Current Science

Richard W. Ojakangas ¹, R. Srinivasan ², V. S. Hegde ³, S. M. Chandrakant ³, S. V. Srikantia ⁴

Affiliations
1 Department of Geological Sciences, University of Minnesota Duluth, Duluth, Minnesota 55812, US
2 Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru 560 012, IN
3 SDM College of Engineering and Technology, Dharwad 580 002, IN
4 No. 201A-Block, Ushas Apartment, 26 Cross, 16th Main, IV Block, Jayanagar, Bengalaru 560 011, IN

Abstract

The ∼2700 Ma Talya Conglomerate is Comprised of 15 Diamictites (i.e. Matrix-supported Conglomerates) Interbedded with Mudstone and Sandstone Units, and is Interpreted as a Glaciomarine Deposit. the Entire Thickness of This Conglomeratic Member within the Vanivilas formation, the Lowest formation of the Chitradurga Group of the Neoarchean Dharwar Supe Rgroup, is Exposed in a 543 M-thick Measured Section. it is in a Sub-vertical Attitude, is Highly Sheared, and has Undergone Greenschist Facies Metamorphism. the Diamictites had an Original Matrix of Laminated Mud/Silt and Fine Sand. while Including Diamictites Throughout, the Talya is a Fining-upward Sequence with Intercalated Sandstones Dominant in its Lower Portion and Mudstones Dominant in its Upper Portion. we Interpret that the Talya Conglomerate was Deposited in a Marine Environment, with Diamictites Composed of Ice-rafted Detritus (ird) Deposited from Icebergs Calved from Tidewater Glacier Tongues And/or possibly from Ice Shelves. in these 'rainout Diamictites' the Larger Clasts were Dropped into Finegrained Bottom Sediment Deposited by Sediment Plumes and Currents. the Source Ice Sheet was Located to the West and Southwest on a Land Mass that Included the Older than 2720 Ma Bababudan Group of Quartzites and Mafic Volcanics and Older than 3000 Ma Basement of Granitic/gneissic Rocks. Application of Walther's Law Indicates that the Mudstonebearing Portion of the Talya was Deposited upon the Sandstone-bearing Portion as the Sea further Inundated the Land Mass Due to Glacial Retreat and a Decrease in Glacial Mass, thereby Resulting in the Fining- upward Nature of the Talya Conglome Rate. we also Interpret the Lower Portion of the Kaldurga Conglomerate, Located 50-75 Km to the Southwest of the Talya, to be Equivalent with the Talya. the Kaldurga Contains mostly Granitic Basement Detritus, perhaps Exposed Due to Basement Uplift Related to Isostatic Rebound Caused by Glacial Melting or Due to Tectonism Related to Westward Subduction.

Keywords

Archean, Diamictites, Dropstones, Dharwar Craton, Glaciomarine Deposit.

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