0016-7622/2009-73-6-747/$ 1.00 © GEOL. SOC. INDIA

JOURNAL GEOLOGICAL SOCIETY OF INDIAVol.73, June 2009, pp.747-758

A Review of the Stratigraphy of Marwar Supergroupof West-central Rajasthan

D. K. PANDEY and TEJ BAHADUR

Department of Geology, University of Rajasthan, Jaipur – 302 055Email: dhirendrap@hotmail.com

Abstract: The lithostratigraphy, depositional environment and age of the Marwar Supergroup have been reviewed in thelight of report of δ13C depletion recorded in the carbonates of the Bilara Group (middle part of Marwar Supergroup) anddiscovery of trilobite-like trace fossils from the “Red beds” of Nagaur Group (upper part of Marwar Supergroup). Theδ13C depletion observed in Bilara carbonates is not a result of glaciation rather due to rapid burial and poor watercirculation in the low energy water of the protected basin. Secondly, the trace fossils are, in fact, traces of notostracancrustaceans found in shallow fluvial and shallow lacustrine environment. The present paper also records a spiral, burrowingtrace-fossil, possibly Gyrolithes, from a cross-bedded sandstone of the Jodhpur Group.

Keywords: Lithostratigraphy, Depositional environment, Age, Gyrolithes, Marwar Supergroup, Rajasthan.

fossils, known to be “produced by trilobites”, from “solesof the thin brownish-red coloured silty shale bedsintercalated with the light coloured reddish-brownsandstones” in the upper part of the Nagaur sandstone ofthe Nagaur Group (Marwar Supergroup) from the Bikaner-Nagaur Basin on the northeastern part of Rajasthan shelf.The trilobites (Phylum Arthropoda) are known to havelived exclusively in marine water and during palaeozoic era,i.e. no freshwater forms have ever been found and theyhave only been found in oceanic fossil beds. It is also notknown if trilobites alone are responsible for such traces.They could be only arthropod member. They occupied manydifferent ocean environments, from shallow flats and reefs,to deeper ocean bottoms, and even the water column, asfloating plankton or free-swimming forms. They appearedin the beginning of Cambrian and extinguished at the end ofPermian. The preservation of the trace fossils are moderatelygood, however, the authors have not discussed any accountof depositional environment, which present authors feel isvery important in general and particularly for trace-fossilsassociated with trilobites. In absence of a proper discussionabout the depositional environment, assignment of anytrace-fossil to trilobites may be doubtful and determinationof age of the host rock on the basis of such trace fossilsbecomes irrelevant. The present paper deals with a shortreview of the Marwar Supergroup, its lithostratigraphy,depositional environment and age, which are significant

INTRODUCTION

The trans-Aravalli Vindhyan Supergroup is attractingattention of geologists for its hydrocarbon prospective andbuilding materials for last four decades. The recent studies(Shrivastava, 1971; Barman, 1980, 1987; Awasthi andPrakash, 1981; Pareek, 1981, 1984) have revealed that thecoeval Vindhyan sediments across the Aravalli axis havemuch closer relationship with the Tethyan sediments (SalineSeries) of Salt Range and tectonically belong to the Bikaner-Nagaur sedimentary Basin (Marwar and Birmania Basins)(Fig.1A). Lithostratigraphically, the sediments (about 1000– 2000 m thick) have been grouped into lower Jodhpur,middle Bilara and upper Nagaur Groups of MarwarSupergroup (Khan, 1971; Pareek, 1984; Das Gupta andBulgauda, 1994; Das Gupta, 1996; Roy and Jakhar, 2002;Mazumdar and Bhattacharya, 2004: see Table 1). Therelative age of Marwar Supergroup ranges from LateNeoproterozoic to Early Cambrian (Kumar et al. 1997;Chauhan et al. 2004). The geological and geophysical studyindicate that these Late Neoproterozoic – Early Cambriansediments covers a vast area on the Rajasthan shelf(Pareek, 1984; Sibal and Murty, 2005; Sharma, 2005)(Fig.2), which was the westerly dipping eastern flank of theIndus shelf of the Indus-Baluchistan geosyncline orIndo-Arabian Geological Province (Fig. 1B; Gansser, 1964;Kaye, 1970; Rehman, 1963; Shrivastava, 1992).

