PALAEOBOTANICAL FEATURES OF THE THAR DESERT

GURDIP SINGH

Birbal Sahni Institute of Palaeobotany, Lucknow

INTRODUCTION

The Great Indian Desert, occupying northwestern India and southeasternW. Pakistan, centres on a very dry area (less than 5" annual rainfall) known astlhe That' Desert. Pahieobotanically, the area has continued to be one of theleast worked out sections of the country and hence is very remotely understood.Since not much is known from the Thar Desert proper it is proposed to include,in this review, palaeobotanical features of the entire arid or semi-arid territorywnich lies approximately west of the Aravallis, hut within the State of Rajasthan,and some aojoining areas in the N. Gujarat State and W. Pakistan; here collect-ively called as the 'Rajasthan Desert'.

In this vast region most of the geology of the area is hidden under amantle of desert sand. The rock formations that rise above the sand dunes aremostly ascribed to the Pre-Cambrian and Vindhyan Systems. At a few sites areexposures of the Talchir boulder-beds, and sandstones of tbe Damuda and Maha-deva Series. Besides these, rocks of the Jurassic age occur at Bikaner and Jaisal-mer. The Cretaceous is represented by Balmir (Barmer) and Himmatnagar sand-stones. The Balmir sandstones are estuarine in character and contain plantfossils. The Eocene, with its beds of limestone. shales and lignite is representedin Jaisalmer and Bikaner. Most extensive of all, however, is the unconsolidatedveneer of the Quaternary deposits in which lie salt-lakes, gypsum deposits and thepresent-day drainage of the area. In the light of these broad geological featuresone can look hack at the advances so far made by palaeobotany in the 'RajasthanDesert', and also dwell upon the scope of the subject in this region.

RESUME

The earliest record of plant fossils in tbe 'Rajasthan Desert' is in the formof unidentified fossil wood remains discovered at L:;Jthiby Dr. Impey and reportedby Carter (1861). Later Blanford (1877) visited the area and mentioned the occu-rrence of large blocks of unrolled, silicified wood, found associated with horizo-ntal beds of sandstones, near Lathi between Pokaran and Jaisalmer. In the"Summary of Geological Observation", Blanford (loc. cit, p. 19) refer!' to somefossil wood, from sandstones near Lathi, as dicotyledonous. These beds, which

PALAEOBOTANICAL' FEATURES OF THE THAR DESERT (J.89

were equated with Barmer sandstones by Blanford (loc. cit.) were further correla-ted by him with similar sandstone containing fragments of silicified wood occu-rring beneath the marine Jurassic beds of Jaisalmer. La Touche (1911), whocollected a few leaf impressions from sandstones at Barmer suggest that, as theplant fossils contained in the Barmer sandstones are dicotyledonous, 'the beds arenot older than Cretaceous'. La Touche (loc. cit;), however, observed that sinceBlanford (loc. cit.) had distinctly stated that the sandstones, namely the Lathigroup, contained dicotyledonous fossil wood, it must either be supposed that inthis region dicotyledonous plants appeared at an earlier stage of geologicalhistory than they did in Europe, or that the sandstones of Lathi did not reallyunderlie the Jurassic strata of Jaisalmer but were faulted against them, or that thelatter were not really Jurassic, but belonged to a higher stage among the Meso-zoic strata. He thus, counselled that, as the palaeontology of these Jaisalmer rockswas so little known the question ought to be left unsettled for the moment.

A long time after this, Sahni (1936) reported fossil fronds of WeichBtiliareticulata (Stockes and Webb) Ward, and a new species of Matonid'um, M.indicum. from Himmatnagar sandstone which is regarded as Cretaceous in age.The fossils comparable to M. indicum have since been described as M. goeppere.by Roy (1966). M. goepperti is known widely from Middle Jurassic to LowerCretaceous. WeichBelia reticulata, which is also widely distributed, is a bettcrindex to tlie age. All the known records lie within the Cretaceous, and mostof them in the Wealden. Gothan had suggested that W. reticulata was mostprobably a xerophytic fern inhabiting sand dunes but Sahni (loc. eit.) saw noevidence to that effect.

