PROBL~MES ET TENDANCES

]ODITIONS DU CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE 15, quai Anatole-France - PARIS V I I ~

SOME ASPECTS OF THE PLEISTOCENE PERIOD

IN SOUTH CENTRAL MAHARASHTRA

by S.N. Rajguru (Poona)

RESUME. - Les systkmes actuels des rivikres au Maharashtra s'expliquent par des mouvements tecto- niques qui se sont poursuivis jusqu'au dCbut du PleistocBne, e t par les conditions climatiques. L'importance de ces deux facteurs a C t C gknkralement sous-estimke. Les dkpBts quaternaires des vallkes, trBs Bpais, et variCs, sont difficiles dater avec prCcision. Leur mode de formation est expliqui: en dCtail.

SUMMARY. - The study of the alluvial bodies preserved in some of the streams in Maharashtraindi- cates that this region experienced epeirogenic movements and milder climatic changes almost troughout the Pleistocene. The assessment of the exact nature of the climatic changes and their ultimate correlation with those changes from higher latitudes is a t present very difficult. The exposed as well as buried alluvium from these valleys do not date earlier than the Upper and Late Middle Pleistocene respectively.

The various river systems in Maharashtra have been studied for a number of years now. The present author had an opportunity to investigate many of them and also of comparingthe available data regarding their formation, etc. I t seems that proper emphasis has not been laid on the epeirogenic factors in previous studies. Although small-scale or local tectonic activity like warping or faulting is taken note of, the general nature of tectonic activity over the entire area has not been given due consideration. Epeirogenic activity and climate, as two factors of general occurrence in the whole area, offer a better explanation of the nature and form of present day river systems in Maharashtra.

About a hundred years ago an agate flake, having every appearance of human workmanship, was picked up by Wynne from the gravels of the river Godavari near Paithan. Large number of mammalian fossil bones were also collected from the alluvial deposits of the rivers Krishna and Godavari by geologists and palaeontologists like Twemlow, Cook, Pilgrim (1905) and others. These bones mostly belonged to species like Elefihas Namadicus, Bos Namadicus, Hippofiotam~s fialaeindicus, Epuus Namadiczbs, etc. All these studies established the presence of Pleistocene alluvium in the Godavari and other rivers of the region under consideration. Later Vredenburg (1906) studied the various river profiles from central India and Maharashtra and showed that a verv extensive. though moderate. tectonic disturbance has affected the Peninsula in the Pleis- toce& period. i'hese 7ectonic diskrbances in the form of gentle warping produced rock basins in many rivers and thus provided suitable traps for the accumulation of alluvium. Vredenburg also postulated that alluvial sediments belong to a single age.

The first systematic archaeological study of the ancient alluvium in this region was carried out by Sankalia (1943-1964) and he established the existence of two Stone Ages in the Pleistocene period. Handaxes, cleavers, choppers, etc. form the Early Stone Age culture and belong to the 1st aggradational cycle while the tools of Middle Stone Age period belong to the 2nd aggrada- tional cycle. The Middle Stone Age tools are smaller in size (5-10 cm in length) and consist mainly of scrapers and points. On the basis of palaeontological evidence Sankalia dated these industries to Late Middle Pleistocene and Upper Pleistocene periods respectively. Zeuner (1950) made a geological study of the Godavari alluvium near Nasik and showed that the drainage of the Godavari during Pleistocene was not the same as it is today. The river Godavari aggraded its bed with alluvium due to increasing aridity in the dry phases of the Pleistocene whereas in the wetter phases it was dominantly eroding.

PLEISTOCENE PERIOD I N SOUTH CENTRAL MAHARASHTRA

forests with pockets of monsoon ephemerals are present while in areas receiving rainfall between 100 cm-zoo cm deciduous woodland savanna predominate, dry deciduous and thorn shrub forests occur in regions receiving rainfall in between 50 cm and 100 cm. Soils in the major part of the region are of grassland pedocal (A/C) type and range in colour from grey to red brown, dark brown, etc. In the higher rainfall zones red lateritic, slightly acidic soils predominate. The soils are immature and thin in hilly terrain and they attain considerable depth and maturity on the plateaus and in river flats.

