Sedimentary Environments Lesson

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From Sediments to Rocks

Sediments are broken bits of rock. They can be many different shapes, sizes, compositions and can be found in many different types of environments. In fact, all of these variations are unique to specific depositional environments.

There are three steps necessary to the formation of sedimentary rocks: Diagenesis, Recrystallization, and Lithification.

Step 1: Diagenesis

These three processes form and move sediments.

Soils and sediments are the end products of weathering. There are three types: Mechanical, Chemical, and Biological.

Mechanical Weathering involves the physical breaking apart of Earth materials.

Chemical Weathering alters the internal structure of minerals, usually via water. Minerals differ in their tendency to weather chemically. This is dependant upon the type of bonding within the mineral, the type of cleavage present (or not present), in addition to the temperature and pressure at which the mineral forms. Minerals that form first in Bowen's Reaction Series are the least stable, while those that form last are the most stable.


Biological - Organisms often important chemical weathering agents


Physical weathering speeds chemical weathering. An increase in surface area accelerates chemical attack, while the chemical weakening of the substance increases surface area via breakage. The shape of the object is also important. Block geometry influences weathering. The corners weather fastest; as there are 3 sides of attack. Edges weather at a moderate rate (2 sides). Flat faces weather slowest (1 side). Weathering rates vary due to changes in mineral stability, the degree of compaction or cementation and subtle differences in texture, etc. These in turn control the surficial expression of a rock or landscape.




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