Palaeogeographic Significance of 'Yasin-Type' Rudist and Orbitolinid Fauna of the Shyok Suture Zone, Saltoro Hills, Northern Ladakh, India

Along the Shyok Suture Zone in northern India, a ∼200 m thick limestone succession within the larger Saltoro Formation has been identified as a carbonate platform margin with build-ups. This limestone succession is overlying volcanic rocks of island arc affinity, most probably a volcanic ridge. The partly recrystallized reefal limestone contains abundant rudists, echinoid spines, gastropods, algae and a rich orbitolinid assemblage. This faunal assemblage reflects a shallowwater tropical environment and also shows a close affinity with that recorded from the Yasin Group sediments exposed along the Northern Suture Zone in Kohistan, northwestern Pakistan. The rudist fauna from both sites resembles the Horiopleura haydeni/Eoradiolites gilgitensis association from the Yasin Group, and even the very distant classic latest Aptian-Early Albian rudist fauna of the Santander area in NW Spain. The presence of Late Aptian Horiopleura, Radiolitidae and different forms of Orbitolina and other microfaunal assemblages in the Saltoro reefal limestone dates the underlying volcanic edifice as middle Cretaceous or older. Rudists, nerineids, corals and foraminifers of Early-Middle Cretaceous age are widely distributed as reefal frameworks all along the tropical and subtropical Euro-African-Asiatic regions of the northern and southern margin of the Tethys. However, rudist build-ups may also occur far from the continental margins, associated with volcanic edifices like in the Caribbean, Sicily, and seamounts in the central Pacific region or, in our cases, volcanic arcs within the Tethys.