The paleoposition of India

Abstract

In most of the plate tectonic models of paleocontinental assembly, the supercontinent Pangea has been disassociated into independent Laurasia and Gondwana, separated by a vast oceanic Tethys. The position of India remains problematical, but geological and geophysical data support a Pangea reconstruction. Traditionally India has always been regarded as a part of Gondwana as it shares two unique geologic features with other southern continents. These are the Upper Paleozoic glacial strata and the Glossopteris flora. However, neither line of evidence definitely proves continuity of land; together they indicate zonation of cold climates. The recent discovery of Upper Paleozoic glacial strata in the U.S.S.R., southern Tibet, Saudi Arabia, Oman, China, Malaya, Thailand, and Burma demonstrates that the Permo-Carboniferous glaciation was far more extensive beyond the Gondwana limit than is usually thought. Similarly the Glossopteris flora has been found farther north of the Indian Peninsula, in the Himalaya, Kashmir and Tibet. Moreover the floral similarities are explained easily by wind and insect dispersal. On the other hand, the distribution of large terrestrial tetrapods is strongly influenced by the distribution of continents. To terrestrial tetrapods, sea constitutes a barrier. In consequence, they are more reliable indicators of past land connections than are plants, invertebrates and fishes. The postulated separation of India from Antarctica, its northward journey, and its subsequent union with Asia, as suggested by the plate tectonic models, require that during some part of the Mesozoic or Early Tertiary India must have been an island continent. The lack of endemism in the Indian terrestrial tetrapods during this period is clearly inconsistent with the island continent hypothesis. On the contrary, Indian Mesozoic and Tertiary vertebrates show closest similarities to those of Laurasia, indicating that India was never far from Asia. The correlation of faunal similarity is extremly poor between India-Antarctica and India-Australia. This suggests that India cannot be placed alongside Antarctica or Australia in a pre-drift assembly. Moreover, the distribution of marine rocks indicates that India faced an open sea at its eastern margin during Proterozoic, Upper Paleozoic and Mesozoic. Before the drift, India probably occupied the position between Somalia and Asia, and the Tethys was narrow and intracontinental. With the spreading of the Carlsberg Ridge in the Upper Cretaceous, the Indian block rotated counter-clockwise in relation to Africa to converge to Asia, with the opening up of the Arabian Sea. The rotational movement of India is supported by hot spot trajectory and reversal of paleoslopes of the ancient Gondwana rivers. There is a possible genetic relation between the Arabian sphenochasm and the origin of the Himalaya. With continued convergence of India to Asia, limited subduction occured at the Indus Suture along the axis of the Tethys; the further compression led to the closure of the Tethys followed by foldings, faultings and large-scale intracratonic subductions to form the Himalaya. The Himalayan uplift probably began in the Miocene, but went more actively in the Quaternary.