The identification of crocetane in Australian crude oils

The C-20 irregular isoprenoid crocetane (2,6,11,15-tetramethylhexadecane) h as been unambiguously identified in a series of Western Australian crude oi ls From the Canning (Ordovician/Devonian) and Perth (Lower Triassic) Basins . PMI (2,6,10,15,19-pentamethylicosane) was found to co-occur with crocetan e in the same samples. In addition, a newly observed series of C-22-C-24 ir regular isoprenoids possessing the same carbon skeleton have also been tent atively identified in each of these crude oils on the basis of GC retention times and mass spectral characteristics. This may indicate a source for cr ocetane, in the Canning acid Perth Basin crude oils, from the diagenesis of PMI. The stable carbon isotopic composition for combined crocetane/phytane in these samples suggests crocetane is not unusually depleted in C-13 comp ared with all previous reports. This is the first reported occurrence of bi omarkers attributable to methanogenic archaea in crude oils. (C) 2001 Elsev ier Science Ltd. All rights reserved.