Neogene palaeobiogeography of the Indian subcontinent with special reference to fossil vertebrates

Palaeogeography, Palaeoclimatology , Palaeoecology, 31(1980): 39--62

39

© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

N E O G E N E P A L A E O B I O G E O G R A P H Y O F T H E INDIAN SUBCONTINENT WITH SPECIAL R E F E R E N C E TO FOSSIL V E R T E B R A T E S ASHOK SAHNI 1 and HARISH CHANDRA MITRA Geology Department, L u c k n o w University, L u c k n o w 226007 (India)

(Received April 19, 1979; revised version accepted January 22, 1980) ABSTRACT Sahni, A. and Mitra, H.C., 1980. Neogene palaeobiogeography of the Indian subcontinent with special reference to fossilvertebrates. Palaeogeogr., Palaeoc]imato]., Palaeoecol., 31: 39--62. The geologicalhistory of the Indian subcontinent during the Neogeneshows firstly, a progressive continentality in sedimentation; secondly, variable climatic trends ranging from warm, tropical rain-forest conditions throughout the Mioceneup to the Early Pliocene, with a drier climate in the P]iocene, graduallychangingto glacialconditions by the Middle Pleistocene;thirdly, a southerly and easterly shifting of climatic zones; and lastly, a remarkable stability in marine and non-marinesedimentaryregimes, with the Himalayas representing the main source of sediments for north India from the Mioceneonwards. This stability is also evidencedby marine and non-marinefaunas. Thirty to forty percent of the species of the Miocenemarine molluscsand elasmobranchsare common to Recent taxa in the Arabian Sea and Bay of Bengal. Pliocene Siwalikfishes are referable to present-day forms in the Indo-GangeticPlain rivers with the exception of Heterobranchus which is presently restricted to Africa. In contrast to the Palaeogene,coal occurs less frequently in the Neogene. The Neogene also shows a widespread distribution of mammalianfaunas, which constitute the main criteria for stratigraphic correlation of non-marinedeposits. The occurrence of certain Miocene and Pleistoceneplain-dwellingmammalsin areas which today are highly elevated (Kashmir)testifies to Neogene impulsesof the Himalayanorogeny. Early Neogene (Lower Miocene) mammalsfrom the Indian subcontinent show an intermixture between southern Russianand African forms.

INTRODUCTION This paper is a sequel to an earlier study which dealt with the Palaeogene palaeobiogeography of the Indian s u b c o n t i n e n t (Sahni and Kumar, 1974). In view of the rather varied and new data t ha t have been obtained as a result of studies c o n n e c t e d with a plate-tectonics model of the subcontinent, it becomes necessary to evaluate data c o n c e r n e d with marine zoogeographic and terrestrial p h y toge ogr aphi c provenances during the Late Tertiary. O t her parameters such as a chronological d o c u m e n t a t i o n of transgressions and regressions mark i m p o r t a n t stratigraphic da t um lines and also give the relative I Present address: Centre of Advanced Study in Geology, Punjab University, Chandigarh 160014 (India).

40 distribution of land and sea. The paper also deals with the distribution of pre-Siwalik (Lower Miocene) vertebrates as well as Siwalik mammals, with special reference to affinities and palaeoecological conditions. The major palaeoenvironments throughout the Neogene in various parts of the subcontinent have been reconstructed on the basis of sedimentological, palaeontological and palaeobotanical criteria and the development of coal and lignite. The study is mainly based on data already published in the literature, though an attempt has been made to revise the nomenclature of the taxa involved. In most instances the original classifications have been retained. LOWER MIOCENE The Gaj Series (Aquitanian--Burdigalian) of Sind and Baluchistan and their equivalents in the Indian subcontinent, represent deposits which were essentially laid down in transgressing seas, n o t only across the axis of the Sindhu Sea (Sahni and Kumar, 1974) but intermittently across the coastal peninsular region of India and Sri Lanka (Fig. 1). In fact, the close of the Gaj Period is marked by increase in non-marine conditions of deposition. The end of the Early Miocene epoch is therefore similar to the end of the Early Eocene, as both periods marked facies of increasing continentality. Floristic evidence pertaining to the distribution of the contemporary flora and the climatic conditions is derived in large part from bore-hole data and is consequently based on palynological samples. The present data indicate that there were about 48 plant families during this period, of which over 60% were angiosperms. It appears that in the western sector, the climate was tropical, while in the extreme eastern sector of the Garo Hills (Assam), the climate was variable, ranging from warm, humid to drier, temperate to subtropical conditions (Banerjee, 1964). Megafloral remains comprising leaf impressions and petrified woods are reported from Kasauli (Sahni, 1953; Sitholey, 1954; Sahni and Bhatnagar, 1958; Pascoe, 1964; Krishnan, 1968), Murree (Sitholey, 1954), Kangra (Pascoe, 1964), Assam, Burma and South Arcot (Sitholey, 1954) and Kutch (Poddar, 1963). The dominant form is the palm, Sabal major, which has been reported from Murree in Pakistan (Pascoe, 1964), Kasauli (Sahni and Bhatnagar, 1958), Kangra (Pascoe, 1964), Ladakh Molasse (Tewari, 1964), South Shillong Front in Assam (Banerjee, 1973) and Kutch (Poddar, 1963). Pinus also appears to be fairly widespread, being reported from the Garo Hills and Shillong in Assam (Banerjee, 1964, 1973), Kutch (Poddar, 1963), Cambay Basin (Banerjee, 1973) and from the sub-Himalayan region, presumably from the Lower Miocene equivalents of the Dharamsala region in Himachal Pradesh (Banerjee, 1964). The widespread occurrence of Pinus can be reasonably expected in the sub-Himalayan zones and Assam as these areas were undergoing uplift. However, in the Kutch and Cambay Basins the relief was n o t so high, being controlled mainly by Deccan lava flows, and Pinus pollen may have airborne from the northern sector.

