Abstract. The orbitolinid- and rudist-bearing carbonates of Tibet were informally named 'Calcaires a Orbitolines et a Radiolites' by Douville and assigned to a broad age range, notably Barremian to early Cenomanian. The material studied and illustrated by Douville represents a mixture of samples from the Lower-mid-Cretaceous Langshan Formation of southern Tibet (Lhasa Terrane) and the Upper Cretaceous Tielongtan Group of northwestern Tibet (Aksai Chin area) notably the Dongluokezong Formation both bearing orbitolinids as well as rudists. An Aptian-Albian age is confirmed for the Langshan Formation although a late Barremian (or even earlier) age at the base, or an early Cenomanian at the top, might be possible locally but needs further evidence. 'Praeradiolites' hedini Douville, a typical rudist of the 'Calcaires a Orbitolines et a Radiolites' was described from orbitolinid-bearing samples of the Aksai Chin area with an assumed early Cenomanian age. This stratigraphic assignment is here considered misleading to be due to the incorrect identification of Neorbitolinopsis conulus (Douville) with Upper Cretaceous forms such as Calveziconus lecalvezae Caus & Cornella, described more than half a century later from the Campanian of the Spanish Pyrenees. The occurrence of orbitolinids is still today sometimes taken as an argument for parts of the Tielongtan Group to belong to the Lower to mid-Cretaceous interval, a view that has to be corrected. The determinable larger benthic foraminiferan assemblages provide evidence for a Campanian age; however, older strata at the base or younger at the top still lack micropalaeontological data. Compared with the time-equivalent Yigeziya Formation of the western Tarim Basin, the microfauna of the Tielongtan displays only a few common but several unique taxa.
Keywords: Orbitolinidae, Radiolitidae, biostratigraphy, palaeobiogeography, Langshan Formation, Tielongtan Group, Cretaceous.