Palynological stratigraphy of the Late Cretaceous and Cenozoic collision-related conglomerates at Qiabulin, Xigaze, Xizang (Tibet) and its bearing on palaeoenvironmental development

Abstract: The stratigraphy, age, depositional environment and correlation of the collision-related variegated sandstone and conglomerate beds exposed along the southern side of the Gangdise Mountains to the north of the Yarlung Zangbo suture in the Xigaze region, Xizang (Tibet) have been much debated. Generally referred to as the Dagzhuka Formation, these beds of great thickness have, until recently, not been reported to contain any convincing fossils. Two distinctly different palynological assemblages, indicating Late Cretaceous and Oligocene–Early Miocene ages respectively, have now been recovered from lithologically distinguishable units of the sedimentary succession at Qiabulin to the west of the town of Xigaze. This means that instead of one stratigraphic unit, as has been generally accepted hitherto, at least two are represented. As a result, the Dagzhuga Formation is considered here to refer only to the Cenozoic deposits and the Qiabulin Formation, previously regarded as a synonym, is resurrected to accommodate the Cretaceous beds. These two formations were juxtaposed by tectonic movements. Our finding indicates that the stratigraphic successions on the southern Laurasian continental margin of Xizang reflect changes from a deep forearc basin through shallow littoral environments to a mountainous landscape during the Late Cretaceous and early Cenozoic. This interpretation compares well with those documented from the Gamba and Tingri districts to the south of the Yarlung Zangbo suture. [Copyright &y& Elsevier]