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There are very few intracontinental localities for plant fossils, most of them being confined along the margins of the subcontinent. During the Gaj Period, there are no marked differences between the various floras described from different sectors of the subcontinent. In contrast to the more widespread distribution in the previous epochs, coal has been reported from a few localities only, as the Aquitanian-Burdigalian was a time of major transgressions. Coal has been reported from north Minbu (Pascoe, 1964) and in the northern part of Burma (Ball and Simpson, 1913). Lignite occurs throughout the subcontinent, being reported from the Cambay Basin (Metre, 1968), Ratnagiri (Pascoe, 1964; Krishnan, 1968), Godavari Valley (Ghosh, 1959), Bengal Basin (Biswas, 1963) and upper Assam (Krishnan, 1968). Pre-Siwalik (Lower Miocene) vertebrates have a widespread distribution across the Indian subcontinent. Approximately 101 mammalian species belonging to 52 genera have been reported from various parts of the subcontinent, mainly from north-central Pakistan and the coastal Tertiary deposits. The generic and specific numbers are apparently exaggerated mainly because of extreme taxonomic splitting by earlier workers. Mammals are represented by terrestrial as well as marine forms and reflect oscillatory, marine and non-marine sedimentation which is a constant feature of Lower Miocene coastal deposition. Terrestrial mammals are known from Bugti Hills and Fatehjang in Pakistan (Pilgrim, 1912, 1926, 1932; Cooper, 1924;

42 Savage, 1967; Krishnan, 1968), Kutch (Lydekker, 1876; Venkatappaya, 1955; Prasad, 1964a; Sahni and Mishra, 1975), eastern Kathiawar (Sahni, in press), western Sind (Blanford, 1879), Ladakh (Savage et al., 1977) and Udhampur in Kashmir (Khan et al., 1971} in the western sector as well as from the Garo Hills in Assam (Lakhanpal, 1952), Tripura (Trivedi, 1966) and Burma (Chhibber, 1934; Savage, 1967) in the eastern sector of the subcontinent. Marine mammals are also recorded from Kutch (Sahni and Mishra, 1975; Savage and Tewari, 1977), Piram Island (Sahni, in press) and Sri Lanka (Deraniyagala, 1969). There is as yet no record of intermediate faunas between the Middle Eocene mammals of Pakistan and India and the Lower Miocene Gaj faunas of the Bugti Hills (Pilgrim, 1940; Dehm and Oettingen, 1958; Sahni and Khare, 1973; Gingerich, 1977). The Gaj mammals are best known from the Bugti Hills of Pakistan. In comparison with the Lower Manchhar faunas (Middle and Upper Miocene), the Gaj fauna (Lower Miocene) shares only six species and these are believed to be closely allied to the later forms. The Bugti fauna is a well-represented fauna, comprising approximately 39 genera and 73 species, with a predominance of herbivores over carnivores, in which anthracotheres and rhinocerotoids dominate. The anthracothere Brachyodus is common in the Bugti beds as well as in eastern Kutch (Prasad, 1964a). Deinotherium was widespread all along the western sector during the Lower Miocene, being found in Udhampur in Kashmir (Khan et al., 1971) as well as in Kutch (Lydekker, 1876; Sahni and Mishra, 1975). The Indian Lower Miocene mammals appear to have affinity with the African and southern U.S.S.R. localities. Recently, Savage et al. (1977) have shown that the northwestern part of the Indian subcontinent, represented mainly by the Bugti deposits, has a faunal intermixture with Paraceratherium (giant rhinoceroses) derived from southern Russia, proboscideans from Africa and anthracotheres probably not far distant from their centre of origin. In western Sind, the only mammal yet obtained from the Gaj Series is Rhinoceros sivalensis, which has also been reported from the Siwaliks, but its identification needs to be confirmed (Blanford, 1879). In Udhampur (Kashmir), fragmentary Deinotherium molars have been recorded (Khan et al., 1971). From Gogha (Kathiawar) a suid, Paleochoerus, has been reported (Sahni, in press). From Kutch, Sahni and Mishra (1975) have reported Dicoryphochoerus, Brachyodus and Deinotherium. In the eastern sector of the subcontinent, reports of Lower Miocene mammals are confined to Tripura and are represented by Trilophodon and Dorcatherium (Trivedi, 1966). From the Garo Hills (Assam), teeth of Anthracotherium have been noted by Lakhanpal (1952) and from Burma Dorcatherium, Telmatodon and Cadurcotherium have been reported (Chhibber, 1934; Savage, 1967). Marine mammals are known from Piram Island, in the Gulf of Cambay, by a ~ingle delphinid cetacean. Its affinities lie with the common dolphin, 'l~lphinus (Sahni, in press). The sirenians Halitherium, Indosiren and Metaxytherium have been reported from Kutch (Sahni and Mishra, 1975;

43

Savage and Tewari, 1977). From Sri Lanka, Miodugong, Miotursiops and Mioceta have been reported, belonging to the Families Dugongidae, Delphinidae and Cetotheridae, respectively (Deraniyagala, 1969). The coastal Tertiary of peninsular India both along the western and eastern coasts are characterised by similar assemblages of sharks, rays, teleosts, turtles, crocodiles, sirenians and cetaceans. Further, the presence of 30 40% of species of the Miocene marine vertebrates and molluscs in the present Indian Ocean shows the existence of a stable environment. It is inferred that, apart from some minor eustatic transgressive and regressive phases, the palaeoecology of the peninsular shield shorelines has altered but little since the Early Miocene (Sahni, in press). The Sindhu Sea was continuously shrinking southwards, a process that had been initiated in the Middle Eocene (Sahni and Kumar, 1974). By the beginning of Gaj time, the strand line along the Indus River Valley axis lay somewhere between 30°N and 31°N. (Fig.2). During the later part of the

