FROM A LIMESTONE BED
IN
CHURU DISTRICT, RAJASTHAN by K.S. Raghav, Jour. Geol. Soc. India, 2000, v.55, pp.269-274.2. DISCOVERY OF FORAMINIFERA FROM BILARA GROUP, JODHPUR DISTRICT, RAJASTHAN by
K.S.
Raghav, Jour. Geol. Soc. India, 2000, v.55, pp.395-397.V.P. Laul, 101805, Malviya Nagar, Jaipur - 302 0 17 comments:
The papers of Raghav on the discovery of foraminifera from Bilara Group have generated a lot of discussion (Jour. Geol. Soc. India, 2000, v.56, pp. 110-1 19). This indicates that one has to be very careful while attempting a change in the stratigraphic status of rocks from ca. 600 Ma to 60 Ma. Though Raghav's fossil records and field observations may not be questionable, it is difficult to digest the observation that the entire BiIara and Nagaur Groups are of Tertiary age. In the geological map of western Rajasthan, the Nagaur-Ganganagar basin (Marwar basin), exposes the Marwar Supergroup represented by Jodhpur Group (mainly arenaceous), Bilara Group (mainly calcareous) anci Nagaur Group (mainly arenaceous). Badhaura Formation and Bap Boulder Bed of Permo-Carboniferous age are developed around Bap. Pokaran Boulder Bed is considered to be the basal part of Marwar Supergroup by some workers (Kumar, 1999). Tertiary (Paleocene-Eocene) beds are developed in Barmer, Jaisalmer and Bikaner basins.
During the course of mapping in Jaisalmer district, the present author had described the geology of Jaisalmer basin (Laul, 1979, 1991; Laul and Kumar, 1980; Laul and Srivastava, 1985). These studies have shown that Tertiary beds are well exposed in the western and northern parts of JaisaImer district and exhibit variable trends. In western part it trends N-S, while further south it takes a turn south-westwards as observed from well data. In northern part, well-exposed scarp sections have a general E-W trend, but in the eastern extremity its intersections in wei! and tube- well sections suggest a turn south-eastwards indicating NW-SE trend. Similarly in Bikaner area, Tertiary beds show a general trend in E-W direction, but the subsurface geology suggests a swing towards southwest on the western side, while in the eastern side it turns southwards, towards Merta Road. These observations clearly indicate that the Tertiary beds have not only overlapped various Mesozoic rock formations as well as those of Marwar Supergroup in the Marwar basin,
but the Paleocene-Eocene sea possibly invaded the interior parts, i.e., mainly the topographically low areas of the Marwar region. Now it has become necessary to review the entire palaeogeographic and tectonic setting of western Rajasthan during the Paleozoic, Mesozoic and Tertiary periods. In this connection, the following observations are pertinent:
1. The development of Marwar basin is characterised by Sardarashahar fault in the east, Nachna- Devikot high in the west and Jodhpur-Pokaran-Malani ridge in the south.
2. The absence of Marwar rocks in the Jaisalmer and Barmer basins to the west of Marwar basin clearly indicate that Jaisalmer and Barmer areas were positive areas during Marwar sedimentation (Neoproterozoic to Cambrian).
3. The gap between Jaisalmer and Bikaner basins is of great significance, because this area has witnessed Neoproterozoic glaciation (Pokaran Boulder Bed), Permo-Carboniferous
DISCUSSION
glaciation (Bap Boulder Bed) and marine transgression (BadhauraFonnation). The Nachna- Devikot high also passes through this area. The southward invasion of Paleocene-Eocene sea in the Jaisalmer-Bikaner gap possibly encroached the Marwar rocks and there are possibilities of Eocene rocks overlapping Nagaur sandstone and Bilara limestone on the western side of Marwar basin.
