Multi-proxy constraints on the significance of covariant δ13C values in carbonate and organic carbon during the early Mississippian

Authors

Amanda M. Oehlert, Rosenstiel School of Marine and Atmospheric SciencesFollow
Peter K. Swart, Rosenstiel School of Marine and Atmospheric Sciences
Gregor P. Eberli, Rosenstiel School of Marine and Atmospheric Sciences
Samantha Evans, Boise State University
Tracy D. Frank, University of Nebraska at LincolnFollow

Date of this Version

2019

Citation

Sedimentology (2019) 66, 241–261

Comments

© 2018 The Authors.

doi: 10.1111/sed.12502

Abstract

This study investigates the covariation between carbonate and organic δ¹³C values in a proximal to distal transect of four outcrops in the Madison Limestone in the Western United States Rockies, combined with δ³⁴S values of carbonate associated sulphate, the concentration of acid-insoluble material and measurements of total organic carbon. These new geochemical datasets not only allow for an evaluation of carbon isotope covariance during one of the largest perturbations to the global carbon cycle over the past 550 Myr, but also constrain the cause of the excursion in carbonate δ¹³C values. The results support the hypothesis that a period of anoxia did not play a role in generating the positive carbonate δ¹³C values, but rather favour interpretations by previous workers that the proliferation of land plants destabilized the Carboniferous carbon cycle, setting the stage for a significant change in the carbonate δ¹³C values of contemporaneous marine carbonates. These results also demonstrate that one of the largest perturbations to the global carbon cycle did not produce synchronous variations in carbonate and organic δ¹³C values, emphasizing the importance of local depositional controls on carbon isotope covariance in the geological record in both modern and ancient environments.