Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

S. Sinha-Roy ¹, M. Mohanty ¹, G. Malhotra ¹, V. P. Sharma ¹, D. W. Joshi ¹

Affiliations
1 Geological Survey of India, 15-16 Jhalana Dungri, Jaipur 302 004, IN

Abstract

The Proterozoic sequences of South-Central Rajasthan are contained in the Lower to Middle Proterozoic Aravalli and Middle to Upper Proterozoic Delhi fold belts. The stratigraphic relations within these fold belts as well as the basement-cover relations are beset with several problems. The conglomerate horizons have been studied to address some of these problems. Based on the conglomerate horizons, representing erosional unconformities, the Aravalli Supergroup has been sub-divided into three groups and the Delhi Supergroup of the South Delhi fold belt into two groups with constituent formations. These horizons are also useful in identifying three stages of basin evolution for the Aravalli fold belt. The Middle Aravalli Conglomerate is the most prominent representing mid-Aravalli hiatus, and corresponding to the Debari Transgressive Stage which followed the Delwara Rifting Stage in the Lower Aravalli in a system of ensialic distensional tectonics where triple-junctions and pull-apart basins are formed. The Upper Aravalli has been the Jharol Ocean Opening Stage, the oceanic/transitional crust having been consumed at a median ultramafic suture line during the formation of the Aravalli fold belt. The South Delhi fold belt has also multi-stage development history with the Barr Conglomerate representing the base of the youngest Delhi sequence.

Keywords

Proterozoic, Conglomerate, Aravalli Fold Belt, Delhi Fold Belt, Rajasthan, Basin Evolution.

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L. S. Shekhawat ¹, D. W. Joshi ¹, M. K. Pandit ²

Affiliations
1 Geological Survey of India, Jhalana Dungari, Jaipur 302 004, IN
2 Department of geology, University of Rajasthan, Jaipur 302004, IN

Abstract

Detailed geological mapping (1 :25,000) of the Jaisamand-Salumber area in south Rajasthan has brought out modifications and additions to the existing published maps. Significant modifications in the outcrop pattern relate to the disposition of (a) polymictic conglomerate, feIdspathic quartzite and calcareous quartzite-dolomite unit in the Ora- Jaisamand area, (b) granitoid bodies, and (c) polymictic conglomerate occurring southwest of Salumber. A better understanding of the inter-relationship of significant litho-units has necessitated a relook into the Aravalli stratigraphy of the area, particularIy with respect to the granitoids and conglomerate. Geological mapping has also helped in identifying some stratigraphically important litho-units, such as polymictic conglomerate from northwest of Paluna, calcareous grit1 calcareous quartzite-dolomite from west of Piladhar, and calcareous quartzite-dolomite along the northeastern limb of Ora - Jaisamand anticline. The Aravalli sequence exposed in the area can be divided into Salumber Group (lower Aravalli) and Jaisamand Group (upper Aravalli), separated by an unconformity. The two groups also differ in lithologic assemblages. The granitoids are intrusive into the volcano-sedimentary sequence of the Salumber Group and form the basement for the Jaisamand Group. On the basis of overlapping relationship with Salumber Group litho-units and clast composition, the stratigraphically controversial Ora-Jaisamand-Salumber conglomerate and correlatable units have been interpreted as the basal unit of the Jaisamand Group (upper Aravalli).

Keywords

Stratigraphy, Conglomerate, Granitoids, Palaeoproterozoic, Aravalli Fold Belt, Rajasthan.

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