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