Evaluating the Impact of Early Marine Diagenesis on the Ediacaran-Cambrian carbon isotope record from Sonora, Mexico

Jacob Thompson

Mentor: Dr. Emmy Smith

Johns Hopkins University, Department of Earth and Planetary Sciences

The Ediacaran-Cambrian transition marks a pivotal moment in Earth’s environmental and biological history. This moment in time records a number of crucial changes in Earth’s biosphere, including the disappearance and possible extinction of the Ediacaran biota, some of Earth’s first macroscopic multicellular lifeforms, and the subsequent appearance and diversification of complex animal life. Also recorded during this time is a major perturbation to the carbonate carbon isotope record, a negative carbon isotope excursion known as Basal Cambrian carbon isotope excursion (BACE). Carbon isotope data, captured as carbonate rocks precipitate from seawater, can reveal shifts in the global carbon cycle and thus the mechanisms by which Earth’s environment functioned and changed. However, these data can also record local alteration events, like the introduction of a fluid with foreign geochemical composition that is not reflective of primary, global ocean chemistry when the carbonate formed.

This project aims to determine whether the BACE, as recorded by Ediacaran-Cambrian carbonate strata from Sonora, Mexico, is the product of global seawater changes or local and/or secondary, “diagenetic” processes. To answer this question, major and minor element data were analyzed from a set of carbonate rocks that record the BACE. These data do not point toward a diagenetic origin for the recorded carbon isotope excursion, although they do suggest a change in mineralogy from aragonite or calcite to dolomite. These data provide a glimpse into the geochemical and mineralogical histories of the Ediacaran-Cambrian carbonate strata from Sonora, Mexico. Future work pairing these data with calcium and magnesium isotope data will further elucidate the impact of diagenesis on the Sonoran Ediacaran-Cambrian carbon isotope record.