The word ‘sedimentary’ is derived from the Latin word ‘sedimentum’ meaning “settling down”. The sedimentary rocks are formed when the weathered and eroded fragments of rocks and the remains of plants and animals are deposited in the water bodies. These are called sediments. Gradually, the accumulated layers of sediments are compressed and compacted into sedimentary rocks caused by the increasing weight and pressure of the overlying materials. The compacted sediments are then cemented by the cementing element such as silica, clay etc. They are also known as Stratified Rocks.
- These rocks contain fossils of plants and animals.
- They cover a large part of the globe for about 75 % of the earth surface.
- The sediments are deposited sequentially and appear as well-defined strata.
- They do not form crystals and are permeable in nature.
Fossils in Sedimentary Rocks
Types of Sedimentary rocks:
- Clastic Sedimentary Rocks: The rocks disintegrated into fragments of various size due to the mechanical or physical weathering are carried and deposited by various agents such as water, wind, glaciers forms the sedimentary rocks called as Clastic Sedimentary rocks. Sandstone, silt, clay are examples of this type of rock.
- Chemical Sedimentary Rocks: When the rocks materials become soluble in the water, it precipitates and forms sediments. Such rocks are called chemical sedimentary rocks. Gypsum, iron ore , limestone are examples.
- Organic Sedimentary Rocks: The rocks are formed from the deposition of plants and animal remains. Coal and Chalk are the examples.