The Indian Subcontinent constitutes a distinctive geographic entity that can be divided into three geomorphic provinces: (a) the Indian Peninsula, (b) the Himalayas, and (c) the Indo-Gangetic Alluvial Plains. The Indian Peninsula is a triangular-shaped landscape of ancient landmass with record of a prolonged history of erosion, denudation, and resurgent tectonic activities. The present-day geomorphic characteristics of the entire terrain have resulted because of more recent block uplift-type tectonic activities. Evidence of ancient gently rolling, almost featureless ‘peneplain’ surfaces marking the top of upland areas like plateaus and mountains provides proofs of a prolonged period of denudation reaching the base level of erosion much before its elevation to the mountainous height. The Indo-Gangetic Alluvial Plains are the youngest geomorphic unit that evolved as a foreland basin in the frontal region of the rising Himalayas. The Himalayan mountain range is divided axially into six morphotectonic units, each showing a distinctive lithostratigraphic, tectonic, and geomorphic (mainly topographic) characteristics and evolutionary history. The geophysical characteristics of the Indian Subcontinent provide clear evidences of reconstitution of the Indian Shield simultaneously with the pruning of the pristine Precambrian Indian Shield with the formation of the present-day Indian Subcontinent.
The Indian subcontinent has three physiographic components: the Himalayas in the north, the Indo-Gangetic Alluvial Plain in the middle and the Peninsula of Precambrian rocks with younger cover in the south. The continental core of Precambrian terrane called Proto-India is a cluster of smaller fundamental nuclei, here termed ‘Protocontinents.’ Proto-India enlarged its initial dimension through the accretion of granulite terranes. The subcontinent attained its present geomorphotectonic character during successive Phanerozoic geological events: (1) magmatism at ~ 550 Ma; (2) Late Palaeozoic-early Mesozoic Gondwana basin opening; (3) Jurassic Gondwanaland breakup at ~ 165 Ma;. (4) Plume impingement under Indian lithosphere during the Cretaceous-Eocene; (5) Himalayan collision at ~ 45 Ma; and (6) Post collision neotectonism.
The Indian subcontinent is a part of a very dynamic crustal plate. The heavier lower layer of this crust is splitting and spreading in the ocean around (Plate 1.1) and the lighter upper layer is moving northeastwards. Encountering resistance at its leading edge, the spreading heavier lower layer sank into the interior of the earth or slid locally under the lighter upper layer of the Asian plate as well as the Burmese microplate. In contrast, the lighter upper layer of the crust making up the Indian continent broke up along faults and moved upwards and obliquely eastwards like a passive passenger. The movement speed varied in time and space. The advancing plate then either slipped under or rode over the part in front of it; in the east, it moved sideways and rotated a bit.
Plate 1.1. The shaded relief map of Indian ocean shows the floor. The floor of the Indian Ocean is splitting and spreading laterally, pushing away northeastwards. Continental India is riding like a passive passenger on the spreading lower crust that forms the Indian Ocean floor. (Base map is prepared by using GMT).
Within the fragmented framework of the Indian continental crust (Plate 1.2), older faults developed millions of years ago, which were also reactivated in some places and at some points of time. The movements that took place on older and newer faults and fractures are quite apparent on the ground surface in the displacement of landforms, the uplifting and/or sinking of the land, and the deflection and offset of rivers and streams. More often than not, the rupture planes failed to reach the surface, and the manifestation of movement on the ground was minimal. These are the blind faults, which are faults that are in the process of development, and in time will express themselves on the surface.
Plate 1.2. DEM image of fractured framework of the Indian subcontinent. The sketchmap shows important zones of faults, thrusts, and shears, many of which were and are prone to reactivation.
(DEM map source: http://worldview.earthdata.nasa.gov; The sketchmap modified from Valdiya, K. S. (2016). The Making of India: Geodynamic Evolution (2nd ed.). Switzerland, Cham, Dordrecht, Heidelberg, New York, London: Springer International Publication (924 p.). (Base map from: Amante, C., & Eakins, B. W. (2009). ETOPOI 1 Arc-minute global relief model: procedures, data sources and analysis. NOAA Technical Memorandum NESDIS NGDC-24 (19 pp.).)
