Chapter3 - Chapter 3 Sedimentary Rocks Rivers that flow into the Gulf of Mexico through Alabama and other Gulf Coast states are typically brown

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33 Chapter 3 Sedimentary Rocks Rivers that flow into the Gulf of Mexico through Alabama and other Gulf Coast states are typically brown, yellow-orange or red in color due to the presence of fine particulate material suspended within the water column. This particulate material is called sediment , and it was produced through the erosion and weathering of rocks exposed far inland from the coast (including the Appalachian Mountains). Sediment transported by rivers eventually finds its way into a standing body of water. Sometimes this is a lake or an inland sea, but for those of us that reside in southern Alabama, it is almost always the Gulf of Mexico. When rivers enter standing bodies of water (e.g., the Gulf), the sediment load that they are carrying is dropped and deposition occurs. Usually deposition forms more or less parallel layers called strata . Given time, and the processes of compaction and cementation, the sediment may be lithified into sedimentary rock . It is important to note that deposition of sediment is not restricted to river mouths. It also occurs on floodplains surrounding rivers, on tidal flats, adjacent to mountains in alluvial fans, and in the deepest portions of the oceans. Sedimentation occurs everywhere and this is one of the reasons why your humble author finds sedimentary geology so fascinating. Sedimentary rocks comprise approximately 30% of all of the rocks exposed at the Earth's surface. Those that are composed of broken rock fragments formed during erosion of bedrock are termed siliciclastic sedimentary rocks (or clastic for short). Sedimentary rocks can also be produced through chemical and biochemical deposition. These processes give Figure shows a schematic diagram of a delta complex prograding over top of shallowly dipping strata. From: LeConte, J., 1905. Elements of Geology. D. Appleton and Co., New York, NY, 667p.
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Chapter 3: Sedimentary Rocks 34 rise to a variety of sedimentary rocks including limestones, cherts and the evaporites. Organic sedimentation, which involves vegetation, is a special form of biochemical sedimentation. Plant-rich sediment can accumulate to form peat and various types of coal. Chemically and biochemically produced sediment is frequently deposited in the exact same place it is produced. This is known as in situ deposition . However, siliciclastic sediment can be transported a long distance from its source (the area where weathering and erosion of bedrock is occurring), through the action of wind, water and ice before it is finally deposited. As a result, siliciclastic sedimentary rocks frequently retain physical evidence of sediment transport in the form of cross-stratification or other sedimentary structures. Sedimentary rocks are classified on the basis of their origin, mineralogy and texture. In
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This note was uploaded on 02/04/2012 for the course GLY 111 taught by Professor Haywick during the Fall '11 term at S. Alabama.

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Chapter3 - Chapter 3 Sedimentary Rocks Rivers that flow into the Gulf of Mexico through Alabama and other Gulf Coast states are typically brown

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