Biomarker assemblage of some Miocene-aged Bulgarian lignite lithotypes

Two homogeneous (humovitrain and xylain) and one heterogeneous (humoclarain) lithotype macerals, separated from a lignite, were subjected to mild reductive treatment by NaH. The extensive chromatographic separation of the decalin-soluble fraction revealed some structural peculiarities. A strong predominance of alpha-phyllocladane was characteristic for all macerals. Series of n-, iso-, and anteiso-alkanes, regular isoprenoids, alkylbenzenes and 1-methyl-4-n-alkylcyclohexanes were identified by mass spectrometry. An angiosperm source input was represented by friedelane, lupane and seco-hopane structures. Products of des-A and des-E-ring cleavages and C-10 demethylation were registered by mass spectrometry. The main difference was in the hopane distribution pattern. A strong prevalence of extended beta beta-hopanes was found in the humoclarain sample. The mass spectral data revealed the existence of a basic difference in hopane precursors-diploptene or diplopterol for the homogeneous lithotypes and bacteriohopanetetrol for the heterogeneous lithotype. (C) 1996 Elsevier Science Ltd.