fossil fuels and sedimentary rocksbrownk/es105/es105.2007.0215...base level local and ultimate •...
TRANSCRIPT
-
EROSION, DEPOSITION AND SEDIMENTARY ROCKS
Reading: Earth ScienceTarbuck and Lutgens
Chapter 5: pages 124-133Chapter 3: pages 52-54, 61-69
-
Base LevelResistant bed
• Resistant bed creates a local base level
-
Local Base LevelNiagara Falls
-
Base 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 level
Base Levelultimate
-
Base 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 stream
-
Base Level
• Lower base level allows more erosion• Raise base level reduces erosion
-
Incised meanders
-
Stream Erosion
• Cut their own channels• Cut three main ways
1. Deepening2. Widening3. Headward erosion
-
Deepening
• Yellowstone River
-
Stream Processes and Floodplain Development
Widening
-
Headward ErosionPecos in NM
http://www.lib.utexas.edu/maps/new_mexico.html
http://www.lib.utexas.edu/maps/national_atlas_1970/ca000043_large.jpg
http://www.lib.utexas.edu/maps/national_atlas_1970/ca000043_large.jpg
-
Headward Erosion
http://www.lib.utexas.edu/maps/colorado.html
-
Stream Valleys
• V shaped in headwaters• Wide with flat floors nearer to mouth
-
Broad, flat-bottomed Valley
• Low gradient• Stream cuts into valley walls• Mass wasting delivers sediment to stream
-
SLOWING OF VELOCITY• Decrease in gradient• Decrease in discharge
– Evaporation– Infiltration
• Loss of channelization– Flood stage– Body of water
Deposition
-
Deposition
• Flows into a body of water• Creates delta
-
Delta Formation
• Deposition decreases gradient• Flood stage--gets out of its deposit
-
Delta Formation
• Flood stage--gets out of its deposit• Forms set of ‘DISTRIBUTARIES’
-
Delta Formation
• Forms set of ‘DISTRIBUTARIES’
-
Mississippi Delta
-
SLOWING OF VELOCITY• Loss of channelization
– Enters body of water– Flood stage—out of banks
Deposition
-
Stream Processes and Floodplain Development
Natural Levee Formation
-
Natural Levee
Creation
• Competence lost when stream leaves its channel
• Deposits largest particles first
• http://www.ucpress.edu/books/pages/6664/6664.ch04.html
-
Natural Leveesfloodstage
-
Natural Leveessediment deposits
-
Yazoo River
http://www.mvk.usace.army.mil/offices/pp/yazoobackwater/basics.asp?category=basics
-
• Badwater Fan, Death Valley, California
Alluvial Fan
http://www.windows.ucar.edu/earth/geology/images/alluvial_fan_lg.jpeg
-
Alluvial Fan
http://wiseman.brandonu.ca/earthscience/newpage35.htm
-
Drainage Patterns
• Channel layout within a drainage basin• Described by overall shape formed
– Dentritic– Radial– Rectangular– Trellis
-
Drainage patterns
-
Dendritic
-
Radial
-
Rectangular and trellis
-
Rock Types
• Igneous• Sedimentary• Metamorphic
-
Rock cycle diagram
-
Sedimentary 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• Fossils
-
Bedding and bedding planes
• http://www.birdandhike.com/Hike/General_Info/Glossary/Gloss4.htm
-
Fossils
• 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
places
-
Features of sedimentary rocks• Porosity• Permeability
-
Sedimentary rocks
Sediment is derived from weatheringCarried by fluidFormed at Earth’s surfaceImportant to reconstruct much of Earth's
history
-
Sedimentary rocks Economic importance
• Coal• Petroleum and natural gas • Precipitation of iron and
aluminum • Deposition of gold and tin• Sand, gravel, clay
-
Sedimentary rocks
Two 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 deposition
-
Lithification
Process 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 oxide
-
Types of Detrital Rocks
• Shale (most abundant)• Sandstone• Conglomerate
-
Shale with plant fossils
-
Shale
• Composed of very fine grained sediment• Shows obvious tendency to split along
planes (fissile)• Usually gray• Most common type of sedimentary outcrop
-
Sandstone
-
Sandstone• 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 dunes
-
Conglomerate
-
Conglomerate
• Composed of particles larger than 2 mm• Usually particles are rock fragments
-
Detrital (clastic) rocks
• Shale is the most common one• Made from solid particles• Classified by particle size
-
Chemical 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 limestone
-
Chemical rocksLimestone
• Composed of the mineral calcite (calcium carbonate)• Much of this calcite was precipitated by organisms• Considered an ‘organic chemical sediment’ if from
organisms• Most common type of chemical rock—• second most common type of sedimentary rock
-
Coquina
-
Close up of coquina
-
Chalk
-
Rock salt
-
Chemical rocksDirect mineral precipitation from water
• Evaporites such as rock salt or gypsum• Microcrystalline quartz (precipitated
quartz) known as chert, flint, jasper, opal or agate
• Travertine (calcite) and sinter (silica) from hotspring deposits
-
Evaporites
• http://www.bonnevillehealeyclub.org/
• http://www.paintersflat.net/saltflat.html • http://www.nv.blm.gov/Winnemucca/blackrock/BRHR_Planning.htm
• http://www.img.uni-karlsruhe.de/925.php
• http://www.pitt.edu/~cejones/GeoImages/1Minerals/2SedimentaryMineralz/Gypsum.html
• http://www.flickr.com/photos/snogun/191723596/
http://www.pitt.edu/~cejones/GeoImages/1Minerals/2SedimentaryMineralz/Gypsum_Halite/GypsumOneSatinSpar.jpg
-
Chert
http://geomaps.wr.usgs.gov/sfgeo/geologic/stories/marin_sedimentary.html
• http://homestake.sdsmt.edu/Photos/Surface_geology_photos.htm
• http://www.mii.org/Minerals/photochert.html
-
Travertine
• http://njminerals.org/travertine.html
• http://www.gonomad.com/destinations/0409/hot_springs_of_the_sierras.html
• http://www.cis.nctu.edu.tw/~whtsai/World%20Highlights/New%20Side%20Show%20Webpages/imagepages/Turkey%202001---Travertine%20stones%20and%20water%20in%20Pamukale.html
-
Classification of sedimentary rocks
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 rocks