Chromate-mass spectrometry with a computerized data processing system
has been used to study the qualitative and quantitative composition of
sterane (C-21-C-29) and terpane (C-19-C-35) hydrocarbons - biomarkers
- in crude oils from the Volga-Urals oil- and gas-bearing province. C
onclusions have been drawn concerning the geochemical types and the co
nditions of formation of the Volga-Urals crude oils. It has been shown
that the oils studied can be divided into two very different types wi
th respect to the geological and geochemical conditions of their gener
ation - Proterozoic and Paleozoic. Oils of the two types were generate
d by marine organic matter and differ in the composition of the hopane
and sterane biomarkers. Crude oils of the Proterozoic type were gener
ated in carbonate deposits and have moderate catagenetic maturity. The
Paleozoic crude oils (Devonian-Carboniferous) were generated in clay
deposits and are noted for a higher degree of maturity.