Recently, Kumar and Pandey (2008) have recorded trace

JOUR.GEOL.SOC.INDIA, VOL.73, JUNE 2009

748 D. K. PANDEY AND TEJ BAHADUR

for any worker dealing with trace-fossils of arthropod originfrom the Marwar Supergroup of the Bikaner-Nagaur Basin.

LITHOSTRATIGRAPHY OF THE MARWARSUPERGROUP OF THE BIKANER-NAGAUR BASIN

The lithostratigraphy of the Marwar Supergroup has beensubject to modification from time to time. The earliestworkers (Hacket, 1881; Oldham, 1888; La Touche, 1902;Heron, 1932, etc) named the older Palaeozoic siliciclasticsediments (red beds) and associated calcareous sedimentsin the Trans-Aravalli region as Vindhyans of Rajputana.There are two schools as far as the lithostratigraphy of theMarwar Supergroup is concerned.

Shrivastava (1971, 1992, 2005a, b) on the basis of fieldrelationship classified the older Palaeozoic sediments ofwest-central Rajasthan, which tectonically fall into theBikaner-Nagaur Basin, into two formations; the older

Jodhpur Formation, consists predominantly of siliciclasticsediments, subordinately carbonates and evaporites, whereasthe younger, overlying unconformably the Bilara Formation,consists of stromatolitic and cherty limestones (Table 1).Further, Shrivastava recognized three mapable units; Pokranboulder bed, Sonia shale (salt psuedomorph shale) andBandero limestone as formal members of the JodhpurFormation. According to Shrivastava (1971) the red bedsof the western Rajasthan, previously called as ‘VindhyanSystem’, should be preferably called as Jodhpur sandstone(Blanford, 1887), which subsequently along with associatedsediments was grouped as Jodhpur Formation. In theclassification of Shrivastava, the red beds and othersiliciclastic sediments were not been given any formalmember status.

Khan (1971) proposed Marwar Supergroup for the olderPalaeozoic sediments of the Bikaner-Nagaur Basin, whichwas subsequently followed by later workers (Pareek, 1981,1984: 20; Das Gupta et al. 1988; Chauhan et al. 1991;Chauhan and Bhanwara Ram, 1999; Kumar and Pandey,2008). The Marwar Supergroup has been classified intothree groups; lower Jodhpur Group, middle Bilara Groupand upper Nagaur Group (Table 1). This Supergroup issandwiched between Malani Igneous Suite (LateProterozoic) and Bap boulder beds (Permo-carboniferous).The oldest sedimentary unit of the Jodhpur Group, thePokaran boulder bed, rests unconformably over MalaniIgneous Suite, whereas the youngest unit of the NagaurGroup, the gritty and pebbly Tunklian sandstone, isunconformably overlain by Bap boulder bed. The MarwarSupergroup forms a most conspicuous geomorphologicalrelief in the Nagaur-Bikaner Basin running from south ofNagaur in the east to north of Pokaran in the west (Fig. 2).

Later, one more group/formation of rocks consisting oflimestones, dolomites with gypsum, anhydride, halite, etc.has been described as Hanseran Group/Formation (DasGupta, 1996; Chauhan et al. 2004; Kumar et al. 1997)stratigraphically above the Bilara Group. However, closeresemblance of lithological and C-isotopic profiles ofHanseran evaporites and Bilara carbonates allows intra-basinal correlation and suggests that they are coeval faciesvariants (Mazumdar and Bhattacharya, 2004; Mazumdar andStrauss, 2006) (see Table 1).

FOSSILS FROM THE MARWAR SUPERGROUP

Unfortunately, either due to time-interval of deposition,water geochemistry or the facies, fossils in the MarwarSupergroup are rare. The absence of index-fossils or otherinvertebrate body-fossils also may be due to either high

Fig.1. (A) Map showing structural elements in western Rajasthan(modified after Misra et al. 1993). (B) A geological sectionacross the Indo-Arabian geological province (modified afterGansser, 1964; Kaye, 1970; Rehman, 1963; Shrivastava,1992).

