Age of the radiolarian chert from the Zhilong section in Gyangze, southern Tibet and its implications

Bedded cherts are well exposed in the Zhilong section near Zhilong Village, Gyangze County, southern Tibet, China. Abundant and moderately- to well-preserved Late Jurassic to Early Cretaceous radiolarians extracted from 31 cherty samples from this section are attributed to 95 species in 40 genera. As compared with the Mesozoic radiolarian zonation in other areas, especially in the West Tethys, the radiolarian assemblages from Zhilong are considered late Kimmeridgian-earliest Hauterivian in age and therefore Units 5 and 6 at the Zhilong section were deposited during the same interval. The stratigraphical sequence of the Zhilong section is considered to be reversed and the Jurassic/Cretaceous boundary interval probably occurring in the Unit 5.