Annals of Arid ..(one-16(2), 221-230, 1977

The source of salt in Rajasthan - An investigation ofthe salt lake of Didwana

B.S. PALIWAL

Department of Geology, Govt. Bangur College,Didwana, (Rajasthan - India).

(Received on 1.12.1975)

ABSTRACT·

The origin of salt in different salt lakes of Rajasthan had been a longcontroversial problem, which remained unsolved inspite of numerous effortsmade by a number of workers. The recent investigation carried out in the saltlake of Didwana as well as the occurrence of halite in it and the Bikaner area,gave a new turn to the problem. The investigation revealed that the sourcesalt in all the salt lakes of Rajasthan appears to be associated with the Aravallirocks, probably in the form of salt domes and intrusives, situated below recentdeposits at a good depth. This salt appears to be Precambrian evaporitic inorigin which must have been pushed out at a number of places, during differentphases of tectonic deformation of the Aravalli rocks in western Rajasthan.

INTRODUCTION

The well-known controversy about the origin of salt in different salt lakesof Rajasthan dates back to 551 A.D. with a reference to the story of goddessShakambari Devi. A popular story regarding the origin of salt in the Sambharlake (27°: 75°) is linked with the temple of the same goddess, situated nearthe lake (Aggarwal, 1951). Surprisingly, at Didwana and Pachbhadra also,there is one temple each, of a goddess having akin story about the origin ofsalt in these lakes (Aggarwal, op. cit.). Hacket (1880) was followed by a numberof workers like La Touche (1902), Holland 'and Christie (1909), Walther(1912), Holland (1914), Godbole (1951, 1952), Auden (1952), Sarin (1952),Ghosh (1952), to review the problem from different angles, without reachingat any satisfactory conclusion. Aggarwal (op. cit.) in his book "The Sambhar

Note: The paper has been presented and discussed at the "Workshop" on 'the Problems ofthe Deserts in India' organised by Geological Survey of India, Western Region, atJaipur, during September, 16 to 18, 1975 and abstract published.

222 : B.S. PALIWAL

Lake Salt Source" has mentioned all the views about. the ongm of salt inthe sa t lakes of Rajasthan. Recent reporting of halite by Sinha et al. (19"73) fromBikaner area and Khandelwal (1975a) from Didwana salt lake, has given anew turn to the problem. The detailed investigation carried out in the Didwanasalt lake (27°24': 74°34') and the area surrounding it, has revealed a new factabout the origin of salt in this lake and other salt lakes of Rajasthanas well.

GEOLOGY

The 51h kilometres long and 21h kilometres wide lake area is occupied bya 20 metres thick pile of recent deposits (the thickness varies from place toplace), overlying the repeatedly folded Aravalli metasediments. No doubt therecent deposits (at some elevated places covered by alluvium) occur in the en-tire Didwana area, but they differ from those occupying the lake area, as thelatter appear to be derived from the surrounding area. Below these recent al-luvium and kanker deposits, Aravalli group of rocks are exposed in form of anisolated patch around Tikali Dungari hills in the west of the lake. These rocksshow a strikewise (bedding) continuity below the recent deposits of the lake areaand are further exposed in wells in the east. Heron (1953) has mapped thesehills as Aravalli quartzite. Aravalli group of rocks here is represented by pureorthoquartzite, highly ferruginous and carbonaceous quartzite, grading tocarbonaceous phyllite and slate and phyllite grading to feldspathic grawacke (ex-posed around Khatu, further west of the present area), intruded by a number ofquartz veins and post AravaUi granite, which appears to be equivalent to Jaloreand Siwana granite. Lithologically, the Aravalli rocks of this area resemble veryclosely to the Precambrian rocks of Udaipur area studied by Roy et 01. (1971)and Damle and Sharma (1970). In the Tikali Dungari hills, at a place 3 lcilo-metres west of Marwar Balia, a small intrusive body of amphibolite has beenreported (Paliwal, 1976). In the lake area, recent deposits rest either on the postAravalli granite or the Aravalli rocks, which in turn are unconformably underlainby the well-known Banded Gneissic Complex. Table 1 gives the detailed succes-sion of recent deposits occupying the lake area, recorded in dug wells and tube-wells within the lake as well as the area surrounding it, and Table 2 gives thegeological succession of the entire area under study.