In all cases the rupturing of the ground, the dislocation or sliding of rock masses, and the sinking and uplift of the land caused the crust to tremble. Depending on the extent of movement, some earthquakes were felt by humans, but quite a few others were only noted by sensitive instruments recording ground motion. If one were to prepare or to look at a map of sites of occurrences of earthquakes (Plate 1.3), one would be convinced that a great many belts in the Indian crust are indeed in tectonic turmoil. In these sites of earthquake occurrence, the pulling apart or pressing-pushing hard rock masses were related to the lines or belts of ruptures formed in the present or in the past. In the vast expanse of the Indian subcontinent encompassing India, Nepal, Bhutan, Bangladesh, Sri Lanka, and Pakistan, such regions or belts of ruptures are far too many (Plate 1.2).
Plate 1.3. Epicentral distribution map shows location of sites of moderate to large earthquakes, obviously related to tectonic boundaries of geological terranes.
(Modified from the cover page of Ramalingeswara Rao, B. (2015). Seismic activity: Indian scenario Hyderabad: Buddha Publishers.)
One part or the other of the Indian subcontinent is always in tectonic ferment—it is structurally deforming, bodily shaken by earthquakes and recurrtly visited by tectonically induced hazards.
The Indian subcontinent has a unique geographic position. In north, the Himalayas’ snowcapped ranges feed the great Himalayan rivers, one fifth of their flow being snowmelt. In South India, the tropical seas latitudes are spread, which are the generation zone of tropical cumulus clouds. India's average annual surface runoff generated by rainfall and snowmelt is estimated to be approximately 1869 billion cubic meters (BCM). However, in reality, it is estimated that only approximately 690 BCM or 37% of the surface water resources can be mobilized (seeChapter 4.5). This is because (1) more than 90% of the annual flow of the Himalayan rivers occurs over a 4-month period and (2) potential to confine such resources is low due to inadequate suitable storage reservoir sites. There are approximately 1500 glaciers in the Himalayan region and several natural lakes such as Dal and Wullar lakes in Jammu and Kashmir, Chilka in Orissa, Kolleru in Andhra Pradesh, and Pulikat in Tamil Nadu. There are thirteen major river basins in the country (Figure 1): the Brahmaputra, Ganga (including the Yamuna subbasin), Indus (including the Satluj and Beas subbasins), Godavari, Krishna, Mahanadi, Narmada, Cauvery, Brahmini (including the Baitarni subbasin), Tapi, Mahi, Pennar, and Sabarmati, which occupy approximately 82% of total drainage basins, supply 85% of total surface flow, and provide for the needs of 80% of the country's population. There are also several desert rivers, which flow for some distance and vanish in deserts. There are also completely scorched areas where evaporation equals rainfall, and hence there is no surface flow. The medium and minor river basins are mainly in the coastal areas. On the east coast and part of Kerala, the riverine length is approximately 100 km, whereas the rivers on the west coast are much shorter, as the width of the land between sea and mountains is less than 10–40 km. Yet, in spite of nature's gift, deterioration of water quality is an issue of national concern.
The Indian subcontinent experiences wet summers and dry winters. It has four monsoonal seasons (June–September); 75 % of the annual average precipitation (1100 mm) is contributed to this season. The Indian monsoon is credited to the intense solar heating that travels from the equator to the north. India follows a plethora of heterogeneity, both in spatial and temporal spaces. Due to its massive geological variation, the mean rainfall from region to region has not been distributed uniformly. During monsoon, the temperatures in the Northern Indian Ocean, sea surface, plains of northern India, and the Tibetan Plateau are significantly warm. One reason is that they are situated at an elevation of more than 4500 m on average. However, as the southern part of the country faces cooler climate during the same time, a temperature and pressure gradient is created, resulting in atmospheric movement carrying moisture evaporated from the warmer Indian Ocean to the cooler mountains Indian west coast and finally to the Bay of Bengal. It is more commonly known as “monsoon trough” of northern India, where more rain falls. On the other hand, the western part of its region (Rajasthan) receives only 100 mm of mean rainfall, while the eastern region holds the record of the highest rainfall point in the world with around 11,700 mm in Chirapunji, Meghalaya. The magnitude of annual rainfall is large in north eastern states and south western regions, which experience both southwest and northeast monsoons. In India, maximum mean rainfall value of 395.02 mm was observed during the month of August, which is also the peak time of southwest monsoon. Similarly, the minimum mean rainfall value of 5.47 mm was observed in the month of April, which is again the peak summer season (Climate Variability and Its Impacts on Water, inpress6). We should always keep in mind that even a slight deviation in this pattern can at times bring significant mutilation in the country’s assets. As cited in the next paragraph, India has faced the outcomes in all its corners, showing that climate change and its impact show no partiality, regardless of time and region.
