Alluvial fan to shallow marine sedimentation record in the ~3.0 Ga Keonjhar Quartzite, Singhbhum Craton, India: An example of Phanerozoic style passive margin sedimentation from the Mesoarchean

Abstract

The arenite-dominant Mesoarchean Keonjhar Quartzite (>700 m) succession unconformably overlies the granitoid-greenstone core of the Singhbhum craton in the north and west of the Keonjhar town in eastern India. The Keonjhar Quartzite is characterized by eleven lithofacies. The lower part of the succession represents proximal subaerial fan association dominated by cohesive and cohesionless mass-flow conglomerates deposited in a falling stage to lowstand systems tracts (FSST-LST). The channelized conglomerates are likely to be incised valley fills (IVF) from the FSST. The differentiated mass-flow deposits interbedded with tractional deposits such as trough cross-stratified sandstone with ubiquitous evidence of wave-reworking represent subaqueous delta front setting. The upper 3/4th of the succession is dominated by mature wavy bedded arenites and is arranged in aggradational stacking pattern representing TST to early stage of HST of a tectonically driven sea level rise cycle. The Keonjhar Quartzite is a rare example of well preserved record of stable siliclastic shelf development during the Mesoarchean time. The arenite-dominated Keonjhar Quartzite is comparable to only a few well studied examples of such Mesoarchean stable siliciclastic shelf sedimentation, for example, the arenite-dominated units of the Mozaan Group of the Pongola Supergroup and its correlatable Westrand and Centralrand Groups of the Witwatersrand Supergroup in the Kaapvaal craton. The presence of thick mature arenite and wave-tide reworking implies existence of Mesoarchean stable shelf depositional setting similar to the modern day passive continental margins at least in the Singhbhum and in the Kaapvaal cratons.