The Jodhpur-Malani Divide Separating the Barmer and Jaisalmer Basins
A comparative study of ,the Ba,rmer and the adjacent Jaisalmer basins brings out striking differences in the stratigraphy, palaeontology and heavy mineral suites of the sediments.
Sedimentation in the Jaisalmer basin started with the deposition of the PermoCarboniferous tiliites and continued with breaks through (?) Triassic, Jurassic, Cretaceous and Eocene. The total computed thickness of sediments appears to be more than 7000 feet in the centre of the basin; and there are evidences of a thickening northwestwards.
Sedimentation in the Barmer basin started with the Lathi formation (? Triassic); and after a major break during the Jurassic, continued intermittently from Cretaceous through Eocene to the Late Tertiary. The total thickness of the sediments in the Barmer basin is only of the order of 1500 feet, very much less than in the Jaisalmer basin.
The Jaisalmer sediments were deposited on a platform dominantly under marine conditions. On the other hand, the Barmer sediments were deposited in a narrow embayment under changing conditions, viz., fresh, marine or brackish water. Throughout the entire sedimentary column the Jaisalmer sediments are characterised by the presence of staurolite, garnet, and kyanite. Staurolite is markedly absent in the Barmer basin sediments which have hornblende, garnet and kyanite.
Subsurface and surface geological data show that the two basins were separated by a ridge formed by the Malani Igneous suite and Vindhyan sediments. The ridge acted as a barrier preventing the intermigration of the fauna, and also as a watershed separating the two distinct provenances of the Barmer and Jaisalmer basins.
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