Sedimentary Rocks Weathering Mechanical Weathering Types of ...

LithificationSedimentsDepositionSedimentary RocksWeatheringThe sediments that make up sedimentary rocks are produced by:Mechanical & Chemical WeatheringTransportErosionWeatheringhttp://www.teachnet-lab.org/ps101/bglasgold/rocks/EFCycleP2.gifTypes of mechanical aka physicalweatheringMechanical 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 deformationChemical Weatheringbig point: someminerals are morestable than others…MineralStabilityhydrolysis, oxidation,dissolution, dehydration,solutioning, bio-chemicalweathering1

Products of WeatheringErosion & 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.)WaterWindIceGravityCommon Depositional EnvironmentsMarine shoreline and near-shoreenvironmentsSedimentLithificationCementationTypical Cements:•Calcite•Quartz•Iron oxideRock2

Types of Sedimentary RocksSedimentary RocksIdentificationDetrital or clastic RocksChemical RocksNote: Use many of the same terms to describesediments & sedimentary rocks.Only difference is lithification!vs.Difference: TextureDetrital (Clastic Texture)vs.Chemical (Crystalline Texture)Detrital Rock CompositionDetrital Rocks• Lithic Fragments• Quartz• Clay Minerals• Fossil Fragments• Rust Minerals• Orthoclase• Muscovite / BiotiteClastic Texture• Grain Size• Grain Sorting• Grain Rounding• Sediment MaturityDetrital Rock Texture•Gravel2mm•Sand1/16 mm•Mud - Silt1/256 mm•Mud - ClayGrain Size3

Detrital Rock Names(Based Primarily on Grain Size)SortingGravel -Sized:ConglomerateSand Sized: SandstoneMud-Sized:MudstoneSiltstoneShaleGravel Sized Detrital Rocks(Subdivided Based on Grain Roundness)ConglomerateBrecciaMaturityMature•Well Sorted•Well Rounded•All QuartzImmature•Poorly Sorted•Angular grains•Mixed Compositionincluding clayQuartz SandstoneLithic SandstoneSandstones(Subdivided basedon maturity)Arkose (Sandstone)Greywacke4

Sandstones Under a ScopeDetrital Sedimentary Rock IDChemical Rock TextureCrystalline Texture• Coarse• FineChemical Sedimentary Rocks(Names based primarily on composition)Composition• Calcite• Quartz (silica)• Halite• Gypsum• “Carbon” / PlantRemainsBasic Rock Name• Limestone• Chert• Rock Salt• Rock Gypsum• Peat or CoalCrystallineLimestoneChemical Rocks(Names based mainly on composition)LimestonesChemical Rocks (cont.)EvaporitesFossiliferous LimestoneChertRock SaltChalkRockGypsumCoal5

Sedimentary RocksInterpretationsWhat do Sedimentary Rocks Record?•Source of sediment•Erosion and Transport Agent•Distance of Transport•Depositional Environment•Paleogeography/Tectonic SettingChemical Sedimentary Rock IDInterpretation of CompositionDetrital Rocks:• Source of sediment• Exposure to Weathering(Distance of Transport)(Type of Climate)Note About Detrital RockColor & Composition• Grain SizeSmaller is often darker• CompositionCarbon - black or brownQuartz - tan, clear, whiteOrthoclase – orange or pink• Depositional EnvironmentIron on land - redIron in deep, oxygen poor water - greenDetrital Rock Names(Based Primarily on Grain Size)Interpretation: Grain SizeGravel -Sized:ConglomerateSand Sized: Sandstone• Gravel• Sand• High Energy• River, Beach• River, Beach, Desert• Silt• Delta, Shallow OceanMud-Sized:Mudstone• Clay• Low Energy• Deep Ocean, Lake,SwampSiltstoneShale6

Interpretation: SortingClast Supported Conglomerate(River Deposits)Interpretation:Poorly SortedWell SortedTransport AgentGravity and Glaciers (and Rivers)Water and WindMatrix Supported Conglomerate(Glacial/Landslide Deposits)Interpretation: Grain Roundness2.2 Gyr Conglomerate“Modern”Glacial SedimentsShortInterpretation:Distance of TransportFarLimestoneFormation of LimestoneCrystallineLimestoneCalcite Precipitates inWarm WaterWater Under Low Pressure (Shallow)Fossiliferous LimestoneOrIt is secreted by biological organismsClams, Mussels, Scallops, etc.CoralsForaminiferaChalk7

Limestone Represents:Shallow Tropical OceanChalk(Foraminifera)Black SeaTravertine(Limestone)Black SeaChert (Flint, Jasper, Agate…)Diatom SkeletonsChemical sed. rk formedvia silicious ooze in thedeep sea. Source of silica= tests (tiny shells) ofradiolarians and diatoms(which are made of silica)Radiolarians8

Evaporites:Bonneville Salt Flats, UtahChertRepresentsRockGypsumRock SaltDeep OceanIsolated,Arid,SaltySea/LakePeat and CoalSwamp, BogCoal beds in Puget Group sedimentary rocks near AshfordSedimentary features andstructures• beds• crossbeds• ripple marks• graded beds• fossils• mud cracks• raindrop imprints• etcChannel fill~315 MaSharon Conglomerate, Cuyahoga River valley,Ohio9

Crossbedded sandstonedune depositionby wind!Planar cross bedsSharon Conglomerate,lower PennsylvanianAge (~315 Ma),Cuyahoga River valley,Ohio; interpreted as abraided streamsedimentaryenvironment (lens cap~52 mm) – dunedeposition by water!Zion National Park. Festooned cross beds deposited by wind.How crossbeds form—migrating dunes!Turbidity currentsaD:\digital_content\animations_library\0009.swf10

Modern mudcracksAncient mudcracks in shalemodern mud cracks,Ceres Road 2007flood-deposited mudsCurrent ripples in wet sediment,Baja CARipple marks in sandstone, CapitolReef National Park, UtahPat Pringle, photoRipple marks in tilted Puget Group sedimentary rocksof Eocene age near Wilkeson WA11

Fossil shells in sandstone, CAFossil fish from Eocene Green River Shale in westernWyomingFossil metasequoia leaf from rocksseveral miles east of Packwood,Oligocene ageLithologic Indicators of Climatehttp://www.scotese.com/legend.htmdipping beds in CentraliaCoal Mine, view to southfossils from SkookumchuckFormation12

Photo donated by Larry McMIllanhttp://www.ci.tenino.wa.us/TeninoQuarry1_small.jpgEocene McIntosh Formation:Tenino Sandstoneoutcrop along rr tracks near Chehalis R., Galvin WARock Units• FORMATION-– Extensive enough to show on a map– Distinctive from neighboring rock units– Named locally• CONTACTS– Sedimentary contacts – bounding surfacesbetween two sedimentary unitsGrand Canyon – an awesome place to see strata!Monument CreekGrand CanyonThe great unconformityTrack of 1984 debris flowBob Webb, photo, 198614

Granite Rapid, Grand CanyonBob volcanologist Webb, photo, 1986 for scale15