International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

Nannofossil biostratigraphy of the Lower Cretaceous Shadui Formation (Northern Tethyan Himalayas, Southern Tibet)

Published: Oct 2010

Pages: 383 - 391



Abstract: Calcareous nannofossils of Aptian-Albian age were found in the basal part of the Shadui Formation, Northern Tethyan Himalayas, Southern Tibet. The predominantly shale strata are exposed near the northeastern tip of Yamdrock Tso Lake at the locality of Bangbu and they were previously considered to be of Late Cretaceous age. Occurrence of the nannofossil species Prediscosphaera columnata and Cribrosphaerella ehrenbergii indicates the Upper Aptian–Lower Albian Zone BC23. Nannofossil species of Late Albian, Cenomanian or younger Cretaceous age were not present in the studied part of the Shadui Formation. Nannofossils are badly preserved and hardly identifiable probably as a result of strong post mortem etching and dissolution during burial. The depositional setting of the Shadui Formation is interpreted as hemipelagic to pelagic. A horizon of dark shale in the lower part of the Shadui Formation may be stratigraphically correlated with ocean anoxic event OAE1b. The discovery of calcareous nannofossils at the Bangbu locality increases the stratigraphic precision in the correlation of Cretaceous strata between hemipelagic-pelagic facies and shelf depositional areas in the Tibetan Tethyan Himalayas.

Keywords: Lower Cretaceous, Northern Tethyan Himalayas, Shadui Formation, biostratigraphy, oceanic anoxic event, calcareous nannofossils

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