Persistence of a shallow-marine environment in the western Kunlun area (northwestern Tibet) until the early Maastrichtian: evidence from radiolitid rudist bivalves

Abstract

The closing of the Tethys Ocean during the Mesozoic and Cenozoic dramatically affected the palaeogeography, palaeoenvironment and biotic evolution of the Tibetan Plateau and surrounding areas. The timing of closure of the Tethys Ocean in different areas is recorded by the youngest marine deposits. In the western Kunlun area of northwestern Tibet, the Tielongtan Group represents the youngest marine deposits, and is rich in rudist bivalves; however, its depositional age, particularly the age of final deposition, is poorly constrained. Systematic and palaeobiogeographic analyses were conducted on rudists from the Tielongtan Group in the eastern Loqzung Mountains. Four genera and two species were identified: Biradiolites boldjuanensis, Gorjanovicia acuticostata, Durania sp. and Radiolites sp. The occurrence of the lower Maastrichtian index fossil, Biradiolites boldjuanensis, indicates that deposition of the Tielongtan Group continued until the early Maastrichtian. Therefore, the results of this and previous studies indicate that deposition of the Tielongtan Group spanned from at least the Turonian to the early Maastrichtian. Palaeobiogeographical analyses show that B. boldjuanensis was endemic in Central Asia, whereas G. acuticostata might have extended beyond the Mediterranean region. During the Late Cretaceous, the shallow ocean in the western Kunlun area contained both cosmopolitan and endemic rudists.