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GEOL 105 Test 3 Notes

by: Alaina Notetaker

GEOL 105 Test 3 Notes Geology 105

Alaina Notetaker
University of Louisiana at Lafayette
GPA 3.5

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About this Document

Covers: Chapter 6 - Weathering, Erosion, and Soil Chapter 7 - Sedimentary Rocks
Geology and man
Elisabeth Boudreaux
weathering, erosion, Soil, sedimentary, Rock, Geology
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This 7 page Bundle was uploaded by Alaina Notetaker on Tuesday September 20, 2016. The Bundle belongs to Geology 105 at University of Louisiana at Lafayette taught by Elisabeth Boudreaux in Spring 2016. Since its upload, it has received 5 views. For similar materials see Geology and man in Geology at University of Louisiana at Lafayette.

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Date Created: 09/20/16
Weathering, Erosion, and Soil • Weathering and Erosion ⿞Weathering- little to no movement ‣ Process of breaking down rocks and minerals • Physical (mechanical) weathering ⿞Creates dramatic features ‣ Breaks rocks into smaller pieces ‣ Same composition ‣ Increases surface area ⿞Frost Wedging ‣ Water freezes, expands 9%, cracks rocks ‣ Talus- accumulation of angular fragments ⿞Exfoliation/Pressure Release ‣ Sheet joints form parallel ⿞Thermal expansion and contraction ‣ When exposed to the same heat, Quartz expands about 3x as much as feldspar ⿞Activities of Organisms ‣ Animals • Crushing • Burrowing ‣ Plants • Crush • Roots widen cracks ⿞Growth of Salt Crystals ‣ Hot, arid regions ‣ Coastal regions • Chemical weathering ⿞Changes in the chemical composition of minerals and rocks that are unstable at the Earth's surface ⿞Solution (dissolution) ‣ Limestone ⿞Oxidation- rust ‣ Rust forms when oxygen reacts with minerals which contain iron ⿞Hydrolysis ‣ Acidic water reacts with rock forming minerals such as feldspar ‣ H+ (hydrogen ions) and OH- (hydroxyl ions) displace ions in a mineral ‣ Changes feldspar to clay ‣ Quartz and other silicate-rich minerals are more stable and are generally unaffected • BOTH WORK TOGETHER • Spheroidal Weathering ⿞Rounded boulders ‣ Factors in weathering • Climate ⿞Water and temperature ‣ Reaction 2x increase with each 10degreeC increase in temperature • Time ⿞More time = more weathering • Organisms ⿞Plants ⿞Animals ⿞Bacteria • Mineralogy ⿞Bowen's Reaction Series ‣ Why study weathering? • Obtain equilibrium with a new environment ⿞EX: igneous rocks- form under higher pressure, temps ‣ Surface conditions= low pressure and temperatures ‣ Weathering at the surface= equilibrium ‣ Weathering and Resources • Aluminum (from bauxite- aluminum ore) • Clays ⿞Kaolinite- used in cosmetics, ceramics, toothpaste, whitening agents, etc. ⿞Bentonite- used in drilling muds, landfill liners, cleaning agents, binders, etc. ⿞Erosion ‣ removal of weathered material by water, wind, ice ⿞Parent material- the original rock before any weathering has taken place • What is soil and how does it form? ⿞Soil is a mixture of weathered rock material, water, air, and organic matter ‣ 45%mineral matter ⿞Soil Horizon ‣ Soil horizons differ in texture, structure, composition, and color ‣ The soil profile • O Horizon ⿞Just a few centimeters ⿞Organic matter- plant remains, humus (decomposed leaf and grass litter) • A Horizon ⿞Top soil ⿞Intense biological activity- plants, roots, fungi, bacteria, worms ⿞Mostly clays and chemically stable minerals like Quartz • E Horizon ⿞Zone of leaching • B Horizon ⿞Subsoil ⿞Less organic matter, fewer organisms ⿞Zone of accumulation ‣ Caliche • Minerals are leached from A horizon • Accumulate in the