Geology 101 Section 2 Notes

Geology 101 Section 2 Notes - Sedimentary Rocks: Form on...

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Sedimentary Rocks: Form on the surface of the earth. Formation of Sedimentary Rocks 1. Weathering: turns big rocks to small rocks a. Freezing and thawing of water b. Tectonic movements c. Chemical (some rocks can dissolve with water) d. Tree Roots pry rocks apart e. Burrowing animals (groundsquirrels) 2. Erosion 3. Rainfall causes the sediments to be moved from high to low ground. Through wind, water, ice(glaciers), and landslides 4. Deposition a. Sediment settles out somewhere as loose sediment 5. Lithification: The process of turning sediments into rock a. The sediment is compacted Types of Sedimentary Rocks 1. Biogenic (bioclastic): Dead animals (plankton, marine life, Shells, algae) form mineral deposits 2. Chemical Sediments (evaporates): Salt. 3. Clastic Sedimentary Rocks: formed by bits and pieces of other rocks Features of clastic sedimentary rocks 1. Composition of the clasts gives us the composition of the source area 2. Size of the particles tells us how the sediment was eroded. a. Fast rivers can carry larger particles that slow rivers. Particle size carried by a river decreases as the velocity of the river decreases. Particle size is related to the energy of the transporting medium. (wind – water – ice) 3. Degree of sorting. Poorly to well sorted. A river would sort sediment much more uniformly than a glacier would. This determines the type and constancy of the transporting medium. 4. Rounding. Angular sediments to rounded sediments Features of Biogenic/Bioclastic Sedimentary Rocks 1. Most are produced in shallow saltwater near the equator. 2. Forms the main mineral Calcite CaCO 3 Chemical Sediments 1. Most common evaporate is salt: Halite Nacl 2. Gypsum CaSO 4 * 2H 2 O 3. Formed in hot arid deserts Layering in sedimentary rock is caused by changes in the environment. -water velocity and deposition: If you have coarse grains in the layer then the water is fast and carrying away all of the fine grains. Finer grain material is slower.
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-waterfalls cause large poorly sorted conglomerates because the speed goes from fast to slow immediately. Blackboard Picture: identify the types of sedimentary rock that will form 1-Clastic-angular, poorly sorted, conglomerate. Composition = mountains 2-clastic- well sorted, rounded, conglomerate, siltstone. Composition = More variable 3-evaporite 4-clastic-Big clasts, poorly sorted, angular. Composition = Mountain 5-Clastic-well sorted, sand (shale), well rounded. Composition = more variable. More fossils 6-clastic, sand (waves keep silt and clay from depositing on the beach), very well sorted, sandstone 10-Biogenic-(grow away from a source of castic sediments)-Limestone The Mediterranean Sea: At one point there was a large DEEP desert where the Mediterranean sea is. This is proved by the thick layer of evaporate sediments located on the floor (gypsum and halite crystals) Sand Dunes: crossbeds-gentle angle is the bottom and the higher angle is the top
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This document was uploaded on 10/28/2011 for the course GEOL 101 at UNC.

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Geology 101 Section 2 Notes - Sedimentary Rocks: Form on...

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