Redox State of Atmosphere and Ocean at the Archaean-Palaeoproterozoic Boundary

What is it about?

The Sausar belt on the southern flank of the Satpura Mountain Belt of Central India comprises several generations of granite gneisses and migmatites, and the metasedimentary rocks of the Sausar Group. A suite of ~3200–2450 Ma old rocks comprising of an older Tonalite-Trondhjemite-Granodiorite (TTG) gneiss and younger quartz-monzonite plutons (Tirodi Gneiss-I) constitutes the basement complex for the Sausar Group. The contact of Tirodi Gneiss-I and the Sausar Group records the geological history at Archaean–Palaeoproterozoic boundary. A paleosol horizon at this contact contains unusual minerals such as siderite, ankerite, uraninite, and alumino-silicate minerals. The geochemical data of the paleosol indicate a reducing environment of formation and oxygen deficient conditions in the atmosphere at the time of development of this paleosol at the Archaean–Palaeoproterozoic boundary. The Sausar Group is reported to contain coarse clastics, volcanics, glaciogenic sediments, cap carbonates, and fine clastics with manganese ore deposits. Geochemical data from the cap carbonate horizon above the glaciogenic unit and manganese bearing horizons above the cap carbonate confirm presence of reducing environment in the shallow ocean.

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Why is it important?

To understand early evolution of the atmosphere, hydrosphere and biosphere.