SOURCE OF mDWANA SALT 223

Table 1. Succesion of deposists in Didwana salt lake area

Recent

Deposits:

Encrustation of fine white sand (10-15 c.m. thick)

Alternating layers of fine white sand and grey silty clay(50-75 c.m. thick)

Yellowish grey sticky clay (20-25 c.m. thick)

Black sticky clay with fracture fillings of grey clay(l00-II0 c.m. thick)Mottled clay with grey and black stains (60-70 c.m. thick)

Kanker bed encountered in dark grey clay (20-30 c.m. thick)

Medium to coarse sand (5-6 metres thick)

Fine to medium sand (5-6 metres thick)

Very fine sand (5 metres thick)

Table 2. Geological succession of study area

Recentdeposi ts

AravalliGroup.

AlluviumKanker and other recent deposits.

Pure orthoquartzite. Highly ferruginousand carbonaceous quartzite grading tocorbonaceous phyllite and slate. Feld-spathic grewacke grading to phyllite.

Intruded by postAravalli granite,amphibolite and anumber of quartzveins.

Pre-AravalliGroup.

STRUCTURE

Banded Gneissic Complex. (Not exposed in the area).

Structural investigation carried out in the area surrounding the Didwana SaltLake, specially the Tikali Dungari hills, has revealed that the recent deposits aretectonically undisturbed, where as the underlying Aravalli rocks show a low gradeof regional metamorphism and display a very high degree of structural complexity,akin to those in the area around Udaipur (Rajasthan) Roy et at. (op. cit.). Thepresent architecture of the Aravalli rocks exposed around the Tikali Dungari hills

224 : B.S. PALIWAL

and the same underlying the recent deposits in the lake area, owes its shape toatleast four phases of tectonic deformation. The major fractures (schistosity orslaty cleavage) in these rocks are along the axial planes of either E-W to NW-SEtrending, tight, isoclinal, reclined to recumbent folds (F-l) of first generation or

) .

INDEXo ALLUVIUMD RaJENi' DEPOSITs

. [J ARAVALLI ROCKS...... ;, IQJ SA Lx LAKS' -:.:- :,.,-,. .... I '----I ROAD

" .. '..' e;J RIVER.

SCALE I..•...•.' RAItWAY

9 KM ~ [!J OBSERVATIONMILE 174° 35' WELL

Location map of the salt lake, Didwana.

N-S to NNE-SSW trending, tight, upright, isoclinal folds (F-2) of second genera-tion. Gently inclined strainslip cleavage associated with northerly trending poly-clinal folds (F-3) of third generation as well as E-W to NW-SE trending discretefracture planes associated with kink folds and conjugate folds (F-4) of fourthgeneration are also common in the area. However the intrusive bodies of amphiboliteas well as post Aravalli granite tend to be paraIlel to the major fractures in the area,

SOURCE OF DlOW ANA SALT 225

DISCUSSION

In the lake area around 'B' Mata-Sector (27°21'40" :74°33'50"), the recentdeposits OCClJronly up to a depth of 7 metres, below which there is a layer ofhalite, associated with anhydrite and fine dark grey silt (Khandelwal op. cit.). Thechemical analysis of the halite in comparison with sub-surface brine is given inTable 3. The detailed investigation carried out in the lake and dug-wells around it

Table 3. Chemical analysis of the halite in Didwana salt lake area

Sodium chloride

Sodium sulphate

Sodium carbonateand bi-carbonate

Discovered Sub-surface Didwana brine Didwanahalite [Report Salt· Expert Com- Salt(Khandelwal, mittee (1950) p. 50 & 85]1975 a)

78.291* 77.190 83.370

16.634 20.650 12.390

3.040 2.160 4.240

Calcium sulphateand undeterminedinsolubls. 2.035

*Percentage on dry basis

has revealed a very interesting fact, that nowhere in the salt lake area, including itsentire margin, there is any trace of such halite, except in the 'B' Mata-Sector".Except this central portion everywhere the recent deposits rest directly either ongranite or Aravalli rocks. The halite layer continues up to the bottom of the wellsat 'B' Mata-Sector and to the author it appears to continue upto a great depth,because of the fact that with this small horizontal extension, halite obviouslycould not be the source of tons of salt every year, for the last five hundred years.Secondly if it had been the source of salt, the chemical composition of the brinein the lake would not have remained constant for a long time, which according

226 : B.S. PALIWAL

to Salt Experts Committee's Report is constant in all the salt lakes for last somany years. Moreover a 9 ft. thick layer of halite, possibly cannot be deposited bya simple process like super encrustation.

