USING C AND O ISOTOPES TO CONSTRAIN THE SOURCES OF CARBONATE CLASTS IN A CRYOGENIAN GLACIAL DIAMICTITE

Glacial diamictites of the Cryogenian Nantuo Formation of the Yangtze Craton of South China reflect the major environmental transitions during the Marinoan glaciation (~639 to 635 Ma). While the provenance of the siliciclastic components of the Nantuo Formation have been investigated via detrital zircon analysis, the source areas for the abundant carbonate clasts within the formation have yet to be examined. The Mesoproterozoic Shennongjia Group, the only major extant pre-Cryogenian sedimentary carbonate succession in South China, has been proposed as a source of the Nantuo dolostone clasts in the northern Yangtze Craton. It also may have been a major source of Cryogenian carbonate clasts across the entire Yangtze Craton, but this provenance has not been tested. To test this hypothesis, we present δ¹³C and δ¹⁸O data along with petrographic examination of 18 clasts from the Nantuo Formation collected in the Three Gorges area, Yichang in Hubei Province. Our data show that the δ¹⁸O and δ¹³C values of these clasts are distinct from those from the Shennongjia Group, suggesting that the Shennongjia Group is not likely the source of these clasts. Instead, we propose the Nantuo carbonate clasts in the study area were derived from either (1) pre-Marinoan carbonates in South China that were lost due to erosion (the Wujiatai Formation may be the remnants of that carbonate succession) or (2) another region (e.g., the Indian Craton) that was adjacent to the Yangtze Craton during the Cryogenian. Given that paleogeographic reconstructions and detrital zircon provenance analysis suggest separation between the Yangtze Craton and the Indian Craton during the Cryogenian Period, we favor the autochthonous, pre-Marinoan carbonates lost to erosion as the likely source of carbonate clasts. This poster is based on research presented in https://doi.org/10.1016/j.precamres.2022.106734.