Biomarker similarities between the saline lacustrine Eocene Green River and the Paleoproterozoic Barney Creek Formations

The Paleoproterozoic Barney Creek Formation, which is currently interpreted as a restricted, deep marine paleoenvironment, plays a disproportionate role in our understanding of Proterozoic ocean chemistry and the rise of complex life. The Barney Creek Formation hosts several unusual biomarker features, specifically its methylhopane and carotenoid signatures. Herein, we demonstrate that the saline lacustrine Eocene Green River Formation shares a similar distribution of methylhopanes and carotenoids, which is characteristic of saline lacustrine organic matter more generally. These distinct methylhopane and carotenoid patterns are not observed together in marine organic matter of any geologic age. These results imply a saline lacustrine depositional environment for the Barney Creek Formation, which agrees with earlier but now abandoned depositional models of this formation. As a result, models of Proterozoic ocean chemistry and emergence of complex life that rely on a marine Barney Creek Formation should be re-examined. Alternatively, if Paleoproterozoic marine biomarker signatures resemble those of younger saline lacustrine systems, then this must be recognized to accurately interpret geologic biomarker and paleoenvironmental records.