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

B. Parkash ¹, R. K. Goel ¹, Pankaj Sinha ¹

Affiliations
1 Department of Geology & Geophysics, University of Roorkee, Roorkee, U. P., IN

Abstract

The present paper deals with a study of thickness of cross-bedding units and palaeocurrents as deduced from cross-bedding foreset dip azimuths of the Siwaliks of Panjab, Haryana and Himachal Pradesh. All the three sub-divisions of the Siwaliks-Lower, Middle and Upper exhibit mainly southerly palaeocurrent directions and the variance of cross-bedding foreset dip azimuths seems to decrease from the Lower to Upper Siwaliks. Consistent southerly paleocurrent direction in the Upper Siwaliks suggests that they were probably deposited in a single continuous basin instead of two separate basins.

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B. Parkash ¹, R. K. Goel ¹

Affiliations
1 Department of Geology and Geophysics, University of Roorkee, Roorkee, U.P., IN

Abstract

Synthesis of the stratigraphy, paleocurrents and depositional environment of the Siwaliks and sediments suggests that Lower and Middle Siwaliks were deposited predominantly in the form of overlapping, mega alluvial cones of rivers emerging from the Himalaya and flowing southward. Forerunners of some of the modern rivers of great antiquity played an important role in their deposition. During the Upper Siwalik times the Himalaya attained great heights and several important rivers developed on the southern slopes of the central range and deposition continued as before with the difference that a wide piedmont deposit of coarse conglomerate formed near the foot hills. During Siwalik times, an easterly flowing river close to the southern boundary of the area of deposition drained the rivers emerging from the Himalaya.

The present geomorphic set up is essentially a continuation of the one developed during Siwalik times with only minor changes.

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A. K. Awasthi ¹, B. Parkash ¹, B. B. S. Singhal ¹

Affiliations
1 University of Roorkee, Roorkee, IN

Abstract

Dispersal pattern of sandstones of the Jodhpur Formation around Bhopalgarh (Rajasthan) was studied by measuring dip azimuths of cross-bedding foresets. Variance components of paleocurrents due to various sources were analysed. Low variance of paleocurrents, profusely cross-bedded character of sandstones and mainly arenaceous nature of the formation, suggested that the deposition of the major part of the Jodhpur Formation took place under braided fluvial conditions.

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Rakesh Mohindra ¹, B. Parkash ²

Affiliations
1 Wadia Institute of Himalayan Geology, Dehradun-248 001, IN
2 Dept. Earth Sciences, Univ. of Roorkee, Roorkee-247 667, IN

Abstract

Based on remote sensing mapping, field study of morphology and soils, and laboratoty analysis of soils, the Gandak mega-fan and adjoining areas are divided into ten major geomorphic units - Gandak Floodplain, Young Gandak Plain, Older Gandak Plain, Oldest Gandak Plain, Old Rapti Plain, Old Ghaghra Plain, Ganga-Ghaghra Interfluve Plain and floodplains of the Ganga, Ghaghra and Rapti. The present study indicates that the Gandak river has shifted over its mega-fan from west to east from the Oldest Gandak Plain to Gandak Floodplain over a distance of about 105 km. One way shifting is due to slow eastward neotectonic tilting of the mega-fan. As the Gandak shifts across the mega-fan, it leaves behind numerous ponds, channels, lakes etc., which, with time, get integrated into fewer channels and drainage improves. Slow tilting has resulted in deposition of a flick ( > 1.7 m) vertical accretion silt layer over most of the mega-fan, even on the proximal portion deposited by the braided Gandak Channel. It has also been responsible for higher degree of soH development from east to west on the Gandak mega-fan. The whole region of the Gandak mega-fan is subsiding, but in the area of the Young Gandak Plain the sedimentation rate is slow and is not keeping pace with subsidence. This has resulted in impeded drainage, waterlogging and ponding on a large scale.

Keywords

Gandak Mega-Fan, Neotectonics, Gangetic Plain.

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