Kota Formation

 ( Geologic Formations Of India ) 

The carbonate layers with iron-rich grains and mudstones suggest a transition zone between a lake margin and wetland in a rift valley, in a marsh that experienced periodic influxes of iron-rich and barium-rich waters through faults. These waters briefly increased acidity but were neutralized by mixing with alkaline surface water, allowing carbonate formation. Iron-oxidizing microbes likely helped deposit iron oxides, cementing the sediment. During high water flow, these deposits were eroded and transported to deeper waters, forming iron-rich coatings. Thin sandy layers suggest that freshwater influxes occurred, forming carbonate bodies near water discharge points. As the water returned to being more alkaline, carbonates could form again, supporting freshwater Bivalvia, similar to modern geothermal areas of New Zealand.