CHEMOSTRATIGRAPHY AND BIOSTRATIGRAPHY OF NORTHERN MONGOLIA'S KHUBSUGUL BASIN: LINKS BETWEEN GEOCHEMISTRY AND EVOLUTION IN THE EDIACARAN AND EARLY CAMBRIAN

Sustained perturbations in the global carbon cycle accompanied the rapid diversification of biota during the Cambrian Explosion. Northern Mongolia’s Khubsugul Basin contains < 6 km of strata that record these geochemical and evolutionary events. The basin was deposited in the late Neoproterozoic and Early Cambrian and contains a series of deep-water carbonates, siliciclastics, and one of the world’s largest phosphorite deposits. As such, the succession is a promising target for integrated stratigraphic, geochemical, and paleontological studies of this pivotal time period of Earth’s history.

We examined a suite of the Khubsugul Basin’s late Neoproterozoic and Early Cambrian limestones and dolostones for which the inorganic carbon isotope record has already been documented. Here we present new organic carbon isotope data paired with the existing inorganic carbon data. We compare these records to a radiometrically-calibrated composite isotope record from Morocco. Furthermore, we report the first carbonate-associated sulfate sulfur isotope data set from the Khubsugul Basin. The samples were screened for diagenetic alteration by analysis of major and trace cation abundances.

By documenting the Khubsugul Basin’s organic carbon and carbonate-associated sulfur isotopic variability as well as its small shelly fossil biostratigraphy, we hope to better constrain the depositional chronology of the basin and contribute to the growing body of work describing the redox conditions of the oceans in which early animals evolved.