The Bangalore flood of July 2016 as a result of heavy rainfall disrupted many lives, terminating normal conveyance (The Hindu, 2016). The flash flood of the south that occurred in Tamil Nadu and Andhra Pradesh, 2015, touched nearly 4 million people, bringing confiscation of around 3 billion US dollars (Kotteswaran, 2015). The Mumbai flood of 2005 claimed approximately 1094 lives (Kumar, Dudhia, Rotunno, Niyogi, & Mohanty, 2008). However, the outpouring of Uttarakhand in 2013 led to financial depreciation of more than 3.8 billion US dollars, along with the death of nearly 6000 people (Rapidly Assessing Flood Damage, 2014). A cross-country flood of India–Pakistan in September 2014 affected Jammu and Kashmir in north India, claiming 277 people in India and 280 people in Pakistan. It also brought economic damage of around 1.5 billion US dollars (Trenberth, Dai, Rasmussen, & Parsons, 2003). In the northeast, the annual flooding in Assam between June and July 2012 reported that around 4.65 lakh hectares of farmland were submerged, affecting 3,829 villages and 23.08 lakh people (https://thewire.in/environment/kaziranga-rhinos-assam-brahmaputra-flood). The June 2005 flood in the west, i.e. Gujarat, affected 4547 villages, 31 towns related to electricity supply. Also, 108 people were reported to have lost their lives either due to drowning and collapse of building walls (https://reliefweb.int/report/india/india-gujarat-floods-situation-report-2-jul-2005-500pm). These are just a few examples of the outcomes of climate change on rainfall pattern that has caused serious floods in many parts of India, recently. There are also other similar devastating flood events caused by heavy rainfall not reported here. However, from all the observations, a conclusive idea can be drawn that India is now experiencing an atypical motif of rainfall events, sometimes bringing high-intensity saggy damages, from infrastructure to loss of precious lives.
The Indian subcontinent (Fig. 1) is a storehouse of ~ 3.8 Ga of geological history spanning from the Eoarchean period to the Recent period, assembling crustal blocks of various ages at different times along major orogenic belts (Santosh et al., 2014, 2015), and involving extensive volcanism, plutonism, metamorphism, sedimentation, and tectonic deformation. The basement rocks of the Indian Peninsular Shield are dominantly composed of granites and granitic gneisses. The exposed Precambrian basement comprises four major cratons, namely, the Dharwar, Aravalli, Singhbhum, and Bastar (Figs. 2 and 3). In the southernmost part of the Peninsula, south of the Dharwar Craton, is a series of crustal blocks ranging in age from Archean to latest Neoproterozoic, welded together by intervening suture zones, and it is termed the Southern Granulite Terrane (Santosh et al., 2015 and references therein). Sedimentary successions of Proterozoic intracontinental basins unconformably overlie the basement rocks. More or less unmetamorphosed Proterozoic deposits occur in the Cuddapah Basin, and Late Paleozoic-Jurassic sedimentary deposits are preserved in the Narmada-Son, the Mahanadi, and the Godavari (Fig. 2) rift valleys. Basins related with intra- to intercontinental rifting of India, namely the Gondwana basins and those of the east and west coasts, record the Phanerozoic history of India from the Permian to Cenozoic periods (Ramkumar et al., 2016). The basement rocks are covered in the north by Indo-Gangetic alluvium and in the west central region by Deccan flood basalts. Except where exposed, all these older formations are concealed in their most part by Quaternary relict alluvium, calcrete-ferricrete, and Holocene-Recent alluvium and coastal sediments (Fig. 3). The coastal zone of the peninsular region south of the Narmada-Son rift can be broadly classified into Eastern Continental Margin (ECM) and Western Continental Margin (WCM). Except the southern margin (where granulites crop out on the surface exclusively), Precambrian, Proterozoic, and Gondwana deposits occur between the ECM and the WCM.
