4 Geographical and Geological Provinces of India : Background to the study of Indian Prehistory

Ravi Korisettar

The Indian Subcontinent: Natural History and Habitability

The Indian subcontinent is one of the few regions of the Old World which has a history of more than one hundred fifty years of Palaeolithic research. Prehistoric archaeology in the region is a British foundation. The 1860s made a big beginning of Palaeolithic discoveries in the subcontinent. Robert.Bruce Foote discovered up a Lower Palaeolithic stone tool (biface) from Pallavaram near Madras (Chennai). Similarly A.C.L. Carllyle picked up another biface from Marfa in central India and W.R. Dickinson is credited to have picked up Palaeoliths from Rohri Hills in Sindh, Pakistan.

Prior to Partition the Archaeological Survey of India carried out extensive documentation, excavation and preservation of the subcontinent’s heritage of all ages. It was the chief authority regulating archaeological research and encouraged participation of scholars from university and institutions in India and abroad. Partition ushered in the establishment of Pakistan Archaeological Survey that continued to promote international collaboration under license from it. In comparison with the Archaeological Survey of India the frequency and number of international collaborations is much higher in Pakistan that have contributed to enhancing our knowledge of the Bronze Age civilization in particular and prehistory and early history in general, clearly reflected in high quality publications.

On the other hand owing to greater research emphasis on the Indus Civilization in Pakistan our knowledge of the Palaeolithic and Neolithic reveals wide gaps, which need to be filled by organizing focused surveys in potential areas. A study of the recorded distribution pattern of Palaeolithic sites in the subcontinent in an environmental frame of reference has helped in understanding the patterns of settlements across the subcontinent as well as the routes of dispersal and expansion within the subcontinent.

2. General Geography of the Indian Subcontinent

During the last 50 million years combined geological, tectonic and geomorphic processes have given rise to the present physical expression to the subcontinent’s landmass. Prior to this timeline the Indian tectonic plate was separated from rest of Asia by the Tethys Sea. The plate tectonics processes led to the collision of the Indian plate with the Asian around 50 million years ago. This collision was a critical landmark in the series of geological events that eventually led to the formation of the Indian subcontinent as we see today (see below).

The Indian Subcontinent is generally referred to as South Asia and appropriately it occupies the whole of southern Asia including the modern states of India, Pakistan, Bangladesh, Nepal, Sri Lanka, Maldives, Bhutan and Afghanistan. While Nepal and Bhutan are Himalayan states, Maldives and Sri Lanka constitute island nations of the Indian Ocean. Bangladesh and Pakistan occupy the north-western and eastern portions of the Indian subcontinent respectively. The Indian state comprises the mainland continental area and the archipelagos of the Andaman and Lakshadweep. Both the oceanic and continental areas are the property of the SAARC nations and among them modern India has control over the large continental and oceanic areas, nearly 70%.

Afghanistan lies outside the natural boundaries of the subcontinent. The mountain ranges in the northern, western and eastern regions include : Sulaiman, Kirthar and Hindukush mountain ranges on the northwest, by the 2000 km long Himalayan arc in the north-west, north and north-east and further east by the Arakan Yoma (the Burma mountains). The entire southern peninsula is bounded by the Indian Ocean on the south. Physiographically the Indian subcontinent comprises montane, inter and intra-montane and submontane terrains, large alluvial plains, hill ranges (ghats), rocky plateaus with braided stream networks, coastal plains and a vast expanse of hot desert (the Thar). This physiographic configuration has facilitated the formation of the regional climate, particularly the monsoon circulation over the region on the one hand and the formation of a network of vegetation zones governed by the latitudinal and longitudinal variation in the distribution of rainfall between the proximal southwestern peninsula and the Himalayan range in the north. These vegetation zones or ecosystems can be broadly categorized as mangrove, evergreen, deciduous, dry evergreen scrubland, high altitude grass lands (margs), alpine zones, The rainfall circulation is referred to as Southwest monsoon and Northwest monsoon. While the SW monsoon is referred to as Indian summer monsoon (ISM), the Northeast monsoon is referred to aswinter monsoon.

