Integrated stratigraphy of the upper Neoproterozoic succession in Yunnan Province of South China: Re-evaluation of global correlation and carbon cycle

This study provides a chemostratigraphic and sequence stratigraphic framework of a relatively unfossiliferous sub-Cambrian marine sedimentary succession in Yunnan Province of South China. Our results allow its global stratigraphic correlation and provide an improved understanding of marine carbon cycle during the late Neoproterozoic. The succession has a basal glacial diamictite (“Nantuo” Formation) and comprises two large-scale depositional cycles towards the Precambrian-Cambrian (PC-C) boundary, each of which changes from siliciclastic to carbonate sediments with environments ranging from shallow subtidal to evaporitic supratidal. In the absence of biostratigraphic control, attribution of the tillite has remained equivocal between the ∼710 Ma Sturtian and ∼635 Ma Marinoan glaciations. A compilation of known paleomagnetic and other geochronologic constraints suggests that the Nantuo glaciation in South China was at least diachronous, in which the “Nantuo” tillite in Yunnan belongs to the older glaciation. Stratigraphic patterns of the diagenetically-screened δ 13C variation and depositional sequences during the carbonate-dominated interval show a striking similarity with those of the upper Cryogenian and entire terminal Proterozoic carbonates at widely-separated other localities rather than the terminal Proterozoic alone, supporting the view that deposition of the “Nantuo” tillite in Yunnan reflects the Sturtian rather than Marinoan glaciation. Further considerations of the δ 13C results provide three important implications for the late Neoproterozoic marine carbon cycle. First, comparison of different δ 13C profiles suggests considerable variability in the absolute values of carbonate on both intra- and inter-basinal scales, which differs profoundly from their relative homogeneity in marine Phanerozoic counterparts and may therefore reflect lateral isotopic heterogeneity in the oceanic carbonate reservoir during the late Neoproterozoic. Second, an empirical correlation between the δ 13C and relative sea-level changes was applied to evaluate hypothesized explanations for δ 13C temporal variation in surface sea, yielding short-term inverse and long-term positive relationships. The short-term trend marks periods of the negative δ 13C excursions and is compatible to most of the existing arguments for the δ 13C events. On the other hand, mechanisms causing the long-term trend remain enigmatic in the absence of comparable data from other localities. Our observ