Fig. 2. Location and regional structural trends of Peninsular India and its environs.
After Ramkumar, M., Menier, D., Manoj, M.J., Santosh, M., 2016. Geological, geophysical and inherited tectonic imprints on the climate and contrasting coastal geomorphology of the Indian peninsula. Gondw. Res. 36, 52–80.
Fig. 3. Major geological provinces of the Peninsular India.
Modified from the Geology of India map, Geological Survey of India. After Ramkumar, M., Menier, D., Manoj, M.J., Santosh, M., 2016. Geological, geophysical and inherited tectonic imprints on the climate and contrasting coastal geomorphology of the Indian peninsula. Gondw. Res. 36, 52–80.
The ECM is a 2600 km long rifted passive margin evolved through separation of India-Antarctica-Australia from the Gondwana supercontinent during the Late Jurassic to Early Cretaceous periods. Four stages of magmatism, that is, Early Cretaceous (Rajmahal equivalents—Kerguelen and Crozet plumes—Bastia et al., 2010; Radhakrishna et al., 2012a), post-Albian, K/Pg (Deccan magmatism), and post-Eocene have influenced tectonic processes and structural styles. During its evolution, the Bay of Bengal (BOB) lithosphere witnessed two major hotspots, namely, the Kerguelen and the Crozet, resulting in the emplacement of linear N-S trending aseismic 90°E and the 85°E ridges, respectively (Fig. 2). The east coast of India is geomorphologically and tectonically segmented due to subcrustal distinctions (Lal et al., 2009; Bastia and Radhakrishna, 2012) into Bengal/Ganges, Mahanadi, Godavari, Krishna, and Kaveri basins/deltas. Each of these subcrustal blocks behaved differently and mimicked the inherent subcrustal mosaic during the Gondwana period, and carved out for itself an exclusive basin of the Mesozoic-Cenozoic age (Lal et al., 2009). All the east coast basins are connected to the open sea in the east, and are bordered on the west by highlands and the discontinuous Eastern Ghats. These basins have also developed into deltaic systems since the Neogene era (Ramkumar, 2003b), and have been shaping the east coast of India.
The 2200 km long WCM consists of Precambrian granites, Mesozoic sediments, Deccan flood basalts, and Paleocene to Recent sediments. The sedimentary basins of the WCM consist of thinned continental crust overlain by volcanogenic, volcaniclastic, and terrigenous sediments. The WCM is a rifted passive continental margin (Gombos Jr. et al., 1995). Prominent among major structural features are the West coast fault, Panvel flexure, Cambay rift, Kachchh rift, (Fig. 4) Laxmi and Laccadive-Chagos ridges, and Vishnu Fracture (Fig. 2). Block faulting owing to extensional tectonics, thinning, and shear rifting, and uplift of Western Ghats affected the coastal tract, and manifested through several major lineaments. The edge of the continental shelf of the west coast is remarkably straight, representing a fault line that formed/reactivated during Late Pliocene time (Jayalakshmi et al., 2004). Several basement arches trending perpendicular to the west coast divide the shelf region into sedimentary basins, namely, the Kachchh, Saurashtra, Mumbai (Ratnagiri), Konkan, and Kerala basins along the western offshore of India.
Fig. 4. Location, distribution, and drainage morphology, major structural trends, and Western Ghats Escarpment along the west coast of India.
After Ramkumar, M., Menier, D., Manoj, M.J., Santosh, M., 2016. Geological, geophysical and inherited tectonic imprints on the climate and contrasting coastal geomorphology of the Indian peninsula. Gondw. Res. 36, 52–80.
