Ch. 6 notes
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This 2 page Class Notes was uploaded by Jamila Ruffin on Tuesday February 2, 2016. The Class Notes belongs to GEO 101 at University of Alabama - Tuscaloosa taught by Laura Whitaker in Spring2015. Since its upload, it has received 7 views.
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Date Created: 02/02/16
Geo. Ch. 6 Sedimentary rocks rocks formed near or at the surface of Earth by cementing together loose grained that have been produced by: 1. Physical or chemical weathering of preexisting rocks 2. Precipitation of minerals from water 3. Growth of masses of shellproducing organisms What is weathering? The process of forming sediment Also, the physical breakdown and chemical alteration of rock at Earth’s surface Parent material: rock being weathered Types of weathering: Physical: without altering the chemical composition of the rocks Chemical: chemical reactions occur that change he composition of the rock Physical Weathering is the breaking of rocks into smaller pieces How does this happen? Frost wedging expansion of water in cracks by freezing, wedging the rock apart Unloading rocks expand and fracture in large sheetlike layers Thermal expansion and contraction heating/cooling of a rock’s surface Biological activity cracking and expansion of rocks Chemical Weathering is when air and water chemically react with rock to alter its composition and mineral content. Includes dissolution, hydrolysis, and oxidation Dissolution the dissociation of a mineral into its constituent ions as it dissolves in water Hydrolysis water reacts with a mineral to form a new mineral with water as a part of the crystal structure Oxidation the chemical reaction of a mineral with molecular oxygen Factors affecting Rates of Weathering: 1. Surface area fractures in rock 2. Rock composition calcite dissolves in weekly acidic solutions 3. Climate chemical weathering most effective in warm, moist climates Greater surface area= faster weathering because more of the rock is exposed What happens with the rocks that have been weathered? 1. Stay at surface, evolve and change into soils 2. Get buried and change into sedimentary rocks Soil a combination of rock or sediment that has been modified by physical/chemical weathering; AND has reacted with organic matter from plants and animals remains and forms humus *Humus is the most important substrate in soil that supports the growth of plants Sedimentary Rocks when weathered material becomes stuck together, the material is laid out into layers and buried Five steps in forming sedimentary rocks: 1. Weatheringphysical breakdown and chemical alteration of rock at Earth’s surface 2. Erosion soil and rock are removed from earth’s surface by wind, water flow, ice 3. Transportation 4. Deposition 5. Lithification the deposited material compacts into and entity Four groups sedimentary rocks based on their origin: 1. Clastic sedimentary rocks *ex sandstone 2. Biochemical sedimentary rocks *exchert 3. Organic sedimentary rocks *exlimestone 4. Chemical sedimentary rocks Sediment structures are the places where the sediments/rocks were transported to and laid into layers *Examples Bedding planes, crossbedding, ripple marks, and mud cracks Definitions: 1. Bed a single layer of sediment with a recognizable top and bottom 2. Bedding plane the boundary between two beds 3. Strata several beds together 4. Stratification the overall arrangement of sediment into a sequence of beds 5. Stratigraphic formation sequence of strata that is distinctive enough to be traced across a large area 6. Geologic map shows distributions of formations
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