B horizon • C Horizon ⿞Partially altered bedrock grading down to unaltered bedrock ⿞Little organic matter ⿞Factors controlling soil formation ‣ Climate • Most important! • Arid vs. Humid regions = different color/thickness ‣ Parent material • Grain size • Composition ‣ Ex. Quartzite = thin soil layer ‣ Ex. Granite = thicker soil layer ‣ Organic Activity ‣ More organisms= more soil • Plants • Animals • Fungi, algae, bacteria ‣ Topography • Relief- the difference in elevation between high and low points • Slope ⿞Slope angle- steep slopes erode faster- little or no soil ⿞Slope direction- dies it face north? South? ‣ North facing slopes receive less sunlight, cooler temps, different vegetation ‣ Time • More time = more soil accumulation ‣ Climate and Vegetation • Rate of reaction increases two-fold with each 10degreeC increase in temperature • Hot, humid regions will have more intense chemical weathering and more amounts of soil overall ⿞Expansive Soils ‣ Soils with clay minerals can expand when wet and shrink when dry ‣ Expands by 6% or more ‣ Bad for roads, construction, foundations, sidewalks, etc. ⿞Soil degradation erosion ‣ Removing vegetation, plowing, grazing, etc. ‣ Destruction of rainforest or other vegetation cover increases erosion ‣ Erosion • Contour plowing • Rill erosion • Ravines ‣ Degredation • Chemical Deterioration ⿞Fertilizers ⿞Crop rotation • Salinization and pollution • Compaction • Arches National Park ⿞Differential weathering and erosion ⿞Uplift due to salt rising to the surface ⿞When rocks are uplifted, they are more exposed to erosion Chapter 7 • Sedimentary Rocks ⿞Importance of Sediments ‣ Coal ‣ Oil ‣ Natural gas ‣ Iron ‣ Aluminum ‣ Water ‣ History book to the geologist! • Fossils and environment ⿞Sediment ‣ Detrital Sediments ‣ Chemical Sediments ⿞Sedimentary Rock ‣ Thin layer, barely 5% of the Earth's crust ‣ 75% of exposed rocks on Earth ‣ Layering or stratification: most obvious feature of sedimentary rocks ‣ Weathering, Erosion/Transportation (running water, wind, glacial ice), Deposition (in various environments such as rivers, deltas, beaches, Lithification (compaction, cementation) ⿞Sediment Transport ‣ Grain size • Wind- find grained (sand and smaller) • Ice (glaciers)- all sizes • Water (waves/marine currents/running water)- all sizes ‣ Driven by pull of gravity • Water • Wind • Ice ‣ 10 billion tons of detrital sediment is deposited into the world's oceans annually ‣ Detrital Sediment- transported some distance from its source • Rounding (abrasion)- wears away any sharp corners and edges • Sorting- grains separated by size, shape, or density ‣ Chemical sediment- forms in the area where it is deposited ⿞Sediment Deposition ‣ Can be carried a considerable distance from its source ‣ Depositional environment • Continental • Transitional • Marine ⿞Lithification of Sediments ‣ How does sediment turn into rock? • Lithification by ⿞Compaction ⿞Cementation ⿞Crystallization • All processes remove pore space between the grains ⿞Types of Sedimentary Rocks ‣ Detrital • Particles derived from parent material ⿞Fragments of igneous, metamorphic, or other sedimentary rocks • Classic texture- composed. Of fragments (coasts) • Classified by size (name modified by composition) • Types ⿞Conglomerates (rounded) ⿞Breccias (angular) ⿞Sandstone ‣ Sand-sized particles ‣ Classified by material content • Quartz sandstone • Arkose ⿞Siltstone- silt sized particles ⿞Mudstone- silt and clay ‣ Shale- mudstones and clay stones that break along parallel planes ⿞Clay stone- clay sized particles ‣ Low energy • Lake, lagoon, flood plains, deep marine ‣ Chemical (inorganic) and Biochemical (organic) Weathering • Products of chemical weathering (solution) ⿞Precipitated by chemical reactions (inorganic) OR ⿞Metabolism of organisms (organic) • Most common chemical sedimentary rocks: CARBONATES (most often calcite- CaCO3) ⿞Limestone is made of CaCO3, but it can be inorganic OR organic • Limestones ⿞Inorganic ‣ Very fine-grained, crystalline • Calcite • Bahamas and Florida • Caves ⿞Biochemical Limestones ‣ Chalk • Inorganic ⿞Water evaporates ‣ Halite ‣ Gypsum ⿞Chemical ‣ Chert- micro crystalline silica • Can occur as irregular masses (chemical) • Can occur as distinct layers made of microscopic shells from organisms (biochemical) ‣ Also called flint (black rom organic matter) or jasper (red from iron oxide) • Calcium-Carbonate vs. Silica-Secreting Organisms ⿞Calcium carbonate oration is controlled by the CCD (carbonate compensation depth) ‣ Actual depth depends on pH, temperature, salinity levels, and pressure levels ‣ Below this point, CaCO3 dissolves faster than it accumulates • Coal formation ⿞Coal = biochemical sedimentary rock ‣ Peat -> Lignite -> Bituminous Coal -> Anthracite ⿞Coal seams • Sedimentary Facies ⿞Sequence of rocks that form at the same time in different deposition all environments ‣ River = conglomerates and breccias ‣ Beach = sandstones ‣ Near shore/shelf = Shales ‣ Deeper marine = limestones ⿞Facies vs. Sequence ‣ FACIES- Sediment deposited at the same time in adjacent or neighboring environments ‣ SEQUENCE- Transgression/Regression • Layers deposited at different times in one location that can show changes in sea level • Transgression ⿞Deeper water sediments over shallow water sediments • Regression ⿞Shallow water sediments over deeper water sediments ‣ Transitional Environments • Found along the edges of continents ⿞Where land meets ocean ⿞Delta ⿞Beach ⿞Tidal Flat ⿞Barrier islands ⿞Lagoons ⿞Swamps ‣ Reading the story in sedimentary rocks • Sedimentary structures ⿞Strata or beds ‣ The most characteristic feature of sediments!! ‣ Principle of original horizontality ‣ Principle of Superposition • Top (youngest) -> Bottom (oldest) ⿞Cross-bedding ‣ Currents • Wind • Water ⿞Graded bedding ‣ The largest grains are deposited first ‣ As you move up a layer, the pieces get smaller and smaller ⿞Ripple marks ‣ Symmetric ‣ Asymmetric ⿞Mudcracks ‣ Occurs when clay-rich sediments dry out and shrink • From Sedimentary Rock ⿞Determining the environment of deposition ⿞Paleo-stuff: paleogeography, paleocurrent, paleontology, paleomagnetism • Fossils- traces or remains of ancient organisms ⿞Body fossils vs. Trace fossil ⿞Fossilization ‣ Unaltered • Unaltered remains ex: preserved in ice • Hair has even been preserved in some of the specimens preserved in ice • Other ways: drying in arid environments, encasement ‣ Altered • Replacement- original minerals in bone can be dissolved and replaced • Permineralization- spaces filed • Altered remains ex: carbonization • Hydrogen and oxygen is driven off by heat/pressure: Carbon is left behind • Other ways: permineralization, replacement, molds, and casts • Older = less likely to be unaltered ‣ What else can be preserved? • Coprolites • Ichnofossils (track or trace) • Casts- when material fills up a track or trace • What information can we get from these? • Paleontology- the study of fossils ‣ Rock Formations • Formation ⿞Large enough to be mappable ⿞Distinguishable from surrounding formations ⿞Can be composed of more than one bed • Contact ⿞Economic Importance ‣ Petroleum and natural gas- made from the remains of micro-organisms • Source rock • Reservoir rock ‣ Uranium ‣ Banded Iron Formation- chert and iron oxide minerals


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