SEDIMENTOLOGICAL AND GEOCHEMICAL STUDIES OF JAISALMER BASIN, RAJASTHAN

Abstract

The present work represents tectonic, sedimentological and geochemical analysis of Jaisalmer Basin of west Rajasthan. This basin came into focus, primarily due to gas discoveries across the border in Pakistan. In order to have a focused approach to considerably reduce the involved risk in hydrocarbon exploration, it becomes pertinent to have an absolute understanding of the geological model in term of sedimentology, tectonics, paleogeography and sequence stratigraphy. The relative sea level changes and sedimentation cycles in different parts of the basin is also necessary to establish in order to understand the tectono-sedimentation of the basin using paleontological control from different stratigraphic successions. The Jaisalmer basin has late Palaeozoic-Mesozoic and Cenozoic sequences dipping about 3° to 5° towards northwest. Five major unconformities / hiatuses of varying span i.e. at the top of Archean basement, Cambrian, Jurassic, Cretaceous, and Eocene are marked. These unconformities / hiatuses created the foundation for establishing stratigraphic framework. On the basis of faunal and floral succession the basin is characterized by Proterozoic-Early Cambrian (Randha & Birmania formations), Permo-Triassic, (Bhuana Formation), Jurassic (Lathi, Jaisalmer, Baisakhi & Bhadasar formations), Cretaceous (Pariwar, Habur, Goru & Parh formations), Paleocene (Sanu) and Eocene (Khuiala and Bandah formations) sequences. Each of the Formation is characterized by rich micro and mega fossil assemblage. The richest fossiliferous unit is Jaisalmer Formation, represented by mega and micro faunas. Tectonically, The Jaisalmer Basin is divided into four sub-basins from north to south. These sub basins are, Kishangarh shelf, Ramgarh - Kanoi graben, Shahgarh depression and Miajlar depression. These unit has several phases of tectonic modifications with geological time viz. 1) E-W/NE-SW trending - Pre-Cambrian intracratonic rift setting below related to Rodinia fragmentation during Late Proterozoic. 2) NE-SW or NNE-SSW trending growth faults developed during the passive margin setup (Paleozoic-Mesozoic). 3) NNW-SSE to NW-SE sinistral strike-slip movement in Late Cretaceous-Paceocene associated with separation from Madagascar and Himalayan collision.