Luminescence Chronology of river terraces of Hel River in foothills of Assam – Bhutan Himalayas: Implications to Tectonics and Climate

Boipai, Bhanu Priya (2021) Luminescence Chronology of river terraces of Hel River in foothills of Assam – Bhutan Himalayas: Implications to Tectonics and Climate. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Bhanu Priya Boipai (16MS187)) 16MS187_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (3MB)

Abstract

The luminescence chronology of the Hel River in geologically dynamic Assam – Bhutan Himalayas suggests that the evolution of present landscape of the Ripu block was affected by both climate and tectonic variations in the region. The present study location witnessed different events like formation of fan, and upliftment of region. The formation of fan in this area started before 75 ka ago and continued till 43 ka and afterwards. Since we need data from upper part of section as well, we cannot constrain age range of formation of fan properly for this study area. There was some tectonic activity after fan formation around 43ka, 66ka and 75ka which caused the blockage of southeast flowing Hel river and hence the deposition of clay along the river section. Significant sedimentation is observed around 66 – 75 ka. In the span of 9 ka, ~25 m of clay has deposited in one sedimentary unit. After that sedimentation occurred in episodes around 43ka and 54ka. All this suggests fluctuation in the river system and hence changes in climate of the region. Also the block started to uplift after 43 ka. The northern part of the block close to FBT is uplifted more than the southern part. Thus both the upliftment and change in the fluvial system played a role in the evolution of current landscape of the Ripu Block.

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