EROSION, DEPSOTION AND SEDIMENTARY ROCKSBase Level Resistant bedLocal Base Level Niagara FallsBase Level local and ultimateBase Level ultimateBase LevelBase LevelIncised meandersStream ErosionDeepeningStream Processes and Floodplain Development Headward Erosion Pecos in NMHeadward ErosionStream ValleysBroad, flat-bottomed ValleyDepositionDepositionDelta FormationDelta FormationDelta FormationMississippi DeltaDepositionStream Processes and Floodplain Development Natural Levee CreationNatural Levees floodstageNatural Levees sediment depositsYazoo RiverAlluvial FanAlluvial FanDrainage PatternsDrainage patternsDendriticRadialRectangular and trellisRock TypesRock cycle diagramSedimentary rocks Bedding and bedding planesFossilsFeatures of sedimentary rocksSedimentary rocksSedimentary rocks Sedimentary rocksSediment grainsLithificationCementTypes of Detrital RocksShale with plant fossilsShaleSandstoneSandstoneConglomerateConglomerateDetrital (clastic) rocks Chemical rocks Fossiliferous limestoneChemical rocksCoquinaClose up of coquinaChalkRock saltChemical rocksEvaporitesChertTravertineClassification of sedimentary rocksEROSION, DEPOSITION AND SEDIMENTARY ROCKSReading: Earth ScienceTarbuck and LutgensChapter 5: pages 124-133Chapter 3: pages 52-54, 61-69Base LevelResistant bed• Resistant bed creates a local base levelLocal Base LevelNiagara FallsBase Levellocal and ultimate• Over time, the resistant bed is eroded• Local base level becomes closer to ultimate base level• Eventually resistant rock is eroded to ultimate base levelBase LevelultimateBase Level• Erode to ‘BASE LEVEL’• Cannot erode below base level• Local base level (temporary)• Gradual decrease in gradient from head to mouth• Ultimate profile is idealized graded streamBase Level• Lower base level allows more erosion• Raise base level reduces erosionIncised meandersStream Erosion• Cut their own channels• Cut three main ways1. Deepening2. Widening3. Headward erosionDeepening• Yellowstone RiverStream Processes and Floodplain Development WideningHeadward ErosionPecos in NMhttp://www.lib.utexas.edu/maps/new_mexico.htmlhttp://www.lib.utexas.edu/maps/national_atlas_1970/ca000043_large.jpgHeadward Erosionhttp://www.lib.utexas.edu/maps/colorado.htmlStream Valleys• V shaped in headwaters• Wide with flat floors nearer to mouthBroad, flat-bottomed Valley• Low gradient• Stream cuts into valley walls• Mass wasting delivers sediment to streamSLOWING OF VELOCITY• Decrease in gradient• Decrease in discharge– Evaporation– Infiltration• Loss of channelization– Flood stage– Body of waterDepositionDeposition• Flows into a body of water• Creates deltaDelta Formation• Deposition decreases gradient• Flood stage--gets out of its depositDelta Formation• Flood stage--gets out of its deposit• Forms set of ‘DISTRIBUTARIES’Delta Formation• Forms set of ‘DISTRIBUTARIES’Mississippi DeltaSLOWING OF VELOCITY• Loss of channelization– Enters body of water– Flood stage—out of banksDepositionStream Processes and Floodplain Development Natural Levee FormationNatural Levee Creation• Competence lost when stream leaves its channel• Deposits largest particles first• http://www.ucpress.edu/books/pages/6664/6664.ch04.htmlNatural LeveesfloodstageNatural Leveessediment depositsYazoo Riverhttp://www.mvk.usace.army.mil/offices/pp/yazoobackwater/basics.asp?category=basics• Badwater Fan, Death Valley, CaliforniaAlluvial Fanhttp://www.windows.ucar.edu/earth/geology/images/alluvial_fan_lg.jpegAlluvial Fanhttp://wiseman.brandonu.ca/earthscience/newpage35.htmDrainage Patterns• Channel layout within a drainage basin• Described by overall shape formed– Dentritic– Radial– Rectangular– TrellisDrainage patternsDendriticRadialRectangular and trellisRock Types• Igneous• Sedimentary• MetamorphicRock cycle diagramSedimentary rocks Features of sedimentary rocks• Strata, or beds (most characteristic)• Bedding planes separate strata May have important characteristics• Size, shape and distribution of grain sizes• FossilsBedding and bedding planes• http://www.birdandhike.com/Hike/General_Info/Glossary/Gloss4.htmFossils• Traces or remains of prehistoric life • Are the most important inclusions • Help determine past environments • Used as time indicators • Used for matching rocks from different placesFeatures of sedimentary rocks• Porosity• PermeabilitySedimentary rocksSediment is derived from weatheringCarried by fluidFormed at Earth’s surfaceImportant to reconstruct much of Earth's historySedimentary rocks Economic importance • Coal• Petroleum and natural gas • Precipitation of iron and aluminum • Deposition of gold and tin• Sand, gravel, claySedimentary rocksTwo main types • Rocks formed by deposition of sediment—Detrital• Rocks formed by precipitation from water--Chemical(includes rocks formed by organisms)Sediment grains• Particle loosened from pre-existing rock• Transported to place of deposition• Shape, size, and sorting of grains can tell about the environment of depositionLithificationProcess of becoming stone• Burial and compaction• Precipitation of cement• Each reduces ‘pore space’Cement• Brought in by water• Mineral material between grains• Fills in pore spaces• Commonly calcite, silica, and sometimes iron oxideTypes of Detrital Rocks• Shale (most abundant)• Sandstone• ConglomerateShale with plant fossilsShale• Composed of very fine grained sediment• Shows obvious tendency to split along planes (fissile)• Usually gray• Most common type of sedimentary outcropSandstoneSandstone• Composed of sand-size particles– Between 1/16 mm and 2 mm diameter– Particles may be individual mineral grains or rock fragments– Quartz most common type of grain• Environments include•Beach, •river, •shallow sea, •sand dunesConglomerateConglomerate• Composed of particles larger than 2 mm• Usually particles are rock fragmentsDetrital (clastic) rocks • Shale is the most common one• Made from solid particles• Classified by particle sizeChemical rocks Material was once in solution and precipitates to form sediment • Directly precipitated as the result of physical processes, or • Through life processes (biochemical origin)Fossiliferous limestoneChemical rocksLimestone• Composed of the mineral calcite (calcium carbonate)• Much of this calcite was precipitated by organisms• Considered
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