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Introductory Study to Sedimentary Rocks

Sunday 1 January 2017, by Imeru Alfonzo Hernandez

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75% of the continental surface materials are of sedimentary origin, however in volume the sedimentary rocks constitute only 5% of the outer 15 km of the crust. Their great importance is that they contain more than 95% of the materials that provide energy to our civilization, such as hydrocarbons, carbons and radioactive elements.

Sedimentary rocks are formed by the accumulation of diverse sediments. These sediments may consist of fragments of rocks of different sizes, remains of animals or plants, substances produced by them, and minerals resulting from the evaporation of solutions or chemical precipitation.

Rocas Sedimentarias

SEDIMENTARY ROCKS

They are those formed by consolidated or lithified sediments. The processes that lead to the formation of sedimentary rocks from unconsolidated sediments are called DIAGENESIS
The genesis of sedimentary rocks involves four stages that occur in strict order and which are:

1- METEORIZATION OF PRE-EXISTING ROCKS.

2- EROSION. (TRANSPORTATION OF MATERIALS)

3- DEPOSITATION.

4- DIAGENESIS

SEDIMENTS: Materials without primary cohesion formed by the deposition of mineral or rock particles, shells or skeletons of animals, algae, corals and plant remains, or by chemical precipitation of salts dissolved in water.

Sediments can have two types of depositional textures: clastic and non-clastic.

CLASSIC SEDIMENTS: Are those sediments deposited by physical sedimentation, which occurs when the transport of the material ends, due to a decrease in the energy of the transport agents, for example: decrease in wind force, culmination of the movement of an ice mass or decrease in the energy of a river. This sedimentation can be considered as a gravitational process.

The sediments formed exclusively by the accumulation of mineral particles and rocks, also called detritus, are classified as SILICLASTIC SEDIMENTS, due to their predominantly silicate composition, and include gravel, sand, silt and clays among others, and are differentiated from each other by the size of the detritus. Those sediments formed by the accumulation of varied organic remains are called BIOCLASTIC SEDIMENTS, and include remains of organisms such as corals, bivalves, foraminifera, algae, Etc.

NON-CLASSIC SEDIMENTS: They are the result of chemical sedimentation, can be deposited by chemical precipitation (oxides, carbonates and phosphates) or by evaporation of waters in restricted circulation basins (chlorides, sulfates, carbonates, nitrates and borates)


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