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

Lithium isotope constraints on terrestrial clay formation during the Ediacaran–Cambrian transition

Paper number: 251-1
Program: Technical Sessions
Time: 8:05 AM – 8:20 AM

Authors

Abstract

The Ediacaran–Cambrian transition represents a crucial period in Earth’s history, marked by global tectonic reorganization, potential glaciation, and sea level fall leading to the widespread development of marine evaporites, as well as the demise of the enigmatic Ediacara biota and rise of early metazoans during the Cambrian Explosion. Redox fluctuations across this transition have been linked to faunal turnover, which may be related to changes in organic carbon burial rates, but the driving force(s) associated with the wax and wane of organic burial fluxes remain unclear. Here, we present new lithium isotope data from three marine carbonate sections of the northern Siberian Platform that record a profound rise in δ7Li values (up to 32‰) associated with the BACE event. Petrographic and geochemical screening suggest that the upward trend in carbonates reflects that of contemporaneous seawater. Mass-balance modeling and geochemical constraints suggest that this rise in seawater δ7Li cannot be explained by local alteration or evaporite-associated sinks. Instead, we interpret it as reflecting a global change in the continental weathering regime from more congruent weathering throughout much of the Precambrian to more incongruent weathering, linked to intensified clay formation on land. The onset of the terrestrial “clay mineral factory” could have enhanced the efficiency of organic carbon burial through clay-organic matter complexation, supporting at least transient and heterogeneous oxygenation of Earth’s surface environment. Our findings reveal a fundamental link between clay formation, ocean chemistry, and biospheric evolution at the dawn of the Phanerozoic.

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

doi: 10.1130/abs/2025AM-414714

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