GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 115-2
Presentation Time: 8:30 AM


MA, Haoran1, SHEN, Bing2, PENG, Yongbo3, LANG, Xianguo4 and HUANG, Kangjun1, (1)School of Earth and Space Sciences, Peking University, Yifu NO.2 Buliding(New Geology Building), Peking University, No.5 Yiheyuan Road Haidian District, Beijing, 100871, China, (2)School of Earth and Space Sciences, Peking University, Beijing, 100871, China, (3)Geoscience, Louisiana State Universtiy, Baton Rouge, LA 70803, (4)Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing, 210008, China,

The Marinoan global glaciation represents the most extreme icehouse condition in Earth’s history. The ‘Snowball earth’ hypothesis proposed that the whole planet might have been covered by thick ice for tens of million years, resulting in a synglacial reduction of life activity and marine biogeochemical cycles. In order to investigate deglaciation impacting on marine biogeochemical cycles, here we measured carbon isotopic compositions of organic carbon (δ13Corg) and sulfur isotopic compositions of pyrites (δ34Spy) of the Nantuo Formation in South China. The Nantuo Formation, equivalent to Marinoan glaciation, consists four lithological units, in ascending order, the lower diamictite (45 m), lower sandstone unit (60 m), upper diamictite unit (80 m), and upper sandstone unit (50 m). The diamictite unit is the deposition of glaciation, while sandstone unit, though containing thin diamictite layers, can be regarded as interglacial and deglacial depositions, respectively. In the early glaciation, δ34Spy retains constant (~+29‰), but δ13Corg shows a gradually increase from -30‰ to -24‰. In the interglacial interval, δ34Spy becomes more variable (ranging from -17‰ to +32‰), while δ13Corg show small range of variation (-27‰ to -24‰). Both δ34Spy and δ13Corg remain more or less constant (+12~+17‰ and -25~-27‰) during the upper glacial interval. In the following deglaciation process, δ13Corg first show a slightly positive excursion followed by a 3‰ negative shift to the top of the Nantuo Formation, whereas δ34Spy shows a gradual increase to ~+32‰, and become extreme variable at the top 5-m of the Nantuo Formation. Carbon and sulfur isotope data suggest that active biogeochemical cycles during the Marinoan glaciation, particularly the interglacial and deglacial processes, confirming active life activities as shown by the fossil record.