The Diagenesis of Plant Lipids during the Formation of the Krepoljin Coal Basin (Serbia) - Using Multivariate Statistical Analysis in the Saturated Biomarkers

Abstract

The composition of the saturated hydrocarbon fraction of soluble organic matter (bitumen) from the Krepoljin brown coal basin (East Serbia) of Miocene age was investigated. The Krepoljin basin is especially interesting from a geochemical point of view. Namely, by the end of Tertiary Period, the basin was covered by powerful Mesozoic formations of great possibilities, the bedding became hermetically enclosed and protected from subsequent external influences. The nature of early diagenetic processes in the environment with abundant accumulation of organic substance is defined by the molecular content of bitumen through the connections of molecular structures to potential precursors in paleoplant phylla, as well as by the degree of their diagenetic transformations. The hierarchy of parameters based on molecules of saturated hydrocarbons was determined by applying the principal component analysis to the soluble organic matter. The most significant, most "loadings" values of component C1, are the plant types such as precursors or participants in early diagenetic transformations of steranes Cs(27)-algal precursor material, Cs(28)-moulds, Cs(29)-higher land and water plants; resinous from the group of higher plant gymnosperms (G); also triterpanes alpha and beta-amirin-dicotyledonous angiosperms (A) and bacterial and/or terrestrial plants population represented by hopanes/moretanes; as well as the parameters which describe the degree of diagenetic/maturation transformation of precursor biomass, and based on next reactions: (1) shifting of methyl group, influenced by the inorganic sediment constitutents, sterane-rearranged steranes, (2) isomerization in the ring system, alpha alpha alpha ->beta beta beta C(29) sterane as well as (3) isomerization on chiral center of the side chain sequence R -> S C(29) sterane S/(S+R). Additionally, a pyrite-derived inhibitory effect on the rearrangment of C(29) steranes must be taken into account, but not on triterpanes reaction. Nonappearance of statistically important correlations, before all with maturational depended parameters, and after all also with source indicators contributies to the affirmation of the newly-suggested parameter alpha-Phyllociadane/S(27) as the real source biomarker of coal. Indicators derived from the distribution and abundance of n-alkanes and isoprenoid alkanes are of less significance in hierarchy of parameters.