The Paleogene complex of the southeast of the Russian platform contains several clastic strata, which consist of sandstones and siltstones interbedded with regional seals - clays and siltstones. This complex is very favorable for accumulation of hydrocarbons. In the southwest part of the North Caspian depression (Armey dome, Kirikilin area) and Tsaryn depression small pools of oil and gas have been found in Paleogene sediments, but they were assessed as not commercial. In recent years, however, several of these fields and pools (Kazanlin, Bazarno-Karabulak dislo- cation, Khlebnov and Surov) have now been classified as commercial and are being produced successfully. This has been due to development of infrastructure in the region and increase in the price of oil.
Detailed lithologic study of the Paleogene clastics of the study area has now become of practical importance. The carbonates do not make good reservoirs. These clastics are represented by a wide range of facies from continental and near-shore marine sands and gravels to relatively deep- water muds.
Gravel and sand-gravel sub-complex. These are generally limited to basal horizons of the various stratigraphic levels - lower Syzran, Kamyshin, Proley, Tsaritsyn, Khadum (Maykop). They were deposited in near-shore, shallow-water zones of the marine basin and rarely under continental conditions. They are friable or in various degree consolidated. Thickness of the beds is 0.5-0.7 m. The gravels consist of rounded fragments of opoka, chert, quartz, phosphorite along with marine fossils.
Sand sub-complex. This is the most important component of the clastic complex. It consists of sands that collected in shallow-water near-shore parts of the basin. It is best repre- sented in the north of the study area, where thick (from 10 to 100 m) sand beds compose partly or fully the sections of the Sygran, Saratov, Kamyshin, Proley, Tsaritsyn, and Mechetkin Formations.
These sands are largely quartz and quartz-glauconite. Feldspar is rare. They are light gray, in some places almost white. As a rule they are fine-grained and well sorted. Silt and pelite fractions are practically absent. Quartz content reached 98 percent. The grains are in various degree rounded. Silica content in the purest varieties is 96-99.7 percent. These sands are used in the glass industry.
Glauconite sands are present largely in the Eocene sediments between the Volga and Dono-Khoper Rivers. Glauconite distribution is uneven in beds and lenses.
The Paleogene sands commonly carry ilmenite, rutile, sphene, anatase, leucoxene, and zircon. These may be present in economic amounts.
Taken from Akhlestina, Malyshev, and Ivanov, 2001;
digested in Petroleum Geology, Vol. 37 (Planned Annual Volume).
Copyright 2003 James Clarke. You are encouraged to print out
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