Sum11.208.rockssed - Lithification Sedimentary Rocks...

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Unformatted text preview: Lithification Sedimentary Rocks Sediments Weathering The sediments that make up sedimentary rocks are produced by: Mechanical & Chemical Weathering Deposition Transport Erosion Weathering Chemical Weathering Mechanical Weathering p.22 Mineral Stability Products of Weathering • Lithic (Rock) Fragments Common Products (granite, basalt, schist, etc.) • Dissolved Ions Occasional Products (Calcium, Potassium, Sodium, etc.) • Rust Minerals (Hematite, Goertite, etc.) • Clay Minerals Rare Products (Bentonite, Montmorillonite, etc.) • Residual Minerals (Quartz, Orthoclase, Muscovite, etc.) Erosion & Transport Water Wind Ice Gravity Deposition Lithification Cementation Sediment Typical Cement: •Calcite •Quartz Rock Rock Identification is based on: Sedimentary Rocks Identification Note: Use the same terms to describe sediments & sedimentary rocks. Only difference is lithification! • Composition What minerals make up the rock? • Texture What is the shape, size and orientation of the mineral grains that make up the rock? Major Difference: Crystalline vs. Clastic Types of Sedimentary Rocks Detrital Rocks Chemical Rocks Difference: Texture Detrital (Clastic Texture) vs. vs. Chemical (Crystalline Texture) Detrital Rock Composition Detrital Rocks • Lithic Fragments • Quartz • Clay Minerals • Fossil Fragments • Rust Minerals • Orthoclase • Muscovite / Biotite Detrital Rock Texture Clastic Texture • Grain Size • Grain Sorting • Grain Rounding • Sediment Maturity Grain Size Detrital Rock Names (Based Primarily on Grain Size) Gravel Sized: Conglomerate •Gravel 2mm •Sand 1/16 mm •Mud - Silt 1/256 mm •Mud - Clay Sand Sized: Sandstone Mud Sized: Mudstone Siltstone Shale Grain Roundness Sorting Angular Sub-Rounded Rounded Maturity Gravel Sized Detrital Rocks (Subdivided Based on Grain Roundness) Conglomerate (Well rounded to sub-rounded) Breccia (Angular) Mature • Well Sorted • Well Rounded • All Quartz Immature • Poorly Sorted • Angular grains • Mixed Composition including clay Sandstones Under a Scope Quartz Sandstone Lithic Sandstone Arkose (Sandstone) Sandstones (Subdivided based on maturity) Greywacke p. 29 Detrital Sedimentary Rock ID Chemical Rock Texture Clastic (Detrital) Sedimentary Rocks Grain Size Roundness S orting Composition N ame R ounded Moderate to p oor Fragments of any rock type CONGLOMERATE Angular Moderate to p oor Fragments of any rock type BRECCIA R ounded Well All Quartz - usually white to tan QUARTZ SANDSTONE Subrounded to Angular Moderate to poor (few grains >2mm) Feldspar (usually orthoclase), micas, quartz, and other minerals ARKOSE (Arkosic Sandstone) Subrounded Moderate to well Quartz, lithic fragments, and other minerals LITHIC SANDSTONE Rounded to a ngular Moderate Quartz and rock fragments mixed with >15% clay; often gray colored GRAYWACKE SANDSTONE Silt-sized (feels gritty) (to small to s ee) Well Clay and quartz (but usually too small to see) SILTSTONE (to small to s ee) Clay (but usually too small to see); Massive MUDSTONE Clay-sized (feels smooth) Well Clay (but usually too small to see); Breaks into semi-flat layers SHALE Gravel-sized (> 2 mm) Sand-sized (visible grains up to 2 mm) Crystalline Texture • Coarse • Fine Chemical Rocks Chemical Sedimentary Rocks (Names based primarily on composition) Composition • Calcite • Quartz (silica) • Halite • Gypsum • “Carbon” / Plant Remains (Names based mainly on composition) Limestones Crystalline Limestone Basic Rock Name • Limestone Acid test • Chert Scratches Glass • Rock Salt Salty