Tricyclic terpenoid composition of tasmanites kerogen as determined by pyrolysis GC-MS

Abstract

The high abundance with which tricyclic terpenoids have previously been detected in Tasmanite oil shales has led to the strong suspicion that the source of these compounds is the Tasmanites microfossil prevalent in these oil shales. In this study, the hydrocarbon composition of a Tasmanite oil shale and isolated Tasmanites were separately investigated by laser micropyrolysis gas chromatography–mass spectrometry, a recently developed technique that facilitates the analysis of small samples such as microfossils. Major products comprised C19–C28 tricyclic terpanes, including the ubiquitous 13-methyl, 14-alkylpodocarpanes, as well as a number of additional tricyclic terpane isomers, a C19 monoaromatic hydrocarbon, and several C19–C21 tricyclic terpenes (one and two orders of unsaturation). There have been few previous reports on the tricyclic terpenes and their production is likely attributable to the pyrolytic cleavage of analogous (probably saturated) tricyclic precursors within the macromolecular biopolymer. The only major difference between the tricyclic terpenoid compositions observed from these samples was the absence of the less concentrated oil shale products in the Tasmanites analyses, probably due to the lower organic content of the preextracted fossil. The very similar tricyclic content of both samples strongly supports the proposal of an inherent relationship between the Tasmanites and tricyclic terpenoid production. The integrity of the laser data was confirmed by comparison to a conventional data set obtained by the pyroprobe pyrolysis of the Tasmanite oil shale.