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

V. V. Sastri ¹, A. T. R. Raju ¹, R. N. Sinha ¹, B. S. Venkatachala ¹, R. K. Banerji ¹

Affiliations
1 Institute of Petroleum Exploration, Kaulagarh Road, Dehra Dun, IN

Abstract

Outcrops ranging in age from Late Jurassic to Recent are located nearer the western margin of the basin. The eastern parts of the basin are covered by alluvium and contain a relatively thicker and more complete sedimentary sequence. The exposed and subsurface sedimentary sequence are adequately fossiliferous and several faunal as well as palynological zones are established.

The basin was formed during Late Jurassic by sagging of a part of the Indian shield, mainly along the dominant NE-SW Eastern Ghat trend. The basin was well differentiated into depressions and ridges formed owing to taphrogenic fragmentation and block faulting along the dominant basement trends during the onset of Late Jurassic. Initial sedimentation was under non-marine environment. The first marine transgression occurred during the close of Late Jurassic. Marine environment of sedimentation continued till Cretaceous, although through a series of minor transgressions and regressions. The depocentres were mainly due west.

A major regression occurred during the close of Cretaceous. The basin underwent an easterly tilt and the depocentres shifted due east prior to marine transgression during the beginning of Tertiary. The differentiation of the basin into depressions and ridges was almost lost during Eocene. Sedimentation during the Tertiary period was marked by repeated transgressions and regressions as is evidenced by biofacies, isopachs, and several sedimentation breaks which are relatively more pronounced in the western parts of the basin.

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K. Mahender ¹, R. K. Banerji ²

Affiliations
1 Department of Geology, N. Wadia College, Pune, IN
2 Department of Earth Sciences, Indian Institute of Technology, Bombay, IN

Abstract

The textural parameters of sand grains from rocks of Jaisalmer Formation were systematically analysed for reconstruction of the depositional environment. These sands are fine- to medium-grained, moderatety sorted to well sorted, negatively to positivety skewed, and leptokurtic, The variations in mean size, sorting, skewness and kurtosis indicate a change in environmental energy conditions. The environmental interpretations based on various bivariate and multivariate plots of size and shape parameters indicate river transportation of these sands and deposition in a beach- to shallow-marine environment. The surface textures of these sand grains reveal transportation in an aqueous media and deposition in a shallow-marine littoral environment. The subangular to subrounded shape and the presence of abundant feldspars and mica show that these sands are less matured and have undergone little of transportation mostly through saltation process from a nearby source.

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