Sediments, Weathering, & Sedimentary rocks

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Week 6

What is sediment?

-Uncosolidated fragments of rock and/or organis matter produced by weathering.
-Erosion, transport, & deposition concentrates sediments in basin such as stream beds, laked, valleys, & ocens.

How do u CLASSIFY sediment?

Detrital, Biological, & Chemical sediments
-Dissolved minerals

How do u INDENTIFY sedminet?

Grain size & compostion

Detrital sediments

Fragments of rock or mineral ranging is size from less than 0.1mm to several cm's. Sometimes referred to as clastic sediment. Properties-->grain size (ranging from silts to cobbles), shape (ranging from angular to well-rounded), & sorting

Biological sediments

Consisting of plant or animal fragments (shell, bone, plant fiber, etc.). Sometimes grouped w/ chemical sediments (calcite, hydrocarbon, silica) & referred to as biochemical sediment

Chemical sedminets

Produced by chemical reactions w/in or evaporation of a solution containing dissolved minerals (e.g. saltwater). Sometimes groups w/ biochemical sediment.

Dissolved minerals

Have been broken down into ions (electrically charged fragments of atoms). In many geology txtbk's, these aren't recognized as a sediment.

How does sediment form?

By chemical and/or mechanical breakdown (weathering) of rock and/or organic material (bone, shell, or plant remains).

Chemical weathering

Occurs when minerals in the rock chemically react w/ water & gases in the atmosphere. Rate @which this occurs depends on the minerals being weathered & climate (temp. & precip.) Types: Hydrolosis, Oxidation, Solution.

Mechanical weathering

The breakdown of rock by impact, abrasion, changes in temp. or pressure, or the activity of plants or animals. Types: Abrasion, Thermal stressing, Unloading, Wedging. (Also called physical weathering)

Hydrloysis

The breaking down of a mineral when it reacts w/ water. (Chemical weathering)

Oxidation

The addition of oxygen to a mineral or the loss of electrons from atoms in the minerals. (Chemical weathering)

Solution

When minerals r completely dissolved in water. (Chemical weathering)

Abrasion

Where rock is broken down when other rocks strike against it or when rocks or sediments r drug over it by water, wind, or ice. (Mechanical weathering)

Thermal stressing

When rock goes thru abrupt changes in temp. When the sun heats rock it expands, when the rock cools it contracts. If this occurs repeatedly, the shrinking & swelling of the rock eventually breaks it apart. (Mechanical weathering)

Unloading

Where the rock formed deep w/in the crust expands & cracks as it's brought 2 the surface. This happens b/c the rock is formed @high pressures due to the weight of the rock on top of it. As the rock's brought to the surface weight of the overlying rock decreases, allowing it 2 expand. (Mechanical weathering)

Wedging

Where the rock's pried apart by water freezing or salt precipitating w/in cracks in the rock or plants taken root w/in the cracks. (Mechanical weathering)

What is a sedimentary rock?

Composed of consolidated rock fragments or organic remains, or precipitated minerals.

How do u classify a sedimentary rock?

By composition & texture. Major types--> Detrital & biochemical rocks.

How r sedimentary rocks formed?

By lithification of sediments.

Lithification

Occurs where sediments r buried, compacted, & cemented 2gether.

Whats sedimentary rock composed of?

lithic fragments (bits of rock), organic matter (plant & animal residue), or minerals produced by evaporation or chemical precipitation.

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