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A REVIEW OF THE STRATIGRAPHY OF MARWAR SUPERGROUP OF WEST-CENTRAL RAJASTHAN 749

Fig.2. Geological map of West-Central Rajasthan (modified after Shrivastava, 1971; Pareek, 1984).

influx of siliciclastic sediments or incompatible waterchemistry, which made conditions unsuitable for thrivingshelly organisms. Among previous records, Stromatolites;Stratifera, Weedia, Collenia, Nucleea, Concollenis,Cryptozoon, Irregularia, and algal nodules (Khilnani, 1966,1968; Barman, 1987), a few post Cambrian Acritarchs (DasGupta, 1977: 228), several micro-phytofossils of Ediacaran

affinity from the chert specks of Gotan Limestone Formationof Bilara Group (Babu et al. 2007), Chordophyceous tracks(Pascoe, 1975), Orthis (Khan, 1973) and casts oflamellibranchs (Barman, 1987) have been cited. The recordof Orthis (Khan, 1973) was examined by Kumar et al.(1997) and it was found to be a pellet. The records ofChordophyceous tracks and casts of lamellibranchs have

JOU

R.G

EO

L.SO

C.IN

DIA

, VOL

.73,JU

NE

2009

75

0D

. K. P

AN

DE

Y AN

D T

EJ B

AH

AD

UR

Igneous and metamorphic rocks

Shrivastava (1971, 2005a)Age

BadhauraFm.

Bap Boulder

Pal

aeoz

oic

Ca

mb

ria

n

Bila

ra F

orm

atio

nJo

dhpu

r F

orm

atio

n

Stromatoliticlimestone

Khichanlimestone

Banderulimestone

Sonia Shale

PokaranBoulder Bed

Malani Igneous Suite of Late Proterozoic Volcanic770-750 Ma

(Torsvik et al. 2001)

Mar

war

S

uperg

roup

Bap Boulder Bed of Permo-Carboniferous age

Pareek (1984), Das Gupta and Bulgauda (1994), Das Gupta (1996),Mazumdar and Bhattacharya (2004)

AgeAge

Carbon Isotopic Profile(after Pandit et al. 2001)

DepositionalEnvironment

Glacial

Nag

aur

Gro

up(7

5-50

0 m

)Jo

dhpu

r G

roup

(12-

240

m)

Bila

ra G

roup

(=

Han

sera

nev

apor

ite u

p to

60

m;

clay,

silts

tone

, do

lom

ite,

anhy

drite

, ha

lite)

(100

-300

m)

TunklianSandstoneFormation

NagaurSandstoneFormation

PondloDolomiteFormation

GotanLimestoneFormation

DhanapaDolomiteFormation

GirbhakarSandstoneFormation

SoniaSandstoneFormation

PokaranBoulder Bed

Gritty and pebbly sandstone with pebblesof Malani granite, rhyolite, Bilara chert,dolomite and Delhi quartzite

Brick-red sandstone, siltstone, shalewith greenish clayey blotches, evaporite,conglomerate (Khichan conglomerate)

Dolomite, cherty dolomite, stromatoliticlimestone, siliceous oolites, pisolites

Limestone with bands of chert anddolomite

Brick-red siltstone, shale and sandstone,current bedded, pisolitic with pellets

Stromatolitic limestone, dolomite, chertydolomite

Maroon siltstone and shale; creamishsandstone, pisolitic;Salt psuedomorph shales; banded chert-jasper dolomite

Pebbles to boulders of Malani granite,rhyolite in maroon silty/clay matrix

Late

N

eopr

oter

ozoi

c -

Cam

bria

n

No

n-m

ari

ne

-Ma

rin

e

Warm,hypersaline,marginalmarinelagoonal

Fluvial,deltaic, beach

Warm,hypersaline,marginalmarinelagoonal

Fluvio-Glacial

MA

RK

ED

OS

CIL

LAT

ION

S

Ven

dian

-To

mm

otia

n

broa

dly

low

neg

ativ

eδ

13C

val

ue

gradualpositive shift

low < -4.3 ‰PDB

low -6.5 ‰PDB

Table 1. Lithostratigraphic succession of the Marwar Supergroup, Rajasthan

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A REVIEW OF THE STRATIGRAPHY OF MARWAR SUPERGROUP OF WEST-CENTRAL RAJASTHAN 751

also been questioned (Mathur, 1998). Mathur (1998), onthe other hand also recorded cylindrical, spiral and radialtrace fossils from the Jodhpur groups. These have beendoubtfully described as Bergauria, Gyrolithes andProtomedusae, respectively. Present paper also records aspiral burrowing trace-fossil showing spreite (possiblyGyrolithes) in a cross-bedded sandstone of JodhpurGroup exposed in Mehrangarh fort area, Jodhpur (Pl. 1,Fig.2).

