sediments and sedimentary...

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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)


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


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”)


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


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)


Types of sedimentary environmentsTransitional (shoreline)

Tidal flats

LagoonsDeltas



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

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Natural casts of shelled invertebrates Dinosaur footprint in limestone

Dinosaur Dinosaur footprint in limestone

More trace fossilsMore trace fossils

End of Chapter 7End of Chapter 7

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