Cretaceous palaeogeography of Tibet and adjacent areas (China): tectonic implications

Abstract

During the Berriasian–Early Barremian, littoral facies were present only on the southern half of the Qiangtang block and the central Lhasa block. In the Late Barremian–Albian, neritic deposits were preserved in the northern Lhasa block, and a littoral environment dominated southern Qiangtang, southwesternmost Tarim, and southern Lhasa. In the Early Cretaceous, the rest of Tibet, including Qaidam, the majority of Tarim and western Qiangtang, Songpan-Ganzi, and the Longmenshan Mountains, may have been uplifted, because only coarse continental deposits are preserved in these areas. In the Late Cretaceous, a littoral environment predominated in Tarim, southern Qaidam, westernmost and southern Qiangtang, the western part of the Sichuan Basin, and Lhasa. Meanwhile, western Qiangtang and Songpan-Ganzi were elevated but the latter not more than 1000m in the Eocene. These facts indicate that during the Late Cretaceous the topographic relief of Tibet, including the present Longmenshan Mountains and Songpan-Ganzi, may have been a rather low peneplain, close to sea level, and that Tibet was intensively elevated after the end of the Cretaceous, its high topography only being the product of the Indo-Asian collision. During the Cretaceous, Tibet and adjacent areas generally were under the influence of a gradual transgression although in southern Tibet a major transgression took place during the Late Barremian–Albian. This fact, and the presence of a thick, widespread, Upper Barremian–Albian inner shelf limestone in northern Lhasa, suggests that southern Tibet underwent intensive back-arc extension deformation during the late Early Cretaceous.