Environmentalist would classify the region into arid, semi-arid, humid, sub-humid, biodiversity hotspots, climax forests, hot and cold deserts, swamps, marshes, etc. The mountain and oceanic barriers have played a major role in shaping the history and culture of south Asian populations since prehistoric times. The early settlement history of the region was governed by the passes in the northwestern range (the Bolan and Khyber valleys) as well as dispersal of hominin populations out of Africa both during Early and Middle Palaeolithic times. Long and short term fluctuations in the monsoon climate over the subcontinent have governed the habitability of the internal network of ecosystems. The geographical features of India and Pakistan are relevant to our understanding of Subcontinent’s prehistory and history.

3. Geological Evolution of the Indian Subcontinent

Although our knowledge of the Quaternary period is more relevant to understanding cultural evolution we are sure a background information of the geological and physiographic evolution of the landmass i.e. the Indian subcontinent equips us to obtain a general account of environment of the region, which definitely played a major role in the habitability of distinctive congenial environments that determined patterns of hominin expansion and gave rise to a clear pattern in the distribution of early settlements. This also helps in delineating the settlement patters during distinctive cultural periods.

The terms Indian subcontinent and South Asia are interchangeable and in the present study the term Indian subcontinent is preferred to South Asia as it represents a large and continuous continental landmass lying between the Himalayas in the north and the Indian Ocean in the south. Modern India is equal to Europe without Russia. It has 15,200 kilometers of land frontier and 57 000 kilometers of sea frontier. Its area is 3, 267,500 square kilometers. The seventh largest country in the world. India extends 3200 kilometers in the north-south direction and 2960 kilometers in east-west direction. The subcontinent includes modern Pakistan, Nepal and Bhutan. This is considered a part of the Old World in view of the evidence of Early Palaeolithic settlements, similar to the ones found in Africa and Europe. On the present showing of Palaeolithic evidence of settlements Sri Lanka remained isolated during the early Paleolithic times and was colonized by modern humans around 50 kyr ago, hence it can regarded as part of New Wolrd, like those of Australia and the Americas.

The physiographic configuration of the subcontinent is the result of geological processes involving crustal evolution and plate tectonics. Crustal evolution refers to the formation of successive geological strata and the emergence of Shield landscape. Plate tectonic s refers to movement of crustal landmass under influence of rifting, drifting and collision of these landmasses.

The subcontinent is part of the larger Indo- Australian plate. There are six such plates (composed of continental and oceanic crusts). The continental crust lies above the sea level and oceanic crust is submerged under sea/ocean (forming the ocean bottom) because of the varying thickness of the crustal mass. Therefore each plate is formed of both continental and oceanic crusts. The Himalayas occupy 2400 km long and 250-300 km wide area along the northern frontier of the subcontinent and constitutes a formidable mountain barrier. This snow-covered barrier prevents the flow of cold winter winds from Siberia and causes relatively warm winters in north India.

The subcontinent is broadly divisible into three physiographic zones, viz., the peninsula, the Indo-Ganga Plain and the Himalayas. The Himalayas are spread over a length of more than 2000 km and form a great northern arc. The Burma Mountains (Arakan Yoma), the Baluchistan and Hindu Kush mountains separate the subcontinent from north Asia and East Asia. The Himalayas occupy 2400 km long and 250-300 km wide area along the northern frontier of the subcontinent and constitutes a formidable mountain barrier. This snow-covered barrier prevents the flow of cold winter winds from Siberia and causes relatively warm winters north India.

The formation of the Indian Shield is attributed to fusion of a series of small Archaen cratons by Proterozoic Mobile Belts under mountain building activity (orogenic cycles), during the time period from Palaeoproterozoic and early Palaeozoic. The Himalayas and the Indo-Ganga basins have come into existence as a result of northerly drift (migration) of the Indian Plate, from south of the Equator, and consequent collision with the larger Eurasian Plate.