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44 Tertiary, fluvial sediments gradually filled up the Indus Basin from the north, resulting in a complete withdrawal of the sea by the Pliocene (Crookshank, 1965). This southward withdrawal of the sea has also been documented by Niyogi (1959), Krishnan (1968) and Graham et al. (1975). In Orissa, Travancore (Kerala) and along the eastern coast of the Peninsula, marine transgressions have been reported by Krishnan (1968). The widespread occurrence of Archaias malabaricus in Sri Lanka, Quilon and Kathiawar (Gujarat) suggests a contemporaneity (probably Burdigalian) for the faunas (Rao et al., 1957). In Kutch, the deposition of Aida rocks (Aquitanian) took place in a transgressing sea under tranquil conditions. The environment of deposition was epineritic to neritic. This indicates that the Miocene Sea had penetrated quite far inland. In fact, offshore exploration in the Arabian Sea and Gulf of Cambay has shown the existence of Lower Miocene beds over 100 km west of the present coastline. In the SuratBroach region, the Lower Miocene is transgressive (Narayan Rao and Singh, 1956). According to Lakhanpal (1970), the migration of fruits and seeds of the dipterocarps shows that a land connection was in existence between eastern India and Burma and Malaya during the Early Miocene. In Assam, the end of the Oligocene Period was marked by a gentle differential movement, as a result of which the Shillong Plateau and Mikir Hills were elevated to a higher level. The Bangla Sea receded southwards to the Arakan region. Antecedent streams comprising mainly the Brahmaputra and its tributaries (Sabansiri, Manas and Santokh) became active and reached the Early Miocene coastline at about latitude 26°N. Further eastwards, the Proto-Irrawaddy delta was accumulating sediments at about latitude 24°N (Dutta, 1976). Sri Lanka was first separated from the Indian mainland during the Early Miocene, when a wide arm of the Tertiary Sea extended across the southern portion of the peninsula as evidenced by the presence of marine deposits in the northern and northwestern parts of Sri Lanka, including the Jaffna Peninsula in the north (Jacob, 1949). The sedimentary regimes invarious parts of the subcontinent have been discussed by man:z workers. In the northern sector, the Murree, Dharamsala and Ka, auli Beds bear the impress of Himalayan uplift. In fact, the Early Miocene marks the time of the first sedimentary contributions from the Himalayan Front. According to Chaudhri (1976), Kasauli sediments are characterised by undecomposed rock fragments, as are the underlying Dagshai sediments. The increase of percentage of the fragments of carbonaceous schists suggests that the source rocks which supplied detritus for the Dagshai sediments still supplied sediments for the overlying Kasaull sediments. Chaudhri (1976) also noted that the end of the Kasauli (Burdigalian) is marked by low relief of the source region and a reduced rate of erosion and sedimentation. At the end of the Early Miocene, the relief in the source area became rejuvenated, resulting in the erosion of still deeper metamorphic sediments comprising kyanite schists, garnetiferous mica

45 schists and associated schistose rocks. Rivers discharged their load into a sedimentary basin running transverse to the main Himalayan axis after a short transport. According to Venkatachala (1972), the Upper Dharamsala sediments were deposited under predominantly fluviatile conditions. Khan et al. (1971) noted that near Udhampur (Kashmir) during the deposition of the Upper Murree (Burdigalian) sediments, the area probably had a predominantly deltaic or near-shore environment. In the Baluchistan, Sind and Kutch areas of the western part of the subcontinent, a gradual transition from marine to non-marine conditions can be observed between the Aquitanian and the Burdigalian (Sahni, in press). In the Cauvery Basin (south India), there was a transition from marine to continental conditions, as a result of which a continental facies developed in the western part, while a marine environment continued in the eastern part as well as in the offshore areas. In the Assam--Bangladesh region in the eastern sector, the major Himalayan uplift is marked by the presence of a regional unconformity at the Oligocene--Miocene boundary. The Surma Series (Lower Miocene) of Assam indicates a fluvial, deltaic, brackish and marine succession from north to south, thickening towards the south and southeast (Bhandari et al., 1973). According to Chhibber (1934), the Burmese Gulf retracted southwards concomitant with the Sindhu and Bangla seas. In west Bengal, the Lower Miocene sediments were deposited ifl an open, marine environment (Biswas, 1959). MIDDLE AND UPPER MIOCENE The flora comprises about sixty plant families, of which over 50% are angiosperms. Megafloral remains comprising leaf impressions and petrified woods are reported from western Sind (Blanford, 1879), Kangra and Kalka in Himachal Pradesh (Lakhanpal, 1965; Gupta, 1976), Mohand and Tanakpur in Uttar Pradesh (Rawat, 1964; Lakhanpal, 1970), Darjeeling (Pascoe, 1964), Tripura (Ghosh and Kazmi, 1961), Mikir Hills in Assam (Prakash, 1967) and South Arcot (Ramanujam, 1956, 1958; Navale, 1958; Lakhanpal and Awasthi, 1964). From the Cuddalore Sandstone near Pondicherry, 21 genera and 50 species have been reported. An analysis of about 200 fossil woods gives the relative distribution of Leguminoceae 30%; Dipterocarpaceae 22.5%; Combretaceae 10%; Guttiferae 7.5%; Anacardiaceae and Euphorbiaceae 10% and other families 20% (Ramanujam, 1968). The common occurrence of the Dipterocarpaceae throughout the subcontinent (Ramanujam, 1956; Navale, 1958; Pascoe, 1964; Rawat, 1964; Awasthi, 1972) suggests that during this period the climate was tropical, humid with plenty of rainfall over a large part of the subcontinent (Ramanujam, 1958; Awasthi, 1972). According to Ghosh and Ghosh (1958), a high percentage of angiosperms (mostly palms and grasses) in the Kangra District of Punjab suggests a tropical, coastal-plain vegetation. According to Krynine (1937), in the Tanakpur area (Uttar Pradesh), the mean annual temperature varied between 21 ° and 25°C and the annual rainfall was 125 cm.