In early 1948, Mr. S. K; Borooah, Director, Department of Mines andGeOlogy of the then Jodhpur State, sent to the late Professor Birbal Sahni a pieceof 'Barmer sandstone' bearing a leaf impression, which was identified by Bose(1949) as a badly preserved, incomplete impression of a dicotyledonous'leaf.later. Bose and Borooah, together collected four more fossil specimens of dicoty-'ledonous leaves and some incrustations of unidentified pieces of fossil stems froma bed of dark carbonaceous clay from a locality near the Barmer Hill (Bose.lococit.). On maceration of a piece of the leaf-bearing matrix Bose (loc. eit)recovered a large number of fossil pollen grains and spores. According to )lose(1952). the majority of polJen grains in the carbonaceous clay belong to dicotyle-donous plants and of these some were found to be comparable to members ofBetulaceae. Sapindaceae, Fagaceae, Rosaceae and Sarraceniaceae. The fewspores belong to Pteridophy,ta and Fungi. Besides these, Bose (loc. eit.) idsodescribed unidentified fossil leaf impressions from sandstones at Lunu, regardedby Borooah as contemporaneous with the Barmer sandstones. Because of the

GURDIP SINGH

PALAEOBOTANICAL FEATURES OF THE THAR DESERT 191

·iswood which has undergone decay and disintegration and has been preserved asthin continuous bands and finely divided tissues. The associated ingredientsare resinite, exinite and sclerotinite; resinite forming an abundant constituent.

An important palaeobotanical work on the 'Rajasthan Desert', that hasappeared in recent years, is on the Jurassic microflora from Rajasthan bySrivastava (1966). The material for this study came from the Iaisalmer limestoneand the Lathi Formation from two wells drilled in the Jaisalmer area. Thecomponents of the microfloral assemblage of the samples studied by the authorhave been referred to plant groups such as pteridophytes, Cycadales-Bennettitale~and Coniferales The pteridophytic spore types, which are relatively low inquantity, show affinities with a variety of families, viz., Cyatheaceae, Osmund-aceae, Dicksoniaceae, Schizaeaeeae (Lygodium), Selaginellaceae and Polypodiaceae.On the other hand, representatives of Cycadales and Bennettitales have beenshown to be fairly well represented. Coniferalean disaccate grains are very rare,and the few that 'are present, all belong to the genus Podocarpidites. ClassopolU8grains. probably produced by genera like Oheirolepis, Brachyphyllum andPagiophyllum have been shown to be dominant. On the basis of the acuteshortage of coniferous disaccate pollen, an abundance of cycadalean-bennttitaleanand inaperturate grains, a good representation of pteridophytes and dominanceof Clossopollis classoides together. with the geological evidence. Srivastava(loc. cit.) concludes that the Lathi and Jaisalmer Formations are Lower toMiddle Jurassic in age. He has further brought out that most of the spores andpollen in the Lathi and Jaisalmer Formations greatly resemble forms recoveredfrom Mesozoic strata of various regions, especially the Lower Jurassic ofWestern Australia (Balme, 1957) and Western Siberia (Bolkhovitina 1956), theJurassic of Jabalpur series (Dev, 1961) and the Mesozoic of Western Canada(Pocock, 1962). Commenting on palaeoecology and the depositional conditions,he remarks tha t the pollen grains like Olassopol/is are not suited for transportby wind to long distance and therefore it is reasonable to su'ppose that theplants producing them were located very close to the place of sedimentation. Itis interesting to note that Pocock and Jansonius (1961) speculate that the plantsproducting such pollen favoured a coastal environment. On the nature ofclimate. Srivastava (lac. cU.) adds, the combinatioll'of a good representation ofcycadalean-bennettitalean pollen grains with a few pteridophytic spores and analmost absence of coniferous disaccate grains, suggests a prevalelltly dry climate.

Studies .of recent and sub-recent deposits in the 'Rajasthan Desert' are evenmore rare than the studies so f9r carric;:dout in the older horizons. Jacob, et al.(1952) recovered well preserved nucul~s of Ohara from the bed of impure gypsumin a quarry at Jamsar near Bikaoer. Fossil nucules of Ohara. whicbare indicative

of £n;sh water conditions, are of stratigraphic value for rocks ranging fl10m Jura-ssic, 0 Eo,Cene. In deposits younger than the Eocene the nucules are similar tomoaeFn foroms. The same authors (loc. cit.) also examined samples from thegypsum deposit at Siasar-a locality west of Jamsar-and recovered similar nucules0fi Ohara together with shells of Vivipara benga1ensis (Lam.), a genus of purely freshwater habitats, and found only in recent and sub-recent deposits. The autliors,tnerefore, suggested that the Siasar gypsum bad been precipitated, most probablyin sub-recent times in land-locked basins into which nucules of Chara and shellsVivipara were brought in by fresh-water aftluents.

