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The Rivers of Indian Peninsula: Their Salient Geomorphic Characteristics and Ancestry Journal of Indian Geomorphology Volume 8, 2020 l ISSN 2320-0731 Indian Institute of Geomorphologists (IGI) The Rivers of Indian Peninsula: Their Salient Geomorphic Characteristics and Ancestry Vishwas S. Kale Formerly at Department of Geography, Savitribai Phule Pune University, Pune 411007 E-mail: [email protected] Abstract: The Indian Peninsula dominantly displays an erosional landscape. Bedrock landforms and bedrock rivers are more common. The diversity in topography, drainage and landforms visible today has developed during the nearly 9000 km long northward journey of the Indian Plate since the breakup of the Gondwanaland. Some of the distinctive topographic and drainage network characteristics of this ancient landmass are described in this paper. An attempt has also been made to tentatively reconstruct the ancestry of the main-stem rivers on the basis of available geological and geomorphic data.Multiple lines of evidence suggest that many of the river systems of the Peninsula consist of segments of different ages, and the complete integration of the older and younger drainage has taken place during the Cenozoic. Recently acquired geochronological data strongly suggest that climate rather than tectonics is primarily responsible for the modern-day relief of this ancient landmass. Introduction With an area of about 2.1 M km2, the from the Gondwanaland and onset of the Indian Peninsula is the largest and the oldest northward drift, the Indian landmass has been geomorphic province and morpho-tectonic chiefly fashioned by fluvial erosion, apart unit of India. Underlain by rocks of Archean from weathering and mass wasting processes. to Cretaceous-Eocene age and bordered by In spite of their modest catchment size (0.2 passive margins to the east and west, the to 3.2 × 105 km2), the major Peninsular fluvially sculpted landscape of the triangular- rivers, such as Godavari, Krishna, Mahanadi, shaped Peninsula bears the legacy of its long Narmada, Tapi, Kaveri, Pennar, Son, Mahi, denudational history that dates back to the Sabarmati, Subarnarekha, and others (Fig. 1), late Mesozoic times (Kale and Vaidyanadhan, have played a crucial role in the evolution of 2014). The spatial diversity in topography, the present prominent topographic features, drainage and landforms displayed by this such as the valleys, ridges, plateaus and ancient landmass is the product of the rifting escarpments. and drifting of the Indian Plate and Deccan In the last two to three decades, the volcanism as well as significant changes in availability of high resolution remote the regional climate and erosional base level sensing data, DEM derived morphometric (sea level) since the breakup of the Gondwana data and geochronological data of rocks, land in the late Jurassic. bedrock landforms and Quaternary deposits Rainfed rivers are the backbone of the have enabled earth scientists to make Peninsular landscape. Since its separation better observations and interpretations THE RIVERS OF INDIAN PENINSULA: THEIR SALIENT GEOMORPHIC CHARACTERISTICS 31 Figure 1. Map of the Indian Peninsula showing the major relief features and rivers. The map also shows the location of noteworthy geomorphic features mentioned in the text. about regional denudation rates, landscape Geology and geological history of the evolution and denudation chronology on Indian peninsula different spatio-temporal scales that were not The Indian landmass attained its possible previously. Some of the noteworthy present outline between 130 and 65 Ma findings about the Indian Peninsula and its ago (Chatterjee and Bajpai, 2016), but rivers that have emerged from recent as well as the basement rocks and major geological some previous studies are briefly summarised structures are much older (Valdiya, 2016). here.The two main objectives of this review Even though the Indian Peninsula formed a are: (a) to outline the salient features of the part of the Gondwana super-continent from Peninsular Rivers, and (b) to tentatively Cambrian until its breakup in Mesozoic reconstruct the ancestry of the Peninsular times, it constituted part of three older super- rivers on the basis of available geological, continental configurations, namely the Ur, geomorphic and geochronological data. the Columbia andthe Rodinia (Meert et al., In order to appreciate the distinctive 2010).Geologically, the Indian Peninsula, geomorphic characteristics of the Peninsular described as the Indian Shield, is composed rivers, it is imperative to have a general idea of several Archean cratonic blocks bordered about the litho-structural setup of the Peninsula by rifts and Proterozoic orogenic (fold) belts. as well as the geological and climatic history The Bundelkhand-Aravalli, Singhbhum, spanning