δ13C values from the Cenomanian–Turonian passage beds of southern Tibet

Abstract

A group of bituminous sediments of mid-Cretaceous (late Cenomanian–early Turonian) age are well exposed in the Tingri–Gamba basin of southern Tibet. The characteristics of microfossils and geochemistry in the strata show that paleoceanographic environmental changes took place in the Tethys–Himalayan Sea. The δ 13C profiles of southern Tibet are characterized by a low–high–low cycle. The maximum positive excursion of 2.0% occurs at the position just above the Cenomanian and Turonian boundary in Tingri and 2.74% occurs underneath the Cenomanian and Turonian boundary in Gamba. The mid-Cretaceous in southern Tibet is a short period of expansion of the Tethys–Himalayan Sea, which brought about local sea-level rise. The positive excursion of δ 13C coincides with both global and local sea-level rises. The correlation of the δ 13C spike and well-dated occurrence of layers rich in organic carbon indicate that intense orgC burial took place during the latest Cenomanian to earliest Turonian. The positive δ 13C excursion reflects the burial of total dissolved carbon. The positive excursion and excess carbon burial in southern Tibet are coincident with the oceanic anoxic event during the time.