Archean Biogeochemical Cognizance from Dharwar Craton, India - A Review

Abstract

The Banded iron formations (BIFs) and manganese formations of Chitradurga, Shimoga and Sandur greenstone belts of Dharwar craton, associated with the stromatolitic carbonates, carbonaceous phyllites and shales along with gold mineralization, are best geological entities to evaluate the Archean biogeochemical processes and transformation of a habitable Earth. The geochemical anomalies along with C, O and S isotopic signatures of stromatolitic carbonates, carbonaceous phyllites and sulphidic BIFs reflect on biogenic signatures, fluctuating Archean ocean temperatures from 25-75°C and anoxic to euxinic redox conditions. The U-Pb detrital zircon ages of these stromatolitic carbonates indicate 3.5 to 2.6 Ga whereas the carbonaceous shales indicate 3.2-2.2 Ga reflecting the transportation of organic matter to the ocean basin during the growth of stromatolitic carbonates. The gold content of carbonaceous phyllites and sulphidic BIFs indicates hydrothermal source. The O2 produced due to stromatolitic activity has deposited Mn and Fe of the Archean oceans as BIFs and Mn formations. The biogenic matter of the stromatolites along with other siliciclastic material, gold and sulphides derived from the volcanic activity mixed and formed as carbonaceous shales in the ocean basin under euxinic conditions. The comprehensive geological, geochemical including isotopic studies on these rock types collectively indicate the interaction of lithosphere-hydrosphere-atmosphere-biosphere in the Archean oceans which paved the way for the advanced forms of life.