296 INDIAN SUBCONTINENT counterclockwise rotational underthrusting of the Indian continental block beneath the Tibetan Plateau after the latest Miocene Quaternary Sedimentation and Neotectonics The Quaternary geology, which began with the waning phase of the Siwalik sedimentation, came to an end with the most recent upheaval of the Himalayas The depocentres had by then shifted to their subsiding southern parts which ultimately evolved as the IndoGangetic Alluvial Plains (IGAP) Geographically, apart from the Indus-Ganga flood plains, the IGAP also include the narrow basin of the Brahmaputra River in the east and the Thar Desert (along with the North Gujarat Plain) in the west The alluvial sediments over the entire IAGP belt range between 400 m and 800 m, with a maximum thickness of about km along the edge of the Himalayas The belt is divided into a number of sub-basins by several submerged ridges (basement highs) lying across it Quaternary sediments outside the IGAP occur in the Narmada and Tapti Basins in Peninsular India, and along the eastern coastlines Thick laterite formations (some of which contain rich bauxite deposits) were produced at this time in parts of central India, eastern Ghats and the Konkan coasts in the western Ghats The formation of the Thar Desert in the east of the Indus Basin, which had a fluvial pre-history, is linked with the establishment of the monsoon system over the Sub-Continent by the mid-Pleistocene, with the high rising Aravalli Mountains producing the rainshadow zone to its west The series of saline lakes that dot the entire desert-land were formed by the segmentation and blocking of river channels due to neotectonic movements The Quaternary neotectonic movements caused spectacular geomorphic changes in the entire SubContinent, primarily through movements of faultbounded blocks The Rann of Kachch in northern Gujarat is a classic example of regional uplift during historical times The development of the GangaBrahmaputra-Megna Delta Complex (also known as the Sundarban Delta) is a very important geological landform feature which evolved in three stages of tectonically-influenced delta sedimentation processes during the Late Pleistocene A point of interest in the delta sediments is the arsenic toxicity in the groundwater aquifer within the Holocene sediments See Also Gondwanaland and Gondwana Further Reading Dasgupta S and Sengupta P (2003) Indo Antactica correl ation: a perspective from the Eastern Ghats Granulite Belt, India In: Yoshida M, Windley BF, and Dasgupta S (eds.) Proterozoic East Gondwana: Supercontinent As sembly and Breakup Geological Society of London, Special Publications 206: 131 143 Mahadevan TM (1994) Deep Continental Structure of India: A Review Geological Society of India Memoir 28 Mahadevan TM (2002) Geology of Bihar & Jharkhand Bangalore: Geological Society of India Mukhopadhyay D (2001) The Archaean Nucleus of Singhbhum: the present state of knowledge Gondwana Research 4: 307 318 Naqvi SM and Rogers JJW (1987) Precambrian Geology of India New York: Clarendon Press Oxford: Oxford University Press Radhakrishna BP (1983) Archaean granite greenstone terrain of the South Indian Shield, 46 In: Naqvi SM and Rogers JJW (eds.) Precambrian of South India Geological Society of India Memoir Radhakrishna BP and Vaidyanadhan R (1997) Geology of Karnataka Bangalore: Geological Society of India Raval U and Veerasswamy K (2003) India Madagascar separation: Break up along a pre existing mobile belt and chipping of the craton Gondwana Research 6: 467 485 Roy, Abhinaba, Raamachandra HM, and Bandopadhyay BK (2000) Supracrustal belts and their significance in the crustal evolution of Central India Geological Survey of India, Special Publication 55: 387 406 Roy AB (2004) The Phanerozoic reconstitution of Indian Shield as the aftermath of break up of the Gondwana land Gondwana Research 7(2): 387 406 Roy AB and Jakhar SR (2002) Geology of Rajasthan: Northwest India: Precambrian to Recent Jodhpur: Scientific Publishers (India) Sastry MVA, Acharyya SK, Shaw SC, et al (1977) Strati graphic lexicon of Gondwana Formations of India Geo logical Survey of India Miscellaneous Publication 36, 170 Searle MP, Windley BF, Coward MP, et al (1987) The closing of Tethys and tectonics of the Himalaya Geo logical Society of America Bulletin 98: 678 701 Soni MK, Chakraborty S, and Jain VK (1987) Vindhyan Supergroup A review Geological Society of India Memoir 6: 87 138 Subbarao KV (1999) Deccan Volcanic Province Geological Society of India Memoir 43(1) and 43(2), 947 Valdiya KS (1998) Dymanic Himalaya Hyderabad: Universities Press