Abstract
Twenty-five samples of recent and late Pleistocene sediments collected from the tropical Atlantic Ocean, the Peru area of the Pacific, the Black Sea, and the Caspian Sea have been degassed by a special vacuum apparatus. In all samples of the extracted gases, in addition to nitrogen and oxygen of air origin, CO2, CH4, and heavier gaseous hydrocarbons from ethane to hexane were found to be the products of early diagenesis. The amount of heavy gaseous hydrocarbons in the total volume of hydrocarbon gas reaches one percent or more in the case of initial water-autochthonous material and decreases to 0.004 percent or less in sediments containing organic allochthonous material.
In the light of new data not only methane but also heavier gaseous hydrocarbons may be generated during the deposition and earliest diagenesis of sediments. Accordingly, the writers suggest the regional importance of the initial (early diagenetic) stage of the formation of a complete spectrum of gaseous hydrocarbons. The role of the gases generated during early diagenesis is essential in the formation of commercial accumulations. In the USSR, such gas accumulations have been discovered at depths shallower than 1,000 m in (1) Eocene deposits of the pre-Caspian depression, (2) upper Miocene sediments of the pre-Carpathian outer belt, (3) Miocene-Oligocene deposits of the Crimea, (4) Cretaceous sediments of the Karakum arch and Amu Dar’ya depression, and (5) elsewhere.
