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

Ajit Bhattacharyya ¹, S. K. Chanda ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta, IN

Abstract

Earlier studies on the geology of the Krol Belt in general have included little detailed information pertaining to the petrology and mineralogy of the Krol Group. The work reported herein represents a part of a comprehensive petrological study of the Krol Formations and provides information mainly about the petrology and probable environment of deposition of the basal unit of the Krol Group, namely the Krol sandstone, that overlies the Infra-Krols.

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S. K. Chanda ¹, Ajit Bhattacharyya ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta, IN

Abstract

There has been some disagreement between Medlicott and Matley as regards the stratigraphy of the Lameta-Jabalpur contact in the type area. On the basis of fieid evidences integrated with petrologic data, it is shown in the present work that there is a well-marked unconformity at this contact, and the paraconformity observed in the eastern part actually passes into an erosional unconformity of a greater magnitude towards the south-west. The "apparent presumption of an unconformity" by Medlicott is thus confirmed. Post-Jabalpur tectonism, visualised on the basis of this presumption of the unconformity, although a cause for Lameta sedimentation, did not effectively change the tectonic framework in the type area.

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Ajit Bhattacharyya ¹, Bankim Mukherjee ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta, IN

Abstract

Coals from two major seams viz., Karo and Bermo seams, East Bokaro Coalfield, Bihar were washed in the laboratory at different specific gravity medium. Chemical and petrological analyses of unwashed coals and the washed fractions from these were undertaken. Reflectance measurements (by Seyler's method) were made on the vitrinites for the unwashed coals and for different Iloat fractions after washing. The clean coals show an improved assemblage of macerals and reflecting components from the point of view of their physical and coking properties. It is also noticed that at 1.50 to 1.55 specific gravity cuts, the floats show a good reduction in ash content and a definite concentration of vitrinite and reflecting components, responsible for developing better coking characters. It is further observed that the coals from bottom section of the Bermo seam is more amenable to cleaning than the coal from the top section.

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S. K. Chanda ¹, Ajit Bhattacharyya ¹, Soumen Sarkar ²

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta 700035, IN
2 Geological Sciences Unit, Indian Statistical Institute, 203, B. T. Road, Calcutta 700035, IN

Abstract

An important outcome of recent research on carbonate diagenesis has been the increasing realization that compaction may be as important as cementation in the lithification of carbonate sediments. Absence of compaction-deformation features should no longer be relied upon as unique evidence against compaction in limestones. The paucity of such features arises from the fact that the load-bearing capacity of allochems (grains) is hardly exceeded in the normal course of lithification of carbonate sediments. Their load-bearing capacity seems to have been exceeded only in the presence of rigid bodies (nodules) or surfaces (hardgrounds or ernersion surfaces). Wherever this prerequisite is met, compaction-deformation may be set into motion in the adjacent sediments, irrespective of their environments of deposition.

So far as the mud-supported carbonate sediments are concerned, they may undergo autolithification entirely through solution-reprecipitation without the benefit of subaerial exposure. In the case of grain-supported carbonates too, there are indications that an appreciable amount of their cement may be derived from elsewhere in adjacent rocks undergoing deeper burial diagenesis within the same basin. While burial diagenesis seems normal, subaerial diagenesis is exceptional for carbonate sediments, other than those of the nearshore areas.

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Ajit Bhattacharyya ¹, K. R. Gupta ²

Affiliations
1 Dept. of Geological Sciences, Jadavpur University Calcutta, IN
2 ESS Division DST, New Delhi, IN

Abstract

No Abstract.

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Ajit Bhattacharyya ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta - 700 032, IN

Abstract

The Kaimur Group of the Vindhyan Supergroup in Son Valley is represented by a 8 to 400 m thick siliciclastic sequence covering an area of around 12,000 sq.km. Following the reinterpretation of the Dhandraul Sandstone (the uppennost unit of the Kaimur Group) as deposits of braided ephemeral river, punctuated by aeolian deposits, the long-prevailing shallow-marine interpretation of the sub-Dhandraul sequences has been reexamined. The sub-Dhandraul sandstones and shales reveal that their deposition took place at different depths in a large lacustrine basin affected by fair-weather as well as storm waves.

Keywords

Vindhyan Supergroup, Depositional Environment, Son Valley, Madhya Pradesh.

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Ajit Bhattacharyya ¹

Affiliations
1 Jadavpur University Calcutta - 700 032, IN

Abstract

No abstract.

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