The recent finding of trace fossils of trilobites (Cruziana,Dimorphichnus and Rusophycus) and gastropods(Aulichnites) from the upper part of Nagaur sandstone(Kumar and Pandey, 2008) certainly adds a lot to thecuriosities about the age and subsequently about thedepositional environment of the host rocks. As known,Cruziana ichnofacies is typical of subtidal, poorly sortedand soft substrates, from moderate to low energyenvironments between the fair-weather and storm wave base.Morphologically, Cruziana is a bilobed trail with“herringbone” (chevron-like) ridges defining a mediangroove, interpreted as a locomotion trace made by a trilobiteor trilobite-like animals as it crawled along a sedimentsurface. The trace fossils photographed by Kumar andPandey (2008: Figs. 4a-b) show moderate preservation,however, the lithology of the host rocks. i.e. “from the solesof the thin brownish-red coloured silty shale bedsintercalated with the light coloured reddish-brownsandstones”, which in all possibility represents a continentalto protected marginal marine depositional environment. Thisis very unlikely suitable for trilobites. On the other hand inthe non-marine realm, similar assemblage of trace fossils tothose of Cruziana ichnofacies have been reported in shallowfluvial and shallow lacustrine mud, silt and fine sand softgrounds (Walter, 1983; Aceñolaza and Buatois, 1991, 1993;Pickerill, 1992 etc). These traces may be formed bynotostracan crustaceans (Bromley and Asgaard, 1979).These small bilobite trace fossils produced by notostracancrustaceans (Phylum Arthropoda, Subphylum Crustacea,Class Branchiopoda, Order Notostraca; colloquially referredto as notostracans, called Triops, tadpole shrimp or shieldshrimp) have been recorded in red beds of Devonian andTriassic age (Trewin, 1976; Hakes, 1976; Seilacher, 1978,1985; Pollard, 1981, 1985). Notostracans have also beenrecorded from Cambrian (Briggs, 1978). Therefore, therecord of trace-fossils from the red-beds of the Nagaur Group(Kumar and Pandey, 2008) may also be assigned tonotostracan crustaceans (see Bromley, 1996: 182, 282, Fig.8.13).

Dimorphichnus is interpreted as a lateral grazing tracemade by a trilobite, where the prod marks are toe impressions

and the scratch marks are from raking movement.Rusophycus is a horizontally oriented bilobate, ovoid-shapedburrow with parallel to subparallel scratch marks laterallyextending from a central bisecting plane. Rusophycus is aresting trace made by trilobites or trilobite-like arthropods.Aulichnites is a horizontally oriented trail having twobilaterally symmetrical convex ridges that are commonlydivided by a medial groove. Aulichnites is interpreted as acrawling or grazing trace made by gastropods. These tracefossils also occur in Ordovician (Aceñolaza and Aceñolaza,2002).

AGE OF THE MARWAR SUPERGROUP

Neither Pokaran boulder bed and the gritty and pebblyTunklian sandstone have been dated by any means, nor haveany of the sedimentary units of the Marwar Supergroup havebeen dated for their age. The estimated age of the MarwarSupergroup, which had no basis except for its stratigraphicposition above the Malani Igneous Suite (Pl. 1, Fig. 1), isNeoproterozoic to Early Cambrian, as the Malani rocks havebeen dated thoroughly as to range from 779-681 Ma (Pareek,1984; Rathore et al. 1999). Among the recent dates of MalaniIgneous Suite, the one of U-Pb Zircon age (770-750 Ma),determined by Thermal Ionization Mass Spectrometry(TIMS) Method (Torsvik et al. 2001) is being frequentlycited. Recently, Malone et al. (2008, fig.15) analyzed detritalzircons from the Girbhakar sandstone and Sonia sandstone,which yielded a age peak for the Marwar Supergroupbetween range of 800-900 Ma (206Pb/238U). This suggeststhat the provenance of zircons is from older rocks of thistime interval, most probably Erinpura or Sendra granites(Choudhary et al. 1984 and Tobisch et al. 1994). Regardingthe upper age limit of the Marwar Supergroup there was noevidence, except for an assumption that it is continuation ofVindhyan Supergroup across the Aravalli axis (Heron, 1932;Shrivastava, 1971). The age of Upper Vindhyan has recentlybeen considered 500 Ma older than is commonly thoughtand further the youngest sandstone detrital suites of upperVindhyan on the east of Aravalli Range and MarwarSupergroup on the west of Aravalli Range have virtually nosimilarities (Malone et al. 2008). The Bap boulder beds ofBadhaura Formation (Permo-carboniferous) are the cappinghorizons, which restricts speculation for the time-range ofdeposition of the Marwar Supergroup to the olderPalaeozoic. In the geological records the older Palaeozoicsequence, i.e. Marwar Supergroup, has been correlated withsaline series (Cambrian) of Salt range (Pakistan) (Narayanan,1971; Shrivastava and Srinivasan, 1964; Shrivastava, 1971,1992; Kumar et al. 1997; Pareek, 1981, 1984; Chauhan

