Weathering and Sedimentation: A Geology Perspective - Prof. Robert E. Behling, Study notes of Geology

Download Weathering and Sedimentation: A Geology Perspective - Prof. Robert E. Behling and more Study notes Geology in PDF only on Docsity! GEOL 101 Lecture 7 Weathering, Sediments S. Kite Photo Bear Butte S.P., SD Rock Cycle Weathering Ch. 5 Physical – (later) Chemical – (now) Bowen’s Reaction Series vs. Goldich’s Weathering Series for sand-size grains under surface conditions Hi Lo T Least Stable Most Stable Weathering of Orthoclase Feldspar Mineral in Rock + Weak Acid = Clay + Ions in Solution (Weathering Products) • Clays Are Resistant Minerals Where Is Acid Coming From? CO2 + H20 = H2CO3 Carbon Dioxide + Water = Carbonic Acid Where Is CO2 Coming From? Plant Respiration, Burning Fossil Fuels K-Feldspar = Orthoclase Clastic (Sedimentary) Rocks • Particle Size (= Texture) • Wentworth (Geologists’) Scale –Gravel >2 mm –Sand 0.062 mm to 2 mm –Silt 0.004 mm to 0.062 mm –Clay <0.004 mm Gravel • Granules 2 to 4 mm • Pebbles 4 to 64 mm • Cobbles 64 to 256 mm • Boulders >256 mm (~ 10 in) • Gravel is a Particle Size, NOT a Rock Type Maturity Immature Sediments Mature Sediments Facies Maturity • What Happens to Rock Fragments as They are Transported • Increase In Resistant Minerals (e.g. Quartz) vs. Unstable Minerals • Increase In Rounding • Increase In Sorting Mature Immature Rounded Angular Mature Immature ~ 100% Quartz Mixed Composition Quartz Sand Plag Px Volc Mature Immature Well Sorted Poorly Sorted Types Of Clastic Rocks • Based on Texture & Mineralogy • Classification Reflects History of the Rock Very Coarse-Grained Rx With Lots of “Gravel” • Breccia: Angular Clasts • Conglomerate: Rounded Clasts • Which is Most Mature?... 60 % Qtz, 35% F-spar, 5% Lithics: Arkose 100 % Qtz 100 % F-spar 100 % “Lithics” Arkose Greywacke Lithic Sandstone Quartz Sandstone 50% 75% 95% Quartz Sand Plag Px Volc Which Sandstone is Most Mature? ~ 100% Quartz Mixed Composition Qtz Sandstone Greywacke Quartz Sandstone: Resistant Well-Rounded Quartz Grains Last Two Rocks 100 % Qtz 100 % F-spar 100 % “Lithics” Arkose Greywacke Lithic Sandstone Quartz Sandstone 50% 75% 95% Qtz Sandstone Greywacke ~ 100% Quartz Mixed Composition 100 % Qtz 100 % F-spar 100 % “Lithics” Arkose Greywacke Lithic Sandstone Quartz Sandstone 50% 75% 95% Fine-Grained Clastic Rx • Siltstone Silt = Grit or Flour Size (Usually Quartz) • Shale –Layered Clay Minerals – ( “Slate” to Local Miners) • Mudstone –Massive Silt & Clay Review 3 Basic Types of “Sed Rx” • Clastic ( = Detrital) –Made of Rock Fragments • Biochemical –Formed by Organisms • Chemical –Precipitated from Solution Biochemical Sedimentary Rx Brachiopods in Limestone Pendleton County, WV www.wvgs.wvnet. edu/www/museum/ musefoss.htm • Example: Limestone • Calcite Shells or Reefs - Biochemical Sediments • Fossils Common Biochemical Sedimentary Rx • Plant Fragments – Wet Low-Oxygen Environments - Little Decay – Compaction, Breakdown of Volatile Organic Compounds: Increase in Carbon • Peat • Lignite • Bituminous Coal –All Coal in WV, MD,Western PA Sediment Sed Rock In cr . P re ss ur e & T em p. Plant Fragments - Peat - Lignite - Bituminous Coal Plant Frags. Peat Lignite Coal Horizontal Bedding: U.S. Rt. 19, Powell Mtn., WV J.S. Kite Photo Cross-Bedding Photo by Gary Fleeger, Pa. Geol. Surv. Loyalhanna Formation, SW Pennsylvania formed by tidal currents Sedimentary Structures • Graded Bedding Sand Silt Sand Silt Sand Silt etc. Sedimentary Structures • Ripple Marks agcwww.bio.ns.ca/.../images/ripple_marks_modern.jpg Photo: Robert Grantham, Nova Scotia Museum of Natural History Sedimentary Structures • Mud Cracks www.eos.duke.edu/ss/ss055.gif mudcracks in old pond. Sandhills of NC. Photo © Duncan Heron • Fossils More Sedimentary Structures Trilobites • Trace Fossils More Sedimentary Structures Dimetrodon Tracks, Ritchie Co. WV Last two images are fron the Mini-Museum of Geology & Natural History http://www.wvgs.wvnet.edu/www/museum/museum.htm Diagenesis: Define • Up to 150oC (200oC in Text Book) & 1 Kb Pressure • What’s a Kb?