07.03 sedimentary rocks
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Sedimentary Rocks
From sediments to rocks
Dr Marcus Matthews
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Sedimentary Rocks
Sedimentary rocks and the rock cycle
Sedimentary Environments
Facies
Diagenesis
Classification of Sedimentary rocks
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Sedimentary Rocks and theRock Cycle
Weathering parent rocks decomposed and orfragmented
Erosion carries particles away
Transportation moves particles to new locations
Deposition
particles settle, minerals areprecipitated
Burial layers of sediment accumulate
Diagenesis physical & chemical changes that
transform a sediment into a rock
Sedimentary rocks are the product of severaloverlapping processes
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Weathering and Erosion Yieldthe Raw Materials
Particles and dissolved substances
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Clastic sediments Chemical depositsCementing materials
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Weathering and Erosion Yieldthe Raw Materials
Transported solid fragments
Boulders to clay
Often called siliclasticStable minerals e.g. quartz found unaltered
Less stable minerals e.g. feldspar often absent or partiallyaltered
New minerals e.g. clay minerals
Mineralogy of sediment reflects intensity of weathering as wellas length and type of transport
Clastic sediments generally accumulate more rapidly than othertypes of sediments
Clastic sediments
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Weathering and Erosion Yieldthe Raw Materials
Dissolved products of weathering
Chemical sediments are formed at or near place of deposition
(e.g. rock salt, limestone)Biochemical sediments contain un-dissolved remains oforganisms (e.g. chalk)
In practice many chemical and biochemical sediments overlap
Chemical and Biochemical Sediments
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Transportation and Deposition
Most particles are transported by currents of water or air (wind).Rivers annually carry a solid and dissolved sediment load of morethan 20 billion tonnes. Currents in air move material globally but inmuch smaller quantities
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Transportation and DepositionCurrents sort sediments into different size groups
L.S. Fichter (1993, 2000)http://csmres.jmu.edu/geollab/fichter/sedrx/simpbasclas.html
Clastic rocksChemical & biochemical rocks
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Transportation and DepositionTransportation changes the character of the particles.The key factors are time, distance and mode of transport.
Transportation results in reduced particle angularity and size
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Transportation and Deposition
Example: Clastic particles eroded at the headwaters of
the Missouri River in the mountains of western Montanatake hundreds of years to travel the 2000 miles to theGulf of Mexico. These particles may be affected byphysical weathering (rounding) as well as intermittent
chemical weathering.
Transportation changes the character of the particles.The key factors are time, distance and mode of transport.
Transport by glaciers does not result in rounding ofparticles. The particles are reduced in size.Transport by wind rounds and polishes particles.
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Sedimentary Environments
Type and amount of water (ocean, lake, river, aridland)
Topography (lowland, mountains, coastal plain,shallow ocean, deep ocean)
Biological activity (coral reefs, swamps)
Asedimentary environment is a geographic locationcharacterised by a particular combination of geologicalprocesses.
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Sedimentary Environments
Continental EnvironmentsAlluvialDesertLakeGlacial
Shoreline EnvironmentsDeltaic
Tidal flatBeachMarine EnvironmentsContinental shelfContinental slope
Organic reefsDeep-sea
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Facies
Facies are combinations of sediments orsedimentary rocks characteristic of a particularsedimentary environment.
Examples: Alluvial facies and deltaic facies
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Sedimentary Facies:Alluvial
The sediments deposited by a meandering river form a sequencewhere each bed forms in a different part of the channel. As thechannel migrates they are deposited in sequence on top of eachother. The sequence is cyclic with each cycle ending in over-bankflooding.
Fining upwardsequence
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Sedimentary Facies: DeltaicThe river delta is a complex environmentas it involves the combination of river,tides and wave action. Channel switchingby river causes delta lobes to beperiodically abandoned resulting in a cyclicsequence of sediments.
Progradingdelta lobe
Marine shale
Coal (abandonment)
Onedeltacycle
Onedeltacycle
Coarseningupwardssequence
Active delta lobe
Abandoned delta lobe
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DiagenesisPhysical and chemical changes thattransform a sediment into a rock
Mud (clay) Mudstone & shale
Sand Sandstone
Gravel Conglomerate/breccia
Carbonate Limestone & marlrich muds
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Diagenetic Processes:Compaction
10-20% water
50-60% water
Compaction (primarily of muds)
Pressure due to overburden
(burial) squeezes water outof pore space.
Particles forced closer
together as pore volumereduces
NoteGeologists say compactionGeotechnical Engineers say consolidation
To a Geotechnical Engineer compaction means removal of air throughapplication of energy
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Diagenetic Processes:Cementation
Common cements
Iron oxideCalcium CarbonateClay minerals
Silica
Precipitation of new minerals
Loose sand Cemented sandstone
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Diagenetic Processes: Re-Crystallisation
New crystal faces precipitated on existing mineral grains
Loose sand
Example: development of a strong quartzite throughprecipitation of silica on original quartz grains
Cemented sandstone= same mineral
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Diagenetic Processes:Dissolution
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Classification of Clastic Sedimentary Rocks
Cobbles 60-200mmm, Boulders >200mm
ClaySiltSandGravel
0.002mm0.06mm2mm60mm0.
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Breccia(angular fragments)
Conglomerate(rounded fragments)
Sandstone SiltstoneClaystoneShale
Grains visiblewith naked eye
Grains visible withnaked eye (course),with aid of x10 handlens (fine)
Grains not visible with aid ofx10 hand lens
Mudrocks
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Classification of ClasticSedimentary RocksMajor types of sandstone based on mineral/rock content
Quartzite Arkose Lithic Sandstone Greywacke
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Classification of SedimentaryRocks
Classification of chemical and biochemical sedimentaryrocks
Sediment Rock Composition Minerals
Sand & mud Limestone CaCO3 Calcite
Siliceous sediment Chert SiO2 Opal,
ChalcedonyQuartz
Peat, organic matter Lignite, Coal Carbon (Coal)Organics compounds (Oil)
(Gas)
Biochemical
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Classification of SedimentaryRocks
Sediment Rock Composition Minerals
Evaporite Evaporite Sodium chloride HaliteCalcium sulphate Anhydrite
Gypsum
Iron oxide sediments Iron formation Iron oxide HematiteLimoniteIron carbonate Siderite
Formed by diagenesis Dolomite Calcium-magnesium Dolomite(Dolostone) carbonatePhosphorite Calcium phosphate Apatite
Classification of chemical and biochemical sedimentaryrocks
Chemical
o
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Cl ifi ti f S di t
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Classification of SedimentaryRocks
Classification of chemical and biochemical sedimentaryrocks
Sediment Rock Composition Minerals
Sand & mud Limestone CaCO3 Calcite
Siliceous sediment Chert SiO2 Opal,
ChalcedonyQuartz
Peat, organic matter Lignite, Coal Carbon (Coal)Organics compounds (Oil)
(Gas)
Biochemical
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Cl ifi ti f S di t
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Classification of SedimentaryRocks
Sediment Rock Composition Minerals
Evaporite Evaporite Sodium chloride HaliteCalcium sulphate Anhydrite
Gypsum
Iron oxide sediments Iron formation Iron oxide HematiteLimoniteIron carbonate Siderite
Formed by diagenesis Dolomite Calcium-magnesium Dolomite(Dolostone) carbonatePhosphorite Calcium phosphate Apatite
Classification of chemical and biochemical sedimentaryrocks
Chemical
o
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