the last approximately 200 million Bastar, and Dharwad cratons (Fig. 2) contain years (~200 Ma in the standard notation). In some of the oldest granitic rocks ranging in the following section the geological setup and age from 3 to 4 billion years (Valdiya, 2016). the geological history are briefly described. The cratons include intra-cratonic basins 32 JOURNAL OF INDIAN GEOMORPHOLOGY: VOLUME 8, 2020 Figure 2. The main geological terranes of the Indian Peninsula. The map is based on the Geological Map of India published by the Geological Survey of India (GSI) filled with Proterozoic sediments (areas of Until the end of the Jurassic Period (~145 sandstones/limestones, etc. in Fig. 2). The Ma), Precambrian rocks formed the land cratons are separated by rifts or grabens, such surface over much of the Peninsula. Only as the Son-Narmada-Tapi (SONATA) rift Gondwana basins (Fig. 2) contained Mesozoic zone, the Mahanadi graben, and the Godavari sediments. However, this scenario changed rift (Fig. 2) and in some cases the cratons are during the Cretaceous following voluminous flanked by Proterozoic fold (orogenic) belts, outpouring of lava around 113–118 Ma in such as the Aravalli, the Satpuda, and the eastern India (Rajmahal Traps) and around 65 Eastern Ghat (Fig. 1). The Palghat-Kaveri Ma in western and central India represented Shear Zone forms the boundary between the by the Deccan Traps (Valdiya, 2016).The Dharwad Craton and the Southern Granulite Deccan lava flows flooded and buried the Terrain (Fig. 2). While the SONATA and the ancient rocks and the Gondwana landscape Palghat-Kaveri Shear Zone are much older over an area of ~1.5M km2. The split between (Precambrian), the roughly W–E and NW–SE India and Seychelles immediately after the oriented grabens of Damodar, Mahanadi and end of Deccan volcanism created the present Godavari attained their final form during the western margin of India. The Western Ghat rifting of the Gondwana landmass in the early escarpment is the product of the erosion and Permian (Valdiya, 2016). In comparison, the inland retreat of this 65 Ma old continental formation of the Cambay rift is considered edge (Kale, 2010). to be coeval with the split between India During the terminal Cretaceous- and Seychelles, during terminal Cretaceous- Paleogene, when the Indian Plate was Palaeogene (Biswas, 1999). drifting northward as a huge island, partially THE RIVERS OF INDIAN PENINSULA: THEIR SALIENT GEOMORPHIC CHARACTERISTICS 33 Figure 3. Major geological, geomorphic and climatic events during the last 200 Ma. Global climatic events are mainly based on Huber et al. (2018), Westerhold et al. (2020) and other sources. PETM = Paleocene-Eocene Thermal Maximum. The temporal changes in the rate of drift of the Indian Plate from 200 Ma to the present estimated by Yoshida and Santosh (2018). Major weathering events (yellow boxes) after Jean et al. (2020). covered by Deccan Traps, and at unusually (Zachos et al., 2001; Gasson et al., 2012). high velocities of ~18 cm yr–1 (Yoshida and Recent analyses of high-fidelity palaeo Santosh, 2018), the Earth’s climate was climatic records reveal that warmhouse extremely warm (Fig. 3) and the eustatic sea and hothouse states have prevailed during level was higher by several tens of meters Palaeocene and Eocene (~66 to 34 Ma), and 34 JOURNAL OF INDIAN GEOMORPHOLOGY: VOLUME 8, 2020 hothouse conditions (temperatures > 10°C depressions (rift valleys) and the short and warmer than present) were experienced swift flowing west coast rivers drain into the during early Eocene between 56 to 47 Ma Arabian Sea. (Westerhold et al., 2020). The analyses further indicate that the present coolhouse Structurally controlled drainage state began in the early Oligocene and lasted Rifts or grabens are structural forms that until the terminal Pliocene (~34 to 3.3 Ma). act as major drainage corridors on geological The Quaternary period (the last 2.6 Ma) has time scales. The intra-cratonic grabens, filled been dominated by icehouse conditions (Fig. with sediments of the Gondwana period, 3) with alternating glacial-interglacial periods exist as linear belts and it is along these driven by cyclic changes in the Earth’s elongated depressions that the present river orbital parameters or the Milankovitch valleys of Pranhita-Godavari, Damodar, and cycles. The hydro-climatic characteristics of Mahanadi occur. Similarly, the Narmada, the peninsular rivers were affected by these Tapi, Mahi, and Sabarmati occupy ancient global changes in the climate as well as the structural depressions represented by the latitudinal position of the Indian Plate during Cambay graben and the SONATA rift zone. the drift. These rivers have the thickest (1–5 km) Palaeogene to Quaternary deposits in the Salient features of the peninsular rivers Indian Peninsula.
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