The geological history of the subcontinent begins from the time of Archaean. This is followed by the formation of a series of rock strata found distributed across major basins that are known as Proterozoic Purana Basins. Some of these basins became part of the Himalayan Mountain formation and are now part of the Lesser Himalayas, the rest of these basins, about seven of them are scattered across the Peninsula, spanning the time period from Mid-to Late Proterozoic. Relatively younger rock formations belonging to the Phanerozoic Era are found in the Gondwana Basins (well known for their coal measures) between the Aravallis in the northwest and Alikulli and Satyavidu hills in the southeast. They range in time from Permian to Cretaceous.

During the Late Cretaceous the Indian Plate split from Madagascar and began to move northwards at a rate of 20 cm per year. Later in the Early Palaeogene the leading edge of the Indian Plate collided with the Asian Plate and was subducted under the larger Plate. This event happened between 50-55 Myr ago and ushered in the formation of the Himalayas, which continue to rise even today. A thick crust of 60-70 km is found in the mountains. The continuous vertical rise of the Himalayas concomitantly gave rise to the formation of foreland basins along the southern margin of the rising Himalayas. Sediment transported from the Himalayas began to accumulate in these basins during the period from Palaeogene to Quaternary through the Neogene. This basin fill was subject to deformation (folding and faulting) and uplift resulting in the formation of the Siwalik hill range all along the southern slopes of the Himalayas. The Indo-Ganga Plain is further southward extension of Siwaliks.

The Indo-Ganga Plain occupies an area of 700,000 sq. km. This Plain is drained by the rivers rising in the Himalayas and the northern slopes of the Peninsular Bulge. While the Himalayas continue to rise the older mountain ranges are known by names such as Aravallis, Sahyadri, etc. Vast plateau areas have formed on the Indian Peninsula, in the central and western parts, e.g. the Deccan Plateau, stretching between the Vindhyas in the north and the Nilgiris in the south. This plateau is surrounded by the coastal lowlands. The Western Ghats (Sahyadri) is known as continental divide and has given rise to east and west flowing rivers. The east flowing rivers have given rise to major deltas on the coastal lowlands. The continental divide has come into existence as a result of uplift of Deccan Volcanic Province.

The Indian Peninsula preserves evidence of fusion of smaller cratons by the Proterozoic Mobile Belts. There are four cratons – Dharwar, Bastar, Singhbhum and Bundelkhand. There are four mobile belts – the Eastern Ghat Mobile Belt, the Pandyam Mobile Belt, the Satpura Moblie Belt and the Aravalli-Delhi Mobile Belt. These crustal features constitute the Peninsular Shield and are composed of greenstone rocks and high grade gneiss -granulite rock formations. These basement formations are succeeded by the Purana rock series, Gondwana sediments, Rajmahal Volcanics (~115 Myr), Deccan Volcanics (~65 Myr), Cretaceous marine incursions (Narmada-Kaveri deltas), Mesozoic-Cenozoic successions in western Rajasthan, Kachchh and Saurashtra, and mid- to Late Quaternary Alluvial sequences. The Gondwana sediments range in time from Permo-Carboniferous to Triassic (290-280 Myr) and mark the resumption of sedimentation in the Peninsula during late Carboniferous. The Indian Shield in its central and western part witnessed voluminous continental flood basalt eruption in the form of Deccan Volcanics around 65 Myr. The Deccan Volcanic Province covers an area of 5×105 sq km. The Deccan basalts are thickest (2000 m) towards Western Ghats and decrease to 200 m towards southeast and east margins.

This gives us a continuous picture of the development of the Peninsular Shield. As we can see the geological history of the Peninsula spans three billion years. The Precambrian Shield comprises cratons of Archaean age, mobile belts and shear zones – such as Narmada, Godavari, Mahanadi rifts. The coming together of the mobile belts occurred around 2.5 billion years ago and has remained stable since then. Upon this large shield several Neoproterozoic Purana Basins came into existence – the Cuddappah, Vindhya, Chchhatisgarh, Pranhita-Godavari, Indravati, Bhima-Kaladgi, Kurnool, etc.

