Sedimentary rocks are formed by the deposition of sediment.
Sedimentology is the study of sediments, such as mud, clay and sand, and of sedimentary rocks. Sedimentologists interpret the history of specific land forms using their understanding of the processes that form sedimentary structures and sedimentary rocks. For example, a sedimentologist might look at a cliff face made from sedimentary rock and be able to interpret its age and composition.
Sedimentary Rocks
Sedimentologists study the formation of sedimentary rocks. Sedimentary rocks are formed when rivers, oceans, winds and rain erode particles from rocks. This material called detritus when deposited, usually at the bottom of the sea or ocean, over time is compressed into sedimentary rock. This type of sedimentary deposition is called classic sedimentation.
Transportation
Sediment is transported by being picked up by the wind, by being carried by running water in streams or ocean currents or by sliding down slopes. The distance the sediment is transported and the energy required to do so inform the sedimentologist as to the mode of transportation.
Deposition
Sediment is deposited when the energy of that transporting the sediment (the wind or the ocean current) becomes too low to continue the process of transportation. If the velocity of the transporting medium becomes too low, the sediment will fall out and become deposited. Sedimentologists can determine the medium of transportation from their analysis of the deposited sediment.
Diagenesis
Diagenesis is the process that turns sediment into sedimentary rock. This process begins with compaction. Compaction occurs when the weight of the sedimentary material increases or the pressure acting on the sedimentary material increases. Compaction forces the grains of sediment together, reducing space and removing water. This water carries mineral components out of the grains of sediment which creates new minerals in between the grains. These new minerals begin to bind the sediment grains together; this is called cementation. Further compaction and burial cause further cementation and the production of harder rock.
Evidence of Transportation Mode
Sedimentologists find clues to the mode of transport and deposition of sediment by analyzing the makeup of sedimentary rock. For example, when sediment is transported and deposited by sliding down a slope, the deposits show a wide range of particle sizes and are generally chaotic in nature. The size of grain and the relationship between grains in a sedimentary deposit or rock informs sedimentologists as to the mode of transportation and deposition.
Tags: sedimentary rock, between grains, grains sediment, into sedimentary, into sedimentary rock
