CHEMICAL-STRUCTURE OF THE ORGANIC-MATTER IN A PLIOCENE MAAR-TYPE SHALE - IMPLICATED BOTRYOCOCCUS RACE STRAINS AND FORMATION PATHWAYS

A maar-type Pliocene oil shale from Pula (Hungary) was examined by Sca nning and Transmission Electron Microscopy (SEM, TEM) bitumen analysis ? spectroscopic analyses (FTIR, solid state C-13 NMR) and pyrolytic an alyses of insoluble material. The investigated samples, corresponding to the ''massive section'' of Pula deposit, exhibit TOC values ranging from 18 to 42%, and Rock-Eval analysis indicated that such samples ar e comprised of low maturity type I kerogen. Electron Microscopy observ ations confirmed that recognizable microfossils in this organic matter -rich material almost exclusively correspond to Botryococcus braunii c olonies, the morphology of which is perfectly retained. Identification of bitumen and pyrolysate constituents (hydrocarbons, ketones, fatty acids), along with morphological and spectroscopic features, indicate (1) that B. braunii provided a major input to the most organic matter- rich section of Pula oil shale; (2) that both the n-alkadienes-produci ng and the lycopadiene-producing strains (A and L, respectively) were present; (3) that the selective preservation of the insoluble and non- hydrolysable macromolecules building up B. braunii outer walls was by far the main process in the formation of this material; (4) that such a process, along with B. braunii prolific growth in the favourable env ironment that occurred in the crater lake, accounts fbr the very high TOC and oil potential of Pula deposit; and (5) that the condensation o f high molecular weight ether lipids from the A race and of some bacte rial lipids also likely contributed to Pula kerogen formation. Copyrig ht (C) 1997 Elsevier Science Ltd.