Salkhan Fossil Park

The 55-hectare fossil park at Salkhan in Sonbhadra district, Uttar Pradesh — holding stromatolites, the layered calcareous structures built by cyanobacterial colonies, dated to around 1.4 billion years ago in the Proterozoic Vindhyan sedimentary basin. The park preserves the Great Oxidation Event evidence (c.2.4 billion years ago) when cyanobacterial photosynthesis changed the Earth's atmosphere — the stromatolites here document the subsequent 1 billion years of life. The site holds about 2,000 individual stromatolite colonies on exposed limestone pavement, among the world's largest surface concentrations. UNESCO tentative list since 2021. The site is reached from Varanasi by road through the Vindhyachal escarpment.