46 The dominance of spores of Polypodiaceae, Pteridaceae and Schizaceae in the microfloral intracontinental assemblage of the lowermost Siwalik of Jawalamukhi (Himachal Pradesh) shows that the majority of the flora belongs to tropical to subtropical humid vegetation with fresh-water species (Nandi, 1975). This statement is further supported by the work of Mathur (1972), who has studied a similar floral assemblage from the Lower Siwaliks of Nepal. The continuity of similar microfloral assemblages in the upper part of the Lower Siwaliks shows a stability of tropical to subtropical humid climate (Nandi, 1975). In the Middle and Late Miocene, coal and lignite development was restricted to the eastern, southern and southeastern sectors corresponding to areas having a hot, humid, tropical climate. Coal has been reported from Upper Assam, the Makum area, Naga, Patkai and the Singpho Hills (Ball and Simpson, 1913) and Darjeeling in India (Pascoe, 1964) and from the Katha and Bhamo Districts of Burma (Ball and Simpson, 1913). Lignite occurs in Darjeeling (Pascoe, 1964), Bengal Basin (Biswas, 1959, 1963), Godavari alluvium (Sarma, 1957), Neyveli (Krishnan, 1968; Lakhanpal, 1970), South Arcot and Pondicherry (Murthy, 1968; Gupta, 1976), Cannanore, Cochin and Travancore along the Kerala coast (Poulose and Narayanswami, 1968; Lakhanpal, 1970). Middle and Upper Miocene mammals once again have a widespread distribution across the Indian subcontinent. Mammals have been reported from western Sind (Blanford, 1879), Kutch (Prasad, 1964b) in the western sector; throughout the Siwaliks (Colbert, 1935; Simons and Pilbeam, 1972), Salt Range (Simons and Pilbeam, 1972), Kargil (Dixit et al., 1971) and the Hundes area (Tewari, 1964) in the northern Himalayan belt, and lastly from Burma (Chhibber, 1934) in the eastern sector of the subcontinent (Fig.3). The Lower Siwalik fauna is quite similar to the Miocene faunas known from other palaearctic localities, because it contains various species of Dryopithecus, primitive carnivores and felids, mastodonts, listriodonts and other primitive pigs, and rather primitive bovids and anthracotheres (Colbert, 1935). The majority of the Asian dryopithecines are reported from the Siwalik Hills in India and the Salt Range in Pakistan (Simons and Pilbeam, 1972). Dryopithecines have been reported from the Kamlial Stage (Middle Miocene), Chinji Stage (Upper Miocene) and Nagri Stage (Lower P!iocene). The faunal and sedimentological assemblages suggest a warm, moist, tropical, rain-forested area of low-relief during Kamliai and Chinji times (Tattersail, 1969). The vertebrate faunas recovered from Sind and Kutch, i.e. distinct from the Siwalik belt, represent the Early Manchhar fauna which is slightly older than the Early Siwalik fauna. Prasad (1964a, b) has reported Brachyodus and Dichoryphochoerus from Kutch. Similarly from the same horizon in western Sind, Blanford (1879) has reported proboscideans, carnivores and ungulates. Pilgrim's (1926) analysis of the Lower Manchhar (Middle and Upper Miocene) fauna suggests that of the 21 species, a third is identical with-the Lower Chinji fauna. Middle and Upper Miocene

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mammals have also been reported from the Ladakh Molasse of Kargil (Kashmir), where Hyoboops have been reported by Dixit et al. (1971), as well as about 4 0 0 km further north in the Hundes area bordering Tibet (Tewari, 1964). In the Irrawaddy Series of Burma, mammalian fossils such as

Hippopotamus, Merycopotamus, Vishnutherium, Hydaspitherium, Hipparion, Aceratherium, Rhinoceros, Tetraconodon, Taurotragus, Cervus, etc. are reported by Chhibber (1934). There is comparatively little detailed work on the Irrawaddy Series, the base of which may be time-transgressive in relation to the more westerly localities of India and Pakistan. Therefore, it is hard at present to assess the equivalence of the basal faunas of the two areas. Approximately 43% of the species found in Burma are c o m m o n to the Siwaliks of the Salt Range and the sub-Himalayan regions (Chhibber, 1934).

