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

An investigation of the local redox landscape of the Middle Ordovician Baltoscandian carbonate shelf using I/Ca records

Paper number: 251-2
Program: Technical Sessions
Time: 8:20 AM – 8:35 AM

Authors

Abstract

The Great Ordovician Biodiversification Event (GOBE) ultimately represents the establishment of modern marine ecosystems as diversity exploded and ecospace utilization expanded. Although the precise causal mechanisms of these profound biotic changes remain contested, several hypotheses involve oxygen, along with paleogeography, sea level, and climatic cooling, in helping initiate and maintain biodiversification. Many studies document the fundamental role of oxygen in driving increases in biodiversity throughout the Phanerozoic, and similar hypotheses have been presented for the GOBE. However, this postulation requires a variety of geochemical data at high spatiotemporal resolution to elucidate the evolution of marine oxygen over this interval as well as more redox-sensitive local proxies to provide context to early changes.

 

Here, we apply the iodine-to-calcium ratio (I/Ca) redox proxy to investigate the local redox landscape of several carbonate-dominated Middle Ordovician sections located in the northern Baltoscandian paleoshelf. Iodine is one of the first elements to respond to variations in upper-ocean oxygen content, making this carbonate proxy especially useful for evaluating early shifts in local marine redox conditions relative to the timings of Ordovician biodiversification pulses. The results of this study suggest these regional marine environments maintained or underwent shifts to comparatively more oxygenated conditions which are coincident with increases in regional diversity. The findings also provide the opportunity to evaluate the relationship between the redox landscapes of the northern versus more central Baltoscandian carbonate shelves. Due to the local-to-regional nature of the I/Ca proxy, this work alone cannot unambiguously connect biodiversity trends to redox conditions on global scales. Nevertheless, this regional study further implicates local marine oxygenation as one of the primary drivers of increased biodiversity on Baltica and provides new insights into connections between habitability, oxygenation, and climate during the GOBE.

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

doi: 10.1130/abs/2025AM-412768

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