4. On the eastern side, the arm of Paleocene-Eocene sea invaded southwards in the interior parts of the Marwar basement. Permian-Mesozoic-Paleogene palaeogeography of Rajasthan has been discussed by Pareek (1979) incorporating the views of Khan and Tewari (1973) on the eastern limit of Eocene sea in Rajasthan. According to this view, the sea had its narrow embayment which extended as far as Merta Road and Arwar, and swung southwards to Chapri, as evidenced by the occurrence of Fuller's earth with pelecypods in these localities. These observations indicate that the terrain of Marwar Supergroup was engulfed by Paleocene- Eocene sea from three sides i.e., west, north and east, and as such, there were favourable conditions for Paleocene-Eocene sea to invade the Marwar terrain of older rocks (Neoproterozoic-Cambrian) at many places. The large time gap between the Cambrian and Palaeocene sedimentation was sufficient to create many topographic lows and depressions favourable for Paleocene-Eocene sea invasion.
5. There is no controversy regarding the age of Bap Boulder Bed. The confusion is between the Bap Boulder Bed (Permo-Carboniferous) and Bap boulder spread (Pleistocene ?). Such spreads have been reported and discussed from various parts of western Rajasthan (Kumar and Laul, f 980).
K.S. Raghav, 228, Shreeji Nagar, Tonk Road, Durgapura, Jaipur - 302 01 8 replies:
I appreciate Laul's observations on the absence of Marwar rocks in the Tertiary basins of Jaisalmer and Banner. However, he has raised the possibility of overlapping of Marwar rocks in the Jaisalmer and Bikaner basins on the western side of the Marwar basin. There is no controversy in the nomenclature of Marwar basin, Nagaur evaporite basin or Marwar terrain since their tectonic set up is characterised by the presence of Sardarshahar fauIt in the east, Nachna-Devikot high in the west and Jodhpur-Pokaran Malani ridge in the south. Since the rocks of the type area of Bilara Group of Marwar Supergroup (MSG) have been found to be fossiliferous up to the depth of 15 rn from the surface and range in age from Eocene to Miocene,
a
doubt arises about the status given to Marwar Supergroup (Raghav, 2000a, b). The relationship between the Bap Boulder Bed and Badhaura Formation has been established by several workers, but nowhere it was authenticated that the rocks underlying these formations belong to Jodhpur, Bilara and Nagaur Groups. The presence of pebbles and boulders of Jodhpur, Bilara and Nagaur Groups i n the Bap and Pokaran spreads do not suggest that these formations are older than the Bap Boulder Bed. There is a ' possibility of the presence of limestone, sandstone and shale sequence under the Paleocene rocks. The relationship of Bap Boulder Bed arid Badhaura Formation (which may be of Proterozoic to Paleozoic age) with the fossiliferous Bilara Group is yet to be established. Only detailed work can establish as to which part of the MSG should go with the Tertiary. The present iJaipur comment:
1. The erstwhile Trans-Aravalli Vindhyan, redesignated as Marwar Supergroup (MSG), is spread over an area of 100,000 km2 i n parts of western Rajasthan with subcrops in northern Rajasthan (Bikaner, Ganganagar) and adjacent states of Punjab and Haryana. The MSG has been broadly divided into the lower arenaceous Jodhpur Group, middIe calcareous Bilara Group and the upper argillaceous Nagaur Group. The subcropping Hanseran Evaporite Group of MSG has been treated as a homotaxial lithofacies variant of Bilara Group.
2&3. MSG unconformably overlies the metasediments and/or granites of the Mesoproterozoic Delhi Supergroup (near Choti Khotu, Bhopalgarh) or rhyolites and granites of Neoproterozoic Malani Igneous Suite (MIS) dated at 745k10 Ma. The Pokaran Boulder Bed, spread over the rhyolites or basalts of MIS near Pokaran, has ill-sorted pebbles, cobbles and boulders of MIS and represent Vendian glacial period in this part. This boulder bed is overlain by the basal conglomerate and sandstone of Jodhpur Group of MSG. Therefore the lower limit of MSG, is either post-MIS magmatism or post-Vendian glaciation (680-530 Ma).
4. MSG is unconformably overlain by either of the following:
(i) Permo-Carboniferous Bap Boulder Bed and Permian Badhaura Formation. (ii) Lower Jurassic sediments of Lathi Formation.
