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

R. T. D. Wickenden ¹, V. V. Sastri ²

Affiliations
1 Geological Survey of Canada, CA
2 Oil and Natural Gas Commission, Dehra Dun, IN

Abstract

The authors have demarcated the Eocene-Oligocene stratigraphic boundary of the sub-crop sediments of the Cambay Basin of Western India on the basis of planktonic Foraminifera belonging to the genera Chiloguembelina, Cassigerinella and Globigerina.

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J. Pandey ¹, V. V. Sastri ¹

Affiliations
1 Oil & Natural Gas Commission, Dehra Dun, IN

Abstract

A new species of Sivapithecus Pilgrim, designated as Sivapithecus lewisi, has been described. The species has been based on the study of a broken right ramus collected from the? Nagri horizon of the Siwaliks. This species is characterised by a very massive and deep mandible, exceptionally large teeth and by the presence of a better defined external cingulum in the first lower molar. The holotype is believed to be the second largest specimen of fossil an· thropoids so far reported from India, next to Sivapithecus (Dryopithecus) giganteus (Pilgrim).

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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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V. V. Sastri ¹, L. L. Bhandari ¹, R. N. Sinha ¹, Kuldeep Chandra ¹

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

Abstract

The Pranhita-Godavari graben, located in the eastern Indian Peninsula, is aligned NW-SE and covers an area of nearly 40,000 sq. km. The graben exposes sediments ranging in age from Proterozoic to Lower Eocene. The oldest, the Pakhal Series, are disconformably overlain by Sullavai Series and together comprise at 1.5-2.0 km thick sequence. The Sullavai Series are unconformably overlain by approximately 6.5 km thick Gondwana sequence which is in turn, unconformably overlain by infra-trappean beds. Deccan Trap effusives contain inter-trappean beds and are unconformable with the underlying infra-trappean beds.

Genesis of hydrocarbons in non-marine sediments containing predominantly vegetal constituents is feasible. The Lower Gondwana sediments of the Pranhita-Godavari graben contain coal seams, and dispersed organic matter. Sediments of Talchir Stage are poor in organic matter content and their hydrocarbon-generating potential appears doubtful. The Barakars contain coal seams and are rich in dispersed organic matter. The carbon ratios, computed from proximate analyses of coals from various localities, indicate that the stage of maturity of organic matter varies within such limits which do not exclude the Barakar sediments from being considered as potential source rocks of hydrocarbons. The Kamthi sediments are dominantly arenaceous and contain small amounts of dispersed organic matter. Lack of relevant analytical data makes it difficult to assess their hydrocarbon-generating potential.

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V. V. Sastri

Abstract

No Abstract.

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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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Ranjit K. Banerji ¹, V. V. Sastri ²

Affiliations
1 Indian Institute of Technology, Department of Civil Engineering, P.O. Indian Institute of Technology, Powai, Bombay-400076, IN
2 Institute of Petroleum Exploration, Oil and Natural Gas Commission, Dehra Dun-248195, IN

Abstract

The paper deals with broad principles of quantified foraminiferal palaeoecology involved and their application in reconstructing the palaeoenvironments for different stratigraphic units (Upper Jurassic-Lower Palaeogene in age) exposed in the western part of the Cauvery Basin. The parameters used are the functions of structurally related characteristics and morphogenetic diversities of the foraminiferal fauna which are resultant of the environmental requirements, tolerance and preferences. The first sedimentary cycle started with fresh water deposits which soon gave way to brackish water and later continued under dominantly marine influence. The major transgressive phases during Neocomian-Albian, Senonian and Paleocene are better reflected in the quantitative bio-facies analysis. Along certain palaeomarginal highs, the environment favoured reef development where terrigenous influx was minimum. The strand-line progressively shifted since Lower Cretaceous times from west to east. The shift during Lower-Middle Eocene was more prominent and a delta front progressively started building with regression in the region bordering the western margin. The resultant sediments now cover a greater part of the exposed area and form the youngest exposed stratigraphic unit of this Basin.

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