High resolution organic carbon isotopic compositions (δ13Corg) were analyzed for the samples from Wangjiawan section, Yichang, south China. Three negative shifts have been recognized in the uppermost Ordovician. The results indicate that the shifts were related to environmental changes during the development and the decline of the Gondwana ice sheet. Carbonate deposited in the ice period records, inorganic carbon isotope (δ13Ccarb) curve showing a different trend from δ13Corg : δ13Ccarb shows a sharp and negative shift while δ13Corg shifts positive. The δ13Ccarb curve is a local trend in the restricted Yangtze basin. The in-situ oxidation of organic matter enhanced by glacier induced oceanic circulation in narrow and shallow Yangtze basin, and decreased δ13Ccarb in the carbonate bed.