The rift-drift events related to the separation of Madagascar during the mid-Cretaceous and the Seychelles in the Late Cretaceous era from India when the Indian Plate moved above the Marion Plume (Raval and Veeraswamy, 2003) gave rise to the formation of major offshore rift basins (Storey et al., 1995). In the northernmost part, the Kutch and the Saurashtra basins are separated by a southwesterly plunging basement high, termed as the Saurashtra Arch (Biswas, 1987). The major conjugate rift systems, the Narmada and the Cambay, cross each other to the south of the Saurashtra Peninsula in the Surat offshore and form a deep Surat depression (Fig. 4). According to Biswas (1987), the northern part of the west coast was the first to be subjected to continental rifting since the Late Triassic, giving rise to three pericontinental Mesozoic marginal rift basins in the onshore such as the Kutch, the Narmada, and the Cambay basins. The subsurface geology and depositional and tectonic history of the Konkan-Kerala (KK) offshore have a genetic linkage to the denudational and uplift history of the Western Ghats (Gunnell and Radhakrishna, 2001).
Vultures on the Indian subcontinent once benefited immensely from the Hindu culture and traditions which hold the cow as sacred and highly prized as a living, working animal. Religious prohibitions dictate that upon death, the bodies of cows (and other livestock) cannot be consumed. Both factors ultimately led to a wide availability of carcasses which drew in scavenging birds and allowed their populations to soar. By the 1980s, vulture presence was prodigious—with some species estimated to number the tens of millions (Fig. 1).
Fig. 1. A wide availability of livestock carcasses on the Asian subcontinent drew in scavenging birds and allowed their populations to soar. By the 1980s, some species of vultures numbered the tens of millions.
Photo credit: Rishad Naoroji.
Somewhat ironically, a frequent fate of common species is that their ubiquity causes them to be neglected and overlooked—not solely by the public, but also by scientists. Hence, a sudden drop in vulture numbers could well have gone unnoticed for quite some time. However, the birds had several human admirers and allies. One of these was Dr. Vibhu Prakash—an Indian biologist with the Bombay Natural History Society—who had been undertaking long-term monitoring of vultures in the Keoladeo National Park in Rajasthan, India. During the 1987/88 breeding season, he counted 353 nesting pairs of Oriental white-backed vultures (OWBVs; Gyps bengalensis). When this nest survey was repeated in 1999/2000, only 20 nesting pairs were found, and no active nests were observed in this or the subsequent breeding season. In parallel, numbers of long-billed vultures (LBVs; Gyps indicus) visiting the National Park had plunged—from 816 in 1985/86—to 25 in 1998/99, and only a single LBV was seen during the 1999/2000 nesting season. Dr. Prakash was finding dead OWBVs in all age classes—including adult birds—which indicated that mortality, rather than poor hatchability, recruitment, or geographic shift of nesting sites, was responsible for the decline. Clearly something was awry.
The central part of the Indian subcontinent consists of several tectonic units, the Narmada-Son lineament and the central Indian suture zone being the most prominent features. Deep seismic studies across the Narmada-Son lineament suggest that major crustal disturbances are confined to the upper crust. The Narmada north and south faults have been active at different times and acted as fissure zones through which molten magma erupted and was emplaced on both sides. The Barwani-Sukta fault divides the region into two parts; east of this fault the upper crust is upwarped between the two Narmada faults. The subcrustal lithosphere in the central Indian region indicates varying structural properties. The central Indian suture represents an obducted oceanic crust due to collision of two microcontinents, represented by the present-day Satpura mobile belt and Bastar craton.
