OCEAN CHEMISTRY DURING THE ORDOVICIAN RADIATION: HIGH-RESOLUTION C- AND S-ISOTOPE PROFILES THROUGH THE YANGTZE PLATFORM, HUBEI PROVINCE, CENTRAL CHINA
Here we present new C- and S-isotope data from the Middle Ordovician of the Yangtze Platform, Hubei Province, Central China. On the Yangtze Platform, Middle Ordovician strata are represented by interbedded argillaceous to nodular limestone and calcareous mudstone of the Dawan Formation (Floian-Dapingian-Darwillian) and massively bedded limestone of the Kuniutan Formation (Darwillian). C-isotopes recorded in these strata fall within the same range (-0.8 to +0.6‰) as those preserved globally at this time. Such isotopic stability has been attributed to reduced productivity driven by stagnant oceans, deep-water anoxia, and resultant phosphorous limitation (Saltzman 2005). S-isotope data from Argentina and Newfoundland (Thompson & Kah 2008) support a hypothesis of nutrient limitation. Here, stratigraphically short-term isotopic shifts of up to 6‰ dominate mid-shelf strata and are interpreted to reflect transient changes in the extent of oceanic bottom-water anoxia and associated changes in redox cycling. New, high-resolution S-isotope data from stratigraphically condensed, deeper-water strata of the Yangtze Platform are critical to investigating the extent to which deep-ocean anoxia in the Middle Ordovician may have controlled organic carbon supply, sulfate reduction, and pyrite burial during this time.