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752 D. K. PANDEY AND TEJ BAHADUR

Plate 1. Photographs showing (1) of a spiral burrowing trace-fossil showing spreite (possibly Gyrolithes) in cross bedded sandstone ofJodhpur Group exposed in Mehrangarh Fort area, Jodhpur. Scale 5 Rupees coin. (2) a panoramic view of a lake west of JaswantThada, near Mehrangarh Fort, Jodhpur. Note different flows of Malani rhyolite underlying Jodhpur sandstone. (3) straight toslightly sinuous crests of wave ripples in the Jodhpur sandstone exposed in a quarry at Sursagar, Jodhpur. The hammer-headshowing the direction of wave propagation. Scale geological hammer. (4) trough cross-beddings in Jodhpur sandstone exposedalong a cliff at the base of TV tower near Mehrangarh Fort. Note an erosional surface in the middle of the photograph. Scalegeological hammer. (5) discontinuously developed lobs and saddles in interference ripples in the Jodhpur sandstone exposed ina quarry at Sursagar, Jodhpur. Such ripples denote shallow water conditions. Scale geological hammer. (6) undulatory andsinuous microwave ripples in the Jodhpur sandstone exposed in a quarry at Sursagar, Jodhpur. Scale geological hammer.(7) stromatolitic structure forming dome in Bilara carbonates exposed in a quarry near Bilara, Jodhpur. Scale geological hammer.(8) sinuous wave ripples occasionally bifurcating, superimposed on a much larger scale wave-ripples of earlier generation in theJodhpur sandstone exposed in a quarry at Sursagar, Jodhpur. Scale geological hammer.

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A REVIEW OF THE STRATIGRAPHY OF MARWAR SUPERGROUP OF WEST-CENTRAL RAJASTHAN 753

et al. 2004) and inferred the upper age limit of MarwarSupergroup as Early Cambrian. Similarly Bilara limestoneGroup (= Hanseran Evaporite Group) in the Bikaner NagaurBasin together with carbonates in west as part of Baghewalaoil field (Birmania Basin; situated further west of theBikaner-Nagaur sedimentary Basin in the Jaisalmer district)have close stratigraphic correlation with Ara Formation(Huqf Supergroup) of south Oman Salt Basin, whichtransgresses late Neoproterozoic- Early Cambrian in age(Mazumdar and Bhattacharya, 2004). In addition a fewauthors have mentioned either Upper/terminal Proterozoicor Cambrian age for the Marwar Supergroup (Shrivastava,1971; Pareek, 1981, 1984; Kumar et al. 1997; Sibal andMurty, 2005)

Lately, Pandit et al. (2001) studied carbon isotope profileof carbonate rocks of lower part of the Bilara Group. Theyrecorded marked oscillation and broadly negative δ13Ccharacter with negative anomalies as low as <-4.3‰PDB nearthe base of Dhanapa Formation (lower unit of BilaraGroup, see Table 1) and <-6.5‰PDB in the overlying GotanFormation (middle unit of Bilara Group, see Table 1). Theupper part of the profile shows a gradual positive shift. Thisnegative value of the carbon isotopic signature in the lowerpart of Bilara has been correlated with end-Neoproterozoic– Early Cambrian (Vendian – Tommotian) carbon isotopicevolution curve (also see Mazumdar and Bhattacharya,2004). They also mentioned that extremely low δ13C valuesindicate glaciations related to cold climatic conditions atthe end of Neoproterozoic followed by warmer conditionsas indicated by positive shift.

Recently, Mazumdar and Strauss (2006) discovered thatthe sulphur isotopic compositions of trace sulphate incarbonate rocks from the Bilara Group (27.2 to 42.0‰, avg:33.8±3.1‰, n = 37) and for calcium sulphate from theHanseran Evaporite Group (27.5 to 39.7‰, avg: 32.4±3‰;n = 25) match well with globally recognized sulphur isotopicenrichment that occurred during terminal Neoproterozoicage, between 600 and 500 Ma. Similarly, they revealedthat the strontium isotopic composition of Bilara carbonaterocks and Hanseran evaporites are comparable to thecontemporaneous global seawater 87Sr/86Sr ratios, recordingan increase during post-Varangerian time.

