Late Albian–early Turonian calcareous nannofossils from southern Tibet — Implications for preservation, biostratigraphy and palaeoecology

Marine strata of Cretaceous age are widely distributed and well exposed in the Gamba area of South Tibet. A pre-requisite for understanding the depositional and palaeoenvironmental processes, which formed these deposits, is a reliable stratigraphic framework. The strata of the Qiangdong section in the Gamba area yielded calcareous nannofossils which provide a powerful tool for establishing a detailed biostratigraphic subdivision. They also allow for supra-regional correlation, ideally on a global scale. The current study investigates the preservational state and stratigraphic significance of calcareous nannofossils from 63 samples. A total of 76 species have been identified in the 159 m thick section, allowing for the recognition of seven bioevents (calcareous nannofossil zones UC0 to UC7) covering the upper Albian–lower Turonian interval. The first occurrences of the calcareous nannofossil marker species Corollithion kennedyi (base UC1a, 100.5 Ma) and Quadrum intermedium (base UC5c, 94.1 Ma) constrain the Albian/Cenomanian and Cenomanian/Turonian boundaries in the Qiangdong section. A regional comparison with findings from the Tingri area, about 150 km west of the studied section, enhances the precision of biostratigraphic correlations in South Tibet. The findings emphasize that preservation and diagenetic influence need to be critically considered when interpreting nannofossil assemblages for palaeoenvironmental reconstructions.