Distribution and origin of ethyl-branched alkanes in a Cenomanian transgressive shale of the Western Interior Seaway (USA)

Monoethylalkanes (MEA, C16–C22) with an even number of carbon atoms are relatively abundant in the saturated hydrocarbon fraction of the basal Graneros Shale (Cenomanian, Western Interior Seaway, USA). On the basis of isomer distribution and isotopic composition, it is proposed that MEA derive from eubacterial organisms, possibly cyanobacteria, living in fresh to brackish water environments.