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ECU GEOL 1500 - Sedimentary Rocks - Notes - Fall 2014

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“Weathering-Erosion-Transport-Deposition Cycle” ↓“Multiple Sedimentary Environments”<http://en.wikipedia.org/wiki/Cementation_(geology)>B. CompositionV. Composition and Classification of Chemical-Biochemical Sedimentary Rocks{Also referred to as Chemical Inorganic-Chemical Organic Sedimentary Rocks}B. CompositionD. Mudcracks – See top part of diagram above ↑ + Photo below ↓C. “Superposition and Crosscutting Illustrated and Animated”SEDIMENTS AND SEDIMENTARY ROCKS[For the WEB Site visuals below that end in “jpg”, you will/may have to “copy and paste” these rather than click]I. Processes of Weathering-Erosion-Transport within the Rock Cycle as a Source of Sediment“The Rock Cycle” <http://imnh.isu.edu/digitalatlas/geo/basics/diagrams.htm>A. Weathering1. Mechanical W. = Physical Disintegration of minerals and rocks into smaller pieces.2. Chemical W. = Decomposition of minerals and rocks into new substances/minerals.B. Erosion (by water, wind, ice, or gravity)C. Transport (by water, wind, ice, or gravity)D. Deposition/Sedimentation or Precipitation of weathered and eroded and transported material “Weathering-Erosion-Transport-Deposition Cycle” ↓Sediments are composed primarily of 3 major minerals, which are the stable by-products of long-term weathering and erosion at the Earth’s surface of all Igneous rocks, Metamorphic rocks, and pre-existing Sedimentary rocks. These 3 minerals are: QUARTZ, CLAY MINERALS, and CALCITE.II. Thus, Sedimentary Rocks are rocks that form from fragments and from dissolved ions derived from pre-existing rocks that have been weathered, eroded, transported, and deposited as Detrital/Clastic Sediments or precipitated as Chemical-Biochemical Sediments. “Multiple Sedimentary Environments” III. Lithification A. Lithification is the process whereby unconsolidated sediment is converted to sedimentary rock. The major sub-processes of Lithification include: See Diagram below1. Cementation - Usually occurs in medium- to coarse-grained sediments. Common cements include: silica, calcium carbonate, iron oxides, dolomite <http://en.wikipedia.org/wiki/Cementation_(geology)> 2. Compaction - Weight from overlying sediments causes sediments to de-water and compact. Usually occurs in fine- to very fined-grained clays/muds as they become shales/mudstones.<http://en.wikipedia.org/wiki/Compaction_%28geology%29>IV. Composition and Classification of Clastic/Detrital Sedimentary Rocks (See Chart below and bring it to class)“Clastic Sedimentary Rocks” <http://hyperphysics.phy-astr.gsu.edu/HBASE/geophys/sedime.html>A. Characteristics - Weathered products/clasts of pre-existing rocks “Clastic Sedimentary Environments” 1. Always have clastic texture.2. Deposited when a stream or current loses velocity and gravity pulls material to bottom of stream channels, lakes, or oceans (Physical Controls)3. Record previous histories of individual particles (i.e., distance and number of cycles of transport, medium of transport, possibly composition of original source rock of clasts). B. Composition1. Major Minerals a. QUARTZ b. CLAY MINERALS (e.g., Kaolinite, Illite, Smectite)2. Minor but Important Minerals and Mineral-like Components a. Feldspars c. Micas b. Lithics (Rock Fragments) d. Iron Oxides (mostly hematite & limonite as cements)2C. Classification1. Primary Criterion = Particle Size of Clasts 2. Secondary Criteria = Particle Shape and Mineral Composition of Clasts “Breccia versus Conglomerate” Breccia ConglomerateGeneral Classification Chart for Clastic or Detrital Sedimentary RocksPrint and Bring this Chart to Class with you!“Dr. Harper’s Sedimentary Rock Index Photos and Description” <http://core.ecu.edu/geology/harper/Sedimentary/Sedimentary_new.cfm>3Back-Up ChartV. Composition and Classification of Chemical-Biochemical Sedimentary Rocks (See Chart below and bring it to class) {Also referred to as Chemical Inorganic-Chemical Organic Sedimentary Rocks}A. Characteristics - Produced by inorganic precipitation or organic (biochemical) precipitation of skeletal material in organisms with exoskeletons (hard shells). “Chemical Sedimentary Environments” 1. May have nonclastic (interlocking grains) or clastic texture.2. Precipitated from lake and ocean waters and is controlled by pH, temperature, concentrations of ions in solution, evaporation rates, and organic activity (Chemical and Biochemical Controls)3. Record environmental conditions at time and place of accumulation (e.g., climate, water depth, temperature, salinity, and pH)B. Composition1. Major Mineral a. CALCITE2. Minor but Important Minerals and Mineral-like Components a. Dolomite d. Halite b. Silica (SiO2)/Microcrystalline Quartz e. Organic Matter c. Gypsum C. Classification1. Primary Criterion = Mineral Composition2. Secondary Criterion = Texture (mostly for different types of Limestones)“Dr. Harper’s Sedimentary Rock Index Photos and Description” <http://core.ecu.edu/geology/harper/Sedimentary/Sedimentary_new.cfm>4Print and Bring this Chart to Class with you!Back-Up Chart “Key to Classification of Sedimentary Rocks” <http://csmres.jmu.edu/geollab/Fichter/SedRx/basickey.html>VI. Note that the term, CARBONATES, is used to refer to all Limestones and Dolostone because these two rock types are composed entirely of the Carbonate minerals, Calcite and Dolomite, respectively. Also, the term, EVAPORITES, is used to refer to Rock Salt and Rock Gypsum because both of these Chemical Rocks form by the process of evaporation.VII. Sedimentary Structures Found in Sedimentary Rocks (some of these can be used to tell us about paleo- environmental conditions and top-bottom criteria) A. Bedding - Defined by differences in grain size and/or composition- Colour - See Diagram and Photo below ↓5B. Crossbedding (only in Clastic/Detrital Sedimentary Rocks) – See Diagrams below ↓6C. Graded Bedding (only in Clastic/Detrital Sedimentary Rocks) – See bottom portion of the large diagram below ↓ and the diagram immediately below ↓7D. Mudcracks – See top part of diagram above ↑ + Photo below ↓E. Ripple Marks (only in Clastic/Detrital Sedimentary Rocks) - 8See the large diagram above ↑ and ones immediately below ↓ “Preserved Current Ripples” “Modern Wind Current Ripples”1.


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