UC Riverside

The Ediacaran (635 – 539 Ma) on Baltica is marked by oligotrophic conditions concurrent with the emergence of the Ediacaran Biota. This study analyzes rocks collected from various localities around Baltica with the intent of understanding the extent of oligotrophic conditions, the nutrient limitation that allowed these conditions to persist for millions of years. To answer these questions, samples from across Baltica were measured for Fe-speciation and P-phase partitioning, lipid biomarkers, C- and N-isotopes, major and trace elements analyses, and detrital zircon age dating. C26/C25 tricyclic terpane ratios, S contents and Fe-speciation indicate two salinity and redox states on Baltica with the Redkino being deposited under predominantly ferruginous, normal- marine conditions and the Kotlin horizon being deposited under dominantly oxic, low salinity coastal brackish conditions. Further evidence for these distinct environments can be observed in the relative abundance of hopanes and steranes which indicate strong bacterial contributions to primary productivity in the Redkino horizon. Conversely, lower hopane/sterane ratios in the Kotlin suggest increased algal contributions. Compound specific C-isotope measurements were made to determine the composition of individual extracted lipids from rocks across Baltica. Samples from the Utkina Zavod drillcore have bulk 13CTOC that are heavier by ~10‰ compared to other localities across Baltica. 13C from individual hopanes and C29 steranes from all sites are within 2‰ of each other, suggesting that Bacteria were likely utilizing the RubisCO-CBB pathway. 13C enrichment in these lipids in Utkina Zavod samples shows that either C-isotope fractionation was muted, or it was reflecting composition of the DIC pool. During Kotlin time, significant environmental heterogeneity existed on Baltica. U–Pb geochronology of detrital zircons from successions in northeast Estonia and the Volyn region of Ukraine was studied to understand sediment provenance and compare it with that for other areas on Baltica. These analyses provide insights into sediment transport and deposition processes, as well as the tectonic settings that influenced Baltica's sedimentary record during the late Ediacaran to early Cambrian. The sedimentary basins across Baltica show a transition during the Late Ediacaran – Cambrian interval from a passive continental margin to a collisional setting.