Many negative δ 13 C 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 δ 13 C 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 δ 13 C values have not been directly evaluated. Here we present paired carbonate and organic δ 13 C records that exhibit a coupled negative excursion resulting from multiple periods of meteoric alteration of the carbonate δ 13 C record, and consequent contributions of isotopically negative terrestrial organic matter to the sedimentary record. The possibility that carbonate and organic δ 13 C records can be simultaneously shifted towards lower δ 13 C values during periods of subaerial exposure may necessitate the reappraisal of some of the δ 13 C anomalies associated with noteworthy biogeochemical events throughout Earth history.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Physics and Astronomy(all)