A biomarker and isotope study of Paleoproterozoic ecosystems in the northern Australian McArthur Basin

Abstract

Biomarkers represent an important source of information about ancient environments, especially in the Paleoproterozoic, where the body fossil record is comparatively scarce. The northern Australian McArthur Basin contains currently the oldest known indigenous biomarkers in the 1.64 Ga Barney Creek Formation (Fm). Based on published biomarker data, the oceans were almost exclusively inhabited by prokaryotic microorganisms, while eukaryotes with complex cell structure still played an insignificant role. However, newly recognized protosteroids in the Barney Creek Fm may record early stages in eukaryotic evolution. This thesis, which consists of four linked research topics, investigates biological community signatures and paleo-environments in a transect through the Barney Creek Fm succession and circumjacent units; explores preservation of organic matter associated with the Paleoproterozoic McArthur River zinc-lead ore deposit; and describes the influence of thermal maturity on compound-specific carbon and hydrogen isotopic composition of lipids in the Barney Creek Fm. Additionally, this research presents the discovery of trimethyl aryl isoprenoids from carbonaceous shales of the 1.73 Ga Wollogorang Fm in the McArthur Basin, revealing the activity of phototrophic bacteria and extending the biomarker record back in time by ~90 million years.