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

S. K. Ghosh ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

No Abstract.

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S. K. Ghosh

Abstract

No Abstract.

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S. K. Ghosh ¹, B. K. Chatterjee ¹

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi-22I 005, IN

Abstract

Siliciclastic rocks around Surgutaria viIIage are mature to sub-mature quartzarenites to quartz-wackes, Quartz-wackes are produced due to extensive readjustment of sericite-chert matrix during phyllomorphic stage of development in the arenite frame work. Various statistical parameters, and current structures clearly reveal that the deposition of siliciclastics took place in a stable shallow marine to tidal flat environment.

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S. K. Ghosh ¹, Abhijit Mukhopadhyay ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, IN

Abstract

Paraconglomerates, with pebble- or boulder-sized phenoclasts of laminated clay in a matrix of medium grained massive. sandstone, occur toward the top of a turbidite sequence in the Talchir Formation at the N. W. corner of the Jharia Coal Basin in eastern India. The soft-sediment folds within the shale phenoclasts are dominantly recumbent. An analysis of the geometry of the structures suggests that a mass of sand with interlayered clay units was liquefied or fluidized. This in its turn generated a plastic mass flow in the course of which tenacious clay yielded slabs which were subsequently rotated and deformed. When the down-slope movement of the sand body had slowed down or had come to rest on the basin floor, the piled up mass of soft sediments was flattened under its own load and the contortions of the clay phenoclasts acquired their recumbent character.

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D. Bhaitacharjee ¹, S. K. ghosh ¹, S. Roychaudhuri ², N. R. Biswas ²

Affiliations
1 Op.E.C.I, Marine Wing, Geological Survey of India, Kolkata - 700 032, IN
2 Marine Wing, Salt Lake, Kolkata - 700 091, IN

Abstract

Sedimentological characteristics, fossil contents and geochemical behaviour of the seabed sediments of the inner continental shelf region off Ganga river mouth, Bay of Bengal reveal some aspects of macrotidal deltaic environment. Seabed sediments between 11 m and 45 m water depths, covering an area of about 1450 sq km, indicate the presence of three characteristic domains from West to East each having specific features. Relict calcareous/ferruginous concretions, oolites, pellets as well as older skeletal matters of bivalve, gastropod, scaphopod and benthic foraminifera occur in the sediments of western domain at about 20 to 35m water depths. The relict taxa generally show worn out tests and ferruginous coated surfaces. The central domain is made up of sand and sandy clay with common occurrence of foraminifera. Some carbonaceous material and minor disseminated grains of heavy minerals are commonly associated with these sediments. The eastern domain is covered by silt and silty sand, mainly composed of quartz, feldspar, muscovite and biotite, which represent recent sediments of Ganga delta.

Gastropod, bivalve, scaphopod, burrows, echinoid spines and benthic foraminifera are abundant in the western, poor in the central and rare in the eastern domain. However, Astrorotalia trispinosa and Astrorotalia-Ammonia are two dominant foraminiferal assemblages in this entire region. They are large and well ornamented in the western part compared to those in the east.

The subrounded ill sorted concretions, oolites and pellets along with the above insitu biota in the western domain suggest very shallow sedimentary facies, probably deposited in a littoral condition during the Late Pleistocene time. On the other hand, the composition and nature of sediments and distinct morphological changes of taxa in the eastern domain corroborates that the Ganga delta is under a process of continuous progradation during the Holocene time.

Keywords

Prodelta, Relict Sediment, Concretion, Benthic Foraminifera, Bay of Bengal.

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S. K. Ghosh ¹, Sudipta Sengupta ¹

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

Abstract

By measuring the ratio of wavelength to arclength of folds in closely associated disharmonically folded competent layers, it is possible to determine which layer has undergone a greater layer-parallel strain and has a smaller competence. This method may lead to a paradoxical situation. For example when foliated quartzite and mica schist layers are folded together, the mica schist laminae show a much larger buckle shortening than the quartzite layers. On the other hand, the geometry of folds in quartzite indicates that quartzite was more competent than the mica schist. The structure can be explained by different modes of buckling, general buckling in quartzite layers and internal buckling in strongly anisotropic mica schists.

Keywords

Arc Length, Wavelength, Multilayer, Buckling, Internal Buckling.

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