ABSTRACT: This investigation of Upper Cretaceous and lower Paleogene sediments from the Tibetan Himalayas, based on three stratigraphic sections from the southern margin of Asian Plate and nine sections from the northern Indian Plate margin, provides the first high resolution biostratigraphic description of the region. The sedimentary successions from these two plate margins evolved during the following depositional stages, which we here divide into eleven new biozones (TLK2-3 and TP1-9); (i) an outer neritic stage from the Coniacian to the Maastrichtian, dominated by keeled planktonic foraminifera (PF), such as Globotruncana (TLK2); (ii) a latest Maastrichtian forereef assemblage dominated by Lepidorbitoides, Omphalocyclus andOrbitoides (TLK3); (iii) an early Paleocene, intermittently occurring backreef/shallow reefal warm environment with benthic assemblages dominated by small miliolids and rotaliids, such as Daviesina and Lockhartia (TP1-2); (iv) a late Paleocene-early Eocene, shallow reefal environment dominated by warm water forms, such as Alveolina, Assilina and Nummulites (TP3-7); (v) a depositional stage showing a slight deepening of the reef, with forereef assemblages, lasting until the end of theYpresian (TP8); (vi) a final, early Lutetian depositional stage characterised by the complete disappearance of the larger benthic foraminifera (LBF) and their reefal environment, which was replaced by PF assemblages with intense reworking of pelagic facies triggered by the tectonics of the India-Asia collision (TP9). During the course of this study two unnamed species have been identified and described, Lepidorbitoides sp. A and Discocyclina sp. A, from the Xigaze forearc basin. The high resolution depositional and biostratigraphic scheme defined here for the southern Himalayan region gives greater insight into the general evolution of this globally important tectonic region.We have confirmed earlier observations that many LBF forms appear about 1Ma later in the eastern part of Tethys than they do in the west, reflecting their previously inferred gradual eastern paleogeographic migration. Additionally, this study has allowed us to refine the biostratigraphic ranges of some LBF of the Eastern Tethys, and for the first time to exactly correlate these Eastern Tethyan zones with the Shallow Benthic Zones (SBZs) of the Western Tethys.
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