Possible origin of high molecular weight n-alkan-2-ones in jurassic bitumens from the Sichuan Basin in Southwest China

Lipid extracts from two Sichuan (China) bitumens have been systematically analyzed using gas chromatography—mass spectrometry (GC-MS). These extracts contain C25-C35 n-alkan-2-ones with predominantly odd-carbon number homologs in the Yangba (YB) extracts and with exclusively odd-carbon number homologs in the Penglai (PL) extracts. We suggest that the n-alkan-2-ones with odd numbers of carbon atoms originated due to degradation (cleavage) of fatty acid salts containing one less carbon atom to form methyl and carbonyl radicals, followed by reaction between the latter. The distribution of n-alkan-2-ones with respect to number of carbon atoms can be used to identify the organic matter in sedimentary rocks from which the fatty acid salts were formed.