Taste • Rock Gypsum • Peat or Coal “Organic” Fossiliferous Limestone Chalk Chemical Rocks (cont.) p. 30 Chemical Sedimentary Rock ID Evaporites Chemical, Biochemical & Organic Sedimentary Rocks Composition Texture N ame Crystalline - medium to coarse (visible) grains CRYSTALLINE LIMESTONE Chert Dolomite (acid reaction) Crystalline - grains too small to see MICRITE Abundant fossils in a fine- to coarse-grained crystalline matrix FOSSILIFEROUS LIMESTONE Fine-grained powder, earthy smell (often black, gray, or white) Calcite (acid reaction) CHALK Crystalline - fine to coarse grained DOLOSTONE Crystalline - grains too small to see; conchoidal fracture CHERT Quartz (scratches glass) DIATOMITE Crystalline - fine to coarse grained ROCK GYPSUM Halite (tastes salty) Rock Gypsum Fine-grained powder, earthy smell (no acid reaction) (often white) G ypsum Rock Salt Crystalline - fine to coarse grained ROCK SALT Fibrous, brownish plant material; soft PEAT Dense, black masses; depending on grade may be dull to vitreous; lower grades may contain minor fossils C OAL Plant Remains (Carbon) Coal Sedimentary Rocks on Earth Sedimentary Rocks Interpretations What do Sedimentary Rocks Record? • Source of sediment • Erosion and Transport Agent • Distance of Transport • Depositional Environment • Paleogeography/Tectonic Setting p.22 Interpretation of Composition Detrital Rocks: • Source of sediment • Exposure to Weathering (Distance of Transport) (Type of Climate) Note About Detrital Rock Color & Composition Mineral Stability • Grain Size More weathered (Far from source, older tropical climate, etc.) Less weathered (Near source, younger, temperate climate, etc.) Smaller is often darker • Composition Carbon - black or brown Quartz - tan, clear, white Orthoclase - orange • Depositional Environment Iron on land - red Iron in deep, oxygen poor water - green Detrital Rock Names Interpretation: Grain Size • Gravel • High Energy • River, Beach, Landslide • Sand Gravel Sized: Conglomerate Sand Sized: Sandstone • River, Beach, Desert • Silt (Based Primarily on Grain Size) • Delta, Shallow Ocean • Clay • Low Energy Mud Sized: Mudstone • Deep Ocean, Lake, Swamp Siltstone Interpretation: Sorting Interpretation: Transport Agent Poorly Sorted Gravity and Glaciers (and Rivers) Well Sorted Water and Wind Shale Clast Supported Conglomerate (River Deposits) Matrix Supported Conglomerate (Glacial/Landslide Deposits) Interpretation: Grain Roundness 2.2 Gyr Conglomerate Short “Modern” Glacial Sediments Interpretation: Distance of Transport Limestone Formation of Limestone Crystalline Limestone Calcite Precipitates in Warm Water Water Under Low Pressure (Shallow) Fossiliferous Limestone Or It is secreted by biological organisms Clams, Mussels, Scallops, etc. Corals Foraminifera Chalk Far Limestone Represents: Chalk (Coccolithophores) Shallow Tropical Ocean Black Sea Travertine (Limestone) Chert (Flint, Jasper, Agate…) Diatom Steletons Evaporites: Bonneville Salt Flats, Utah Rock Gypsum Chert Represents Deep Ocean Isolated, Arid, Salty Sea/Lake Rock Salt Intermission: Quiz Peat and Coal What can you say about the history of this rock? Swamp, Bog Deposited in a beach/ river or desert, very far from the source of the sediment. Quartz Sandstone Intermission: Quiz Intermission: Quiz What can you say about the history of this rock? What can you say about the history of this rock? Deposited in a quiet water environment (deep ocean, lake, lagoon). Dark color implies oxygen-poor environment, rich in organic material. Shale Deposited in a shallow tropical ocean. Limestone ...
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