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G. S. Tiwari ¹, R. N. Tiwari ², K. N. Singh ¹

Affiliations
1 Petrology Division, Geological Survey of India, Lucknow - 226 024, IN
2 Department of Geology, Banaras Hindu University, Varanasi - 221 005, IN

Abstract

Quartz grain surface features of recent sediments saniples collected from vertical profiles developed in channel bar, point bar and natural levee deposits around the confluence of the Ganga and Yamuna rivers at Allahabnd, 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, mechanicaf 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.

Keywords

SEM-Microtextures, Quartz Grains, Fluvial Sediments, Ganga-Yamuna, U.P.

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G. S. Tiwari ¹

Affiliations
1 Petrology Division, Geological Survey of India, Lucknow - 226 024, IN

Abstract

Recent sediments of the Ganga and Yamuna Rivers in three sectors, viz Sector-A , Sector-B and Sector-C were subjected for heavy minerals study to understand their distribution in various facies, and differences and similarities The heavy minerals mciude garnet, hornblende, kyanite, tourmaline, epidote, sillimanite, zircon, chloritoid, apatite and staurolite There exists an mverse relationship between their percentage and gram size Among the heavies, garnet dominates in all the three sectors of study area, followed by hornblende in Sector-A and -B, and epidote in Sector-C with augite and rutile m the Sector-B only Anatase, hypersthene, sphene and corundum are restricted to Yamuna nver sediments Also, brookite is more common m Sector-A Nine lithofacies, namely St, Sp₂, Sp₁, Sr₁, Sr₂, S1, Sh, Fl and Fm (8 SandandlMud- sublithofacies) are identified in the area Irrespective of occurrence in any geomorphic unit, Sr₁, - Sr₂ facies have higher concentration of heavies in coarser fraction while the Sp₁ - Sp₂ facies have higher concentration of heavies in finer fraction Bed forms have significant control on the distribution of the heavy minerals in a vertical profile, with differences m the source of the sediments of the Ganga and Yamuna Rivers reflected well in the respective heavy mineral assemblage.

Keywords

Quaternary sediments, Heavy minerals, Provenance, Ganga and Yamuna rivers, Allahabad, Uttar Pradesh.

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G. S. Tiwari ¹, R. N. Tiwari ², K. N. Singh ¹

Affiliations
1 Petrology Division, Geological Survey of India, Lucknow - 226 024, IN
2 Department of Geology, Banaras Hindu University, Varanasi - 221 005, IN

Abstract

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, SI, Sh, FI and Fm (8-Sand and 1-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, Sp₁, Sr₂, Sr₁, Sh and FI; Sp₂, Sp₁, Sr₁ Sh and FI succession in point bar-and Sp₂, Sp₁, Sr₁, Sh, FI 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.

Keywords

Quaternary Sediments, Facies Architecture, Lithofacies Code, Fluvial Geomorphic Units, Ganga and Yamuna Rivers, Allahabad.

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