Alan T. Baxter

Radiolarian age constraints on Mesotethyan ocean evolution, and their implications for development of the Bangong–Nujiang suture, Tibet

Abstract: Radiolarian discoveries indicate that deep-marine conditions prevailed in central Tibet from the early Middle Jurassic until well into the Early Cretaceous (late Hauterivian–early Aptian; 131–121 Ma) and help to constrain the temporal extent of oceanic conditions along the Bangong–Nujiang suture. These new fossils occur in chert or siliceous mudstone blocks associated with the Lagkor Tso ophiolitic mélange. Basin inversion associated with closure of Mesotethys between the Qiangtang and Lhasa terranes was accompanied by mélange formation and predated regionally widespread deposition of overlying shallow-marine late Aptian–Albian orbitolinid limestones.

Early Cretaceous radiolarians from the Spongtang massif, Ladakh, NW India: implications for Neo-Tethyan evolution

Abstract: The discovery of two Early Cretaceous (mid-Valanginian–mid-Aptian range) radiolarian faunal assemblages from ribbon-bedded cherts collected near Photoskar in northern Ladakh, NW India, provides the first robust biostratigraphic age constraints associated with the Spongtang massif. This klippe of relict Neotethyan suprasubduction-zone ophiolitic rocks and related arc volcanic rocks crops out 30 km south of the Indus suture in Ladakh. The radiolarian assemblages, the age assignment of which lies between published radiometric ages, provide new constraints on the evolution of this intra-oceanic island arc system. Critically, from them it can be inferred that the system was appreciably long-lived (Jurassic–Cretaceous) and more continuous than is commonly considered.