A multi-basin comparison of paleoredox conditions during the mid-Silurian Mulde/lundgreni event

The mid-Silurian Mulde/lundgreni Event was characterized by a widespread biotic crisis among marine taxa (e.g., graptolites, conodonts), associated with a notable double-peaked positive carbon isotope excursion. These biotic and chemical signatures provide evidence that this time interval experienced significant environmental change. While there has been significant research on this critical interval within the Silurian, the oceanic redox conditions encompassing this event remain poorly constrained. Here, we utilize a multiproxy approach to investigate the paleoredox dynamics within two geographically distinct marine basins and paleocontinents spanning the Mulde/lundgreni Event: Abbott River, Twilight Creek (Arctic Canada, Laurentia), and the Priekule-20 core (Latvia, Baltica). We present new organic carbon isotopes (δ13Corg), pyrite sulfur isotopes (δ34Spyr), iron speciation, and trace metal data to reconstruct regional marine paleoredox conditions from three separate localities providing a more global view. Our geochemical records reveal synchronous positive excursions in δ13Corg and δ34Spyr across all sections, indicating increased burial of organic carbon and pyrite. Iron speciation data suggest persistently ferruginous anoxic bottom waters in Laurentia throughout the study interval. In contrast, bottom water redox conditions in Baltica were more variable, fluctuating from possibly oxic to ferruginous anoxic conditions during the Mulde carbon isotope excursion (CIE). Trace metal patterns include an initial enrichment followed by a reduction in all sections suggesting a drawdown during the first Mulde CIE peak, a renewed enrichment during biotic recovery, and a second decrease indicating another drawdown coinciding with the second Mulde CIE peak. Importantly, this two-step enrichment–drawdown pattern mirrors the double-peaked nature of the Mulde CIE, and thereby suggests globally dynamic bottom water conditions. Mo and U enrichment factors suggest differing degrees of restriction, but shared temporal trends still imply a global redox signal. These results support a model in which climate-driven sea-level fluctuations modulated marine deoxygenation, contributing to the timing and selectivity of extinctions among hemipelagic and planktonic taxa.