Saturday, September 13, 2014

Sedimentary rocks

Sedimentary rocks

Sedimentary rocks are those which are made up of pre-existing small particles called sediments. There are two types of sedimentary rocks
  • clastic
  • non clastic


Clastic rocks are those which are made up of sediments that are transported from other places. The sediment supply to the deposition are can be by the help of wind, gravity, water or ice. These rocks have many examples including sandstone and shale. The sandstone are made up of grains clustered together by the means of cements. Cement is the mineral that hold rock together, not splitting them in finer grains. Cement in the sandstone are silica or calcite. The sand particles are carried to the depositional area with the help of wind, an example of desert or the rivers deposits with the help of water. The grains are suspended either in the water or wind and when both medium speed breaks it can not carry the weight so are then deposited. It takes million years in order to the deposited sediments to form a rock as it needs pressure which can be overburden. It forms a rock which is called clastic rock.

Non clastic

Non clastic rocks are those which deposits at the area of origin. These sediments are not reworked by trasporting agents but are thus deposited where it have been formed or at lesser distance travel. These are also formed by the weathering process but not the erosional process. The best example of non clastic rocks are coral reefs. Corals habitat is colonial so when they die, deposits at its origin place. Limestone can also be formed clastically when the shells are reworked by turbiditic currents and drops calcium carbonate shells from shallow marine to deeper portion but eventually that won't be non clastic.