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

C. Ramachandran ¹, M. Ramachandran Nair ¹, S. Datta ²

Affiliations
1 Geological Survey of India, 29/6. 38th Cross, 8th Block, Jayanagar, Bangalore 560 082, IN
2 Department of Applied Geophysics, Indian School of Mines, Dhanbad 826 004, IN

Abstract

The P-wave velocities and their relation to depth of burial, density, porosity and electrical resistivity are studied for the coal measure rocks of Ranigunj and Jharia coalfields. From studies on the P-wave velocities in the dry and fluid saturated states, it is observed that the effect of fluid saturation is significantly more in a direction perpendicular to the bedding plane, than in the direction parallel to the bedding plane. The effect of fluid saturation is maximum in coarse-grained sandstones with low P-wave velocities. The anisotropy factor (Vp/⊥ Vp), decreased after fluid saturation. The absorption-anisotropy relation for sandstones is found to depend on grain-size distribution as well as fluid saturation conditions. The results show that saturating conditions, direction of measurement and anisotropy assume importance in the interpretation of velocity data.

Keywords

Coal, Eastern India Coalfields, Geophysics, Seismology.

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T. K. Biswal ¹, S. K. Jena ¹, S. Datta ¹, R. Das ¹, K. Khan ¹

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology, Powai, Mumbai, 400 076, IN

Abstract

The terrane boundary between Eastern Ghats Mobile Belt and the Bastar Craton in Balangir and Kalahandi Districts of Orissa is distinctly marked by nearly two kilometer wide southeasterly dipping ductile shear zone, designated as the Lakhna shear zone. The shear zone has largely developed in the craton, but for a narrow width within the Fastern Ghats. It is dominated by quartzofcldspathic mylonites characterised by S-C fabric, asymmetric winged porphyroclasts, quartz ribbons and intragranuhr faults. These structures have been effectively utilized in deducing the sense of shear and evaluating the amount of strain. The results show thrusting of the Eastern Ghats over the Bastar Craton. The minimum amount of throw along the thrust has becn estimated to be around 2.5 to 4.7 km assuming a dominant simple shear deformation.

Keywords

Terrane Boundary, Lakhna Shear Zone, Strain Evaluation, Eastern Ghats Mobile Belt, Bastar Craton, Orissa.

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