Investigating Ediacaran-Cambrian carbon isotope variability from the Zuun-Arts Formation in southwestern Mongolia

Abstract:

The carbonate-rich Zuun-Arts Formation of the Zavkhan terrane, southwestern Mongolia, records a 4-6‰ drop in carbon isotope values over ~150-400 m of stratigraphy, locally reaching values as low as -10‰. This negative carbon isotope excursion has been correlated with the basal Cambrian negative carbon isotope excursion (BACE) recognized in end-Ediacaran strata around the globe, and, along with other relative age constraints, has been used to identify the Ediacaran-Cambrian boundary in Mongolia. However, unlike other BACE excursions, the Zuun-Arts carbon isotope record captures lateral variability between localities, across ~120 kms. This variability complicates chemostratigraphic correlation regionally and globally, particularly when lithostratigraphy and sequence stratigraphy are considered.

Here we present high-resolution (0.5-1.0 m) carbon isotope (δ¹³C_carb) records from stratigraphic sections measured across the Zavkhan terrane. To characterize the spatial scale of Zuun-Arts carbon isotope reproducibility, parallel stratigraphic sections were measured meters to hundreds of meters apart. To identify reasons for local carbon isotope record variation, we integrate sedimentological data with carbon isotope data from these sections. We also pair carbon isotope records with proxies for geochemical alteration, including calcium isotope (δ^44/40Ca_carb) and Sr/Ca records.