Isotopically enriched n-alkan-2-ones with even chain predominance in a torbanite from the Sydney Basin, Australia

•n-Alkan-2-ones were identified in the polar fraction of an Australian torbanite.•These had enriched δ13C values similar to those of lipids from Botryococcus.•An unusually strong predominance of even-chain C24, C26 and C28 was noted.•C24, C26 and C28 ketones had more enriched δ13C values, suggestive of a second source.