STRATIGRAPHY, SEDIMENTATION AND STRUCTURE OF A PART OF BHAGIRATHI VALLEY, DISTRICTS UTTARKASHI AND TEHRI, U.P.

Abstract

"The thesis incorporates results on the stratigraphy,structure \nd sedi mentation in an approximately 900 sq.km. of the Lesser Himalayan terrain along BhagiratM river,districts Utt-rkashi and Tehri.U.P. On the basis of geological napping on 2a=l km. scale, various lithostratigraohical units have been established and described with their fie Id,megascopic and microscopic chara cters. The folds, faults and thrusts have been described with their field evidences. The structure of the area deals with their mutual interrelationshin and is elucidated with a number of vertical cross sections. The effects of folding and thrusting of rocks are structurally analysed in a part of the northern region with ir -diagrams. Atectonic setup of the area has been attem pted and is compared with adjoining regions of the Lesser Himalaya between Simla and Kuraaon, A number of thrusts are conspicuous by occurrences of mylonites and metabasics which have been'dealt with respect to their field,megascooic and microscopic characters. The metamorphism,mode of emplacement *md relationship of mylonites and metabasics with thrusting is discussed. The sedimentological studies include insoluble residue and chemical ana lysis of carbonate rocks and heavy mineral investigati ns in arenaceous rocks. The insoluble residues from dolomites and limestones are described. The chemi cal data for calcium and magnesium is used in classification of the carbonate rocks. The insoluble residue and CaO/MgO relationship is compared with carbo nate formations of the Lesser Himalaya. The heavy mineral separations from quartzites are quantitatively,quali tatively and statistically analysed. The lateral and stratigraphies 1 varia bility of zircon and tourmaline varieties from Quartzite Formation of the Garhwal Group is regionally studied to show their importance in stratigraphy, (ill) structure ^nd tectonic interpretation. The grain size data of zircon,tourmaline and quartz from heavy mineral separations of quartzites and thin sections of non-calcareous sedimentary rocks is statistically represented by the Smithson and Haggerraann diagrams for purpose of their application in correlation and sedimentation of rocks. The stratigraphy of the area is separately described and correlated with other Lesser Himalayan formations. On the basis of the above studies, sedimen tation and tectonic history of the area is reconstructed. In the last chapter,the conclusions are briefly enumerated."