These varied ecological settings have interesting effects on the fluvial geomorphic processes in this region. The incomplete vegetational mat and eight months long dry season favour insolation weathering of basaltic rocks, while chemical weathering accelerates during rainy season. The characteristic spheroidal weathering produces ready made boulders of harder basalts while granular disintegration of basaltic rocks gives rise to immense amount of sands. The chemical weathering under the influence of absorbed moisture and humus promotes red to yellow brown soil formation in the hilly terrain and black brown soils on the plateaus and in valley plains. The first onset of monsoon downpour is mostly utilized in saturating the water starved terrain, though there is limited surface runoff. The weathered material is trans- ported to trunk streams through ephemeral nullas or gullies. The major streams and their tributaries have concordant junctions and are almost graded while gullies have at many places discordant junctions with trunk streams and are ungraded.

During heavy rainfall period main streams swell and develop wide flood plains and are quite active in the works of transportation, erosion and deposition. Tremendous amount of mud is carried in suspension and boulders and pebbles are tranctioned along the bed of the streams. This very active nature of fluvial process is not only due to the heavy monsoonal torrents, but due to large catchment areas in the heavy rainfall zones. According to Deshpande (( these upper catchment areas serve as large water collecting basins through which water is forced down the main streams where waters are confined to valley plains by residual ranges )) (p. 4). During flood the flood sheet acts as a local base level to tributaries so that there is deposition of silt in the marginal flooded areas and with the subsidence of floods, many times as sudden as their appearance, erosive action of streams start with the lowering of base level and thus flood-plain terraces are formed at the confluence of the trunk stream and its tributaries. The movement of bed and suspension loads, their subsequent deposition at suitable places in the channels and in flood plains, the erosion of beds and banks, all these actions of streams are restricted to the torrential downpours which occur only occasionally during the rainy season and these streams become almost defunct during the major part of a year.

The slope forming processes, such as mass wasting, scarp retreat, etc. must have played a significant part in sculpturing the landscape, especially in the drier parts. The sinous nature of the western scarp is mainly because of its retreat from the coastal side and the consequent abstraction of the plateau topography. The pediment surfaces, which are better developed in drier parts, have made the valleys broader even in their youthful stages. These geographic, geologic and climatic factors have been described rather in detail so as to make the necessary background for understanding the Pleistocene phenomena and processes clearer.

B. TECTONIC, GEOMORPHIC AND CLIMATIC ASPECTS OF THE PLEISTOCENE PERIOD

Excepting the coastal fringes the major part of the region was never occupied by s . d u r i n g whole of Cenozoic period. Yet the end of Mesozoic and the beginning of Cenozoic wat; a period of tremendous volcanic and tectonic activities. In the Purna valley, a tributary of the Tapi river, considerable step faulting took place almost in the same period. Such faulting provided suitable basin for the accumulation of fluvio-lacustrine sediments, about loom to 250 m thick, of Cenozoic period. Adyalkar (1963) thinks that the lacustrine conditions prevaile$..in the Purna Valley almost throughout the Tertiary and Pleistocene periods and the p e'nt course of the Purna appeared on the silted lake, probably in the early Holocene. Such&ic changes also affected the other river valleys like the Tapi in northern and north-east Maharashtra during early

S.-N. RAJGURU

Tertiary period. The Miocene and/or Pliocene witnessed the great faulting on the western side of Western Ghats. These tectonic forces, though of lesser intensity, probably continued in late Tertiary and early Pleistocene periods. During this period, the formation of many waterfalls, like Venna on river Krishna, Randha on the Pravara, etc., the supposed hypothetical warping in many river valleys like the Godavari, the Tapi, etc., the dissection of laterite plateaus in Western Ghats, probably took place. The absence of major river captures in Western Ghats, and the absence of Early Pleistocene sediments in faulted trough valleys of the Mula and the Pravara again suggest late continuation of tectonic disturbances.

