251 Phanerozoic Earth System Shifts in the Marine Sedimentary Record

This session explores Earth System shifts documented as perturbations to the Phanerozoic geochemical, lithological, and biogeochemical marine records, leading to climate shifts, anoxia, ocean acidification, and extinction events.

Wednesday, 22 October 2025
8:00 AM - 12:00 PM
HBGCC, 303AB

Dynamic Ocean Redox Changes Across Multiple Basins During the mid-Silurian Mulde/lundgreni Event

Paper number: 251-5
Program: Technical Sessions
Time: 9:05 AM – 9:20 AM

Authors

Abstract

The mid-Silurian Mulde (lundgreni) Event was a time of major environmental and biotic change, marked by a widespread extinction among graptolites and other marine taxa and a distinctive double-peaked positive carbon isotope excursion (CIE). Although this event has been extensively studied, the nature and extent of oceanic redox changes during this interval remain poorly understood. To address this gap, we applied a multi-proxy geochemical approach to three successions across two paleocontinents: Abbott River and Twilight Creek (Arctic Canada, Laurentia) and the Priekule-20 core (Latvia, Baltica). New records of organic carbon and pyrite sulfur isotopes, iron speciation, and trace metal concentrations were integrated to reconstruct local to regional paleoredox conditions spanning the Mulde Event. Our results reveal synchronous positive excursions in δ¹³Corg and δ³⁴Spy across all sites, suggesting enhanced organic carbon and pyrite burial. Iron speciation indicates persistently ferruginous bottom waters in Laurentia, while Baltica experienced more variable conditions, oscillating between oxic and ferruginous condtions during the Mulde CIE interval. Trace metal enrichments show a two-step pattern, initial enrichment followed by drawdown, then renewed enrichment during biotic recovery and a second drawdown coinciding with the second CIE peak. This pattern is antithetical to the double-peaked structure of the Mulde CIE and suggests that global bottom-water redox conditions were dynamically linked to the extinction and recovery phases. These findings support a scenario where climate-driven sea-level changes modulated marine deoxygenation, influencing the timing and selectivity of extinctions among planktonic and hemipelagic organisms. Our study highlights the importance of integrating multiple geochemical proxies across paleocontinents to unravel the complex environmental dynamics during this critical Silurian event.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414477

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