14.1 Introduction: Gondwana Formations in the Global Context
The Gondwana Supergroup constitutes one of the significant geological ensembles deposited during the early Phanerozoic Eon in the Indian Subcontinent constituting a part of the pristine Indian Shield. The social importance of the Gondwana Supergroup is vested in the fact that more than 99% of the total coal resource of the Subcontinent is hosted in the Gondwana basins. This post-Precambrian geological formation evolved after a break in sedimentation for more than 180 million years between the Ordovician and late Carboniferous. Development of the Gondwana basins started with the deposition of land-derived sediments, with minor marine input at the initial stage. The Gondwana deposition in the Indian Subcontinent like most other places began with the formation of tillites and glacial boulder beds in close association with marine beds. This was followed by the deposition of fluvial and fluviolacustrine sediments intercalated with enormous deposits of plant remains that ultimately turned into coal seams in linear intracontinental rift basins. These sedimentary successions with coal-bearing beds (called seams) constituted the Gondwana Supergroup.
Precise definition of the Gondwana formations as formal stratigraphic units has suffered because of the inclusion of rocks deposited in diverse geological conditions into its ambit and also because of the overemphasis placed on the floral evidence in the stratigraphic correlation of different formations. In view of that, the Gondwana Supergroup has been redefined to include dominantly continental rift-basin deposits formed between the late Carbonaceous and the time of the Gondwana break-up during the early/middle Jurassic.
The Gondwana sequences of the Indian Subcontinent were part of the Gondwana Supercontinent that also included Antarctica, Australia, Madagascar, Southern Africa, and South America. The eastern Gondwanaland of which India was also a constituent included Antarctica, Australia, and Madagascar, while the rest comprised western Gondwanaland. The global correlation between these constituent landmasses of the Gondwanaland is principally based on the basis of floral and faunal fossils and palaeoenvironmental conditions depicted from the sediments deposited in each of these.
Box 14.1
It was H.B. Medlicott who first coined the term Gondwana in 1872 for the coal-bearing formations of India. The term was derived from the ancient ‘Gond’ tribes of central India, and the name Gondwana is derived by combining two words, ‘Gond’ (land of the Gond tribes) and ‘wana’ (a wood, forest, or grove).
It is not clear when the Indian subcontinent was first colonized. The only Early Pleistocene evidence is a small stone tool assemblage in a secondary context from Riwat, Pakistan, dated to ≥1.9 Ma, and a quarry site at Isampur, Karnataka, for which an ESR date of 1.2 Ma has recently been obtained (Paddayya et al., 2002), but which requires confirmation. At present, the earliest archeological evidence from the subcontinent dates to the Early Middle Pleistocene, as evidenced by Acheulean hand axes from Dinar and Jalalpur, Pakistan, and Bori, India (Petraglia, 1998) (Fig. 11).
Figure 11. Principal archeological sites in India. 1, Riwat; 2, Dina; 3, Jalalpur, Singhi Talav; 5, Dang Valley; 6, Raisen Complex; 7, Bhimbetka; 8, Adamgarh; 9, Durkadi; 10, Chirki-Nevasa; 11, Kukdi; 12, Hunsgi-Baichbal Complex; 13, Attirampakkam. The star represents Hathnora.
The Indian Lower Paleolithic includes several sites and thousands of bifaces and cleavers, but unfortunately few sites and sequences are dated, and faunal remains are very rarely preserved (Petraglia, 1998). Apart from a poorly dated but probably Late Middle Pleistocene cranial fragment from Hathnora in the Narmada Valley (Cameron et al., 2004), there are no hominin remains from India >30 ka. Nevertheless, there is a long cave sequence for rock shelter FIII-23 at Bhimbetka from the Acheulean to the Mesolithic that appears to show an unbroken record of continuity in lithic traditions. Open-air sites are known from Raisen, where more than 90 Early Paleolithic sites were recorded. Best known of all is the remarkable, world-class record from Hunsgi-Baichbal, Karnataka, that contains >200 Acheulean sites (see Fig. 12), and a settlement pattern that appears to have been bipolar, with dry season aggregation camps near water holes, and smaller wet season camps from which plant foods and small game were obtained (Paddayya, 2001). Such is the quality of information from sites such as Isampur that the actions of the hominins that quarried rock to make cleavers can be monitored in detail (Petraglia et al., 2005).
Figure 12. Acheulean sites in the Hunsgi-Baichbal Valleys, India. Paddayya (2001), figure 16.1.