From the palaeo-botanical evidence it is presumed that more humid and warm conditions of the Eocene period in the Deccan became warmer and drier in Miocene period (Mahable, 1965). Geomorphologically extensive pedimentation might have occurred during this drier period and broad river valleys might have been produced. The pedimentation coupled with faulting pro- vided deeper basins for the accumulation of sediments, in some of the river valleys like Pravara, Mula and probably Godavari. The total thickness of the alluvium at some places, is about 30 m and it is laterally quite extensive, about I ooo meters, in these fault affected valleys. While the thinkness of alluvium is not more than 20 m and the lateral extension is also quite limited in the non-fault affected valleys of Krishna, Mula-Mutha, etc. In the latter case pedi- mentation and normal erosional actions of rivers might have provided suitable basins for the accumulation of sediments.

The general nature of the alluvium accumulated in various river valleys has been shown in fig. 2. Generally the lower part of the alluvium is coarser in nature than the upper portion. The gravelly beds occur as lenticular bodies in the finer sandy silty alluvium. The bouldery gravels are generally unsorted, unimbricated, polymodal and are rich in locally derived basaltic, doleritic and silic'eeus rocks. Such beds in the source areas of many of the rivers like Mula-Mutha, Krishna and the Pravara are dominantly colluvial in nature thereby indicating the dominance of lateral transportation in the valley. While these gravels are dominantly alluvial in nature at Paithan on the Godavari. At Paithan the gravel bed is rich in well rounded cryptocrystallilke silica boulders and pebbles, while the modern bed material is finer, thus indicating greater compe- tence of the stream during the Pleistocene. Similarly at Panchwad on the Krishna, about 56 km from the source, the Pleistocene gravel beds contain well rounded lateritic pebbles definitely derived from the source region and transported longitudinally downstream thereby showing considerable competence of the stream. Whether the Pleistocene gravel bed is colluvial or alluvio- _-- - colluvial or alluvial in nature it seemed to have been deposited suddenly by highly turbulent waters. The cementing matrix is mostly trap-derived finer sand, silt and calcareous material. These gravels have yielded tools of Early Stone Age period near Nevasa, Pandharpur, Poona, etc. and Middle Stone Age tools near Paithan. Mammalian fossil bones have been collected at Paithan and Nevasa.

The other type of gravelly beds, commonly encountered are pebbly to fine sandy, richer in chalcedonic silica components than the boulder beds and many times are cross-bedded. The degree of cementation vary tremendously from hard rock like to very loosely held bodies. The well cemented bodies many times form protruding ledges in the silty alluvium. The pebbles and sands are generally subrounded to rounded and the cross-bedding is generaly tabular type. These gravelly beds also occur as lenticular bodies in the silty alluvium and have yielded large number of Middle Stone Age tools along with mammalian fossil bones especially near Nevasa. On the Mula near Rahuri in situ fossil bones of Bos Narnadicus Falconer and Bubalus Bubalis Linlzaezss have been obtained from well cemented coarse sandy gravel bed occurring about 10 m below the present water level of the river. In the same horizon the carbonised logs of fossil woods of Terminalia Arjuna (Mahable 1965) have been found. Large number of molluscan shells were collected by Pilgrim (1905) from the Godavari from cross-bedded gravels. All these palaeontological evidences show that the depositional environments were not probably very much different than those of to-day. From the nature of cross bedding and cut and fill structures it appears that these gravels are channel deposits formed by turbulent currents.