48 The value of the "Hipparion D a t u m " in determining the boundary between the Early and Middle Siwaliks has been a matter of great controversy. Colbert {1935} reported the genus from the Chinji Stage, a statement which receives some support from a tentatively identified Hipparion metatarsal from the Chinji at Daud Khel, Pakistan (Hussain et al., 1977). However, according to an earlier study by Hussain (1971, 1973) and Simons et al. (1971), in the southern Potwar Plateau, the lowest occurrences of this equid have been placed above the base of the Nagri Stage. Skinner and MacFadden (1977) have dealt at length with the biostratigraphic significance of the "Hipparion D a t u m " . However, the contemporaneity of the first appearance of the Siwalik Cormohipparion (Hipparion) with those of the western Old World and New World still needs further study and elaboration, as according to these authors, polyphyletic lineages were involved in the initial Hipparion radiation both in the Old and New Worlds. The Middle Miocene was a crucial time in the subcontinent's geological history and it had a far-reaching effect extending up from the northern Himalayan sector to Sri Lanka. In the Himalayas, the Middle Miocene uplift was one of the strongest orogenic impulses and it initiated the mainly southward dispersal of coarse clastics, sands and muds which characterised the older formations of the Siwalik Group. The initiation of continental conditions from the Middle Miocene to the present is mainly dependent u p o n the relative stability of the palaeoenvironment, i.e. a continuously though somewhat spasmodically rising mountain chain with a concomitantly sinking foredeep of the Indo-Gangetic Basin. The sedimentary regime of this basin even t o d a y does n o t appear to differ from that of Middle Miocene times. D u t t a (1976) has recently correlated the shift in the Brahmaputra with corresponding changes in the Sabansiri, Manas and Santokh with Middle Miocene orogenic impulses. This impulse is also believed to have resulted in the central Indian uplift of a b o u t 300 m in Chhota Nagpur and Bihar (Krishnan, 1953) as well as further south, in oscillatory movements around Karaikal. On the Kerala coast, oscillatory movements have been recorded by Poulose and Narayanswami (1968). During the Middle and Late Miocene, Sri Lanka was again connected with the Indian mainland. The presence of some elements of the t y p e Siwalik fauna in Sri Lanka and south India shows that minor marine oscillations did n o t disturb the migratory land routes between the Indian mainland and the sea (Jacob, 1949). Deraniyagala (1969) states that in the northwest and southeast parts of the island, strong elevation resulted in block faulting. According to Singh and Rastogi (1973) Siwalik sediments were deposited by fluvial process in a foredeep similar to the present-day Gangetic alluvium. The shear zones present t o d a y in the Gangetic Basin were also active during Siwalik sedimentation. Singh (1975} noted the upward fining of grain size in the Lower Siwalik sediments, suggesting a fluviatile environment. The rivers

49 arose in the Himalayas and flowed at right angles to Himalayan strike. This hypothesis was previously suggested by Krishnan and Aiyangar (1940), and is contrary to the earlier and now discarded view of a single east--west flowing Siwalik River, named the "Indo-Brahm" (Pascoe, 1919; Pilgrim, 1919). Further southwards, the southward flows of the rivers were deflected by the peninsular shield rocks, causing the drainage to flow down a southeast palaeoslope. According to Chaudhri (1975), the petrological characters of the Lower Siwalik sediments are suggestive of a steady supply of detritus from the source rocks, which also contributed the sediments for the Dagshai and Kasauli Formations. The relief was low during Early Siwalik time, and as a result the detritus indicates mixed environments similar to the Dagshai and Kasauli. In the Nurpur area of Himachal Pradesh, selective sorting of Lower Siwalik sandstone suggests deposition under migratory deltaic to openchannel conditions (Raju and Dehadrai, 1962). According to Tandon (1971), the Lower Siwalik sediments of Ramnagar, Kumaun Himalayas suggest a dominantly southeastern flow derived from the northwest highlands. In the adjoining Tanakpur area, the sandstones of the middle zone (Kamlial Stage) are characterised by carbonate cement, indicating a warm climate (Misra and Valdiya, 1961). Parkash and Goel (1977) suggested that the palaeocurrents in the area east of Yamuna River were in a southwesterly to southerly direction during Early Siwalik times. This statement is also confirmed by the work of Tandon (1971) from the Kosi River section in Uttar Pradesh. Orogenic impulses caused the migration of the sedimentary basinal boundary southwards towards the peninsula, as a result of which the Lower Siwaliks are overlapped by the Middle Siwaliks. The basin of deposition continued to subside, as is evidenced by the gradual transition from Lower to Middle Siwaliks (Parkash and Goel, 1977). In the Bay of Bengal in the eastern sector of the subcontinent, deposition in the form of a submarine fan by turbidity currents was generated by the easterly flowing rivers since Middle Miocene times (Parkash and Goel, 1977). In West Bengal, the sedimentation during the Middle and Late Miocene was not totally fluvial (Biswas, 1959, 1963). The entire Bengal Basin became more marine in a general southeasterly direction with a basinward decrease in the sand content in various sedimentary formations (Mathur and Kohli, 1964). According to Desikachar (1974), the source area for the Bengal Basin was towards west and north, i.e. the Chhota Nagpur and Shillong plateaus. In the Middle Miocene, marine transgressions spread eastward across the Shan Plateau of Burma. However, in northern Burma conditions were mainly fluviatile, whereas further southwards marine conditions were present. The source area for the Assam and Arakan Basins was mainly eastwards from the Shan Plateau and northwards from the northeasterly Himalayan region. The depositional history of Bengal and the Assam--Arakan Basins was essentially similar after the Palaeogene (Desikachar, 1974).

