The Dnieper-Donets depression is located in the west of the Russian platform between the Ukrainian shield on the southwest and the Voronezh massif on the northeast. It is 280 km in length and 68-120 km in width. Three salt complexes are present: (1) upper Frasnian, (2) upper Famennian, both in the Upper Devonian, and (3) Lower Permian. The stratigraphic levels of penetration of Devonian salt diapirs into the sedimentary section of the depression are: pre-Anthropogene, pre-Paleogene, pre-Lower Triassic, intra- Carboniferous, and pre-Carboniferous.
The upper Frasnian salt complex has a wide areal distribution. It rests transgressively on a volcanic-sedimentary complex. Undisturbed thickness is 200-1000 m. Thicknesses in salt domes penetrated by the drill are 2.5-3.3 km, and from geophysics 4-6 km. Thickness on basement highs is reduced to 400 m, and the complex carries up to 30 percent non-salt material.
Salt accumulation was in a graben and was controlled by border faults. Maximum accumulation was in local depressions on the basement. Depth to salt on plugs is 200-600 m, on domes - 1.2-4 km, and undisturbed - 5 km and more. In most sections this complex has three parts. The upper and lower are carbonate-sulfate rock or fine-rhythm alternation of these rocks with salt. Each rhythm begins with non-salt and ends with salt. The salt part in the middle consists generally of coarse-grained halite that shows signs of flow. This salt complex is a regional seal for pools in underlying Devonian, where direct signs of oil and gas and semi-commercial pools have been found.
Extensive volcanics are associated with this upper Frasnian salt, occurring both beneath and within it. Their total thickness is 200-800 m, and they occur at depths of 1500-5600 m. They are not a regional seal; however, they may serve as local seals. Some of them qualify as poor reservoirs.
The upper Famennian salt complex is much less extensive than the upper Frasnian complex. Following Zadon and Yelets time conditions became favorable again for salt accumulation in local downwarps. This complex has been encountered by the drill in the Maksaki-Bakhmach sector on the northeast border of the downwarp, where it is 25-300 m thick. Very full sections are found on the southwest border, where thickness is up to 400 m. Thickness reaches 700-800 m in the southeast in the Malodavits area. Geophysics indicates presence of this salt in the axial part of the downwarp; however, it has not been drilled.
On a basis of drilling the upper Famennian salt is subdivided into lower (sulfate-carbonate), middle (salt proper), and upper (sulfate-carbonate) members. In some sections, however, the salt is replaced by sulfate rock, marking the end of the regressive cycle of sedimentation.
Taken from Kurilyuk, Bakarchuk, Slobodyan, and Khmel', 1991;
digested in Petroleum Geology, Vol. 31, No. 3, 1997; one map, two cross
sections.
Copyright 2002 James Clarke. You are encouraged to print out this
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