Occurrence of benthic foraminifers across the Jurassic/Cretaceous transition in Gyangze, southern Xizang (Tibet), China

Abstract

A relatively low diversity, bathyal benthic foraminiferal assemblage was recovered from the Lower Cretaceous Rilang and Gyabula formations at Chuangde near Gyangze, southern Xizang (Tibet). The assemblage contains 16 taxa belonging to 14 genera, including epifaunal forms dominated by detritus feeders, such as Ammodiscus tenuissimus, Glomospira charoides and Glomospirella gaultina, and rare tubular forms considered to be suspension-feeders such as Rhizammina indivisa and Nothia excelsa. The infaunal component is dominated by Textulariopsis sp. and Pseudobolivina sp., with rare Psammosphaera sp., Haplophragmoides sp. and Reophax sp., previously assigned to a “Biofacies B” indicative of a mildly oxygen-deficient deep water environment and increased surface water productivity. However, the rare occurrence of robust calcareous forms indicates that taphonomic processes considerably altered the original assemblage. The occurrence of the age diagnostic small morphotype of Lenticulina ouachensis in the upper Rilang Formation indicates a late Valanginian–early Hauterivian age, allowing correlation with coeval sections from the Vocontian Trough, northern Tethys (Bavarian Alps) and eastern Indian Ocean (Ocean Drilling Program Site 766 off northwestern Australia).