(iii) Paleocene to Eocene sediments of Palana basin.
5&6. Bap Boulder Bed overlying MSG consists of cobbles and boulders of rhyolite and granite of MIS, and dolomite, chert and sandstones of MSG representing the Permo-Carboniferous glacial epoch. Thus, in the broad time span, sedimentation in the MSG took place between the Vendian and Permo-Carboniferous glacial epochs.
7. The contact between Jodhpur and Bjlara Groups, being gradational, does not represent any erosional unconformi ty. Similarly, the contact between Bilara and Nagaur Groups is also
I transitional. It is a paradox that the status of older Jodhpur Group and the younger Nagaur
/
Group of MSG has not been questioned, while the age and stratigraphic status of Bilara Group, which is sandwiched between Jodhpur and Nagaur Groups and where microfauna have been reported, remain controversial., 8. The presence of Tertiary sedimentary basin above the MSG, based on the reported occurrences of microfauna cannot be ruled out. This is supported by the borehole data of potash investigation, where a few boreholes have recorded nummulite-bearing limestone . .$ above the Nagaur Group of MSG. Similarly in the Palana basin, Tertiary sediments are
directly underlain by MSG. The nearest Tertiary basin to Bilara is 32 km to the north near Merta town.
9. La Touche (1902) reported some fusiform bodies near Osian, which bear some relation to the trilobite described as Cruzianafusiferu. Pascoe ( I 965) reported Chordophyceous tracks (trilobite markings ?) caused by swimming of the crustacean. A solitary specimen of doubtful brachiopod Orthis sp. from Jodhpur Group was reported by Khan (1973). Barman ( 1 987) recorded a primitive lamel libranch from the calcareous sandstone of Jodhpur Group near Berlu. Mathur (1994) reported ichnofossils and a linear trace fossil from Jodhpur Group.
464 DISCUSSION
The presence of primitive fauna suggests the terminal-Proterozoic to basal Cambrian age of MSG.
K.S. Raghav, 228 Shreeji Nagar, Tonk Road, Durgapura, Jaipur - 302 018 replies:
1. If the correlation of Bilara limestone is acceptable, then the age of Wanseran evaporate sequence should not be older than Miocene, as Raghav (2000b) has reported micro-fossils which are not older than Miocene.
2. Pokaran Boulder Bed consists dominantly of ill-sorted pebbles, cobbles and boulders of granite, rhyolite, quartzite, phyllite, slate and mica schist. It forms the basal part of polymictic conglomerate which is present at the base of Jodhpur sandstone (Paliwal, 1992).
3. No evidence has been recorded so far to assign the age of Pokaran Boulder Red as Vendian. Many workers have raised a doubt about the stratigraphic status of Pokaran Boulder Bed. La Touche (1902) and OIdham (1 886) correlated Pokaran Boulder Bed with Bap Boulder Bed, whereas Heron (1932) felt that Pokaran Boulder Bed represented an agglomerate. 4. What are the evidences for correlating the unfossiliferous/undated lithological units
underlying the Bap, Badhaura, Lathi and Palana shales with the known rocks in the type areas of Jodhpur, Bilara and Nagaur Groups of
MSG?
5. The dolomite, chert and sandstone fragments described as a part of the
MSG
could form a lateral spread in the area of Bap Boulder Becl. Mukhopadyay and Ghosh (1976) have reported the presence of pebbles and boulders of dolomite, chert and sandstone from the known Tertiary and Quaternary sediments. Moreover, Bose et al. (1985) have indicated that limestone and sandstone fragments are very rare in the diamictite clasts in Riyan Shayrndas area which is hardly 5 to 6 km from Tunkalian and 10 to 15 km from Gotan. They have also indicated that no evidences of glacial movement such as striae, grooves etc. were reported from the known bedrocks of MSG. This observation also suggest that the Tunkalian and Gotan Formations are younger in age than the diamictite bed, as suggested by Raghav (2000 b).
