Metamorphism and Metamorphic Rocks (Con't.)

coriandercultureMécanique

22 févr. 2014 (il y a 3 années et 4 mois)

81 vue(s)

Colorado River, AZ

Mary Beth Dougherty

Sedona, AZ

Ryan Conlon

Red Rock Canyon, CA

Hilary 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 loses


energy.

SEDIMENTATION AND SEDIMENTARY ROCKS

GRAIN
-
SIZE

Usually dependent upon energy and nature of the


transporting medium.

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

Hopewell Rocks

Provincial Park

New Brunswick

Courtesy of

Warren Poulin

SEDIMENTATION AND SEDIMENTARY ROCKS

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.

SEDIMENTATION AND SEDIMENTARY ROCKS

SORTING

Sorting provides evidence as to what medium


transported the sediment.


Heaviest particles are usually deposited first, close to


source.

Lightest particles are carried further away from source.

SEDIMENTATION AND SEDIMENTARY ROCKS

SORTING

SEDIMENTATION AND SEDIMENTARY ROCKS

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.

SEDIMENTATION AND SEDIMENTARY ROCKS

SEDIMENTARY STRUCTURES

Clastic sediments often contain
SEDIMENTARY


STRUCTURES
.

SEDIMENTARY STRUCTURES

are physical


indicators, preserved in the rocks that provide


information as to how the the particles were


deposited and what type of environment it was.

SEDIMENTATION AND SEDIMENTARY ROCKS

SEDIMENTARY STRUCTURES

BEDDING OR STRATIFICATION

Deposition of sediments is arranged into distinct layers


of 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 in


sediment type or environment.

SEDIMENTATION AND SEDIMENTARY ROCKS

SEDIMENTARY STRUCTURES

Cape Liptrap, Australia

Courtesy of Lorraine Beane

SEDIMENTATION AND SEDIMENTARY ROCKS

SEDIMENTARY STRUCTURES

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
.

SEDIMENTATION AND SEDIMENTARY ROCKS

SEDIMENTARY STRUCTURES

GRADED BEDDING

SEDIMENTATION AND SEDIMENTARY ROCKS

SEDIMENTARY STRUCTURES

GRADED BEDDING

Graded bedding is usually

found on ocean floors as

SUBMARINE LANDSLIDES
.

Sediment is carried to the

continental shelf and deposited

as an unstable mass.

When dislodged (earthquake) a


TURBIDITY CURRENT

is produced.


TURBIDITY CURRENTS

SEDIMENTATION AND SEDIMENTARY ROCKS

SEDIMENTARY STRUCTURES

Are a dense mixture of


sea water and


sediment.

Cascade down the


continental slope.

Lose energy when they


reach the ocean


floor and velocity


decreases and sediment is deposited rapidly.

Also produced by
lahars

and
mudflows
.

SEDIMENTATION AND SEDIMENTARY ROCKS

SEDIMENTARY STRUCTURES

CROSS
-
BEDDING

Consists of sedimentary layers deposited at an angle to


the underlying set of beds.

Navajo Sandstone

Utah

Coconino Sandstone

Arizona