Abstract:Objectives: The Neoproterozoic Snowball Earth events represent the extreme climate change in the Earth’s history and exert a fundamental impact on subsequent atmospheric and oceanic oxygenation, elemental biogeochemical cycling, and eukaryotes diversification in the Ediacaran Era. However, the apparent lack of primary marine precipitates limited the understanding of the synglacial ocean chemistry during the Snowball Earth. A bed of synglacial dolostone in the Nantuo Formation, Nanhuan Sestem, of a drill core in Guizhou Province, south China, provided the ideal materials for research of ocean chemistry during the Nantuo (Marinoan) Glaciation.Methods: Observation of dolostone lithology was conducted by polarized light microscope and scanning electron microscope; The stable carbon and oxygen isotopic compositions of the dolostone samples were analyzed by Delta V Advantage stable isotope mass spectrometer in Guizhou University; trace elements of the samples were analyzed by inductively coupled plasma mass spectrometry (ICPMS).Results: The results show that the values of δ18OVPDB and δ13CVPDB of the samples are ranged from -16.97‰ to -8.37‰, and from -9.68‰ to -8.42‰, respectively. Compared with the carbon isotopic compositions of carbonate rocks before and after the Nantuo (Marinoan) Glaciation, δ13CVPDB values of the dolostone samples in the Nantuo Formation have significantly low negative values. The results of trace element analyses by ICPMS show that the contents of iron and manganese in the dolostone samples are very high with the average of iron,manganese, and strontium content 92867×10-6, 10644×10-6, and 470×10-6, respectively. The average Mn/Sr in the dolostone samples is 26.89. Based on the correlation of carbon and oxygen isotopes and the characteristics of trace elements, it is suggested that the carbon isotopic composition of dolostone in the Nantuo Formation represents the original sedimentary record.Conclusions: ① The finding of the dolostone bed in the Nantuo Formation indicates that open waters existed during the Nantuo (Marinoan) Glaciation in south China and the open water provided the oases for eukaryotes. ② Marine chemistry was dominated by anoxic and ferruginous conditions during the Nantuo (Marinoan) Glaciation, and negative carbon isotope excursion during the period was mainly ascribed to the anaerobic oxidation of methane (AOM) by iron and/or manganese oxides under the anoxic and ferruginous conditions. ③ Based on the simple isotope mass balance calculation, it is suggested that high fraction of buried organic matters and limited gas exchange between air and ocean—gas contribute to the rise of atmospheric oxygen level during the Nantuo (Marinoan) Glaciation.