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NOTE ON THE PRESENT STRATIGRAPHIC STATUS OF CONGLOMERATE, DISTRICT,

R. L. JAIN,SURENDRA PRASAD and A. K. MATHUR Geological Survey of , Jhalanadungari, Jaipur -302 004

Abstract: Recent geological mapping has shown that Khichan Conglomerate marks the hiatus between the Formation of Marwar Supergroup (Eocambrian ?) and the Permo-Carboniferous Badhaura Formation in Rajasthan.

PREVIOUS WORK 1: 25,000 scale, it was observed that Nagaur Formation (of Sinha (1975) first described the conglomerate at Trans-Aravalli Vindhyan renamed by the Geological Survey Khichan, Malar and Bari Rawari, and suggested its of India as Marwar Supergroup) unconformably underlies stratigraphic position at the base of Nagaur Formation. Khichan Conglomerate that occurs as a cover deposit, Pareek (1984) described this well consolidated pebble bed except in Khirwa-Badhaura area, where Badhaura Formation as Khichan Conglomerate retaining the same stratigraphic overlies this conglomerate. position as suggested by Sinha (1 975). Shrivastava (1992) Recent mining activity for local construction material used the term Khichan breccia for this conglomerate and has exposed the contact between Nagaur Formation and suggested its stratigraphic position at the base of overlying Khichan Conglomerate. This unconformable Formation. In Khirwa-Badhaura area, Farooqui and Ojha contact is exposed at Bhomiyaji Temple on -Malar (1978) mapped this conglomerate as the bedded form of Road just 3 km outside Phalodi town and also in a pond Bap Boulder Bed and merged it with the typical glacial situated near Jain Dadawadi at Khichan village. Lithological Bap Boulder Bed. Consequently, they have suggested Bap succession observed in Phalodi-Khichan-Malar-Badhaura Boulder Bed to occur below Badhaura orm mat ion instead area is given in Table 1. of Khichan Conglomerate occuiring below Badhaura Nagaur Formation is composed of mainly friable Formation. sandstones and siltstones, while BiIara Formation is composed of resistant rocks like dolomite, limestone and chert. Consequently, weathering processes prior to the STRATIGRAPHIC STATUS deposition of Khichan Conglomerate caused the formation During the course of second generation mapping on of uplands of Bilara limestone and low lands of Nagaur

Table 1. Lithological succession in Phalodi-Khichan-Malar-Badhaura area, , Rajasthan r Age I Group/Formation I Lithology 1 Quaternary Reworked pebbles, boulders and clay from Bap Boulder Bed. Pebbles and gravels of cluartzitic sandstones. Sand, soil and settled sand dunes Glacial moraine (clay) with the boulders of igneous (Malani and Erinpura), rnetarnorphic (Aravalli Early Permian Bap Boulder Bed** and ) and the sedimentary rocks of Manvar Supergroup Permo- I Fine grained friable well sorted purple orange sandstone and yellow clayey sandstone Khichan Well consolidated hard and compact calcareous gravely-pebbly bed with major clast of Bilara Fm. i.e., limestone, stromatolitic limestone, chert and cherty limestone, and in minor amount sandstone, Conglomerate clay and calcareous nodule of Jodhpur and Nagaur Formations ------Er~si~t~~lUnc~tlformity------.-.----~--~ .- + Nagaur Fm. Purple coloured sandstone, siltstone and red clay 5.9 a 202Ci 2 = Bilara Fm. Cherty, stromatolitic and dolomitic limestone 3 ggsG w $ a Jodhpur Frn. Fine to medium grained brown sandstone J * Trans-Aravalli Vindhyan of Manvar Region of Rajasthan was renamed by Geological Survey of India as Manvar Supergroup. This is the official view of GSI. In the authors' view the Trans-Aravalli Vindhyan has Group status only. Fm. - Formation. ** Rased on the spore and pollen study of Bap clay sample nnalysed by the scientists of Rirbal Sahni Institute of Pnlacobotany, Lucknow. They have suggested Early Permian age for the Bap Boulder Bed.

JOUII.GEOL.SOC.INL)lA, VOL.58, DEC. 2001 10 I:or~~i;~tion.IJ:lter on, Khich;ln Conglotneri~tcw;~s deposited :irc;ls. The sandstones of B;idh;liira Formation in the area in the basin rn;iinly t!cvelopetl over the mcks of ~;lgaur just wcst of Kllirw;t and Badhaura villages conformably Formation, between post-Nagaur and pre-Baclhaura overlie the Khichan Conglomerate. times. This conglomerate is exposed near Phalodi along References Phalodi-Malar road, southwest of Khirwa, west and west- northwest of Badhaura and near Khichnn. It is hard and FAROOQUI,N. H. and OJ~IA,B. K. (1978) Report on the studies on the age relationship of the Bap Boulder Bed and Badhaura compact, light pink calcareous conglomerate cornposed Formation, Districts Jodhpur and , Rajasthan, (Progress mainly of pebbly and gritty layers. Thickness of this bed is report for the field season 1977-1978, unpublished). Geol. about 2 to 2.5 rn. Average clast size is 3-10 cm. Shape of Surv. India, Jaipur. the ciasts is subangular to subrounded. At places, larger PAREEK,I-I.S. (1984) Pre-Quaternary Geology and Mineral clasts than pebbles are also seen. Clasts are composecl of Resources of northwestern Rajasthan. Geol. Surv. India stroinatolitic limestone, chert, limestone, dolomite, Mem. no. 1 15, 99p. sandstone and calc:~reousnoclule. Interestingly, there are SINIIA,A. A. K. (1 975) Progress report on the geological mapping no clasts of igneoi~sand metamorphic rocks of Arrivalli, in parts of Jodhpur District, Rajasthan for the field season Dclhi and Malani, which are otherwise dominant in thc partly 1 974- 1975 (unpublished). Geol. Surv. India, Jaipur. SIIRIVASTAVA,I3. P. (1992) Significant fourth dimensional unconsoliclatcd glacial Bap Boulder Bed. Attitude of this stratigraphic markers in Palaeozoic sediments of west-central conglomerate is probably the same as the palaeotopography Rajasthan. Palaeogeographic implications and petroleum over which it rests. Dip is almost horizontal at most of the habitat. Indian Jour. Petroleum Geology, v. 1, 110.2, pp.224- places, but is about 10" northerly in Khirwa and Badhaura 244.

(Received: 2 Jirly 2001; Reviseclforttt acceptetl: 26 AL{~IIS~2001)

JOUR.GEOL.SOC.INDIA.VOL.58, DEC. 2001