6. The Sonia Formation (Lower Garsuriya) of Jodhpur Group can be divided broadly into three units. The lower-most unit comprises pol ymictic conglomerate at the base, followed upward by a sequence of dominantly ferruginous sandstone and maroon shale. These are overlain with a disconformity by dolomite/limestone, shale and chert, forming the middle
part of the Sonia Formation. Shrivastava (1971) designated these littlounits as Bandero Limestone. The disconformity at the base of Bandero Limestone is represented by the presence of a conglomerate bed along the nula cutting to the north of Ram Chauki in Jodhpur district, Rajasthan. The middle facies rocks are overlain by a dominantly arenaceous facies. These rocks are fine to very fine sandstones at the base, followed upward by gritty and pebbly sandstones around Dhoru and a conglomeratic bed at places. The conglomeratic bed is overlain by quartzitic sandstone and maroon shale and chert towards the top.
7. Doubtful trace fossils reported by earlier workers are from the lower facies of Sonia shale and sandstone, whereas Raghav (1 997-1 999) has reported Vendjan fossils (Medusoids) near Artiya KaIan, Jodhpur district. The age of the upper facies of Sonia Formation having inter-tonguing relationship with Bilara Group cannot be older than the Mid-Miocene as suggested by Raghav (2000b) on the basis of microfossils.
8. The known Tertiary basin consists dominantly of stratified horizontal rocks of Palana shale and lignite deposits of Paleocene age. This basin is located approximately 10 km northeast of Gotan town. These are overlain by Quaternary deposits. The presence of this basin at the depth of lOOrn in the vicinity of stratified horizontal outcrop of Gotan and Tunkalian Formations of Nagaur Group also indicate a younger age for the Bilara and subsequent groups of rocks.
9. So far no undoubted fossil has been reported from the rocks of MSG except by Raghav (20QOb). La Touche (1902) and Pascoe (1965) possibly recorded doubtful trace fossils from the lower-most lithounits of Sonia Formation of possibIe Vendian age. Khan (1973) and Barman (1987) have recorded a solitary fossil-like mould which has been proved to be
a nodule by the Geological Survey of India. Similarly, Mathur (1994) has reported some sedimentary structures which have resemblance to trace fossils.
References
BARMAN, G. (1987). Stratigraphical position of the Marwar.Supergroup in the light of stromatolite study. In: Three Decades of Developments in Palaeontology and Stratigraphy in India, M.V.A. Sastry et al. (Eds.), Geol. Surv. India Spec. Publ. no. 1 I , pp.72-80.
BOSE, U., THAPA, B.D. and MAJUMDAR, K. (1985). A note on the Pre-Tenairy glacial sediments in the Nagaur basin of northwestern Rajathan India. lour. Earth Sci., v.13(1), pp.38-44.
HERON, A.M. (1932). The Vindhyans of western Rajasthan. Rec. Geol. Surv. India, v.65, pp.457-489.
KHAN, E.A. (1973). Discovery of fossil brachiopod of Cambrian affinity near Jodhpur. Seminar on Recent Advances in the Geology of Rajasthan and Gujant, pp.74-75 (abs).
KHAN, E.A. and TEWARI, R.K. (1973). On the eastern limit of the Eocene sea in Rajnsthan. Seminar on Recent Advances in the Geology of Rajasthan and Gujant, p. 13 (abs).
KUMAR, V. (1999). Evolution and geological set-up of Nagaur-Ganganagar hasin, northwestern Rajasthan. Proc. Symp. on Geological Evdution of Northwestern Rajasthan, India, pp.34-60.
KUMAR, V. and LAUL, V.P. (1980). Records of glaciation in Jaisalmer basin, Jaisalmer district, Rajasthan. 3rd Convention Indian Assoc. Sedimentotogists, p.8 (abs).
LA ToucHE,T.H.D. (1902). Geology of Western Rajasthan. Mem. Geol. Surv. India, v. 35(1), 116p.
LAUL, V.P. (1979). Prospects of industrial grade limestone in Khuiala Formation (Lower Eocene), Jaisalmer district, Rajathan. Indian Minerals, v.33, no.4, pp.34-37.
LAUL, V.P. (1991). Some environmental aspects of Khuiala limestone deposit, Jaisalmer district, Rajasthan, New Sketch, v.LI, no. I I.
