A NEW SCHEME FOR THE FORMATION AND CLASSIFICATION OF BITUMENS

Abstract

This paper discusses models of bitumen formation. Most liquid bitumens are formed during the middle stages of catagenesis (between approx. Ro equivalents of 0.4 and 1.15, respectively).“Progressive”naphthide formation is a process whereby organic matter and its derivatives gradually pass through a number of stages of alteration — three stages are generally recognized. By contrast, “regressive”naphthide formation is a “superimposed” process, involving microbial alteration and biochemical oxidation.In addition to the above two general processes, three other, less important schemes of naphthide formation are recognised:“Pyrodestructive bitumogenesis”results in the formation of “naphthoids”; these are bitumens generated close to an intruded heat source, which causes thermal destruction of organic matter.“Dynamic‐hydrothermal bitumogenesis”results in the generation of a complex group of bitumens, known as “naphthido‐naphthoids”, which are formed under conditions of dynamic metamorphism and hydrothermal activity accompanied by metasomatism. Thirdly, the process of “phase‐migrational” bitumogenesis results in the formation of two groups of bitumens: “asphaltenites” and “beta‐asphaltenites”.This paper summarizes the Author's views on bitumen formation, based on new geological and geochemical data.