In addition to these cratons, a prominent feature of the geology of southern India is the Southern Granulite Province (SGP) which is considered to be made up of three Late Archaean to Neoproterozoic high grade metamorphic blocks that are joined together by a series of shear zones. The Northern Block is separated from the Central block by the Mylar-Bharani Shear Zone. The Central block is divided further into western Nilgiri Block and the eastern Madras Block. The Madras Block is bounded by the Palaghat-Cauvery Shear Zone and is followed southward by the Madurai Block. The northeast-southwest trending Archaean Shear Zone (ACSZ) separates the Madurai Block from the southernmost Trivandrum Block.

3.1 Pakistan: Regional Geography

The northwestern part of the subcontinent is an extension of the Indo-Ganga Plain bounded on its west by Baluchistan Mountain ranges. The major part of the well inhabited Pakistan is the vast Indus flood plain flanked by interconnected Punjab (including the eastern and western sectors), Gomal and Kachi plains. The eastern part of the Indus basin is bounded on the east by the great Indian desert, the Thar (including the Cholistan and Rajasthan expanses of this desert). The monotonous plain is broken by plateaus formed by low lying hills such as Kirana, Rohri and Ongar hills. The Salt Range separates the northern plains from the Potwar Subhimalayas and Peshawar valley. In terms of a macro topography the entire Indus Basin is a bowl shaped depression measuring approximately 1200 km long by 600 km wide at its greatest extents. With the exception of the hills mentioned above the hard rock basement complex is deeply buried, at an average depth of 100 m, under the either the alluvium or desert sands. The southern part of the Basin is the Indus delta and to its west lies the Makran coast, south of the Baluchistan plateau. The major river systems originating in the western and northern highlands drain the entire Basin rendering it the most well-watered region of the world. The Basin topography has been shaped by the migrating/shifting river courses and accompanying denudational processes operating during the Quaternary. Within the Indus Basin the fluvial and aeolian processes have given rise to a network of landforms including floodplains, terraces, doab-highlands (interfluves), meander scarps, oxbow lakes, table lands and large crescentic dunes. The Indus Basin is bounded on the west by the Kirthar, Sulaiman mountain ranges and the Pir Panjal range to the north. The Aravallis and the Indo-Ganga Divide are to the east and northeast of the desert. The major lithic sources are contained in the mountain ranges and within the Basin the only sources of flint and limestone are the hills mentioned above. Obviously the prehistoric hominin adaptations were controlled by these natural factors that are reflected in the archaeological record itself. Major passes such as the Bolan and Khyber, which have facilitated dispersal in out of the subcontinent, need to be tested for raw material resources. The present documented evidence of the distribution of Palaeolithic sites across modern Pakistan indicates dependence on resource availability, particularly stone for tool making.

4. Cenozoic Evolution of Habitats across the Subcontinent

The development of habitats across the south Asia landmass is intimately linked to the Cenozoic tectonic and climatic history of the region which can be seen through three distinctive phases of the Tertiary and Quaternary, viz. Palaeogene, Neogene and Quaternary.

During the Palaeogene the landforms on the Indian Shield evolved under the force of equatorial hot and humid climate when the Indian plate was moving over the equator. The Cretaceous-Eocene volcanism gave rise to the Deccan Volcanic Province that now covers western and central India. Subsequently the equatorial conditions resulted in planation and lateritisation that covered the major part of the shield. Outside this area the shallow marine environments gave rise to the Mesozoic and Palaeogene lithosequence in scattered but widely separated basins. Towards the middle of Palaeogene the Indian plate had established collisional contact with the Eurasian plate.

4.1 Stages in the Development of Himalayas and Faunal Movement

The formation of Tibetan plateau is interlinked with the processes leading to the collision of Asian and India landmasses. The timing of this collision is placed at 54-49 Myr. The Neogene was the period of intense crustal deformation along the leading edge of the Indian plate that set in motion a series of tectonic upheavals giving rise to the formidable Himalayan mountain range. This initiated the evolution of India’s geography, physiography and environment, including a network of habitats across the landmass of continental scale. The rise of the Himalayas and the attainment of an altitude of 8000 m AMSL was the key factor in the initiation of a monsoon system over the region.