The results of the isotopic work do not match withPrecambrian-Cambrian boundary established by earlierworkers (Shrivastava, 1971: 8; 1992: 232; Knoll and Walter,1992; Chauhan et al. 2004). The composition of thesediments also does not match with the climatic conditionsas inferred by Pandit et al. (2001). Principally, carbonatedissolves in cold water. Whether organic or inorganic, itrequires temperature, excessive carbondioxide to precipitate

inorganic carbonates, or conditions suitable for autotrophicorganisms to produce bicarbonate, which resultscrystallization of biogenic carbonates.

In previous records, as mentioned above, the Pokaranboulder beds at the base of Jodhpur Group is at leasthundred meters below the Bilara Group (Pareek, 1984).These Pokaran boulder beds were deposited in fluvio-glacial environmental conditions corresponding to globalVarangerian ice age (610-580 Ma) of end-Neoproterozoic(Shrivastava, 1971, 1992; Knoll and Walter, 1992; Chauhanet al. 2004; Le Guerroué et al. 2005a). The Varangerian iceage was a time of intense climatic oscillations, commonlyknown as “snowball Earth events” correlated worldwide bysharp negative δ13C excursions (Le Guerroué, 2005b).

On the other hand Kumar et al. (1997) did not find anyglaciogenic sediments and mentioned that there is noevidence of Varangerian glaciations from the Indian-subcontinent. In absence of index/guide fossils the precisetime-interval of deposition of the Marwar Supergroup is stillnot known, however, the guiding factors, such assedimentological resemblance of the Marwar Supergroupwith the Saline series (Cambrian) of Salt Range (Pakistan),and continuity of the facies towards northwest, suggest forCambrian age for the Marwar Supergroup (Das Gupta andBulagauda, 1994; Peters et al. 1995; Kumar et al. 1997).The stromatolites of the Marwar Supergroup also showCambrian affinity (Barman, 1987: 75).

To pinpoint a precise Precambrian-Cambrian boundaryin the west-central basin of Rajasthan, present authorsbelieve that a detail investigation of either basal part ofJodhpur sandstone, which is pebbly or conglomeratic atplaces or Pokaran boulder beds around Pokaran forfossiliferous horizons, δ13C excursions, sulphur isotopicenrichment and strontium isotopic composition is required.Unfortunately, calcareous facies in this part of the sequencehas not been recorded, one might take into considerationthe Randha and Birmania Formations of the Birmaniasedimentary Basin (Narayanan, 1959; Misra andShrivastava, 1960; Mukhtinath, 1969; Dhar and Mehta,1974; Misra et al. 1993; Maheshwari et al. 2002). Both theformations, completely or partially overlie Malani IgneousSuite (rhyolite/granite). The lithology, chemical characters,stratigraphic distribution of Randha and BirmaniaFormations in the western part of Rajasthan shelf andMarwar Supergroup in the eastern part of the shelf suggestthat at least part of these formations is coeval in age.Considering the phosphorite deposits in the BirmaniaFormation and its occurrence worldwide at transitionalPrecambrian-Cambrian beds (Brasier, 1992; Tucker, 1992;Maheshwari et al. 2002), which has been related with the

