Block Tectonics and Petroleum Potential of Western Cis-Caucasus
Internet Geology News Letter No. 177, January 6, 2003

The study area is north-northeast of the Black Sea and the Greater Caucasus fold system, east of the Sea of Azov, west of Stavropol arch, and south of Rostov arch. The main structural features within it from south to north are the West Kuban downwarp, Timashev structural terrace and Din arch, Kanev-Berezan arch, Irkliyev syncline, and Leningrad arch.

The Western Cis-Caucasus is broken into blocks by deep faults. These faults have influenced the development of local structural forms, the distribution of facies changes and pinchouts, and the formation of oil and gas pools.

A series of longitudinal and transverse faults divides the West Kuban downwarp into several blocks. Refraction surveys indicate that sediment thickness in the axial part of this downwarp is 12-14 km. The top of the Mesozoic is at depths on the order of 6000 m. The pre-Mesozoic com- sists probably of Upper Proterozoic and Lower Paleozoic metamorphics.

Permo-Triassic rocks are present in several drill holes on the Timashev terrace and Din arch. Basement is Upper Devonian-Lower Carboniferous.

Numerous fault-associated structures are present in the Cretacerous, Jurassic, and Triassic sediments on the Kanev-Berezan arch and Irkliyev syncline. Basement here consists of Permo-Carboniferous clastics, which are in varyious degree metamorphosed.

The Neocomian and Upper Jurassic are absent on Leningrad arch, and thickness of the Lower and Middle Jurassic is reduced. Basement consists of Carboniferous phyllites.

Rostov arch is the southern part of the Ukrainian crystalline shield. The drill penetrated Archean gneisses here at depth of 500 m.

The Paleozoic section certainly contains good reservoir rocks, largely the fracture type, as well as seals. Anticlinal and pinchout traps should be present. Most of these rocks appear to be overcooked, however.

The Triassic section ranges in thickness from 120 to 1740 m. It consists of argillite on the Din block and limestone in the Maykop area. Reefs and fractured limestones are favorable reservoirs as well as sand-clay facies of the Middle and Upper Triassic.

An Upper Jurassic evaporite provides a seal for pools in the Lower and Middle Jurassic. Pinchouts of sand-silt facies are expected in the Jurassic in the area of Timashev terrace. Gas has already been recovered from sub-salt Jurassic in other areas.

The Cretaceous is subdivided into a lower clastic-carbonate complex and an upper carbonate complex. Gas, condensate, and oil pools occur in the clastic-carbonate complex largely in Neocomian and Aptian-Albian sediments. The upper carbonate complex has good reservoir properties in zones of deep faults. Particularly attractive are areas of intersection of faults. Significant faulting developed during Alpine tectonism.

In the Cenozoic section a belt of Maykop sediments in the northwest part of the Leningrad arch is favorable for strat traps in sandy facies. The Eocene is favorable along the south border of the West Kuban downwarp. Then to the west clay diapirs are favorable for gas.

Taken from Lotiyev and others, 1987; digested in Petroleum Geology, vol. 23, no. 9/10, one tectonic map.
Copyright 2003 James Clarke. You are encouraged to print out this News Letter and to forward it to others. Earlier News Letters are available at: http://geocities.com/internetgeology/
This News Letter is distributed without charge in the interest of our science of petroleum geology. To be added to the mailing list please send your e-mail address to: jamesclarke@erols.com
For information on the journal Petroleum Geology please telephone 703 759-4487 or FAX 703 759-3754.
Hear my words, you wise men; listen to me, you men of learning. For the ear tests words as the tongue tastes food. Let us discern for ourselves what is right; let us learn together what is good. - Elihu speaking: Job 34, 2-4. >/HTML>