By 8 Myr the Himalayas had attained the present altitude and defined the physiographic configuration of the subcontinent. This spurt of tectonic activity also affected the Indian Ocean crust that were deformed simultaneously. This tectonic resurgence was of great consequence inasmuch as it was accompanied by abrupt climatic changes over the subcontinent. New landscapes emerged. Senile topography was rejuvenated. The foreland basins were filled up with detritus eroded from uplifting higher terraces. Ecosystems were characterized by shift in vegetation from C3 to C4. Consequently grasslands came into existence in the foreland basins that became the habitat for grazing mammals from Africa, Europe and central and East Asia. This is said to have caused faunal turnover causing marginalization or extinction of indigenous animals. The faunal population considerably increased and was three times richer than the present. There were 30 species of elephantcompared to just one at present, and 15 genera of anthropoid apes. Including the Ramapithecus. Around 9.5 Myr the European three-toed horse, Hipparion, and pigs appeared in the Potwar. Around 7.5 Myr Stegodon, hippo, Hexaprotodon, and Elephas planifrons colonized the foreland Siwalik terrain. This was also the period when the Himalayas witnessed accelerated erosion as a result of accelerated uplift and resultant heavy rainfall.

After a short period of tectonic stability the Plio-Pleistocene transition was marked by tectonic uplift (between 4 and 2 Myr). The uplifted ranges created large cool areas, inducing precipitation of snow, coinciding with the global cooling and the onset of Pleistocene glacials at 2.5 Myr. Between 1.7 and 1.5 Myr the Himalayas experienced increased glaciation and revival of tectonic uplift. This spurt of tectonic movements caused crustal disturbances in the Lesser Himalayas and the Siwalik foreland basins coinciding with the Olduvai Magnetic Polarity Event of the geomagnetic timescale and the onset of a glacial phase. Towards the transition from Early to Middle Pleistocene, around 8-7 Kyr (the reversal of magnetic field from Matuyama to Bruhnes Polarity Epoch) another major tectonic episode occurred that led to increased sediment load into the Bengal Basin. The Himalayan habitats were greatly affected by the vast expanse of snow that spread far and wide over Potwar, Kashmir, Kangra and Tibet including the Central Himalayas. Consequently the SW monsoon weakened causing spells of dry and cold conditions over the pre-existing savanna ecosystems in the Siwaliks and the Lesser Himalayas in north India. Powerful bed load streams, the Boulder Conglomerate phase marking the end of the Siwalik sequence, began flow down the Himalayas. The large grazing mammals were forced to migrate southwards into the peninsular basins, the central Indian Purana and Gondwana Basins. These basins were unaffected by the Himalayan tectonism but were influenced by the changed climatic conditions. It has been documented from the increase in upwelling in the north Indian Ocean was coeval with increased SW monsoon and vice versa, as well as increase in the NE monsoon over peninsular India. Naturally the habitats across the central Indian basins were unaffected and remained stable attracting the immigrant Subhimalayan fauna.

These forces rendered the Subhimalayan terrain inhospitable during the Lower and Early Middle Pleistocene, not only because of strong fluvial activity but also because of severe cold conditions and the low biomass of food resources. The immigrant mammals and hominins from the warmer latitudes could not have adapted to this environment. The Boulder Conglomerate phase marked the end of the Siwalik mollassic sedimentation in the foreland basins. The present network of drainage basins of the Indus, Ganga and Brahmaputra are a southern extension of foreland basins that have emerged in the post-Siwalik phase during Pre- and Late Quaternary. These drainage systems have carved terraces on the Siwaliks through down cutting, lateral shifting and vast alluvial floodplain deposits in their middle and lower reaches and fan systems in the continental shelf under the influence of the Indian Ocean Monsoon. These fan systems preserve an excellent record of the evolution landforms and monsoon variation as well as the terrestrial biodiversity. Though epeirogenic movements have continued through time tectonic uplift of the order of magnitude is not evident during Mid-Late Quaternary. This ushered in the emergence of monsoon ecosystems that began to attract hominid colonization, which followed the immigration of Siwalik grazing mammals.

