Lithification Sediments Deposition Sedimentary Rocks Weathering The sediments that make up sedimentary rocks are produced by: Mechanical & Chemical Weathering Transport Erosion Weathering http://www.teachnet-lab.org/ps101/bglasgold/rocks/efcyclep2.gif Types of mechanical aka physical weathering Mechanical Weathering unloading rx expand when overburden lessened frost wedging H 2 O expands 9% to ice insolation solar heating expansion salt crystals root wedging seismic deformation Chemical Weathering big point: some minerals are more stable than others Mineral Stability hydrolysis, oxidation, dissolution, dehydration, solutioning, bio-chemical weathering 1
Products of Weathering Erosion & Transport Lithic (Rock) Fragments (granite, basalt,schist, etc.) Dissolved Ions (Calcium, Potassium, Sodium, etc.) Rust Minerals (Hematite, Goertite, etc.) Clay Minerals (Bentonite, Montmorillonite, etc.) Residual Minerals (Quartz, Orthoclase, Muscovite, etc.) Water Wind Ice Gravity Common Depositional Environments Marine shoreline and near-shore environments Sediment Lithification Cementation Typical Cements: Calcite Quartz Iron oxide Rock 2
Types of Sedimentary Rocks Sedimentary Rocks Identification Detrital or clastic Rocks Chemical Rocks Note: Use many of the same terms to describe sediments & sedimentary rocks. Only difference is lithification! vs. Difference: Texture Detrital (Clastic Texture) vs. Chemical (Crystalline Texture) Detrital Rock Composition Detrital Rocks Lithic Fragments Quartz Clay Minerals Fossil Fragments Rust Minerals Orthoclase Muscovite / Biotite Clastic Texture Grain Size Grain Sorting Grain Rounding Sediment Maturity Detrital Rock Texture Gravel 2mm Sand 1/16 mm Mud - Silt 1/256 mm Mud - Clay Grain Size 3
Detrital Rock Names (Based Primarily on Grain Size) Sorting Gravel -Sized: Conglomerate Sand Sized: Sandstone Mud-Sized: Mudstone Siltstone Shale Gravel Sized Detrital Rocks (Subdivided Based on Grain Roundness) Conglomerate Breccia Maturity Mature Well Sorted Well Rounded All Quartz Immature Poorly Sorted Angular grains Mixed Composition including clay Quartz Sandstone Lithic Sandstone Sandstones (Subdivided based on maturity) Arkose (Sandstone) Greywacke 4
Sandstones Under a Scope Detrital Sedimentary Rock ID Chemical Rock Texture Crystalline Texture Coarse Fine Chemical Sedimentary Rocks (Names based primarily on composition) Composition Calcite Quartz (silica) Halite Gypsum Carbon / Plant Remains Basic Rock Name Limestone Chert Rock Salt Rock Gypsum Peat or Coal Crystalline Limestone Chemical Rocks (Names based mainly on composition) Limestones Chemical Rocks (cont.) Evaporites Fossiliferous Limestone Chert Rock Salt Chalk Rock Gypsum Coal 5
Sedimentary Rocks Interpretations What do Sedimentary Rocks Record? Source of sediment Erosion and Transport Agent Distance of Transport Depositional Environment Paleogeography/Tectonic Setting Chemical Sedimentary Rock ID Interpretation of Composition Detrital Rocks: Source of sediment Exposure to Weathering (Distance of Transport) (Type of Climate) Note About Detrital Rock Color & Composition Grain Size Smaller is often darker Composition Carbon - black or brown Quartz - tan, clear, white Orthoclase orange or pink Depositional Environment Iron on land - red Iron in deep, oxygen poor water - green Detrital Rock Names (Based Primarily on Grain Size) Interpretation: Grain Size Gravel -Sized: Conglomerate Sand Sized: Sandstone Gravel Sand High Energy River, Beach River, Beach, Desert Silt Delta, Shallow Ocean Mud-Sized: Mudstone Clay Low Energy Deep Ocean, Lake, Swamp Siltstone Shale 6
