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

V. V. Sastri ¹, L. L. Bhandari ¹, A. T. R. Raju ¹, A. K. Datta ¹

Affiliations
1 Institute of Petroleum Exploration, Oil & Natural Gas Commission, Dehra Dun, IN

Abstract

Significant data on the structure, tectonics and stratigraphy of Ganga basin have been obtained from aeromagnetic, ground magnetic, gravity and seismic surveys and the deep drilling conducted in the basin during the last fifteen years, Based on these data, the Ganga basin has been defined as a major platform depression and classified into seven tectonic zones, viz., Monghyr-Saharsa ridge, East Uttar Pradesh shelf, Gandak depression, Faizabad ridge, West Uttar Pradesh shelf, Sarda depression and Delhi-Hardwar ridge. This classification is based on the continuation of major tectonic trends from the Peninsular shield into the Ganga basin, the variations in the total thickness of the sedimentary cover, and the basement configuration as deduced from different surveys.

The sedimentary cover over most part of the Ganga basin is essentially composed of two main stratigraphic cum structural sequences representing the two main sedimentary stages in the geological evolution of the basin. The oldest, probably corresponding to the Vindhyans, is represented by stable to unstable shelf sediments composed of quartz-arenite-limestone-shale alternations. The younger sequence, unconformably overlying the Vindhyans, corresponds to the Neogene terrigenous clastics (Siwaliks). The structural and stratigraphic data of these sediments have been discussed. The presence of a profound unconformity between these two groups of sediments representing a considerable time gap ranging from (?) late Palaeozoic to Paleogene is an important factor in deciphering the tectonic evolution of the Himalaya. However, towards the northernmost depressed parts of the Ganga Basin, the age of the additional thickness of sediments intervening between the two above mentioned groups remains uncertain.

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K. N. Khan ¹, A. T. R. Raju ¹

Affiliations
1 Institute of Petroleum Exploration, O.N.G.C., Dehra Dun, IN

Abstract

Detrital ferruginous chert rock fragments containing many radiolaria have been observed from one of the lithic arenite core sample of the Murree formation in a deep exploration well drilled on Suruin-Mastgarh anticline near Jammu. The age of these radiolarian cherts may range from Jurassic to Eocene. Presence of such reworked radiolaria in the Murree sediments indicates uplift of the main Himalaya providing partially material for the Murree sediments.

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A. T. R. Raju ¹, M. R. Rao ¹

Affiliations
1 Institute of Petroleum Exploration, Dehra Dun, IN

Abstract

The depositional environments of Eocene oil and gas productive sands in Anklesvar field, which are referred to as middle and upper sands, have been studied from three main Jines of investigation, namely litho-associations, petrography and textural attributes. The middle and upper sands show subtle differences in their associational characters, petrographic features and size distributions. The middle sands, appear to have been deposited along distributory channels, over inter channel tidal flats and along tidal inlets in a tidal estuary. The upper sands, belonging to Upper Eocene, were probably deposited along a barrier beach in a transgressive open marine environment.

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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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A. T. R. Raju ¹

Affiliations
1 Institute of Petroleum Exploration, ONGC, Dehra Dun, IN

Abstract

The basin classification, study of the basin fill, and factors influencing localisation of hydrocarbons constitute the major analytical steps in evaluating the hydrocarbon potential of any sedimentary basin. Tectonic classification of Indian sedimentary basins is presented to illustrate major stages in their geological evolution.

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