RELATIVE EFFICIENCY OF THE SELECTIVE PRESERVATION AND DEGRADATION RECONDENSATION PATHWAYS IN KEROGEN FORMATION - SOURCE AND ENVIRONMENT INFLUENCE ON THEIR CONTRIBUTIONS TO TYPE-I AND TYPE-II KEROGENS

A new pathway based on the Selective Preservation of insoluble and non-hydrolysable macromolecules, occurring as such in living organisms, was recently shown to be involved in kerogen formation. Here we discuss the relative importance of this pathway and of the classical ''Degradation Recondensation'' process, in the genesis of microalgae- and bacteria-derived kerogen fractions. To this end, a three-dimensional diagram was established, reflecting the contribution of the Selective Preservation pathway, versus the average composition of the source organisms and depositional conditions. This diagram reveals that the Selective Preservation mechanism probably played a major role in the formation of most of the above kerogens. In addition to emphasizing the quantitative importance of this new pathway, such a large contribution is consistent with the high oil potential typical of type I and II kerogens and accounts for the morphological diversity observed in these fossil materials.