LAUL, V.P. and KUMAR, V. ( I 980). Marine transgression, regression, glaciation and desertification events of Jaisalmer basin. 3rd Convention Indian Assoc. Sedimentologists, Abstract volume.
LAUL, V.P. and SRIVASTAVA, S.C. (1985). Paleogene rocks of Jaisalmer (Rajasthan) and Kutch (Gujarat) - A comparative study. National Sern. On Tertiary Orogeny in the Indian Subcontinent, Abstract volume.
MAMUR, A.K. (1994). Search for invertibnte fossils in Mawar Supergroup of rocks in Jodhpur and Nagaur districts of Rajasthan. Geol. Surv. India Unpubl. Report for 1993-94.
MUKHOPADHYAY. A.K. and GHOSH, R.N. (1976). The problem of the stratigraphic position of the Bap boulders in Rajasthan. Indian Jour. Earth Sci., v.3, 130.2, pp.220-228.
OLDHAM, R.D. (1886). Preliminary note on the geology of northern Jaisalmer. Rec. Geol. Surv. India v.19, pp. 157-160. PALIWAL, B.S. (1992). Tectonics of the post-Amvalli mountain building activity and its bearing on the accumulation of
sediments along the western flmk of the AravaIIi range, Rajasthan, India. In: R. Ahmed and A.M. Sheikh (Eds.), Geology of South Asia-I, Proc. First South Asia Geological Congress, Islamabad, Pakistan, pp. 52-60.
PASCOE, E.H. (1965). A Manual of the Geology of India and Burma. Govt. of India Publ., Calcutta.
PAREEK, H.S. (1979). The Permian-Mesozoic-Paleogene palaeogeography of the Rajasthan and Gujant shelf and correlation with that of I n d k basin. Proc. 4th International Gondwana Syrnp., v:l, pp.23-26.
466 DISCUSSION
RAGI~AV, K.S. ( 1 997-99) A final report on sedimentational hictory of the Marwar Supergroup, Jodhpur district, Rajasthan. Geol. Surv. India Unpubl. Rcport, 75p.
RAGHAV, K.S. (2000a). On the discovery of Middle Eocene larger foraminifera from a limestone bed in Churu district, Ra-ja~than. Jour. Geol. Soc. India, v.55, pp.269-274.
RAGHAV, K.S. (2000b). Discovery of foraminifera from Bilara Group, Jodhpur district, Kajasthan. Jour. Geol. Soc. India,
v.55, pp.395-397.
R A G ~ ~ A V , K.S. (2000~). Sedimentational history of Marwar Supergroup, Jodhpur district. Rec. Geol. Surv. India, v. 133. pt.7, pp. 1- 2.
SIIRIVASTAVA, R.P. (1971). Rock-stratigraphic nomenclature for the sedimentaries of west-central Ra-jasthan. Rull. Geol. Min. Met. Soc. India, v.44, pp. 1-19.
OBITUARY
I 2
b
S.M. Sundarant (1937-2000)
S. Meenakshi Sundaram, Deputy Director General (Retd.), Geological Survey of India (GSI) passed away in the early hours of 17th August 2000 while staying at his daughter's residence in Mumbai. Hailing from an orthodox Telugu family of Kerala, he was deeply religious and duty conscious with a firm belief in righteousness which he practised in letter and spirit all his life and
influenced others around him to follow the same path.
He served the Geological Survey of India for three and half decades. His illustrious career began initially as STA in IBM at Nagpur in 1961. He was promoted as Junior Mining Geologist In 1963 and was transferred to GSI, Chennai in 1966. He carried out mineral investigations for molybdenum in Madurai and Tirunelveli districts, gold in Nilgiris, bauxite in Salem, sulphides in North Arcot district (all in Tamil Nadu), copper in Khetri, Rajasthan and coal in Rarngarh and West Bokaro coalfields of Bihar. He was the team leader in the exploration of bauxite resources at Panchpatmali project in the Orissa sector under the East Coast Bauxite Project of GSI.
