A DATABASE APPROACH TO INVESTIGATING DEPOSITIONAL CONTROLS ON SULFUR AND CARBON ISOTOPE RECORDS

Stable isotope measurements of carbonate rocks are widely used to gain insight into global biogeochemical cycles throughout Earth’s history, as well as the specific depositional and diagenetic history of a sample. Disentangling global signals from regional or local signals is not straightforward, but is a key challenge in using these measurements to create a robust record of Earth’s ancient environments. Paired sulfur isotopes in carbonate-associated sulfate (δ34SCAS) and carbon isotopes (δ13C) provide insight into seawater chemistry, oxidation, and the coupled sulfur and carbon cycles, but a high degree of temporal and spatial variability characterize these records. This variability may be a result of smaller scale heterogeneities related to facies and sedimentological processes which have, themselves, evolved over time. Using over 100 sedimentological descriptors in the style of the Microstrat database (Cantine et al. 2020), over 20 km of stratigraphic section has been digitized, spanning the Late Cryogenian to Late Cretaceous. This detailed work creates the first high-resolution database that pairs detailed facies data with δ34SCAS, δ13C and δ18O stable isotope data.

Our results suggest important links between environmental and sedimentological parameters in δ34SCAS and δ13C records, including microbial influence and reworking. In addition, this work supports findings such as the evolution in carbonate mineralogy (Awramik, 1971; Walter and Heys, 1985; Kennard and James, 1986) and boundstone abundance (Walter and Heys, 1985) over the Precambrian-Cambrian transition. These findings highlight the usefulness of the database approach in investigating sedimentological hypotheses across multiple sections and datasets, and thus require revisions in how we apply stable isotope proxies to reconstruct paleo-sulfur and carbon budgets. Recognition of this complexity provides new geochemical opportunities to interrogate conditions of depositional facies and diagenetic regimes.