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

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/

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