Uppermost Jurassic to Lower Cretaceous benthic foraminiferal faunas of the Weimei and the Bandingsi localities of northern and southern parts of South Tibet – A preliminary analysis

Abstract

Diverse foraminiferal assemblages from the Weimei–Gyabula, and the Menkadun–Gucuo formations have been recorded based on the study of two Upper Jurassic to Lower Cretaceous successions, respectively located in the northern and southern parts of South Tibet. Each section contains three different foraminiferal assemblages. Due to the poor state of preservation and the occurrence of long-ranged cosmopolitan species, these foraminiferal assemblages do not allow a precise age assignment for the fossil bearing strata. However, the identification of the Globulina prisca assemblage indicates a Cretaceous age for the Shale Unit of the Gucuo Formation, although the Jurassic/Cretaceous (J/K) boundary was traditionally delineated above this unit. On the other hand, the occurrence of Dorothia oxycona indicates that the uppermost Gyabula and Gucuo formations cannot be older than Aptian and middle Albian age, respectively.During the Late Jurassic to Early Cretaceous, the northern part of South Tibet was located in a deep marine environment, probably at bathyal to abyssal depths, whereas the southern part of South Tibet was part of the outer neritic shelf environment. Typical foraminiferal associations of mildly oxygen-deficient deep-water environment and increased surface productivity have been recorded during the late Early Cretaceous. The biofacies succession indicates that the late Early Cretaceous was associated with a deepening of the palaeobasin, probably associated with a global Albian transgression.