Browsing by Author "G.S. Tiwari"

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SEM surface microtextures of quartz grains from Ganga and Yamuna river sediments, Allahabad, U.P
(2004) G.S. Tiwari; R.N. Tiwari; K.N. Singh
Quartz grain surface features of recent sediments samples collected from vertical profiles developed in channel bar, point bar and natural levee deposits around the confluence of the Ganga and Yamuna rivers at Allahabad, UP, were examined under the Scanning Electron Microscope (SEM). The study reveals the existence of several surface features as a result of mechanical and chemical action on the quartz grains. In channel bar and point bar deposits, mechanical features like low relief, v-shaped impact pits of coalescing nature and conchoidal fracture are dominating surface textures, which indicate the high-energy fluviatile depositional environment. Features like surface pits and surface solution are common in quartz grains from natural levee deposits. These surface textures owe their origin to chemical dissolution, which is possible only in low energy conditions associated with the deposition of natural levee and flood plain deposits. © GEOL. SOC.INDIA.
Vertical successions of channel bar, point bar and natural levee deposits, Ganga and Yamuna river, Allahabad, U.P
(2004) G.S. Tiwari; R.N. Tiwari; K.N. Singh
The modern sediments of Ganga and Yamuna rivers at Allahabad. Uttar Pradesh are studied in 17 vertical sections of channel bar. point bar and natural levee deposits. Based on this study nine lithofacies, i.e. St. SP2, Sp1, Sr1, Sr2, Sl. Sh. Fl and Fm (8-Sand and l- Mud sub-lithofacies) have been identified. An attempt has been made to evolve a generalised lithofacies succession for channel bar, point bar and natural levee deposits. The channel bar exhibits the lithofacies succession of SP2, Spl, Sr2, Sr1 Sh and Fl; St, SP2, Sp 1, Sr1, Sh and Fl succession m point bar and SP2, Sp1, Sr1, Sh. Fl and Fm lithofacies succession in natural levee deposits. No major difference in channel bar and point bar lithofacies succession have been found. The point bars are characterised by trough cross-bedded lithofacies - St, which are formed by the migration of 3-D dunes. The Fm lithofacies is characteristics of natural levee, the muddy deposits often show desiccation cracks. Deposition of mud takes place in low energy conditions mostly during receding floods. © Geol. Soc. India.