Interpretation: Sorting Clast Supported Conglomerate (River Deposits) Interpretation: Poorly Sorted Well Sorted Transport Agent Gravity and Glaciers (and Rivers) Water and Wind Matrix Supported Conglomerate (Glacial/Landslide Deposits) Interpretation: Grain Roundness 2.2 Gyr Conglomerate Modern Glacial Sediments Short Interpretation: Distance of Transport Far 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 7
Limestone Represents: Shallow Tropical Ocean Chalk (Foraminifera) Black Sea Travertine (Limestone) Black Sea Chert (Flint, Jasper, Agate ) Diatom Skeletons Chemical sed. rk formed via silicious ooze in the deep sea. Source of silica = tests (tiny shells) of radiolarians and diatoms (which are made of silica) Radiolarians 8
Evaporites: Bonneville Salt Flats, Utah Chert Represents Rock Gypsum Rock Salt Deep Ocean Isolated, Arid, Salty Sea/Lake Peat and Coal Swamp, Bog Coal beds in Puget Group sedimentary rocks near Ashford Sedimentary features and structures beds crossbeds ripple marks graded beds fossils mud cracks raindrop imprints etc Channel fill ~315 Ma Sharon Conglomerate, Cuyahoga River valley, Ohio 9
Crossbedded sandstone dune deposition by wind! Planar cross beds Sharon Conglomerate, lower Pennsylvanian Age (~315 Ma), Cuyahoga River valley, Ohio; interpreted as a braided stream sedimentary environment (lens cap ~52 mm) dune deposition by water! Zion National Park. Festooned cross beds deposited by wind. How crossbeds form migrating dunes! Turbidity currents ad:\digital_content\animations_library\0009.swf 10
Modern mud cracks Ancient mud cracks in shale modern mud cracks, Ceres Road 2007 flood-deposited muds Current ripples in wet sediment, Baja CA Ripple marks in sandstone, Capitol Reef National Park, Utah Pat Pringle, photo Ripple marks in tilted Puget Group sedimentary rocks of Eocene age near Wilkeson WA 11
Fossil shells in sandstone, CA Fossil fish from Eocene Green River Shale in western Wyoming Fossil metasequoia leaf from rocks several miles east of Packwood, Oligocene age Lithologic Indicators of Climate http://www.scotese.com/ legend.htm dipping beds in Centralia Coal Mine, view to south fossils from Skookumchuck Formation 12
<= Portunites triangulum Crab, Eocene, Wahiakum Co., Washington http://www.geo-tools.com/fossils.htm More WA fossils! http://orerockon.com/for_sale.htm Dinosaur footprint, Tuba City, AZ Misc. Sedimentary Features Sorting Sorting Roundness Orientation: random vs. preferred Color Preferred orientation Imbrication = strong current Current direction is right to left Color Black = reducing conditions (ex: pyrite, MnO 2, organic matter) Green = near oxidation/reduction margin (ex: glauconite, chlorite) Red = oxidation (ex: hematite, red beds most of these are subaerial) Color is a function of size and composition Finer grained = truer colors Weathering & matrix cement also influence 13
Photo donated by Larry McMIllan http://www.ci.tenino.wa.us/teninoquarry1_small.jpg Eocene McIntosh Formation: Tenino Sandstone outcrop along rr tracks near Chehalis R., Galvin WA Rock Units FORMATION- Extensive enough to show on a map Distinctive from neighboring rock units Named locally CONTACTS Sedimentary contacts bounding surfaces between two sedimentary units Grand Canyon an awesome place to see strata! Monument Creek Grand Canyon The great unconformity Track of 1984 debris flow Bob Webb, photo, 1986 14
Granite Rapid, Grand Canyon Bob volcanologist Webb, photo, 1986 for scale 15