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

A. A. Khan ¹, U. S. Dubey ¹, M. N. Sehgal ¹, S. C. Awasthi ¹

Affiliations
1 Geological Survey of India, C-776, Mahanagar, Lucknow 226006, IN

Abstract

The Ganga system in Garhwal Himalaya comprises of Alaknanda followed by Bhagirathi, Bhalangana, Mandakini, Pindar, Atta Gad and Jalkhur with their terraces. Alaknanda is the trunk stream and the others are tributaries. The Alaknanda and its tributaries include terraces of three domains: glacial, fluvio-glacial and fluvial deposits in three distinct environments in Pleistocene, late-Pleistocene and Holocene. Stratigraphic succession of terraces and sequential stages of valley development in the Ganga system of Garhwal Himalaya has been worked out. There was continuous decrease in rate of uplift of Himalaya from early to late Holocene, as evidenced by the conspicuous divergent disposition of older terraces and convergence of younger terraces all along the length of the Alaknanda river.

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A. A. Khan ¹, A. Sonakia ¹

Affiliations
1 255-A, B. D. A. Colony, Shahpura, Bhopal (M. P.), IN

Abstract

The upper 70 m to 90 m of the Narmada alluvium was deposited in a single aggradational episode with minor pauses when dissection of the alluvium produced two terraces (NT₃-NT₂). The sediments of this aggradation episode constitute three lithostratigraphic units viz., Boulder conglomerate, Sohagpur and Shahganj Fomations. The sediments of the alluvial phase are underlain by a boulder bed of glacio-fluvial origin. Thus, the fossiliferous boulder conglomerate, the basal unit of the alluvium marks a disconformity between the lower glacio-fluvial boulder layer and the upper fluvial sediments. The fossiliferous basal boulder conglomerate is considered to be of middle Pleistocene age.

Keywords

Quaternary, Narmada Alluvium, Hominid Fossils.

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A. A. Khan ¹, S. Hoque ², S. M. I. Huq ², K. Q. Kibria ², M. A. Hoque ¹

Affiliations
1 Department of Geology, University of Dhaka, Dhaka - 1000, BD
2 Department of Soil, Water & Environment, University of Dhaka, Dhaka - 1000, BD

Abstract

The Quaternary sediments and groundwater of the Bengal delta are contaminated by arsenic, a naturally occurring toxic element. The results presented here indicate that arsenic is released from sediments by the acid formation. The activity is indicated by the decrease in pH value from 7.2 to 7, due to the role played by bacteria that acted on the particulate material present in the sediments. The decrease in pH value in the preliminary experiment indicated the presence of the' activity of thiosulphate oxidizers. In a preliminary in vitro study the presence of Thiobacillus activity that was instrumental in lowering the pH by 0.2 unit was noted. However, a detailed microbiological study is yet to be done. The aquifer sediments those contain arsenic, in turn by such release, can contaminate groundwater. It is observed that the values of the incubation study did not show any relationship with the total arsenic content of the sediments. Water extractable fraction of arsenic also did not show any trend with the total arsenic content of the sediments, probably due to solubility product constant of the arsenic compound in the sediments. However, the arsenic concentration in water treated samples and in thiosulphate treated samples show some correlation. All the samples, except one, show much greater concentration of arsenic in thiosulphate treated samples, thus indicating the release of arsenic from sediment by the acid formation.

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