Natural vs. anthropogenic sources of hydrocarbons as revealed through biomarker analysis: A case study in the southern Gulf of Mexico

Resumen

Biological markers are
organic compounds in geological samples with an unambiguous link to
specific precursor molecules in living organisms. They provide
information on the origin and depositional environment of fossil
organic matter as well as about its thermal maturation caused by
geothermal heat flow during burial. Petroleum and its refinery
products carry this biomarker information into the environment when
they are released during anthropogenically-induced pollution. Soils
or aquatic surface sediments in contaminated areas usually contain
binary mixtures of fossil hydrocarbons and recent biogenic
hydrocarbons like higher-plant wax esters, together with (often
olefinic) hydrocarbons from earliest diagenetic transformation of
functionalized biomolecules. Surface sediments collected in the
shelf area of the Campeche Sound, Gulf of Mexico, sampled in the
course of environmental monitoring for possible petroleum pollution
due to industrial activity, however, revealed a third group of
hydrocarbons. GC-MS analysis of biomarkers in the nonaromatic
hydrocarbon fractions of the sediment extracts yielded overlapping
hydrocarbon assemblages indicating multiple sources. Samples taken
close to known asphalt seeps exhibit biomarker patterns virtually
identical to those of reference crude oils. Other sediments contain
mature fossil hydrocarbons and biomarkers that are not typical of
either fossil fuels or immature organic matter in marine surface
sediments. Instead, they come from drill cuttings recovered during
penetration of Tertiary to Cretaceous deposits that were littered on
the shallow sea bottom.