50 PLIOCENE The flora consists of about fifty plant families, of which 55% are angiosperms. The families Dipterocarpaceae, Gramineae, Polypodiaceae and Cyperaceae were widespread throughout the subcontinent (Chowdhury and Tandan, 1952; Ghosh and Ghosh, 1959; Biswas, 1963; Rawat, 1964; Sah and Dutta, 1967; Ramanujam, 1968; Lakhanpal, 1970; Awasthi, 1972; Banerjee, 1973). The microflora collected from Mohand (east), Himachal Pradesh shows the presence of spores of Schizaeaceae, Lycopodiaceae and Polypodiaceae, indicating a tropical marshy vegetation, while the presence of spores of Gleicheniaceae and Cyatheaceae indicate a tropical to subtropical, dry climate. The occurrence of pollen of Palmae and Liliaceae represents humid to drier, temperate to subtropical climate, while those of Betulaceae, Podocarpus, Pinus, A bies, Picea, Cedrus and Tsuga indicate a subtropical to temperate climate (Nandi, 1972). The presence of the family Dipterocarpaceae in Kutch, Jawalamukhi, Mohand (West) in Uttar Pradesh, Bengal, Assam and Pondicherry areas suggests a uniform tropical humid climate with plenty of rainfall over these widely separated areas (Ramanujam, 1968). However, the end of the Pliocene was marked by the start of arid conditions, which resulted in the complete eradication of dipterocarps from northern India. The relative increase of aridity has resulted in restriction of the range of this group to northeastern and southwestern India. This aridity was accompanied by the growing continentality caused by the rise of the Himalayas and the shrinking of the Sindhu and the Bangla seas. The discovery of Pinus from the Middle Siwalik sediments also supports the hypothesis that by this time, the Himalayan Ranges had attained an elevation ranging from 400 m to about 1500 m. The discovery of similar types of spores and pollen from the Middle Siwalik of Raxaul in Bihar (Lukose, 1969) and from Bhakra Nangal in Punjab (Banerjee, 1968) also supports the view of Krishnan (1968), according to which Siwalik sediments have been derived from the north as well as from the south. The contribution of the northern Himalayan source is much greater than that of the southern peninsular shield. The marked climatic change between the Late Miocene and the Early Pliocene is shown by the differing nature of the spore and pollen content of samples collected from the lower and upper horizons of the Middle Siwaliks at the Mohand (east) field, Himachal Pradesh (Nandi, 1972). According to Lakhanpal (1970), the increase in aridity from the Middle Miocene to the Late Pliocene is also represented by the Bhikna Thoree (Bihar) flora which represents a dry environment as shown by its small leaf impressions. The flora collected from Tanakpur (Uttar Pradesh), of Middle Miocene age, has comparatively larger leaves representing a rich mesophytic vegetation. In the Bengal and Kutch Basins, the occurrence of Graminidites suggests drier coastal or lagoonal conditions (Banerjee, 1973).

51 In the Pliocene, coal has been reported from the eastern sector of the subcontinent comprising the Namma, Lashio and Mamsang coal fields in Burma (Simpson, 1906; Lander and Walker, 1926), Singpho, Naga, Patkai, north Cachar Hills, Dibrugarh (Ball and Simpson, 1913) and Darjeeling in India (Pascoe, 1964). Lignite has been reported from Kengtung in Burma (Fermor, 1935) and from the Bengal Basin (Biswas, 1959), Bhutan (Pilgrim, 1906), Pondicherry (Murthy, 1968), Neyveli (Krishnan, 1968) and Cannanore (Lakhanpal, 1970) areas of the eastern and southern sectors o f the subcontinent (Fig.4). The fauna changed radically after the Chinji (Messinian) and primitive forms were replaced by more advanced ones in the Nagri Stage (Zanclian). By the beginning of the Dhok Pathans (Piacenzian), there was a marked increase in the steppe-grassland genera including abundant Hipparion, papionids, bovids and giraffoids. At the same time, the proboscideans were greatly diversified and there was an increase in the taxonomic diversity of carnivores. The appearance of the first hippopotamids, antelopes and cervids occurred at the end of Nagri Stage (Prasad, 1972b). In contrast to the warm, moist, tropical, rain-forested areas of low relief predominant during the Kamlial and Chinji times, the Dhok Pathan time indicates an open country habitat with cold climate, while the climate of the Nagri Stage is intermediate between the Chinji and the Dhok Pathan (Simons and Pilbeam, 1972). The fishes collected from the Pliocene beds of Ladhyani (Haritalyangar), Himachal Pradesh, indicate that this fluvial community has been stable from the Pliocene up to Recent times. There are a number of species such as Clarias batrachus, Rita rita, Mystus seenghala which are identical to their modern-day counterparts. The Pliocene community of Ladhyani was very similar to that found today in the northern part of the Indo-Gangetic Plain, where similar types of fishes, turtles and crocodiles have been reported (Sahni and Khare, 1977). Some primitive types of anthracotherids of Burma persisted until the Nagri Stage (Lower Pliocene) in India, while successive migration of mammals may have occurred in Serravallian, Tortonian, Messinian and Zanclian times (Prasad, 1972b). Further south of the Siwalik foothill localities, Pliocene vertebrates are encountered on the small island of Piram in the Gulf of Cambay. Pilgrim (1926) assigned these fossils to the Nagri Stage but Prasad (1964b) has made a collection which includes Anancus, Stegolophodon, Deinotherium and referred the fauna to the Dhok Pathan Stage. In the northern sector of the subcontinent, the presence of coarse sediments in the Middleand Upper Siwaliks represents a rapid rate o f deposition within flood plains or basins (Prasad, 1972a). According to Tewari (1964), the sediments of the Ladakh Molasse were deposited over a deeply eroded surface of the Ladakh Granitic basement and in a basin which formed south of the rising Ladakh--Karakoram Range. In the Ramnagar area in the

52

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Nainital District of Uttar Pradesh, mechanical analyses of Middle Siwalik sediments show that the deposition of these sediments was by sluggish streams and the main load seems to have a long history of sorting, indicating a long period of tectonic stability (Tandon, 1972). In the extreme western part of the subcontinent, in western Sind, the presence of oblately shaped pebbles in the Upper Manchhar indicates that they ~vere deposited by rapid stream transport (Blanford, 1879). In the Lower Sind, there is a considerable intercalation of marine estuarine sediments within the Manchhars. In Kutch, the Pliocene is represented by typical marine beach and deltaic deposits (Biswas, 1965). A similar environment is reported form the Cambay and Ankelshwar Basins by Mathur and Kohli (1959). In the eastern sector, in West Bengal, sedimentation was not totally fluvial (Biswas, 1959, 1963). The uplift of the Indo-Burman Ranges resulted in an