Obviously the source of salt does not appear to be an outside one as Hollandand Christie (op. cit.) and others have assumed. Secondly halite occurs belowrecent deposits and above Aravalli rocks in the area, as there is no other rockformation in between. Now there are three possibilities: (1) salt is associatedwith recent deposits and was deposited in the first stage of the formation of thesedeposits, (2) salt was deposited after the formation of Aravalli rocks but longbefore the formation of recent deposits i.e., during tertiary period, (3) salt isassociated with Aravalli rocks.

Recent findings of some freshwater species of gastropods from recent de-posits at a place hardly 1 kilometre west of Didwana town (Khandelwal,1975 b)have revealed that marine conditions did not prevail in this part during pleistoceneand recent periods. So the view that salt might have its marine origin duringthese two periods does not hold good. If salt is still considered to be associatedwith recent deposit~, it should certainly have its source in the nearby surroundingarea, as recent deposits of the lake area are derived from it. But nowhere in thesurrounding area there is any trace of such source, not even such rocks whichcould liberate saIt by some natural processes.

Though the fresh water origin of all the three salt lakes of Rajasthan, (Singhet ai., 1972) cannot be overlooked, still there are two strong arguments againstit: (1) for a period of five months or more after the first rains, all the three lakesbehave just like freshwater (sweet) lakes, due to the slow process of dissolu-tion of salt from lower horizons, (2) recent deposits of the lake area appear tobe derived from the area surrounding it and similar might be the case with thepollen grains-study of which was the basis of their interpretation.

If the salt is assumed to be deposited during a period earlier than recent butlater than precambrian, it must certainly have some more rock formations ofthat particular period, overlying the salt layer to protect it against the open denuda-tion for quite a long period. But unfortunately in all the salt lakes of westernRajasthan nowhere such a rock type has been observed.

SOURCE OF DIDWANA SALT: 227

The only other alternative is, that this salt is assumed to be associated withAravalli (Precambrian) rocks. For that, one will have to review whether theconditions favourable for the deposition of salt prevailed during the precambrianperiod. Contrary to observations made by Raja Rao et al. (1970), the isolated out-crops of metasediments exposed in western Rajasthan appear to be the further ex-tensions of Aravalli (precambrian) rocks. This fact is supported by a close litho-logical and structural similarity between the present area and the area aroundUdaipur, studied by Damle and Sharma (op. cit.), and Roy et al. (op.cit.). Phy-llitic rocks exposed arouI)d Khatu certainly indicate their turbiditic origin. Pyritereported from phyllitic rocks around Didwana is also synsedimentary (Paliwal,op. cit.) in origin, similar to that of Zawar near Udaipur.

From all these facts it is clear that conditions necessary for the depo£itionof salt, prevailed here during precambrian period. During the middle part of theperiod this part became slightly disconnected from the main sea, due to theupheaval of the basement. The upheaval during this period is evident from theabsence of sole markings in abundance and the presence of mud-crakes in uppersub-units of phyllite (Damle and Sharma, op. cit.). This particular period seemsto be responsible for the deposition of salt interbedded with Aravalli rocks inthis part.

The second phase of folding with severe fold movement and N-S trendingaxial plane schistosity, appears to be responsible for the elevation of Aravalli rangein Rajasthan. Secondly, almost all the saline water belts in western Rajasthanalso have N-S trend.

This evidently indicates that during first and second phases of tectonic defor-mation, this salt interbedded within Aravalli rocks, being highly vulnerable todeformation, seems to be pushed out along the N-S trending fracture planes ata number of places in the form of salt domes and intrusives. These salt domes inthe elevated parts, were washed out in the later periods, whereas those of de-pressions were preserved due to later covering. During later phases of deforma-tion (F 3 and F 4), a number of synform structures were formed trending N-Sto NE-SW and E-W. These depressed structures must have taken "the shape of thepresent day salt lakes of Rajasthan. Later on, these depressions were filled withrain water which dissolved the salt from underlying salt domes and spread itthrough-out the lake area in dry seasons.

