Geochemical Fossils and Their Significance in Petroleum Formation

Abstract

Diagenesis in young sediments results in two main organic fractions of very different quantitative importance: kerogen amounts to the bulk of organic matter, whereas some free molecules of lipids include hydrocarbons and related compounds. These molecules have been synthesized by living organisms and get trapped in the sediment with no or only minor change (Fig. II.3.1). They comprise specific compounds of relatively high molecular weight (Fig. II.3.2), and can be considered as fossil molecules, or geochemical fossils. Such molecules will be considered later in greater detail (sec. 3.3ff.) They represent a first source of hydrocarbons in the subsurface.