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Lecture 9

GEOG 1120 Lecture 9: Weathering and SED Rocks

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GEOG 1120
John Martin

find more resources at Lecture 9: Weathering and SED Rocks I. Intro - Contain fossils. - Important economics: Soil, oil. - Rock cycle: A. Sedimentary rocks B. Metamorphic rocks C. Igneous rocks D. Sediments - Hardness: Hard rocks will weather slowly, soft minerals will weather quickly due to solubility and oxidation potential (Felsic oxides very fast). - Silicates can be summarized using Bowen's DSI (Olivine weather very quickly, Quartz the strongest). II. Mechanic Weathering - Physical breakdown of rocks. 1. Frost Wedging - requires water and temperature of zero (once there is a crack in the rock, water gets in and freezes). 2. Root Wedging 3. Unloading/Exfoliation - rock forms deep in Earth and in under pressure and when it expands, it results a fracture. - Do not move the rocks, they breakdown on their own. find more resources at find more resources at - When they physically weather, they rare angular shape. - The process of rock breakdown cannot be stopped. III. Chemical Weathering - Chemical breakdown of rocks. 1. Dissolution - some minerals are soluble and dissolve in water. => Ex: Halite dissolves quickly but rocks do dissolve in water slowly. => Halite is the most susceptible to dissolution. 2. Oxidation - most commonly Fe(2+) with O and H2O to form Fe(3+). => The Oxides are the most susceptible to oxidation. 3. Hydrolysis - results in the production of ions, give it's dull appearance. - Mafic rocks cannot be stopped from rusting. - Rates of Weathering: => Three main factors: A. Mineralogy B. Climate C. Process find more resources at find more resources at IV. Erosion - Weathering => doesn't move; Erosion => moving the pieces once they break down, transport of weathered materials. - Erosion Agents: 1. Rivers => Size: small to medium => Can only carry small rocks => Sorting: sorted (good at sorting) => Shape: rounded 2. Glaciers => Size: large => Not sorted, they just move them around => Shape: angular 3. Wind => Size: tiny => Not very sorted => Shape: round 4. Landslides => Size
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