Constraints on end-Guadalupian seawater biogeochemistry from stable calcium isotopes

Adam B. Jost
Stanford University, Department of Geological and Environmental Sciences Stanford, CA 94305 USA
[email protected]

Understanding the calcium cycle is central to understanding global patterns in carbonate deposition. Flood basalt volcanism has been tentatively linked to dramatic changes in seawater calcium concentration and drops in biodiversity. To investigate this issue, I propose to constrain ocean biogeochemistry during the end-Guadalupian extinction event by measuring stable calcium isotopes preserved in marine carbonate sediments and conodonts (phosphatic microfossils). Interpretation is being guided by a coupled numerical model of the global calcium and carbon cycles.

The end-Guadalupian extinction (ca. 260 Mya) has been linked to flood basalt volcanism from the Emeishan LIP (south China) and its environmental effects; however, the exact environmental consequences of volcanism and the causes of diversity loss remain poorly constrained. A negative excursion in the carbonate carbon isotope (δ¹³C) record has been observed during the latest Capitanian, yet carbon isotopes alone are insufficient to distinguish among numerous scenarios for changes in ocean biogeochemistry, such as ocean acidification, ocean stagnation and overturn, and collapse of the biological pump. Because the carbon and calcium cycles are intimately linked via the weathering and burial of CaCO3 sediment, changes in the calcium cycle and calcium isotope record can be used to place further constraints on carbon cycle behavior and seawater chemistry. Early measurements from the Guadalupian/Lopingian GSSP in south China indicate a positive excursion in the δ⁴⁴/⁴⁰Ca record just below the boundary, which is consistent with an increase in seawater alkalinity due to increasing anoxia.

AAPG Search and Discovery Article #90157©2012 AAPG Foundation 2012 Grants-in-Aid Projects