Constraints on the expanse of Greater India in the Early Cretaceous from radiolarians

Abstract

Defining the original size of Greater India is a critical parameter for reconstructing the kinematics and timing of the India–Asia collision. Early Cretaceous paleontology-based paleoceanographic and paleogeographic reconstruction for the northern coast of East Gondwanaland provides independent constraint for the extent of Greater India. In this study, newly discovered Early Cretaceous radiolarian faunas from the Tethys Himalaya were objectively compared with non-Tethyan austral faunas from the Argo Abyssal Plain (AAP) and the typical Tethyan fauna from Italy using the Hayashi's Quantification Method Type III. We found that (1) The occurrence of austral cold-water radiolarian species at the western coast of Australia and northern coast of Greater India is attributable to northward intrusion of circumantarctic cold water via a seaway newly opened during the breakup of East Gondwanaland from ∼136 Ma; (2) Gyangze was under shallow warm-water conditions with typical Tethyan radiolarian fauna (Cluster 3) until the late Valanginian when cold-water species (Cluster 1) arrived from the south. A water mass boundary shift from Tethyan species dominant to austral cold-water species dominant in Gyangze indicates its lower paleolatitude than Ocean Drilling Program (ODP) Leg 123, Site 765 in the AAP; (3) The same austral cold-water radiolarian-bearing intervals from the late Berriasian to Valanginian indicate that Kangma in southern Tibet was proximal to ODP Site 765; (4) Different radiolarian faunas in Italy–Zhongba, Kangma, and the AAP reveal complex water conditions under different degrees of effect by Tethyan warm water and austral cold water at different water depths during the Barremian to Aptian. This radiolarian biogeography is highly consistent with the paleomagnetic reconstruction and indicates that eastern Greater India extended to the Exmouth Plateau (>2400 km) during the Early Cretaceous.