Unusual distribution of monomethylalkanes in Botryococcus braunii-rich samples: Origin and significance

A unique distribution of four homologous series of monomethylalkanes (MMAs) ranging from C-23 to C31+ in the extractable organic matter and the hydrou s pyrolysate of Permian torbanites has been observed for the first time. Th ese components have been identified by gas chromatography-mass spectrometry and cochromatography of authentic standards. Each of the series begins wit h the 2-methylalkane. Each member of a particular homologous series has a c ommon alkyl group, each series differing to the next by two carbon atoms. T he members within each homologous series differ by the number of carbon ato ms in the second alkyl group. These pronounced homologous series of MMAs ar e superimposed over the series of lower abundance, partially resolved, more commonly occurring MMAs. This distinct contrast in the distributions of th e novel MMAs series and the more commonly occurring MMAs suggests two disti nct sources of MMAs in the torbanites. This visual observation is borne out by compound specific carbon isotopic data. A detailed molecular carbon iso topic study in combination with structural data suggests that the unusual M MA series are either derived directly from Botryococcus braunii race A or a re novel biomarkers indicative of intense heterotrophic reworking of the al gal biomass. Copyright (C) 2001 Elsevier Science Ltd.