53 accumulation of a thick succession of Oligocene, Miocene and Pliocene clastic strata from the north in the narrow trough of the Burmese lowland. A longitudinal change in facies from continental and paralic deposits in the north to marine facies in the south has been noted by Tainsch (1950) and Graham et al. (1975). PLEISTOCENE The transition between the Pliocene and the Pleistocene in the Siwalik Foothills region of India and Pakistan is represented by a nearly continuous sedimentary sequence involving the Tatrot and Pinjor Stages. The Tatrot vertebrate fauna includes some typical Middle Siwalik holdovers with the introduction of some new elements towards the top. Recent work by Opdyke et al. (1979) in several sections in Pakistan has shown, on the basis of magnetostratigraphy, that there is a change in the faunal character at about 2.47 m.y., indicating the Pliocene--Pleistocene boundary when the Tatrot Stage (Gauss normal epoch) is gradually succeeded by the Pinjor Stage (Matuyama reversed epoch). Although the Pleistocene, comprising mainly non-marine deposits with some minor marine coastal deposits, is known from several localities in the Indian subcontinent, comparatively little detailed work has been carried out on demarcating the lower and upper boundaries of this epoch. It is true, however, that on the basis of Pleistocene vertebrate faunas from the Siwaliks and its equivalents, it has been possible to work out the geology and palaeontology of Lower Pleistocene Siwalik deposits with a fair amount of precision. In most sections, Upper Pleistocene sediments appear to grade gradually into Holocene deposits as is seen all along the northern part of the Indo-Gangetic Plain. The flora consists about 54 families of which more than 65% are angiosperms, distributed in the northern and eastern parts of the subcontinent. Floral assemblages are known from Karewa Basin in Kashmir (Puri, 1948), Hardwar in Uttar Pradesh (Varma, 1968), Bihar--Nepal boundary (Lakhanpal, 1970) and Bengal Basin (Biswas, 1963). From the Karewa Basin in Kashmir, Purl (1948) has reported the presence of approximately 70 genera of flowering plants. A large portion belongs to the dicotyledons, a few to monocotyledons and only six species to gymnosperms. The flora comprises tropical, subtropical and temperate species. According to De Terra and Paterson (1939), the climate during the first interglacial in the Kashmir Valley was more moist and slightly warmer than at present. Acco.rding to Singh et al. (1973), the dominance of gymnosperms over angiosperms during the Late Siwaliks in northern India indicates a subtemperate to temperate climate. Further eastward, megafloral assemblages consisting of leaf impressions are reported from the Bihar--Nepal boundary, comprising Zizyphus, Bahunia and Cinnamomum (Lakhanpal, 1970). In the Pleistocene, the sites of coal and lignite development shifted northwards towards Kashmir and the Punjab from the Pliocene localities where

54 coal seams were encountered in the eastern and southeastern sectors (Fig.5). Coal deposits are reported from Hoshiarpur and Kangra Districts (Krishnan, 1953). Lignite occurs in Handwara, Nichahom and Raithan areas in Kashmir (Goswami, 1955; Tripathi and Chandra, 1976) and at Nalagarh, Himachal Pradesh (Bhatia emd Mathur, 1971). The Pleistocene was a period of far reaching tectonic disturbances, glacial extensions and climatic changes. According to Mittre (1964), the Pir Panjal Range of Kashmir underwent uplift during Karewa time, as a result of which a change in climate took place with a shifting of vegetational zones towards lower altitudes and southward migration of the monsoon forests. The Pleistocene elevation of the Pir Panjal Range of Kashmir is also supported by the work of Puri (1948). According to him, plants which are at present living at a height of 1500 m are foundas fossils at about 3200 m.

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55 According to Mittre (1964), due to the uplift of the Pit Panjal and concomitant glaciation, the monsoon forest zones migrated southwards. Another striking example of the southerly shift of climatic zones is represented by the present-day south Indian disjunct distribution of Hemitragus hylocrius (the Nilgiri goat) which is a near relative of the Hemitragus ]emlahicus (Himalayan tahr) whose ancestors were fairly common in the Pleistocene. The occurrence of some Rhododendron species in peninsular India are ascribed to similar factors. Siwalik mammals, which had reached a peak of taxonomic diversity during uppermost Pliocene to lowermost Pleistocene times, declined as a result of the onset of glacial conditions. Apart from the Siwalik occurrences, Pleistocene mammals have been reported from sediments all along the major peninsular rivers, from lacustrine deposits of Kashmir as well as from cave deposits in Andhra Pradesh. In the Siwalik occurrences, during the Early Pleistocene (Pinjor Stage}, the fauna was abundant and highly diversified, represented by primates, carnivores, proboscideans, equids, anthracotheres, giraffids, bovids, rhinoceratids and suids. During the latter half of the Pleistocene (Boulder Conglomerate Stage) there was a marked decrease in faunal diversity. Halstead and Nanda (1973} noted that the cyclothems of the Tatrot Stage (Upper Pliocene) of the Chandigarh area are similar to those of the overlying Pinjor Stage (Lower Pleistocene), but contain more argillaceous matter. This indicates a more mature fluvial regime with the extensive development of backswamps. The occurrence of mammalian fauna in the Karewa Basin (Kashmir) was reported by De Terra and Paterson (1939}, who reported species of Bos, Elephas, Equus, Cervus, Felis, Sus, Sivatherium and Rhinoceros from the Sombur and Ningal valley areas. The presence of these fossils indicates a correlation with the Pinjor Stage of the Siwaliks (Krishnan, 1968). From the Narmada alluvium in central India, species of Elephas, Hexap-

rotodon, Bos, Bubalus, Trionynx, Ursus, Sus, Cervus, Leptobos, Rhinoceros, Stegodon, Hippopotamus, Equus, Palaeoloxodon along with some reptiles, have been reported (Tripathi, 1967, Krishnan, 1968). From the Godavari alluvium, skulls and teeth of Bubalus palaeindicus, Equus namadicus,

