton. The sedimentary section below the Lower Permian
Kungurian salt has been penetrated by hundreds of parametric, wildcat and delineation wells along the relatively narrow border zone. Information on the rest of the depression comes from geophysical studies.
Seismic surveys suggest that the North Caspian depression formed
in the Paleozoic as a narrow oceanic rift basin on the passive margin
of the East European craton, the result of partial crustal spreading. This
Paleozoic history is divided into eight stages during a time span from
380 to 250 m. y. from the Middle Devonian to the Late Permian.
During this time of some 130 m. y. the East European craton
moved about 1000 km to the north.
Sectors where the mantle stands high at 32 km depth correspond
with gravity maximums. Since the thickness of the sedimentary cover
with velocity of 4.2-6.2 km/sec is 22 km, the more dense crust in the
central part of the depression is probably oceanic. It occurs in a
relatively narrow belt 150-200 km wide. This rift is probably one of
the failed arms of a system that also included the Dnieper-Donets depression. The age of this rifting is placed in the Middle Devonian.
During the Eifelian-Early Frasnian Stage sandy-clayey facies similar to the "Clastic Devonian" of the Volga-Ural region collected. Lenses of shallow-water carbonate were deposited on the northeast, east, and south.
During the Late Frasnian-Tournaisian Stage coarse clastics were derived from the northeast from the rising Urals. Then in the central parts of the basin deep-water sediments were deposited. Carbonates with extensive reefs formed on the north, west, and south borders of the depression, pinching out toward the interior of the basin.
The beginning of the Early-Middle Visean Stage was characterized by strong uplift of the entire European continent, reaching maximum in the middle Visean. The rift structure, however, continued downwarping. On the borders of the depression carbonate deposition was replaced by clastics.
In the Late Visean-Early Bashkirian Stage the deep-water basin broadened to occupy much of the North Caspian depression. A series of carbonate steps formed on the north and west, at the crests of which numerous reefs are present.
During the Late Bashkirian-Vereiskian Stage deep-water facies were deposited only on the south and east.
The Kashirian-Artinskian Stage was marked by collision of the Central Kazak continent with the East European craton and the docking of the Sythian and Turonian plates onto the East European continent. Clastics were spread far to the west from the rising Urals.
In the Kungurian Stage the North Caspian depression became separated from the open ocean to form an enormous salt lake. Under an arid climate not less than 5 km of salt collected during a time of 3.6 m. y. The most subsided part of the depression associated with the rift graben was finally compensated by evaporites.
Downwarping continued during the Late Permian Stage. Redbeds along with some carbonates were deposited. Salt tectonics probably began during this stage.
During the Mesozoic and Cenozoic the region developed as an interior platform regional low (sineklize). (Taked from Volchegurskiy and others, 1995; digested in Petroleum Geology, vo. 29, no. 11/12, p. 362-369, four paleogeographic maps)
Copyright 2000 James Clarke. You are encouraged to print out this News Letter and the forward it to others. Earlier News Letters are available at
http://geocities.com/internetgeology/
