Sedimentary basins of India

 What are sedimentary basins?

• Sedimentary basins are regions of the Earth where long-term subsidence creates accommodation space for accumulation of sediments.
• As the sediments are buried, they are subject to increasing pressure and begin the processes of compaction and lithification that transform them into sedimentary rock.
• Sedimentary basins occur in diverse geological settings usually associated with plate tectonic activity.
• Tectonic processes that lead to subsidence include the thinning of underlying crust; sedimentary, volcanic or tectonic loading; or changes in the thickness or density of adjacent lithosphere.
• They are classified by their tectonic setting (divergent, convergent, transform, intraplate), the proximity of the basin to the active plate margins, and whether oceanic, continental or transitional crust underlies the basin.

Methods of formation:

Sedimentary basins form primarily in convergent, divergent and transform settings.

• Convergent boundaries create foreland basins through tectonic compression of oceanic and continental crust during lithospheric flexure. 
• Tectonic extension at divergent boundaries where continental rifting is occurring can create a nascent ocean basin leading to either an ocean or the failure of the rift zone.
• In tectonic strike-slip settings, the lower, hotter part of the lithosphere will “flow” slowly away from the main area being stretched, whilst the upper, cooler and more brittle crust will tend to fault (crack) and fracture. The combined effect of these two mechanisms is for the Earth’s surface in the area of extension to subside, creating a geographical depression which is then often infilled with water and/or sediments.
  

Why are hydrocarbon deposits found in sedimentary basins?

• The structures formed in sedimentary basins are known to act as traps for hydrocarbons (i.e. natural gas and petroleum).
• The processes that lead to the formation of these deposits are associated with rifting zones.
• Hydrocarbon traps form in permeable layers of rock (such as sandstone) called reservoir rocks that are ‘capped’ by impermeable rocks (such as shale). 
• Since water is denser than both petroleum and gas, they will not mix.
• Water will then force these fossil fuels through permeable rocks until they pool together in traps formed by cap rocks.

Advantages of sedimentary basins:

• It preserves unique information regarding the history of tectonic, biologic, oceanographic, and atmospheric events during Earth’s evolution.
• Basin fill contains most of the fuel and water, and many of the mineral resources, that are critical for society and industrial civilization.
• Would contribute towards attaining the goal for reducing oil import dependence.