Hexaprotodon namadicus, Cervus, Palaeoloxodon antiquus (namadicus}, Stegodon insignis are known. From the Ganga-Yamuna alluvium, species of Bubalus, Bos, Cervus, Hippopotamus, Equus, Rhinoceros, Stegodon, Trionyx and Batagur have been collected. An analysis of the fauna collected from the Narmada, Ganga and Godavari alluvium shows that out of the 21 peninsular Indian mammalian taxa, 78% are reported from the Narmada alluvium, 52% from the Ganga alluvium and 68% from the Godavari alluvium; 28% of the species are common in these three areas (Tripathi, 1967). From the Krishna alluvium in south India,Bos and Rhinoceros deccanensis have been reported (Krishnan, 1968). From Ariyalur near Madras, Pilgrim (1939, 1944) reported certain equids similar to Equus sivalensis and Equus namadicus. Near Susunia Hill in the

56 Bankura District of west Bengal, proboscideans, rodents, carnivores, equids, bovids, cervids, suids, crocodilians and chelonians have been reported (Sastry and Dutta, 1973; Dutta, 1976). From the Irrawaddy alluvium in Burma, Elephas namadicus, Bos namadicus and Hippopotamus have been reported from the lowermost Pleistocene (Krishnan, 1968). From the Kurnool Cave deposits in Andhra Pradesh, a rich mammalian fauna comprising approximately 22 genera along with some reptiles was described by Foote (1884). In the western sector, in the Kutch region, uplift took place during the Pleistocene, as is shown by the presence of raised beaches and coastlines (Krishnan, 1953). According to Dey (1956), the Cambay--Ahmedabad--Thar region was under the sea during the Pleistocene. The presence of raised beaches and the dead coral reefs a few kilometres inland from the present Kathiawar coastline show considerable variation in the sea level during the Late Pleistocene (Gupta, 1972). In the southern sector, the land connection between Sri Lanka and the Indian mainland existed until the Late Pleistocene, approximately 25,000 years ago. This is borne out by the record of vertebrates in the Ratnapura Beds of Sri Lanka which indicates a post-Pliocene migration into Sri Lanka (Jacob, 1949).

CONCLUSIONS

Early Miocene (1) Both marine and non-marine conditions prevailed in the eastern and western sectors of the subcontinent. Non-marine deposits are confined to the northern sector. The Sindhu and Bangla seas were shrinking southwards along both flanks. (2) The period shows the widespread occurrence of the palm, Sabal major, and Pinus. (3) Mammalian faunas were widely distributed. Mammals show an intermixture of African and southern U.S:S.R. species as well as some endemic forms. (4) Both marine and non-marine mammals are reported from Kutch and Kathiawar. (5) The Kasauli and Murree Formations (Aquitanian--Burdigalian) mark the onset of the first sedimentary contribution from the Himalayas. (6) Coal and lignite development was restricted to the western, eastern and southeastern sectors of the subcontinent.

Middle and Late Miocene (7) Middle and Late Miocene sedimentation is marked by increasing continentality. (8) Prevalence of dipterocarps throughout the subcontinent is suggestive of tropical, rain-forest conditions.

57

(9) Mammalian faunas are once again widespread, extending from the Hundes region in Tibet and Kargil in north Kashmir to many localities in northern India and Burma. Approximately one-third of the forms are common to the Lower Siwalik (Chinji) mammals. (10) Coal and lignite are developed in the eastern and southeastern sectors. (11) During the latter half of the Miocene, the Indo-Gangetic alluvial basin started subsiding. Neogene sedimentary regimes and non-marine terrestrial communities indicate great environmental stability. Pliocene

(12) The Pliocene marks the initiation of more arid conditions with many steppe--grassland faunas including hipparionids, bovids and giraffids. (13) The end of the Pliocene is marked by the complete eradication of dipterocarps from northern India. (14) Coal and lignite are reported from the eastern and southern sectors of the subcontinent. Pleistocene

(15) Lower Pleistocene floras and faunas are widespread throughout the subcontinent. The occurrence of plain-inhabiting species at localities which are highly elevated today is indicative of considerable Pleistocene uplift. (16) Floras indicate subtemperate conditions. (17) The sites of coal and lignite development shifted northwards towards Kashmir and the Punjab from the Pliocene localities where coal seams were encountered in the eastern and southeastern sectors. (18) Glaciation resulted in the south and southeastward migration of climatic belts and the disjunct distribution of many animals and plants. (19) Pleistocene mammals from widespread localities in the subHimalayan and peninsular shield areas show a remarkable homogeneity. Approximately 30% of the species are common to all the major localities. ACKNOWLEDGEMENTS

The authors are thankful to Professor S. N. Singh for his constant encouragement and helpful suggestions. REFERENCES Awasthi, N., 1972. Occurrence of some dipterocarpaceous woods in the Cuddalore Series of South India. Palaeobotanist, 21(3): 339--351. Ball, V. and Simpson, R. R., 1913. The Coal Fields of India. Mere. Geol. Surv. India, 41(1): 13--115. Banerjee, D., 1964. A note on the microflora from Surma (Miocene) of Garo Hills, Assam. Bull. Geol. Min. Met. Soc. India, 29: 1--8. Banerjee, D., 1968. Siwalik microflora from Punjab (India). Rev. Palaeobot. Palynol., 6(2): 171--176.

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