From Neo-Tethyan convergence to India-Asia collision: radiolarian biostratigraphy of the Cretaceous to Paleocene deep-water Tethys Himalaya

Abstract

Deep-water strata preserved in the distal northern Indian margin record the evolution of the Neotethys Ocean before and during the India-Asia initial collision. These strata are however difficult to date precisely as radiolarian are the only fossils present. We here revise the Cretaceous to Paleocene stratigraphy of deep-water sediments deposited in the distal part of the Indian passive margin, located just south of the Yarlung-Tsangpo suture zone near Saga. Four radiolarian assemblages are illustrated and correlated to the Cecrops septemporatus zone to Aurisaturnalis carinatus zone (late Valanginian to Barremian), the Turbocapsula costata zone (Aptian), the Spoletoensis zone (Albian), and the RP6a subzone (lower Selandian). Four units deposited from the Early Cretaceous to the Paleocene are thus identified (bottom to top): Rilang, Duobeng, Chuangde, and Sangdanlin formations. Such a revised stratigraphic scheme allows correlation with the sedimentary successions exposed in the Gyangze and Zhongba areas. Stratigraphic correlation proves that Indian-derived sandstones below the India to Asia provenance reversal (IAPR) were deposited on the Indian passive margin rather than on Neotethys oceanic crust. Sand injection complex preserved in the lower part of the deep-water sediments is related to extensional tectonics associated with Lower Cretaceous volcanism documented all along the northern margin of India. This study provides a much improved framework to interpret the geological evolution of the deep-water edge of the northern Indian margin during progressive closure of the Neotethys Ocean culminated with the onset of the India-Asia collision.