The finer alluvium consisting of sands, sandy silts and silty clays occupies a major portion of the Pleistocene alluvium, and seem to have been deposited mainly as flood plain deposits during monsoonic floods. In present day low rainfall area the silts are highly calcareous and

PLEISTOCENE PERIOD I N SOUTH CENTRAL MAHARASHTRA

range in colour from pinkish grey (7.5 R. 612) to brown (7.5 R. 512) to strong brown (7.5 R. 516) and are alkaline in nature. The mechanical analysis of these silts (coarse sand I5 %, fine sand 35 %, silt 37 % and clay 13 %), the subangular to subrounded nature of quartz grains and the occurrence of fine sandy lenses in these silts all show that this finer alluvium was deposited by fluvial agency. The presence of carbonaceous clayey lenticular body in Mula alluvium near Rahuri indicate the existence of back swamp conditions during the Pleistocene period. The fine sandy lenses have sometimes yielded tools of Middle and Late (?) Stone ages. Otherwise this finer silty alluvium is generally devoid of tools and animal fossil bones.

The sub-recent silts are dark brown (7.5 R. 517) in colour, alkaline but less calcareous than the ancient silts and many times show fine laminations. The top surface of the older silts form broad alluvial terraces in many of the rivers like the Godavari, Krishna, Mula-Mutha, etc. The present day streams have cut down the older alluvium and flow at a lower level between 20 m to 10 m from the terrace surfaces. These streams, therefore, reach this level only during excep- tionally high floods, and they have built up terraces of sub-recent alluvium at much lower levels. These younger terraces abut against the older ones, and thus the subrecent to recent channels have become narrower than the Pleistocene ones.

Because of the lack of exact datable evidence all these various Pleistocene deposits can be dated only tentatively. So far fragmentary fossilized bones of mammalian species have been collected from the gravels. Most of these species have survived throughout the Middle and Upper Pleistocene periods and hence precise dating has become difficult. At Mula Dam, near Rahuri, no Stone Age tools were found in the fossil bearing horizon, while a few Middle Stone Age tools have been recovered from the sandy gravels a t a level of about 25 meters from the rock surface. So it appears that the fossil bearing bed is pre-Middle Stone Age period and probably not older than Middle Pleistocene. Most of the palaeontological materials from the Godavari, Parvara, etc., have been found in association with Middle Stone Age tools and therefore from the meagre palaeontological evidence we can tentatively say that in non-fault affected valleys like Krishna, Mula-Mutha, and probably in the Godavari, the Middle Pleistocene alluvium is preserved at a few places and the alluvium that we see in these valleys is probably not older than Upper Pleistocene and in fault affected valleys like the Mula and the Pravara the lower most alluvium is not older than Middle Pleistocene. Now from the evidence available on tectonism, sedimentation and dating we may briefly reconstruct the palaeodrainage conditions as follows :

The pre-Pleistocene pedimentation and tectonism produced wider valleys and deeper basins respectively. The pre-depositional rocky surface was quite uneven and the rivers like the Pravara and the Godavari were occupying a course much towards the south of the present course and because of gradual aggradation in later periods i.e. from Middle Pleistocene onwards these streams shifted towards North. During the aggradational phase the shifting of channels was frequent and naturally the nature of sediments also varied considerably. Further as the gradient of the streams became less and less more and more finer alluvium got deposited.

All these rivers started eroding their beds in post Pleistocene period. The presence of many knick points in many of the rivers like the Godavari, Krishna, etc., indicate shifting of the river bed in Pleistocene times and the comparative recentness of the present course.

The phenomenon of aggradation and erosion has been observed not only in Maharashtra but also in many of the rivers in Peninsular India. Aggradation has occurred irrespective of local lithology and tectonic history of the rivers. Vredenburg thought that the warping of the basins was the main cause of deposition and later on because of the (( exhausion of the forces that cause the warping of the surface, the gradual lowering of the rock barrier at the points where these rivers emerge from their rock basins, allows the river formations to become redenuded at gradually increasing rate )) (1906, p. 41).