The Purana and Gondwana basins of western and central India were partially buried under the out pouring Deccan flood basalts during late Cretaceous. The Vindhyan sediments are estimated to cover are area 1, 40,000 sq km. Seismic and drilling survey has indicated that the Basin in Northern extent is buried in the Ganga alluvium up to 65,000 sq km. Only 60,000 sq km area of the basin is exposed and the rest is below the Deccan Trap in the south and southwest.

The northern margins of these basins in central India were also partially buried under the Ganga alluvium. The ground water flow in the Himalayan drainage, for instance the Ganga River, has facilitated perennial discharge and the formation of savanna habitats.

Palaeolithic occupations have been well documented from the northern slopes of the peninsular craton, constituting the Vindhyan and Gondwana basins of central India. Therefore understanding these processes is crucial to our understanding of the prehistoric human colonization of peninsular India.

Unlike the molassic sequence of the central and Subhimalayan regions the peninsular basins do not preserve unequivocal record of Neotectonic activity. Though reactivation of lineaments and faults is evident, which was effective in controlling the patterns of drainage in the broad shallow valleys. However, the relative low relief of the landforms and the associated unconformities in the lithosequences facilitated high ground water recharge during high monsoon regimes coeval with the Himalayan uplift episodes. The upland plateaus in these basins were covered with forest and the lowland intermontane and sub-montane valley floors developed grasslands. The upland vegetation cover must have hindered generation of detritus and its transport. Peidmont fans and colluvial deposits along the basin margins represent a combined evidence of neotectonics and scarp retreat processes in the Neogene and Quaternary.

4.2 Western Ghats and the Rise of Monsoon Habitats

The present structural configuration of the Deccan Volcanic Province took place in conjunction with the developments along the leading edge of the Indian plate and the consequent collision of Indian plate with the Asian. This was a period of intense tectonic activity even in the peninsular region, though differing in magnitude and scale. The upwarp of the Deccan Volcanic Province resulted in: (a) establishing the westward flowing drainage,

(2)  gradual beheading (unlike the rapid process in the Himalayas) of the catchments of some eastward flowing rivers and (3) in accentuating the gradient of the pre-existing consequent streams. The absence of typical laterite of Late Tertiary and Early Quaternary age is a clear indication that lateritisation took place in the Early Tertiary times under the influence of tropical humid conditions at near sea level, supported by peneplanation processes and epeirogenic movements. However atypical laterite or ferricrete crusts on the pediments flanking the river valleys, not only on the Deccan Volcanic Province but widespread on the peninsular shield, are dated to Mid-Late Pleistocene and represent relative higher hot-humid conditions, ground water movement and high water tables. Since the Late Tertiary times the upwarp has led to contrasting precipitation regimes between the plateau and the coast resulting in the stripping and erosion of laterite and their re-deposition as secondary laterites, under fluctuating monsoon regimes. The secondary divides have given rise to the formation of broad shallow valleys with well developed black cotton soil mantle on the valley floor. The occurrence of massive lithic calcretes, with relief inversion (rhizoliths and nodules), on laterites and ferricretes of Later Tertiary age in upland Deccan Volcanic Province is a good evidence of climatic fluctuation and the onset of semi-arid monsoonal conditions during Late Neogene to Early Pleistocene times. This is consistent with the onset of global cooling around the beginning of the Pleistocene period 2.5 Myr ago.

The uplift of Western Ghats in the Early Neogene effectively changed the peninsular ecosystem from tropical woodland (Early Tertiary) to a network of savanna ecosystems between the west coast and the plateau along with the establishment of allochthonous river systems in peninsular India. The savanna ecosystem became well-defined in the rocky triangle between the Western and Eastern Ghats, within which Purana and Godnwana basins lie. This orographic configuration resulted in a progressive decrease in the intensity of rainfall along the path of the SW monsoon, the basic element controlling the habitability of an area. Obviously the structure of food resources between the coastal, upland and plateau ecosystems was very different, the key controlling factor would have been the secular variation in the intensity of SW monsoon across the peninsular region.

