Sedimentary rocks originate from the accumulation and lithification of sediments derived from the weathering and erosion of pre-existing rocks. These sediments, transported by water, wind, or ice, undergo compaction and cementation to form layered or stratified structures. Sedimentary rocks are classified into three categories: mechanically formed (e.g., sandstone, shale), chemically formed (e.g., limestone, halite), and organically formed (e.g., coal, chalk).
These rocks are distinguished by their porosity, fossil content, and stratification, offering invaluable insights into past climates, ecosystems, and tectonic events. For instance, coal layers in sedimentary basins reveal ancient swamp environments, while marine fossils in limestone indicate historical sea-level changes. Despite constituting only 5% of the Earth’s crust by volume, sedimentary rocks cover 75% of its surface, highlighting their prevalence in shaping landscapes.
Limestone, a chemically formed sedimentary rock, is primarily composed of calcium carbonate and often forms in marine environments through the accumulation of shell fragments and coral. It is widely used in cement production and as a building material. Sandstone, a mechanically formed rock, consists of sand-sized mineral particles cemented together, often found in desert or riverine environments. Coal, an organically formed rock, results from the compaction of plant remains over millions of years and is a crucial energy resource.
About India: The Gangetic Plains, formed by alluvial deposits from the Ganges and its tributaries, are a prime example of sedimentary accumulation, supporting India’s agrarian economy. The Vindhyan Range, stretching across central India, comprises sandstones and shales rich in limestone, used extensively in cement production. The Damodar Valley coalfields in Jharkhand and West Bengal, part of the Gondwana sedimentary basin, are vital for India’s energy sector.