Proterozoic sedimentation and Pan-African geodynamic development in the Himalaya

Abstract

The Purana or Proterozoic-Lower Cambrian continental-margin sedimentary succession of the Lesser Himalaya comprises three lithological divisions: a lower argillo-arenaceous group, a middle carbonate succession and an upper argillo-calcareous assemblage. The poorly sorted basal sediments consisting of wacke-slate alternations of the lower group were emplaced by currents, including turbidity currents, which in the early stage flowed northwards from the Aravalli and Satpura mountains of Peninsular India. Lenticular deposits of diamictite within the flysch succession represent submarine slides. Penecontemporaneous basaltic lavas and associated tuffs, interbedded with shallow-water arenites making up the bulk of the upper part of the lower group, were related to rifting of the basins. The overlying dolomites and dolomitic limestones were laid down on a very shallow stable shelf and are characterised by columnar-branching stromatolites and lenticular units of crystalline magnesite and associated talc. Lenticular diamictites towards the top of the upper group of slates and limestone are harbingers of tectonic movements culminating towards the end of the Early Cambrian in an upheaval which abruptly terminated sedimentation throughout the Lesser Himalaya and Peninsular India, and caused a pronounced interruption of sedimentation in the Tethyan domain in the northern Himalaya. The Cambro-Ordovician (500±25 Ma) granites intruding the Lesser Himalayan thrust sheets of Lower Proterozoic metamorphic rocks and the upwarped northern front of the Himalaya signify an important tectonic event that terminated the Purana (Proterozoic-Lower Cambrian) sedimentation in the Indian subcontinent. This seems to be related to the tectonic movements that occurred towards the close of the Late Proterozoic or Early Cambrian. The Purana or Proterozoic-Lower Cambrian continental-margin sedimentary succession of the Lesser Himalaya comprises three lithological divisions: a lower argillo-arenaceous group, a middle carbonate succession and an upper argillo-calcareous assemblage. The poorly sorted basal sediments consisting of wacke-slate alternations of the lower group were emplaced by currents, including turbidity currents, which in the early stage flowed northwards from the Aravalli and Satpura mountains of Peninsular India. Lenticular deposits of diamictite within the flysch succession represent submarine slides. Penecontemporaneous basaltic lavas and associated tuffs, interbedded with shallow-water arenites making up the bulk of the upper part of the lower group, were related to rifting of the basins. The overlying dolomites and dolomitic limestones were laid down on a very shallow stable shelf and are characterised by columnar-branching stromatolites and lenticular units of crystalline magnesite and associated talc. Lenticular diamictites towards the top of the upper group of slates and limestone are harbingers of tectonic movements culminating towards the end of the Early Cambrian in an upheaval which abruptly terminated sedimentation throughout the Lesser Himalaya and Peninsular India, and caused a pronounced interruption of sedimentation in the Tethyan domain in the northern Himalaya. The Cambro-Ordovician (500±25 Ma) granites intruding the Lesser Himalayan thrust sheets of Lower Proterozoic metamorphic rocks and the upwarped northern front of the Himalaya signify an important tectonic event that terminated the Purana (Proterozoic-Lower Cambrian) sedimentation in the Indian subcontinent. This seems to be related to the tectonic movements that occurred towards the close of the Late Proterozoic or Early Cambrian.