GEOL 101 Lecture 7. Weathering, Sediments. Rock Cycle. Least Stable. Most Stable. Weathering Ch. 5. Physical. Chemical

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1 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 Least Stable Hi T Lo Most Stable

2 Weathering of Orthoclase Feldspar Mineral in Rock + Weak Acid = Clay + Ions in Solution (Weathering Products) Clays Are Resistant Minerals Where Is Acid Coming From? CO 2 + H 2 0 = H 2 CO 3 Carbon Dioxide + Water = Carbonic Acid Where Is CO 2 Coming From? Plant Respiration, Burning Fossil Fuels K-Feldspar = Orthoclase

3 Orthoclase Weathering 2 KAlSi 3 O H 2 CO H 2 O = Al 2 Si 2 O 5 (OH) H 4 SiO K HCO 2-3 Orthoclase Weathering 2 KAlSi 3 O H 2 CO H 2 O Orthoclase + Acid + Water Orthoclase Weathering Products Al 2 Si 2 O 5 (OH) H 4 SiO K HCO 3 2- Kaolinite (Clay) + Silicic Acid & Ions In Solution

4 Sediment Loose Unconsolidated Particles of Solid Material (that Originate from the Weathering of Rocks, and are Transported by Water, Gravity, Ice, Air, etc.) Soil Earthy Materials that Support Life Out of Doors. (vs. Engineer's Definition: Any Earthy Materials) Dirt: Out-of-Place Soil Sedimentary Rocks Rocks made of Sediments 3 Basic Types of Sed Rx Clastic ( = Detrital) Made of Rock Fragments Biochemical Formed by Organisms Chemical Precipitated from Solution

5 Clastic (Sedimentary) Rocks Particle Size (= Texture) Wentworth (Geologists ) Scale Gravel >2 mm Sand mm to 2 mm Silt mm to mm Clay <0.004 mm Granules Pebbles Cobbles Boulders Gravel 2 to 4 mm 4 to 64 mm 64 to 256 mm >256 mm (~ 10 in) Gravel is a Particle Size, NOT a Rock Type Maturity Immature Sediments Mature Sediments Facies

6 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 Rounded Immature Angular Mature Immature ~ 100% Quartz Mixed Composition Plag Px Quartz Sand Volc

7 Mature Well Sorted Immature 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?...

8 Breccia Sorpresa Zone Breccia, Peru Candente Resource Corp. s/photogallery.asp Conglomerate Photo by Sean Flanagan /geos256/azgeology/ mrenwald/sedrx2.html Sed Rx Made Mostly of Sand Sandstone Names Based on Mineralogy Quartz (= Qtz) Feldspar (= F-spar) Other Rock Fragments (= Lithics)

9 Ternary Diagram Qtz 95% 75% F-spar 50% Lithics Sandstones Qtz 95% Quartz Sandstone Lithic Sandstone 75% F-spar Arkose 50% Greywacke Lithics Example: 60 % Qtz, 35% F-spar, 5% Lithics Qtz 5% Lithics 60% Qtz 35% F-spar F-spar Lithics

10 60 % Qtz, 35% F-spar, 5% Lithics: Arkose Qtz 95% Quartz Sandstone Lithic Sandstone 75% F-spar Arkose 50% Greywacke Lithics Which Sandstone is Most Mature? Quartz Sandstone: Resistant Well-Rounded Quartz Grains ~ 100% Quartz Mixed Composition Qtz Sandstone Greywacke Plag Px Quartz Sand Volc Last Two Rocks Qtz 95% Quartz Sandstone Lithic Sandstone 75% F-spar Arkose 50% Greywacke Lithics

11 Qtz Sandstone Greywacke ~ 100% Quartz Mixed Composition Qtz 95% Quartz Sandstone Lithic Sandstone 75% F-spar Arkose 50% Greywacke Lithics 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

12 Biochemical Sedimentary Rx Example: Limestone Calcite Shells or Reefs - Biochemical Sediments Fossils Common Brachiopods in Limestone Pendleton County, WV edu/www/museum/ musefoss.htm Biochemical Sedimentary Rx Incr. Pressure & Temp. Plant Fragments Wet Low-Oxygen Environments - Little Decay Compaction, Breakdown of Volatile Organic Compounds: Increase in Carbon Peat Sediment Lignite Sed Rock Bituminous Coal All Coal in WV, MD,Western PA Plant Fragments - Peat - Lignite - Bituminous Coal Plant Frags. Peat Lignite Coal

13 Biochemical Sediments Petroleum (Octane) Liquid Hydrocarbons Natural Gas (Methane) Gaseous Hydrocarbons Source Rock Coal Bed or Organic-Rich Shale Reservoir Rock Permeable (Limestone, Sandstone, Possibly Fractured Igneous Rk) Middle East Oil Fields Chemical Sedimentary Rocks Minerals Crystalize from Dissolved Ions in Solution Evaporites - Rock Salt (Halite: NaCl) shown Gypsum not shown Source:solstice02.tripod.com/ sum99/salt4.jpg

14 Chemical Sedimentary Rocks Replacment Dolomite Mg-Rich Sea Waters React w/ Calcite To Form MgCa(CO 3 ) 2 - Dolomite Dolomite = Mineral and Rock Chemical Sedimentary Rocks Replacment Silicification Dissolved Silica Precipitates (H 2 O In Xl Lattice) Geode: amethyst/images/5.jpg Concretion Chert Clovis Points human/archaeo/aspects/ _points.htm Sedimentary Structures Parallel Bedding

15 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 etc. Silt Sand Silt Sand Silt Sand

16 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 mudcracks in old pond. Sandhills of NC. Photo Duncan Heron More Sedimentary Structures Fossils Trilobites

17 More Sedimentary Structures Trace Fossils Dimetrodon Tracks, Ritchie Co. WV Last two images are fron the Mini-Museum of Geology & Natural History Diagenesis: Define Up to 150 o C (200 o C in Text Book) & 1 Kb Pressure What s a Kb?

18 Diagenesis: Examples Compaction Cementation Replacement Recrystalization Diagenesis: Compaction 50 m 10 \m 5 m? Metamorphism: Mineralogical and Structural Adjustment to Physical and Chemical Conditions Over 150 o C (200 o C) and 1 Kb Pressure

19 Study Suggestions Test Covers Plummer Text book CH Old Questions: Multiple Choice Test Questions from All Old Tests Sample Tests: Test 1: 2005: Slides: (Green); (Blue); (Gold); (White)