High resolution Ordovician (Floian-Sandbian) carbon isotope stratigraphy from the Jiangnan slope, South China: The first complete record of the MDICE in δ13Corg and its global significance

The Middle Darriwilian Isotopic Carbon Excursion (MDICE) is one of the globally recognized positive excursions in carbon isotope chemostratigraphy, but mainly documented by δ¹³C_carb data in previous research. In this paper, new stable organic carbon isotope data (δ¹³C_org) are presented from the Hule-1 core from the southern Anhui Province of southern China. The core constitutes an Ordovician siliciclastic succession deposited in the upper Jiangnan slope. The Ordovician graptolite biostratigraphy of this area is already well established, and ranges from the Baltograptus deflexus Zone (Floian) to the Nemagraptus gracilis Zone (Sandbian). Based on the well-constructed graptolite biostratigraphy, a low-amplitude positive excursion of middle–late Darriwilian age within the Hulo Formation is confidently identified as the MDICE. The excursion has an amplitude of ca. 1.1‰ starting from the value of −28.0‰ near the base of this formation, reaching a peak at −26.9‰ in the middle, and decreasing to −28.5‰ in its upper part. Therefore, it reveals to our knowledge the globally best preserved and most complete δ¹³C_org record of MDICE hitherto. Our data elucidate the stratigraphic significance of the MDICE also in deeper depositional environments and as a tool for correlation across different lithofacies belts. The inferred perturbation of the global carbon cycle during this time interval was presumably more pronounced than previously thought, confirming that the Darriwilian was a critical time slice in terms of environmental and biosphere changes.