1. Conditions that Led to the Formation of Oil-Fields in the Ural-Volga Oil-Bearing Region (USSR)

Trofimuk, A. A. (Academy of Sciences, Moscova)


Section I/T.O.P. (*), Paper 1 CONDITIONS THAT LED TO THE FORMATION OF OIL FIELDS IN THE URAL-VOLGA OIL-BEARING REGION BY A. A. TROFIMUK (**) Numerous oil and gas occurrences, forming part of the Ural-Volga oil-bearing region, were found on the vast expanses between the Urals and the Volga River during the past twenty-five years. The eastern border of the Ural-Volga oil-bear- ing region passes along the western slopes of the Ural Mountains. The western boundary of the region is not yet ascertained. At some points oil fields were found much further to the west of the Volga on its right bank. The southern boundary of the region is conditionally traced along the northwestern and northern limit of the near- Caspian depression, and the northern boundary passes along the southwestern slope of the Timansky range. This whole vast territory is formed by Paleozoic strata situated on the eroded surface of the pre-Paleozoic crystalline founda- tion. Only in the southwestern part of the region are there Mesozoic deposits. In the com- position of the Paleozoic Sediments the most ancient ones are mainly terrigenous deposits, which belong to the Sediments of the Lower Paleozoic era and are called Bavlin suite. The Sediments of the Bavlin suite fill the deep immer- sions of the crystalline foundation. Within the limits of the projections of the crystalline foun- dation the Sediments of this suite are absent. In the Sediments of the Bavlin suite no accumu- lation of oil having industrial importance has been found yet, though traces of oil were noted at many points. On the eroded surface of the Bavlin suite and in places where it is absent-on the crystalline foundation-lie the terrigenous Sediments of the Devonian age, classed as of the Zhivetsky stage and lower Fransky stage. The richest oil fields are connected with these Sediments. The upper part of the Devonian deposits con- sists of carbonaceous Sediments of the Fransky and Famensky stages. In some places industrial accumulations of oil are connected with porous and fissurous dolomites in the Famensky stage. The deposits of the carboniferous system, in most cases without evident traces of interruption, overlie the Sediments of the Famensky stage. They are represented mainly by carbonaceous Sediments. The terrigenous deposits are devel- oped at the foundation of the Visé stage of the Lower Carboniferous era. A considerable part of the Visé horizon of the Medium Carboniferous era also consists of these terrigenous deposits. Recently, in the central part of the region, there was found a stretch of meridional exten- sion in the limits of which the Tournée stage of the Lower Carboniferous era is everywhere re- presented by carbonaceous Sediments only, which is completely substituted for terrigenous sedi- ments deeply cut into the thickness of the carbo- naceous Sediments of the Fransky stage. The industrial oil occurrences coincide with the terri- genous Sediments as well as with the underlying