JOUR.GEOL.SOC.INDIA, VOL.73, JUNE 2009

754 D. K. PANDEY AND TEJ BAHADUR

time of global change with increased plate movements andopening oceans and a climatic change from LatePrecambrian glaciations to Cambrian global warming, wemight conclude that at least Precambrian-Cambrianboundary lie in the Birmania Formation. The absence ofphosphorite from the Marwar Supergroup suggests formarginal marine settings in the east in contrast to more off-shore open marine settings in the west. The possibility oftime transgression from west to east cannot be ruled out.That is, the Randha Formation may correspond to Pokaranboulder bed in the Marwar Basin. Birmania Formation maytime-wise correspond to Jodhpur Group and the equivalentof Bilara and Nagaur Groups in the Marwar Basin have norepresentation in the Birmania Basin (Table 2). Interestingly,the sediments of both the basins have been assigned to LateProterozoic to Early Cambrian age (Pandey and Dave, 1998:189, Bhandari, 1999: 132-133). Recently, Cozzi et al. (2008)have correlated successions of the sedimentary basins ofOman (Huqf Supergroup), Salt Range (Khewra, Kussak andJutana Formations) and western Rajasthan (MarwarSupergroup) on the bases of litho- and chemostratigraphy.The most prominent observation is that in all the three basinsthe latest Ediacaran-Early Cambrian basin fills consists ofsiliciclastic sediments (non-marine in Pakistan and India,whereas marine in Oman). This is followed by at least sevenidentical carbonate/evaporate desiccation (waterlessness)cycles in all the three basins. This, although indirectly,suggests for time-equivalent of the successions. Nogeochronological data from Marwar Supergroup of rocks isavailable therefore, dating of sediments would be significantto resolve the issue. The geochronological data from theHuqf Supergroup are already available, establishing it asthe Cryogenian (850-635 Ma) and Ediacaran (635-542 Ma)

(Cozzi and Rea, 2006). According to Cozzi et al. (2008) thesimilar Ediacaran-Early Cambrian tectono-stratigraphicevolution of the sedimentary basins of Oman, Pakistan andIndia has an implication on the latitudinal distribution ofidentical depositional paleoenvironments.

DEPOSITIONAL ENVIRONMENT OF THEMARWAR SUPERGROUP

The sediments of the Marwar Supergroup are results ofa wide-spread marine transgression over Malani IgneousSuite and older metasediments in western India,contemporary to a wide-spread marine transgression over“Supersequence III” in Himalaya (Kumar et al. 1997).

In the two fold classification, Shrivastava (1971, 2005a),mentioned shallow water non-marine to marine, fine tocoarse mixed arenaceous, argillaceous and calcareous faciesfor the Jodhpur Formation. The striated pavement (RochesMountains) of the boulders and unstratified nature of thedeposits of the basal Pokaran boulder bed member havebeen interpreted as possibly deposited by fluvio-glaciersmoving northwards. The polymictic boulders, cobbles,pebbles, etc were derived from the igneous andmetamorphic high ranges in the south. The Sonia shale andBandero limestone have been inferred to have deposited inhypersaline lagoonal and marginal marine depositionalconditions respectively. The variation in the facies has beenattributed to the change in water salinity and depth. TheBilara Group is characterized by shallow marine calcareous(bio-chemical) facies. The limestone (biostrom) has beensuggested to be deposited in low energy, poor circulationlagoon to tidal flats with under warm water conditions(Shrivastava, 1971, 2005b).

Pareek (1984: 19) mentioned it marine sequence ofCambrian age. The three groups represent three facies,i.e. Jodhpur, Bilara and Nagaur Groups representingarenaceous, calcareous and mixed arenaceous andargillaceous facies respectively.

The personal observation of the authors in the areaaround Jodhpur, Pokaran and Bilara suggests that thesesiliciclastic sediments have been mainly deposited in shallowwater above fair-weather wave base both in marine andnon-marine environments as suggested by Shrivastava(1971). The pink, brown, red sandstones exposed aroundJodhpur area display grity to fine-grain sandstone with ripplemarks of various scales and alignments (Pl. 1, figs. 3, 5, 6,8). The cross-beddings, the internal-primary sedimentarystructures, range from trough cross-beddings (Pl. 1, fig. 4),low small-scale to large-scale cross-beddings. All thesesedimentary structures suggest for shallow water above fair-

Table 2. Late Neoproterozoic - Cambrian lithostratigraphic scheme ofthe Marwar and Birmania Basins

Age Birmania Basin Marwar Basin

Bhuana Formation of Bap Boulder Bed ofPermian to Triassic Permo-carboniferous age

Unconformity

UnconformityNagaur Group

Bilara Group(= Hanseran Evaporite)

Birmania FormationJodhpur Group

Randha Formation Pokaran Boulder Bed

Malani Igneous Suite

Ca

mb

ria

nLa

teP

rote

rozo

ic

Mar

war

Sup

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JOUR.GEOL.SOC.INDIA, VOL.73, JUNE 2009

