Sedimentary Conext Matters: That Carbon Isotope Excursion may NOT Mean What you Think it Does

Interpreting carbonate and organic carbon isotope covariance in the sedimentary record

Authors:

Oehlert et al

Abstract:

Many negative δ13C excursions in marine carbonates from the geological record are interpreted to record significant biogeochemical events in early Earth history. The assumption that no post-depositional processes can simultaneously alter carbonate and organic δ13C values towards more negative values is the cornerstone of this approach. However, the effects of post-depositional alteration on the relationship between carbonate and organic δ13C values have not been directly evaluated. Here we present paired carbonate and organic δ13C records that exhibit a coupled negative excursion resulting from multiple periods of meteoric alteration of the carbonate δ13C record, and consequent contributions of isotopically negative terrestrial organic matter to the sedimentary record. The possibility that carbonate and organic δ13C records can be simultaneously shifted towards lower δ13C values during periods of subaerial exposure may necessitate the reappraisal of some of the δ13C anomalies associated with noteworthy biogeochemical events throughout Earth history.

pop sci version.