The Xialabolin Formation in Xiala, Zada, southwestern Tibet is composed of light grey limestone, distinguishable from its underlying Jiejie Formation that consists of dark, fine-grained clastic rocks with intercalations of glaucolitic sandstone. The age of the Xialabolin Formation in the southwestern Tibet is uncertain without enough fossil evidences This study focuses on the study of the planktonic foraminifera at its type locality mainly. New collections of Cretaceous foraminiferas from 75 samples of the Bolinxiala section yielded an array of planktonic species including Ticinella, Biticinella, Planomalina, Rotalipora, Hedbergella, Whiteinella, Helvetoglobotruncana, Dicarinella, Marginotruncana, Heterohelix, Contusotruncana, Globotruncana, Radotruncana, Gobotruncanita, Gobotrucanella, Gansserina, and Abathomphalus and benthic species including Pseudotextularia, Textularia, and Lenticulina. Some of these species are new.
The new assemblage indicates that the basal portion of the Xialabolin Formation is of late Albian age based on the presence of Ticinella primula, Biticinella breggiensis and Planomalina buxtorfi. At 30m above the base of the Xialabolin Formation, Whiteinella archaeocretacaea documents the OAE2 (Oceanic Anoxic Event 2), and thus the Cenomanian/Turonian boundary in this section. The appearance of Gansserina gansseri and Abathomphalus mayaroensis may indicates a Maastrichtian age for the top of the Xialabolin Formation. Therefore, the foraminiferal assemblage points to a late Albian to Late Maatrichtian age for the Xialabolin Formation. Regional stratigraphic correlation indicates that the Xialabolin Formation may be time equivalent to the Chikkim Formation in Zanskar and Spit to the northwest and the Zongshan Formation and the upper Gamba Group in Tingri and Gamba to the east. Cretaceous Oceanic Red Beds (CORBs), which are widespread in the North Tethyan Himalaya, are usually missing in the South Tethyan Himalaya.
This study is financially supported by the National Basic Research Program of China (973 Program; Grant No. 2006CB701400) and the Young Teacher Research Program of Chian (Grant No. 20070491515).
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