Reconstruction of ancient climate and sedimentation systems using multi proxy data on precambrian dharwar group of rocks in South India

Abstract

Worldwide reports of Precambrian weathered profiles comprising palaeosols have significantly increased interest and better understanding of surficial/sedimentation processes, life, climate and newlineatmosphere. However, there have been meagre Precambrian palaeosol studies in India. The Precambrian Dharwar Craton may prove significant palaeosol repositories but lack extensive investigations. Therefore, late Archaean (i.e. ~2.5 Ga) Closepet granite exposures in and around Chitradurga town of Dharwar Craton have been explored. Three palaeoweathered profiles have been identified and carefully divided in to relict and buried profiles. Detailed morphological, micromorphological and geochemical studies of gt2.5m buried profiledivided it into: altered bedrock/protolith (=saprock/lowersaprolite) at gt250-180cm depth whereas regolith (=upper saprolite) newlineabove 180cm. Further, regolith consists of grus material between180-130cm but soil in top 130cm. The lower-saprolite is altered granite, wherein tectonic stresses and late magmatic processes evidences are found. Dominance of endogenic processes based on mechanical stress evidences suggest granite grusformation. The top 130cm shows pedoplasmation features, including illuvial coatings/hypocoatings. It shows highest CIW and PIA values of 80.44 and 75.73 respectively. newlineHydrolysis and leaching values confirm B-horizon and top 25cm being more enriched in REEs suggest either difference in redox conditions and/or weathering type. Palaeosol profiles on Closepet granite formed under oxidative weathering conditions based on spectacular evidences of illuvial clay-ferruginous coatings, indicating freely drained, oxygenated conditions which corroborate with geochemical signatures. Thus, present work is additional evidence to all global studies demonstrating oxygenated environment (i.e. Great Oxidation Event at ~2.4 Ga) and significant oxidative weathering of rocks at Archaean-Proterozoic boundary. newline newline