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Sediments and Sedimentary Rocks
Earth, Chapter 7
Sedimentary rocks: summary in haiku form
Lithification -glue particles togetherglue particles together.Was sand, now sandstone.
What is a sedimentary rock?Products of mechanical and chemical weatheringAccount for about 5 percent of Earth’s crust (by volume)Contain evidence of past environments
Provide information about sediment transportOften contain fossils
What is a sedimentary rock?
Important for economic considerations – may contain:
CoalPetroleum and natural gasSources of iron, aluminum and manganese
Turning sediment into rock
Many changes occur to sediment after depositionDiagenesis
All of the changes that take place after sediments are depositedOccurs within the upper few kilometers of the earth’s crust
Turning sediment into rock
Diagenesis includes:Recrystallization
Development of more stable minerals from less t bl stable ones
LithificationUnconsolidated sediments are transformed into solid sedimentary rock by compaction and cementation
Natural cements include calcite, silica, and iron oxide
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Types of sedimentary rockSediment originates from mechanical and/or chemical weatheringRock types are based on the source of the materialthe material
Detrital rocks ( = “clastic” )Sediment transported as solid particles (clasts)
Chemical rocksSediment that was once in solution
Detrital sedimentary rocksChief constituents include:
Clay mineralsQuartzF ldFeldsparsMicas
Particle size is used to distinguish among the various types of detrital rocks
Clastic (detrital) particle size classification
Size Range(millimeters)
Particle Name
Common Sediment
Name
Rock Name
> 25664 256
BoulderC bbl64 - 256
4 - 642 – 4
CobblePebbleGranule
Gravel Conglomerate or breccia
1/16 – 2 Sand Sand Sandstone
1/256 - 1/16< 1/256
SiltClay Mud
Shale, mudstone, or
siltstone
Detrital sedimentary rocksCommon detrital sedimentary rocks (in order of increasing particle size):
ShaleMud-size particles in thin layers commonly p y yreferred to as laminae
fissility
Most common sedimentary rock
MudstoneBreaks into chunks or blocks
SiltstoneNot fissile
Del Mar fm. / Torrey Pines ss. Del Mar fm.
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Mudstone Mudstone
Detrital sedimentary rocks
SandstoneComposed of sand-sized particlesFormed in a variety of environmentsySorting, shape, and composition of the grains can be used to interpret the rock’s historyQuartz is the predominant mineral
Torrey Sandstone
Esplanade SandstoneEsplanade Sandstone Esplanade SandstoneEsplanade Sandstone
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Esplanade SandstoneEsplanade Sandstone
Detrital sedimentary rocks
Conglomerate and brecciaBoth are composed of particles greater than 2 mm. in diameterConglomerate consists of rounded gravelsBreccia is composed mainly of large angular particles
conglomerateconglomerate conglomerateconglomerate
Breccia in ABDSPBreccia in ABDSP
Breccia in GCNPBreccia in GCNP
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Chemical sedimentary rocks
Consist of precipitated material that was once in solutionPrecipitation of material happens in Pre ipitation of material happens intwo ways:
Inorganic processesOrganic processes (biochemical origin)
Chemical sedimentary rocks
Common chemical sedimentary rocks
LimestoneMost abundant chemical rock
Composed chiefly of the mineral calcite
Marine biochemical limestones form as coral reefs, coquina (broken shells), and chalk (microscopic organisms)Inorganic limestones include travertine and oolitic limestones
Redwall Limestone, Grand Canyon Redwall Limestone, Grand Canyon
Vasey’s Paradise
Tyndall Limestone (Manitoba)
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Fossils in Tyndall Limestone
coquina
coquinacoquina--toto--bebe Chalk – Dover, England
Travertine – malachite and rhodochrosite
Travertine in Arroyo Zamora, near El MarmolTravertine in Arroyo Zamora, near El Marmol
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Travertine in Elves’ Chasm, GCNPTravertine in Elves’ Chasm, GCNP Travertine in Elves’ Chasm, GCNPTravertine in Elves’ Chasm, GCNP
Chemical sedimentary rocks
Common chemical sedimentary rocksDolostone
Typically formed secondarily from limestone
ChertMade of microcrystalline quartz
Varieties include:FlintJasperAgate
dolostone
Chert Nodules in Limestone Chert Nodules in Limestone
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Chert (agate)
Ch t Chert (agate)
Chert (“coprolite”)
Chemical sedimentary rocks
Common chemical sedimentary rocksEvaporites
Evaporation triggers deposition of chemical precipitates
Examples:Rock saltGypsum
Rock salt (halite)
Halite “soda straws” in the Grand CanyonHalite “soda straws” in the Grand Canyon
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GypsumGypsum
GypsumGypsum
Fish Creek Gypsum Mine
Chemical sedimentary rocks
Common chemical sedimentary rocksCoal
Different from other rocks because it is composed of organic material
Stages in coal formation:Plant materialPeatLigniteBituminous
Successive stages in coal formation
Coal depositional environment ?
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Coal depositional environment ?Coal depositional environment ? Coal depositional environment ?
Coal depositional environment ?Coal depositional environment ?
Classification of sedimentary rocks
Classified according to the type of materialTwo major groupsTwo major groups
Detrital (clastic)Chemical
Classification of sedimentary rocks
Two major textures are used in the classification of sedimentary rocks
ClasticDiscrete fragments and particles
All detrital rocks have a clastic texture
NonclasticPattern of interlocking crystalsMay resemble an igneous rock
Classification of sedimentary rocksClassification of sedimentary rocks
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Sedimentary environments
Geographic settings where sediment is accumulatingDetermine the nature of the sediments etermine the nature of the sedimentsthat accumulate (grain size, shape, etc.)
Sedimentary environmentsTypes of sedimentary environments
ContinentalDominated by erosion and deposition associated with streamswith streams
GlacialWind (eolian)
MarineShallow (to about 200 meters)
Deep (seaward of continental shelves)
Sedimentary environments
Types of sedimentary environmentsTransitional (shoreline)
Tidal flats
LagoonsDeltas
Sedimentary environments
Sedimentary environments
Sedimentary faciesDifferent sediments often accumulate adjacent to one another at the same timeE h it ( ll d f i ) Each unit (called a facies) possesses a distinctive set of characteristics reflecting the conditions in a particular environmentThe merging of adjacent facies tends to be a gradual transition
Sedimentary facies
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Sedimentary structuresProvide information useful in the interpretation of Earth historyTypes of sedimentary structures
Strata, or beds (most characteristic of sedimentary rocks)Bedding planes that separate strataCross-beddingGraded bedsRipple marksMud cracks
Strata, or bedsStrata, or beds
Formation of Cross Bedding
CrossCross--beddingbedding
CrossCross--beddingbedding Ripple marksRipple marks
modern
ancient
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Graded beddingGraded bedding Mud cracks (modern)Mud cracks (modern)
Mud cracks (ancient)Mud cracks (ancient)
Fossils: evidence of past lifeTraces or remains of prehistoric life now preserved in rockGenerally found in sediment or
di t ksedimentary rockRarely in metamorphic rockNever in igneous rock (almost)
Fossils: evidence of past lifeGeologically important for several reasons
Aid in interpretation of past environmentsenvironmentsServe as important time indicatorsAllow for correlation of rocks in different places
Natural casts of shelled invertebrates