A LIPID BIOMARKER INVESTIGATION OF OLIGOTROPHIC EDIACARAN MARINE ENVIRONMENTS ACROSS THE EAST EUROPEAN PLATFORM

The Ediacaran (~635 – 541 Ma) marks the transition from prokaryotic to eukaryotic rich oceans but the timing and causes of this transition are poorly constrained due partly to a sampling and preservation bias of biomarkers towards organic-rich sedimentary rocks from productive continental margin settings. Organic-lean deposits however can also preserve biomarkers provided they have avoided excessive thermal stress during burial maturation. In this study, we investigate the organic biomarker assemblages in strata deposited at various marine settings across the East European Platform during the Ediacaran. Some of these samples represent the most thermally immature rocks of their age, making them ideal for biomarker preservation. Samples were selected from a suite of drill cores, screened for biomarker suitability using Rock-Eval analysis and catalytic hydropyrolysis (HyPy) and analyzed using the latest multiple reaction monitoring (MRM)-gas chromatography-mass spectrometry methods. A variety of depositional settings are represented, including shallow marine shelves and epicontinental basins. Preliminary results show elevated hopane/sterane ratios indicating high bacterial contributions relative to eukaryotes; as expected from organic-lean rocks deposited in shallow water, oligotrophic settings. This bacterial dominance is in contrast to the eukaryotic-rich strata found in previous studies of organic-rich Ediacaran rocks from South Oman Salt Basin (Love et al., 2009; Lee et al., 2013). Within the eukaryotic biomarkers, green algae are the major eukaryotic phytoplankton source from strong C₂₉ sterane predominance in the C₂₇-C₃₀ sterane range. Hopane and sterane analysis in this strata revealed extremely immature diastereoisomer profiles consistent with the mild thermal history of the rocks. Paleogeographic mapping of Ediacaran biomarker assemblages across the East European Platform can help us assess the degree of heterogeneity in their biological communities due to variability in the oceanic redox and nutrient budget as well as assess ancient microbial community structures, modes of primary productivity (bacterial versus algal), and presence of early animals in shallow versus deep water marine settings.

Love et al. (2009) Nature 457, 718-722.

Lee et al. (2013) Geobiology 11, 406-419.