Aliphatic components of Victorian brown coal lithotypes

Victorian brown coal occurs in five major lithotypes distinguishable by colour index, petrography and bulk chemical analyses. The distributions of solvent extractable (free) and base hydrolysable (bound) n-alkanes, n-monocarboxylic acids, n-α,ω-dicarboxylic acids, n-ω-hydroxycarboxylic acids and n-alcohols were determined for samples of each of the five lithotypes (lithotype profile) and for seven samples of identical lithotype classification spanning a 100 m interval (depth profile) taken from a continuous bore core. The distributions of free molecular components in all classes are indicative of the predominant higher plant origin of this immature coal and provide strong support for the view that different lithotypes have derived from different, yet fairly specific paleobotanical communities. Despite an overall similarity in the distributions of aliphatic components from samples of identical lithotype classification, changes in the absolute concentrations and carbon preference indices (CPIs) of specific functional classes are observed in response to catagenetic influences even across the very small rank interval of the depth profile samples. Molecular distributions of bound components are similar to those of their free counterparts except that CPIs are generally lower and the relative contributions of lower molecular weight homologues (i.e. <C₂₂) are higher. Thedistributions of bound dicarboxylic acids and hydroxycarboxylic acids appear to reflect variations in the oxic/anoxic nature of the depositional paleoenvironments.