Colorado River, AZ Mary Beth Dougherty Sedona, AZ Ryan Conlon.

Colorado River, AZMary Beth Dougherty

Sedona, AZRyan Conlon

Red Rock Canyon, CAHilary Neff

SEDIMENTATION AND SEDIMENTARY ROCKS

SEDIMENT TRANSPORT AND TEXTURE

Most sediment is clastic.Individual grains are called CLASTS.

Produced by mechanical weathering and erosion.

During transport, clasts move from high elevation to low, generally by influence of gravity.

Gravity is assisted by a transport medium, water, wind,or ice.

Clasts are deposited when transporting medium losesenergy.


GRAIN-SIZEUsually dependent upon energy and nature of the

transporting medium.Also related to the medium’s ability to carry them.

Hopewell RocksProvincial ParkNew Brunswick

Courtesy of Warren Poulin


SORTING

Process by which a transport medium “selects” particles of different sizes, shapes and densities.

Wind is most selective.Produces well sorted sediment.

Glacial ice and flooding rivers are unselective.Produce poorly sorted sediments.


SORTING

Sorting provides evidence as to what medium transported the sediment.

Heaviest particles are usually deposited first, close tosource.

Lightest particles are carried further away from source.


SORTING


GRAIN SHAPE

Clastic particles usually start out angular.Abrasion through transport rounds particles.

Rivers are effective at rounding particles.Greater abrasive activity, the more rounding occurs.Softer minerals tend to round faster than hard

minerals.


SEDIMENTARY STRUCTURES

Clastic sediments often contain SEDIMENTARYSTRUCTURES.

SEDIMENTARY STRUCTURES are physical indicators, preserved in the rocks that provideinformation as to how the the particles weredeposited and what type of environment it was.



BEDDING OR STRATIFICATION

Deposition of sediments is arranged into distinct layersof different composition or grain-size.

These layers are called BEDS or STRATA.One bed is a STRATUM, two are STRATA.Layers are separated by BEDDING PLANES.

BEDDING PLANES usually indicate changes insediment type or environment.



Cape Liptrap, AustraliaCourtesy of Lorraine Beane



GRADED BEDDING

Results in rapid deposition of particles of varying sizes in still water.

Different sized particles settle out at different rates.Generally largest first at the base and then get smaller.Produces GRADED BEDS.



GRADED BEDDING



GRADED BEDDINGGraded bedding is usuallyfound on ocean floors asSUBMARINE LANDSLIDES.Sediment is carried to thecontinental shelf and depositedas an unstable mass.When dislodged (earthquake) a

TURBIDITY CURRENT is produced.

TURBIDITY CURRENTS



Are a dense mixture ofsea water and sediment.

Cascade down thecontinental slope.

Lose energy when theyreach the oceanfloor and velocitydecreases and sediment is deposited rapidly.

Also produced by lahars and mudflows.



CROSS-BEDDINGConsists of sedimentary layers deposited at an angle to

the underlying set of beds.

Navajo SandstoneUtah

Coconino SandstoneArizona

Colorado River, AZ Mary Beth Dougherty Sedona, AZ Ryan Conlon.

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