Being far away from the sea the Pleistocene eustatism had practically no effect on the behaviour of easterly flowing streams. On the basis of the present author's observations it appears that the aggradational and erosional phenomena of these rivers have been controlled by more large scale tectonic factors such as epeirogenic movements, both positive and negative, of the whole Peninsular block and/or by the climatic changes of the Pleistocene period. According to Zeuner (1950) aggrading phase corresponds with increasing dryness and erosional phase with wetter conditions. Most of the eralier Prehistorians have attributed the deposition of gravels

GENERALISED SECTION OF C U T OFF TRENCH O N RIGHT BANK OF

RIVER MULANEAR RAHURI

BLACK BROWN SOIL SANDY XANKARISED SILT @ CROSS BEDDED SANDY GRAVEL CARBONACEOUS LAYER

SANDY PEBBLY GRAVEL TORRENT BOULDER BED If-C BASALT ROCK

- 100 20 0 300 400 500 60 0 700 800 900 METRES

Pi

Fig. 2. - Generalised section of cut off trench on right bank of the river Mula near Rahuri.

PLEISTOCENE PERIOD I N SOUTH CENTRAL MAHARASHTRA

in river channels to the humid conditions and silts to the dry conditions. The problem of climatic interpretations, as based on fluvial studies, is rather complex because of our insufficient knowledge about the large number of factors that control such processes. From the observations of the present day fluvial processes in modern ecological setting it appears that the gravels and silts are likely to have resulted and deposited in both the dry and wet climatic phases and that too concurrently. The area under discussion might not have complete vegetational mat through- out the Pleistocene and the general rainfall pattern is not likely to be different. Naturally the source regions of easterly flowing streams must have received ample rainfall even during dry phases of the Pleistocene, and the behaviour of rivers even in drier parts might have been controlled by the rainfall in the source catchments. Apart from climate and vegetation, the slope, the bed lithology and confugeration, channel patterns, and the general geomorphic setting of the various streams must have greatly affected the movement and deposition of the bed and suspended loads of streams. Because of these varied factors, and because of the lack of pollens in the Pleistocene sediments, the problem of Pleistocene climates has become very difficult. I t does not mean that climatic changes did not occur during the Pleistocene. These changes were definitely not drastic but likely to have been of minor fluctuating nature in the form of iso-wet, dis-wet and non-wet or dry periods. The Iso-wet period was characterised by uniform distri- bution of rainfall, dis-wet period by unequally distributed and occasionally torrential rainfall and non-wet or dry period by overall reduced but still torrential rainfall. All these types of monsoons were followed by the usual winter and summer periods of about 8 months duration. In such climatic changes the following hypothetical geomorphic processes might have probably operated during Middle and Upper Pleistocene.

During the iso-wet period, because of better vegetation mat, the soil stripping was consi- derably reduced and the linear erosion by streams was very limited because of lesser amount of coarser bed load. The streams aggraded their beds even in their source regions and the rise in the bed enabled the streams to migrate laterally and build wider flood plains. In the dis-wet period lesser vegetation cover and torrential rains caused increased soil erosion and increased production of coarser debris which helped streams in downcutting of the bed followed by deposition of coarser alluvium at suitable places. During the dry or non-wet period, fluvial activity was limited. The increased evaporation, the reduced overall moisture and consequently thinner vegetation mat might have favoured mechanical weathering, scarp retreats, calcification of sediments, etc. The dis-wet and non-wet periods seem to have been more frequent on the Late Middle and Early Upper Pleistocene and the iso-wet period was dominant in the Late Upper Pleistocene.

We can thus conclude that tectonism played a greater part in the late Tertiary and Early Pleistocene times and produced suitable rocky basins for the accumulation of fluvial sediments in various river valleys. The streams in the Early Pleistocene and probably in the Early Middle Pleistocene times flowed in wider valleys and swayed widely. There is practically no evidence of the preservation of Early Pleistocene sediments in this region. Perhaps laterite from Western Ghats may belong to this period. In the late Middle and practically whole of Upper Pleistocene times most of the rivers aggraded their beds, initially with coarser alluvium and later with finer alluvium. Considerable shifting in stream channels occurred during this aggradation phase. These streams became eroding in the post-Pleistocene period. These aggradational and erosional phases took place probably, either because of epeirogenic factors and/or because of climatic changes which are difficult to be assessed correctly in the present state of our knowledge of the Pleistocene and the modern fluvial processes in this sub-tropical monsoonal land.