The Western Ghats and the west coast, being proximal to the Arabian Sea monsoon receive the maximum precipitation in summer and the Western Ghats plateau preserves the climax forest with a distinction of being the one of world’s biodiversity hot spots, especially in the region between the mouth of the Tapi in the north and the southern tip of India. This is the major watershed of the peninsular south India. By virtue of its altitude, relief and high precipitation facilitates high recharge of ground water aided by tropical evergreen forest and the underlying lithology.

4.3 Savanna Habitats and Grazing Mammals

Faunal remains have been recovered from fluvial gravels in the peninsular valleys. The Narmada fauna has been broadly divided into Lower and Upper groups of Mid-Late Pleistocene periods. The LowerGroup of the Narmada has also yielded Acheulian artifacts along with fossils of Bos namadicus, Sus namadicus, Hexaprotodon namdicus, Elephas hysudricus, Equus namadicus, Stegodon-insignis-ganesa, come from Middle Pleistocene horizons. Similar fauna is also reported from the Deccan basins. Existence of this fauna attests to the prevalence of savanna, pond, pool and swampy environments along with woodland ecosystems in the Purana and Gondwana basins. This faunal assemblage continued into the late Pleistocene. It should noted that this assemblage of fossil ungulates, probocideae, etc. from the riverine sediments in these basins is not older than the Later Quaternary.

This widespread occurrence of some animals in central and southern India was possible because of similar ecological conditions, climatic conditions across the network of basins on the peninsular shield. The animals seem to have had a zonal distribution in these areas without any definite ecological barriers  between  them. A majority of these forms are late survivals from the Siwaliks of northwest, having migrated from the Himalayan foreland basins, e.g.,theNarmada-Godavari complex, when the conditions in the northwest became inhospitable on account  of  Pleistocene  glaciation  and tectonism.  Many of the species became extinct during the course of such migrations, while some survived and evolved into advanced forms adapting to the  Terminal Pleistocene/ Holocene climatic conditions. It should noted that this faunal composition was made up of both   indigenous and exotic elements. The migratory routes lay east and west of the Himalaya. Most of the larger mammals migrated from Egypt, Arabia, Central Asia and North America through routes across Alaska, Siberia and Mongolia. Hippopotamus and elephant, which had their early origin in central Africa, migrated outward and entered India during the Tertiary period through Arabia  and Iran.  Rhinoceros, horse and camel, all originating in  North America, evolved in some countries  of central and western   Asia before migrating to India. Important  causes  of migration include  population  pressure, evolutionary  pressure and climatic fluctuations throughout the   Tertiary and of course the glaciation which was  a global phenomena.

4.4 Coastal Habitats

The evolution of coastal lowlands along the western seaboard was concomitant with the scarp retreat processes operating along the foot of the Western Ghats during the Neogene, followed by an extensive phase of lateritization of the pediment surface when climatic conditions were conducive for deep weathering. The coastal lowlands are a low relief pediment formed under relative tectonic stability and relative semi-aridity. the present-day monsoonal rainfall is heavy to very heavy with an average of 5,000 mm per annum at the foot of the Ghats. This provides ideal tropical and seasonal hot and humid conditions for the continuation of lateritization, which is observed to have been the case since the Miocene times. Prevalence of tropical climate throughout the Cenozoic is attested by palaeobotanical and palaeoweathering data. Evidence for hot humid seasonal circulation with greater intensity of rainfall has also been dated to at least 8 Myr. Further, prevalence of monsoon climate during Miocene and its influence on pedogenesis is attested to by a series of palaeosols in the Siwaliks of Pakistan and the stable isotopic analysis of pedogenic carbonates from the palaeosols of Late Miocene age

