Trends in occurrence of oil and gas in Lower Carboniferous in eastern Russian platform

Abstract

In order to elucidate the causes of the actual location of coal and petroleum deposits within terrigenous Lower Carboniferous strata of the Ural-Volga region, the paleogeographic setting of the deposits is reconstructed. The author stresses that highest oil output commonly occurs in geological systems with the greatest accumulation of coal. It has been calculated that the total area of plants that trap light by means of chlorophyll is 500 times the surface area of the Earth and that marine algae account for 4—5 times the photosynthesis performed by land plants. Massive accumulations of animal and plant remains occur in marine sediments of shallow epicontinental seas, shelf zones, continental shallows, gulfs and lagoons. Part is the result of influx from rivers. Although petroleum is formed under different conditions from, and more rapidly than coal, it is merely essential that the organic matter come to rest in a reducing environment. However, coal remains in situ at all stages of conversion, whereas oil may migrate. Nevertheless, both processes can occur simultaneously in adjacent areas on two sides of a coastline. The Ural-Volga region is a prime example of this situation. The Early Carboniferous history of the area is discussed, supported by structural contour, isopachous, paleogeographic, and fossil-fuel maps. The margin of any such platform is linked to more active areas and it may become a productive belt of biogenic deposits. About 150 Lower Carboniferous oil and gas deposits are known in the Ural-Volga region; the richest occur in ancient deltas and river valleys.—W. D. Lowry