Guest editorial for the special issue “Tectonics of Bay of Bengal and Arabian Sea with special emphasis on coastal and marine geohazards”

Abstract

The Indian Ocean, the third largest of the world’s oceans, is comprised of diverse and complex tectonic features. The Arabian Sea and the Bay of Bengal, bordering the Indian Peninsula on west and east, respectively, constitute the northwestern and northeastern parts of the Indian Ocean. The evolution of Indian Ocean and the present morphology and tectonics of the bordering continental margins are the consequence of the breakup of Eastern Gondwanaland and subsequent seafloor spreading between the constituent continents viz., Madagascar, Seychelles, India, Antarctica, and Australia, since the Early Cretaceous. There were three main episodes in the disintegration of Gondwanaland (Storey 1995). The rifting started during the Early Jurassic, when Gondwanaland separated into eastern and western parts, causing a seaway separating South America–Africa from Madagascar–Seychelles–India-Antarctica–Australia–New Zealand. The second stage occurred in Early Cretaceous, with South America separating from an African-Indian plate and African-Indian plate itself separating from the Antarctica. Finally, the third stage occurred in Late Cretaceous when Australia and New Zealand got separated from Antarctica. Around this time, Madagascar separated from India, and the latter migrated northward. The initial separation of India from Antarctica (130 Ma) was in a NW–SE direction, and around Late Cretaceous (90–80 Ma), a plate reorganization took place when this orientation changed essentially to N–S. The soft collision between India and Eurasia might have occurred around 59 Ma (Paleocene-Eocene boundary), which resulted in the initiation of Himalayan uplift (Curray and Munasinghe 1989). The hard Continent–Continent collision with the Eurasian landmass occurred at about 15 Ma (Middle Miocene). The massive uplift of Himalayas caused huge sediment influx into the adjoining ocean basins and formed the Indus Fan in the Arabian Sea and the Bengal Fan in the Bay of Bengal, the world’s two largest Fan systems (Curray et al. 2003; Kolla 2007). The earliest studies on the stratigraphy, structure, and tectonics of the northern Indian Ocean during the International Indian Ocean Expedition (IIOE: 1960–1965) evoked considerable nterest on this tectonically complex region. Subsequent geophysical studies during the period from 1970 to this date, mainly by the National Institute of Oceanography, India, and also by other academic institutes and organizations led to the generation of several new concepts on the structure, tectonics, and