A REVIEW OF THE STRATIGRAPHY OF MARWAR SUPERGROUP OF WEST-CENTRAL RAJASTHAN 755

weather wave base depositional environment. Whethermajority of sandstone was deposited in marine or non-marinewater environment is still not clear. Chauhan et al. (2004)interpreted ripple bedded middle part of Jodhpur sandstoneof Jodhpur Group deposited in shoreface-backshoresettings of beach environment of a NNW-SSE trending wideshallow intracratonic sag basin. Further, a detail andcomprehensive study by Chauhan et al. (1991) and Chauhanand Bhanwara Ram (1999) suggested that the three divisionsof Jodhpur Group (Table 1) represents deltaic, beach andfluvial depositional environments process, respectively.The present record of a spiral, burrowing trace-fossil(possibly Gyrolithes) from a cross-bedded sandstone ofJodhpur Group, which is known from Jurassic to Miocenesediments of Europe, USA, etc (Powell, 1977; Gernant,1972), suggest a restricted lake to brackish or marginalmarine environment of deposition (Gernant, 1972; Bromley,1996: 281). Incidentally, Mathur (1998) has also recordeda similar trace-fossil from the Jodhpur Group. If ouridentification is correct its age may lower down fromJurassic to Cambrian.

Bilara Group represents another event of marinedepositional environment, where influx of siliciclasticsediments remarkably reduced, perhaps due to drasticchange of climatic conditions from humid to dry. The highproduction of carbonate sediments points to warm climaticconditions. This is in contrast to glacial conditions inferredby Pandit et al. (2001) and Maheshwari et al. (2003).Whether organic or inorganic, carbonates do not precipitatein cold waters. The lowering of δ13C value in the carbonatesfrom near the base of Dhanapa Formation (lower unit ofBilara Group) and in the overlying Gotan Formation (middleunit of Bilara Group) in cold climatic conditions should beseen in association with increase in δ18O. These short-liveddepletions may be related to the basinal environmentalconditions (Kumar, 1997), such as due to rapid burial,when the decaying or decomposition still continues afterthe burial under anoxic conditions. The methane thus releasemay also deplete δ13C. Similarly, under very low-energycondition “stratification of different Carbon or Oxygenstable-isotope ratio” may give erroneous results.

The carbonates of the Bilara Group, especially DhanapaFormation, are very rich in algal stromatolites. The diversemorphological shapes (domal, columnar or stratiform sheets)suggest for fluctuating low to high energy level conditions.

A range of morphological features and frequency of therecorded organic walled microfossils led (Babu et al. 2007)to interpret the deposition of Gotan Limestone Formationof the Bilara Group in moderate deep marine water withhigh salinity. In general, the limestone units do not showprimary sedimentary structures, like cross-beddings orripple surfaces, which indicate deposition below fair-weatherwave base, however, the moderately thick beds with sharpbedding surfaces suggest for storm events. The richness ofbiogenic microcrystaline ooze suggest for continental shelfdeposition of environment, whereas stromatolitic structurepoints to well lit condition. Shrivastava (2005b) interpretedstromatolites of the Bilara Group as deposited in intertidalto supratidal depositional environments. The dominance ofcarbonates sediments, various forms of stromatolites,absence of primary sedimentary structures, sharp beddingsurfaces and depleted value of δ13C suggest that BilaraGroup of sediments deposited in shallow, low to moderatelyhigh energy marine water with poor circulation in a protectedbasin. The climate was warm and arid.

The Nagaur Group, which begins with Khichanconglomerate (Pareek, 1984), represents a mixed arenaceousand argillaceous facies. It consists of siltstones, shales,greenish clayey blotches, evaporites and brick-redsandstones. The cobbles, pebbles and assorted fragmentsof dolomites and Bilara cherts, etc in the Khichanconglomerate suggest a hiatus between this unit andunderlying Bilara carbonates. The presence of evaporates,stratigraphically above the Khichan conglomerate, suggestfor once again inundation of the area by marine water aftera hiatus. The brick-red sandstones with primary sedimentarystructures point to a low to high energy marginal marine tocontinental, oxidizing depositional environment. Thegreenish clayey blotches may be the result of chemo-organicinfluence, which controlled oxidation. The climatic conditionwas warm and humid.

Acknowledgements: We would like to thank Dr. U. B.Mathur, Dr. R.S. Sharma, Dr. M.K. Pandit, Dr. Salil Agrawaland Late Dr. B.P. Shrivastava, for fruitful discussions.Several field works carried out with M.Sc. Geology studentswere financially supported by the University of Rajasthan.The financial assistance of DRS (UGC) program of theDepartment of Geology, University of Rajasthan is gratefullyacknowledged.

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(Received: 27 May 2008; Revised form accepted: 18 November 2008)