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

Charu C. Pant ¹

Affiliations
1 Department of Geology, Kumaun University, Nainital 263002, IN

Abstract

Gangolihat Dolomite (= Deoban) of eastern Kumaun Himalaya, predominantly made up of micrite, dolomicrite) pelmicrite, dolomitic limestone and talc-associated magnesite, has preserved a variety of stromatolites, of Colonnella group, in its uppermost horizons, best developed soulh of Berinag near Rain Agar, Bora Agar and near the township of Gangolihat. The paper describes four forms of stromatolites which are compared with similar forms described by earlier workers from different parts of Himalaya and the depositional environment has been deduced.

A middle Riphean age (1260 - 1000 m.y.) is assigned to these dolomites because of the presence of Colonnella and Baicalia baicalica. In the present structural superposition, the Gangolihat Dolomites are discordantly succeeded by quartzites and chlorite schist of Berinag Formation which have given a radiometric age of 725 m.y., thus confirming a structural break between the two formations.

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U. K. Shukla ¹, Charu C. Pant ¹

Affiliations
1 Department of Geology, Kumaun University, Nainital-263 002, IN

Abstract

The Proterozoic Nagthat Fonnation of Nainital area is composed mainly of fine- to coarse-grained quartzarenite with subordinate amount of pebbly sandstone, conglomerate, siltstone and silty shales. On the basis of such parameters as grain size, primary structures, palaeocurrent and morphology of lithounits, seven major lithofacies have been distinguished in the Nagthat sequence. These are, medium to coarse-grained gravelly quartzarenite (Lithofacies A), bar cross-bedded medium-grained quartzarentite (Lithofacies B), horizontally laminated fine-grained quartzarenite (Lithofacies C), fine to medium-grained channelised quartzarenite (Lithofacies D), fine-grained quartzitic sandstone (Lithofacies E), silty sandstone-shale (Lithofacies F) and matrix supported conglomerate (Lithofacies G).

Lateral and vertical distribution of constituent lithofacies demonstrate deposition of Nagthat sediments in a progradational (regressive) barrier island system, in subtidal upper shoreface and channels, subtidal longshore bars, foreshore beachface, tidal channels (inlets), intertidal sandflat-channel and mixed flat environments, and occasionally as gravity flows in subtidal gravelly channels.

Keywords

Sedimentation, Proterozoic Nagthat Formation, Lesser Himalaya.

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Charu C. Pant ¹, Ajay Paul ¹

Affiliations
1 Department of Geology, Kumaun University, Nainital - 263 002, IN

Abstract

The seismic network in Kumaun Himalaya has recorded nearly three thousand earthquakes events since April 1999. The data has been analysed to study the seismicity pattern, seismicity rate, stress drop and focal depth pattern. The detailed analyses of 388 events have been carried out. The magnitude of the events is less than 4.2, the focal depth for most of the events lie between 10-25 km and the stress drop values are low. An attempt has been made to delineate seismically active zones and the seismicity pattern indicates that the strain energy is being released along NW-SE direction almost parallel to the regional thrust viz. Main Central Thrust/Munsiari Thrust/Berinag Thrust/North Almora Thrust and orthogonally along N-S/NNW-SSE directions. Considering the fact that the strain energy is continuously building up along the Himalayan front due to convergence of Indian and Eurasian Plates and the region lying between Bihar-Nepal border (1934 earthquake MS 8.4) and Kangra (1905, earthquake MS 8.6) has not experienced a major earthquake (M ≥8). The evaluated low value of seismicity rate and stress drop in the Kumaun Himalaya may be indicative of possible major earthquake in near future.

Keywords

Seismotectonics, Stress Drop, Seismicity, Uttaranchal Himalaya.

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A. Paul ¹, H. R. Wason ², M. L. Sharma ², Charu C. Pant ¹, A. Nirwan ¹, H. B. Tripathi ¹

Affiliations
1 Department of Geology, Kumaun University, Nainital - 263 002, IN
2 Department of Earthquake Engineering, IIT, Roorkee - 247 667, IN

Abstract

The seismic data recorded by the 'Digital Telemetered SeismiC Network' (DTSN) in Kumaun Himalaya during the period May 1999 to November 2000 have been used to calculate some of the source parameters and to comment upon the seismotectonic activity in the Kumaun-Garhwal region of the Himalaya. The source parameters have been calculated using the Brune's model of the earthquake source. The earthquakes are found to have very low stress drops. The maximum stress drop is found to be 95 bars for an earthquake of magnitude 34 with focal depth of 23 4 km. The shallow focus events having low stress drop indicate that the crust has low strength to withstand the accumulated strain energy. An endeavour has been made to empirically correlate the seismic moment magnitude to the source parameters computed in this part of the Himalaya. The epicentral locations indicate that the Kumaun Himalaya region between Main Central Thrust (MCT) and Main Boundary Thrust (MBT) is a seismically active zone.

Keywords

Seismotectonics, Stress Drop Thrust, Kumaun Himalaya.

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