GLACIO-EUSTASY AND GEOCHEMICAL RECORDS OF THE LATE MISSISSIPPIAN CARBONATE PLATFORM AND SLOPE SUCCESSIONS IN THE EASTERN PALEO-TETHYS OCEAN (SOUTH CHINA)

Shallow marine deposits are sensitive to relative sea-level changes, and the geochemical compositions of these deposits, if subaerially exposed, can be altered during meteoric diagenesis and may not be used for reliable global geochemical proxies. Recent studies suggest that these deposits may, however, record the geochemical compositions of local water masses on semi-restricted seas governed by local, sea-level change related processes, which may, in turn, provide clues to a global driver. Here we present a comparative study on the history of sea-level changes and C and Sr isotopic records of late Mississippian carbonate platform (Yashui section) and slope (Naqing section) successions from South China to provide insight into the sedimentary response to the onset of Carboniferous glaciation. Cyclic facies stacking patterns in the carbonate platform Yashui section suggest changes in the inferred duration and magnitude of sea-level fluctuations recorded in the upper Visean to Serpukhovian successions globally. The uppermost part of the platform cycles roughly corresponds to intervals rich in normally graded bioclastic wacke- to packstones and with distinct rises (~1‰) in conodont δ¹⁸O_PO4 in the carbonate slope Naqing section. In contrast, C and Sr isotopic compositions of micrite and brachiopods from the platform carbonates exhibit systematic fluctuations in step with inferred sea-level changes, whereas slope carbonate and conodont isotopic compositions show minimal variability. These differences are interpreted to record the influence of local processes operating on the carbonate platform in response to glacio-eustasy. Repeated large magnitude shifts in C and Sr isotopic compositions of late Visean to early Serpukhovian carbonates likely record large-magnitude sea-level fluctuations driven by the buildup of Gondwanan glaciers. Decreased magnitude of isotopic shifts through the middle to late Serpukhovian is interpreted to record dampening influence of local processes with long-term sea-level rise in the late Serpukhovian. The coupled stratigraphic and isotopic records indicate stepwise initiation of ice-buildup prior to widespread glaciation across the mid-Carboniferous boundary, likely involving retraction of ice sheets in response to purported late Serpukhovian warming.