Archaeobotany, branch of palaeobotany, dealing with plant remains foundaUarchaeological sites but for few achievements, is also in its infancy in the'Rajasthan Desert'. It is known that the plant economy of the Indus Culture,wHich flourished on the outskirts of the Thar Desert in the second and tbirdmillenium B. C, rested on irrigation farming and that the people cultivated cropssuch as bread-wheat (Triticum compactum), barley, peas, sesame, cotton, 'and grewdate palm (Childe, 195b). However, a lot more stili needs to be uncovered atvarious level'!. Recently Vishnu-Mittre (in press) has investigated the plant eco-nomy in ancient Ahar, a Chalocolithic age city of Tambavati in Rajasthan, andhas indentified plant remains occurring in the form of impression on potsherds asrice (Oryza sat?:va) and S01'ghum. There are indications of other millets too, butS0 far they remain undetermined. Rice is known from other Cha1colithic sites ofInoia but millets (Sorghum) have been discovered for first time.

Lately, Si ngh (1967) has emphasized the importance of palynologicalstudies to decipher the origin of the Great Indian Desert and its past vegetationalJlist@ry, pre-historic, agriculture, climatic fluctuations, salinity, past land-andsea-level changes, and dating of archaeological events. Singh and Joshi (unp,u-bJjshed) have also. recently, investigated the history of post-glacial vegetation andclimate of the eastern part of the 'Rajasthan Desert' by means of pollen-analysisof a prefile from the salt-lake at Sambhar. The pollt:'n diagram from Sambhar isdivisible into five stages, each representing a different environment than the~11~cedingone. The vegetation, as deduced from the pollen record, shows a fiveff:ola climatic shift, that is, wet-semi arid-wet-arid to extreme desiccation. Workt0wards the C-14 elating of the pollen sequence is in progress.

SCOPE

192 GURDlP SINGH

PALAEOBOTANICAL F.EATUR~S OF THE THAR DESERT

ments of the 'Rajasth~n Desert'. We.•so far, have some glimpses of tbe florahistory and palaeoecology of the 'Rajasthan Desert' from Jurassic to the earlyTertiary. The picture, before and after this period, except for some disconnectedfinds, is almost blank. This is least surprismg because most of tbe formations ofthe region are buried under sand dUDeSand hence inaccesstble to geologbts andpalaeobotanists. alike. Unless and until large-scale boring operations are under-taken to study the geology of the region the picture is unlikely to change. Iil thefield of recent and sub-recent deposits, however, is different. These depositsfrom only a thiD veneer on the surface and can, therefore, be easily reached byconventioDa~ means. Th~ large Dumber of salt-lake deposits in the 'RajasthanDesert' are a rich source of plant microfossils which can be anafysed to decipherproblems, su.ch as" flo,a histor~, past climatic, oscillations. early agt"1cutturej'progresai.ve deforestatiQ&<'past ~a-transgfCssions tillcoastal area~, and othel' alliedproblems. In fact, work on the 'Rmjutha,n Desert' along thes~ lines, is u.lreadyin progress at the Birbal Sahni Institute of Palaeobotany, Lucknow.

CONCLUSIONThe author gives an outline of the reselTch in palaeobotany in the

'Rajasthan Desert' from the earliest time to the present. It is marked that whilepala~bQtany has sucee¢ded in gi~mg S011)eglimpses of the flora bistoryandpalaeoecology of the 'Rajasthan Desert' from Jurassic. to the early heFt~y, therecords from the relatively older and younger geological horizons, except for afew' disconnected findS from' recent and sub-recent deposits, are lac'king. Sin~most of the-older formations' of the region are buried under sand dunes, theauthor lays stress on carrying out palaeobotanical research on the Quaternarydeposits of the region which are more easily available.

ACKNOWLEDGEMENTS

The author wishes to express his sincere thanks to Drs. R. N. Lakhanpaland S. D. C. Sah for kindly going through the manuscript and to Dr. VishnuMittre\for kindly allowing a'Ccess;to some of his unpublished work'.

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GURDIP SINGH

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