/228 B.S. PALIWAL

CONCLUSION

From the above cited observations and discussion it is quite obvious thatthe saIt of all the salt lakes of western Rajasthan, certainly has got some directrelation with the halite observed recently (at Didwana and Bikaner). Secondly,as the source of salt had not been an outside one, the halite should be associatedwith rocks present within the area, specially AravaIli rocks (Precambrian), asneither marine conditions prevailed here during pleistocene and recent periods,nor there is any other rock formation in between these two. No doubt, condi-tions necessary for the deposition of salt (evaporite) prevailed here duringPrecambrian period. Hence the salt must have been deposited alongwith the otherunits of AravaIli group.

During later periods, these rocks underwent a poly-phase tectonic deforma-tion and the salt being highly vulnerable to tectonic deformation, was pushed outin form of intrusives and domes, specially along the N-S trending major fracturesin the region. In later periods, these salt intrusives and domes were washed outfrom elivated parts, whereas those of depressions were preserved. Surface wateraccumulated in these depressions or synform structures (i.e. existing Salt lakes)dissolved the salt from these intrusives and domes, later spreading and redeposit-ing it in the form of N -S trending saline belts and salt lakes like Didwana,Sambhar, Kuchaman and Pachbhadra etc. At some of the places, redeposited saltoccurs in the form of bedded halite but salt intrusives and domes could also betraced deeper down if investigated through deep drilling.

REFERENCES

Aggarwal, S.c. 1951. The Sambhar Lake Salt Source. Govt. of India, PublicationDivision, p. 365.

Auden, J.B. 1952. Some geological and chemical aspects of the Rajasthan saltproblem. Proceedings of the Symposium on The Rajputana Desert. Bull. Nat.Inst. Sci. India, p. 53-67.

Damle, G.V. and Sharma, B.L. 1970. The nature and significance of sedimentarystructures in Aravalli rocks around Udaipur, Rajasthan. West Comm. Vol.Ind. p. 470-484.

SOURCE OF orDWANA SALT: 229

Godbole. N.N. 1951. Does Sambhar lake owe its salts to Rann of Kutch? Ind.Sci. Congo 1952.

Godbole, N.N. 1952. The salinity of Sambhar lake. Proceedings of the Symp-osium on The Rajputana Desert. Bull. Nat. Inst. Sci. India, p. 89-93.

Ghosh, P.K. 1952. Western Rajputana-Its Tectonics and minerals includingevaporites. Proceedings of the Symposium on The Rajputana Desert. Bull.Nat. Inst. Sci. India, p. 101-130.

Hacket, C.A 1880. Salt in Rajputana. Rec. Geol. Surv. Ind. No. 13: 197.

Heron, A.M. 1953. The geology of central Rajputana. Mem. Geol. Surv. Ind.79: 1-389.

Holland, T.H. 1914. The origin of Desert salt deposits. Proc. Liverpool Geol.Soc. 11: 227.

Holland, T.H. and Christie, W.A.K. 1909. The ongm of the salt deposits inRajputana. Rec. Geol. Surv. Ind. 38: 154-186.

Khandelwal, N.M. 1975 a. The occurrence of halite in Didwana salt lake area,Rajasthan. CUlT. Sci. 44 (1): 13-14.

Khandelwal, N.M. 1975 b. On the occurrence of gastropod fossils in the kankerdeposits around Didwana, Rajasthan. Curro Sci. 44 (1): 737.

La Touche, T.H.D. 1902. The geology of western Rajputana. Mem. Geol. Surv.Ind., 35: 1-116.

Paliwal, B.S. 1976. Occurrence of copper mineralisation around Tikali Dun-gari near Didwana Rajasthan. Sci· & Cult. (In press).

Publication Division, Govt. of India 1950. Report of the Salt Experts Committee.38. 154.

Raja Rao, C.S., Poddar, B.C., Basu, K.K. and Dutta, A.K. 1971. Pre-Cambrianstratigraphy of Rajasthan A Review. Rec. Geol. Surv. Ind. 101 (2): 60-79.

Roy, A.B., Paliwal, B.S. and Geol, O·P· 1971. Superposed folding in the Aravallirocks of the type area around Udaipur, Rajasthan. Jour. Geol. Soc. Ind. 12(4): 342-348.