4.5 Isolated North-east Humid Landforms

While the Subhimalayas and the Bengal basins experienced severe tectonic disturbance and dynamic fluvial environments during Early and Middle Pleistocene times, the northeastern mountain tracts and the Burma Mountains had attained their altitudes and received much higher monsoon precipitation than the northern and northwestern Himalayas. Owing to the present physiographic configuration of the Subcontinent and related geomorphic forces this region received much higher precipitation from the Indian Ocean monsoon system and harbours a forest ecosystem comparable to the equatorial rainforests. This in combination with mountain terrane acted as insurmountable barrier across the southern dispersal route of modern humans into South-east Asia. The nature of archaeological record from this region also does not support the idea that this region lies along the southern dispersal route.

The Monsoon System and Fresh Water Resources

The Southwest summer monsoon is the major source of fresh water over the Indian landmass and has a dominant role in the terrestrial hydrological cycle. A series of multidisciplinary studies conducted on the history of the Indian monsoon have clearly pointed to its great antiquity. A study of multi-proxy records has placed the beginning of SW monsoon between 15 and 8 Myr, and that this monsoon was well established during the Quaternary (the last 2.5 Myr). Palaeoclimate studies have shown that since the onset of glacial climate around 2.5 Myr and the later long term changes in terms of glacial and interglacial cycles the monsoon regimes also fluctuated accordingly. What is important for us is to understand the profound impact such changes could cause on the past hydrology, geography and landform evolution that would enable us to reconstruct habitat and cultural changes through time.

This continental configuration has facilitated the onset of the monsoon regimes over the land. Further the internal orographic features, including the Western and Eastern Ghats, the Deccan plateau, the Subhimalayas and the Aravallis, have played a significant role in the latitudinal and longitudinal variation in the intensity of monsoon precipitation across the landmass. This has given rise to a mosaic of landforms and ecosystems which were governed by the relative variation in the intensity of rainfall. These ecosystems range from arid Thar, semi-arid Deccan plateau, humid coastal and upland landforms, etc. that are characterized by typical vegetation associations. Landform evolution in all these basins was governed by fluvial agencies and processes under the seasonal monsoon regimes as well as their geological makeup and tectonic framework. The Asian highlands (the Himalayas, Tibet and Burma Ranges) are the source of many large perennial rivers such as the Ganga, Indus, Brahmaputra, Mekong, Changjiang, etc. Both glacial melt waters, orographic monsoon rainfall and post-monsoon ground water movement feed the peninsular river systems.

Stronger SW monsoon regimes, during warm and humid interglacials favoured high lake levels, increased flow in the rivers and frequency of floods. Decreased monsoon during cold and dry glacials altered these conditions, further resulting in lowered sea levels and increased continentality. Consequently the monsoon reach over the continental area was affected. Fluvial response to climate change and the resultant landform units have been well documented for the last 1,25,000 years. It has been observed that during the drier conditions the river behaviour was erratic under reduced water flow regimes and that fluvial activity increased during increased monsoon conditions, for instance during the last 10,000 years of earth’s history. Obviously climate, physical and hydrological environments and the biomass resources across the peninsula have exerted greater control on the habitability of the diverse ecosystems since the Palaeolithic times.

With this background of the natural history of the Indian subcontinent let us focus our attention on learning about the Quaternary time period, the period that witnessed the rise of human settlements across the subcontinent in the module on Quaternary Period.

Web links

• www.livescience.com /37706-what-is-plate-tectonics.html
• www.nationalgeographic.org/media/plate -tectonics
• www.indiabix.com
• www.thoughtco.com /geography-and-history-of-india

Bibliography

• R.L. Singh. 1971. India a Regional Geography
• O.H.K. Spate and A.T.A. Learmonth. 1984. India and Pakistan: A general and regional geography.
• 2008Ramakrishnan and R. Vaidhyanadhan. 2008. Geology of India (2 Vols.)
• Arthur L. Bloom. 2003. Geomorphology: A systematic analysis of Late Cenozoic landforms.