The Early Stone Age man probably appeared on the scene in late Middle Pleistocene period. He preferred less rainy, thinly forested eastery region for his habitation to thickly forested hilly parts of the west. He made his handaxes, cleavers, choppers, etc., on the locally available fine grained hard massive basalts and dolerites. He mostly lived along the banks of perennial streams where he could hunt mammals like the wild ox, elephant, etc. The population of the Early Stone Age period was possibly thinner than what it was in the quartzite regions. The Early Stone Age culture continued in the Upper Pleistocene period and was probably replaced by new culture known as Middle Stone Age culture. The Middle Stone Age man had better mastery over the environments and he occupied almost whole of Maharashtra and lived in various ecological

S. N. RAJGURU P1. I, fig. 3

S.-N. RAJGURU

settings. He made his scrapers, points, etc., on fine grained crypocrystalline bright coloured silica minerals and rocks occurring either as pebbles in river beds or as veinlets and geodes in basaltic flows. He hunted games like elephas, bos, etc. These animals many times got trapped in natural situations. In the Purna, near Yeldari, large number of fossilized bones of an elephant (PI. I , fig. 3) were found in situ in the bouldery gravel in a pit 20 m below the bed of the river which is otherwise rocky. The pit 20 m deep, 8 m wide and about 150 m long was probably formed by some natural geological process and served as a natural trap for an elephant. The Middle Stone Age culture continued till the end of Upper Pleistocene and probably gave rise to late Stone Age Culture in the Holocene period.

BIBLIOGRAPHIE

ADYALKAR (P.-G.), 1963. - II Palaeogeography, nature and pattern of Sedimentation and groundwater potentialities of Purna basin, Maharashtra. 1) Proc. of Nat. Institute of Sciences of India, V O ~ . 29, Pt . A, NO. I , p. 25-45,

DESHPANDE (C.-D.) and BHAT (L.-S.). - (( The Upper Panchaganga basin : A study in the geomorphology of the Deccan Traps )I, p. 1-13.

JOSHI (C.-B.) and ARUNACHALAM (B.), 1962. - Maharashtra (A regional study). MAHABLE (T.-S.), 1966. - e Flora of the Deccan 11 : a Past and Present 11. Presidential Address 53 rd Indian

' Science Congress 1966. PILGRIM (G.-E.), 1905. - c On the occurrence of Elephas Antiquus (Namadicus) in the Godavari Alluvium

with remarks on the species, its distribution and the associated Indian deposits 1). Records of the Geol. Survey of India, Vol. XXXII, Pt. 3, p. 199-218.

SANKALIA (H.-D.), 1943. - K Studies in Prehistory of the Deccan (Maharashtra) : A Survey of the Godavari and the Kadva, near Niphad. )) Bull. of the Deccan College Res. Inst. Poona, Vol. IV, No.3, p. 186-203.

- 1945. - II Studies in Prehistory of the Deccan (Maharashtra) : A further survey of the Goda- varl 1) (March 1944). Bull. of the Deccan College Res. Inst. Poona, Vol. VI, No. 3, p. 131-137. 1952. - a The Godavari Palaeolithic Industry I). Deccan College Monograph Series : 10,

p 1-59. - 1964. - I( Middle Stone Age Culture in India and Pakistan. Science, Vol. 146, No. 3642,

P: $5-375. -

VREDENBURG (G.), 1906. - (I Pleistocene movement as indicated by irregularities of gradient of the Narmada and other rivers in the Indian Peninsula n. Records of Geol. Survey of India, Vol. XXXIII, Pt. I , p. 33-48.

ZEUNER (F.-E.), 1950. - Stone age and Pleistocene chronology in Gujarat. Deccan College Monograph Series : 6, p. 1-46.