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study guide exam 2

study guide exam 2 - Holt 1 Geology Test 2 Chapters 5-8...

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Holt 1 Geology Test 2: Chapters 5-8 Sedimentation Chapter 5 Sediments are produced on earth’s surface as a result of weathering or erosion. They are transported and become sedimentary rocks once they come to rest. Examining these rocks can give us clues as to what these ancient sedimentary environments were like. Sediments and sedimentary rocks formed from them are produced by the processes of the rock cycle Weathering (usually of mountains) Erosion Transportation Deposition (sedimentation) Burial and compaction Diagenesis - refers to physical and chemical changes – including heat, pressure, and chemical reactions- by which sediments buried within sedimentary basins are lithified, or converted into sedimentary rocks. OR basically the formation of the sediments into solid rock. Types of sediments Clastic Sediments Siliciclastic sediments – great majority of clastic sediments, they are produced by the weathering of rocks composed largely of silicate minerals. Sandstone, silkstone Chemical Sediments – form at or near their place of deposition, usually from seawater. Example – the evaporation of seawater often leads to the precipitation of gypsum or halite. Other chemical sediments are limestone and rock salt. Biological Sediments – also form near place of deposition, but are the result of mineral precipitation within organisms as they grow. After the organisms die, their mineral remains, such as shells, accumulate as sediment. Sometimes shells can be transported, further broken up, and deposited as bioclastic sediments. Dr. Kelley simplified biological sediments as simply – critters make limestone or they secrete shells.
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Holt 2 Current strength and distance of transport affect… Size of clastic particles Faster currents can move larger particles Finer grains are carried further Sorting of clastic particles Heavier grains settle faster, As the current slows larger particles are settling Rounding of clastic particles Also known as abrasion. There is more abrasion (rounding edges, reducing particle size) in faster currents, but lots of abrasion is usually associated with longer distances of transport. The sight of sediment deposition is called the sedimentary basin Depressions filled with thick accumulations of sediment Rift Basins Deep, narrow, and long, with thick successions of sedimentary rocks and extrusive and intrusive igneous rocks. These basins involve the breaking of crust. Thermal subsistence basins – formed when rifting has led to seafloor spreading and plates are moving apart from each other- the cooling of the lithosphere increases its density, so its sinks below sea-level, forming the basin. Because cooling of the lithosphere is the main process in making them, they are called thermal subsistence basins.
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