Chapter 6: Weathering, Erosion, Sedimentary Rocks

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Weathering

Back 1

The processes by which rocks are broken down at Earths surface to produce sediment particles

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Physical Weathering

Back 2

Weathering in which solid rock is fragmented by mechanical processes that do not change its chemical composition

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Chemical Weathering

Back 3

Weathering in which the minerals in a rock are chemically altered or dissolved

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Siliciclastic Sediments

Back 4

Sediment from clastic particles produced by the weathering of rocks and physically deposited by running water, wind, or ice.

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Chemical Sediments

Back 5

A sediment formed at or near its place of deposition from dissolved materials in certain fixed proportions that produces a new chemical compound

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Biological Sediments

Back 6

A sediment formed near its place of deposition as a result of direct or indirect mineral precipitation by organisms

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Bioclastic Sediments

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A shallow-water sediment made up of fragments of shells or skeletons directly precipitated by marine organisms and consisting primarily of two calcium carbonate minerals- calcite and argonite- in variable proportions

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Sorting

Back 8

The tendency for variations in current velocity to segregate sediments according to size

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Salinity

Back 9

The total amount of dissolved substances in a given volume of water

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Sedimentary Basins

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A region where the combination of sedimentation and subsidence has formed thick accumulations of sediments and sedimentary rock

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Rift Basin

Back 11

A sedimentary basin that develops at a divergent boundary at an early stage of plate separation as the stretching and thinning of the continental crust results in subsidence

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Thermal Subsidence Basins

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A sedimentary basin that develops in the later stages of plate separation as lithosphere that was thinned and heated during the earlier rifting stages cools, becomes more dense, and subsides below sea level

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Continental Shelf

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A broad, flat, submerged platform, consisting of a thick layer of flat-laying shallow-water sediment that extends from the shoreline to the edge of the continental slope

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Flexural Basin

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A type of sedimentary basin that develops at a convergent boundary where one lithospheric plates pushes up over the other and the weight of the overriding plate causes the underlying plate to bend or flex downward

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Sedimentary Environment

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A geographic location characterized by a particular combination of climate conditions and physical, chemical, and biological processes

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Siliciclastic Sedimentary Environments

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A sedimentary environment dominated by siliclatic sediments

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Chemical and Biological Sedimentary Environments

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An area of sediment accumulation characterized by precipitates of chemical or biological origin, principally carbonates or sulfates, and most commonly formed in marine settings

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Sedimentary Structures

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Any kind of bedding or other features formed at the time of sediment deposition

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Bedding

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The formation of parallel layers or beds of sediment as particles are deposited

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Cross-Bedding

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A sedimentary structure consisting of beds deposited by currents of wind or water and inclined at angles as much as 35 degrees from the horizontal

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Ripples

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A very small ridge of sand or silt whose long dimension is at right angles to the current that formed it

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Bioturbation

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The process by which organisms rework existing sediments by burrowing through them

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Bedding Sequences

Back 23

A sequences of interbedded and vertically stacked layers of different sedimentary rock types

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Diagnesesis

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The physical and chemical changes, caused by pressure, heat, and chemical reactions, by which buried sediments are lithified to form sedimentary rocks

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Cementation

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A diagenesis change in which minerals are precipitated in the pores between sediment particles and bind them together

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Porosity

Back 26

The percentage of a rocks volume consisting of open pores between particles

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Compaction

Back 27

A diagnetic decrease in the volume and porosity of a sediment as its particles are squeezed closer together by the weight of overlying sediments

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Lithification

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The conversion of sediment into solid rock by compaction and cementation

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Gravel

Back 29

The coarsest siliclatic sediment consisting of particles larger than 2 mm in diameter and including pebbles, cobbles, and boulders

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Conglomerate

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A sedimentary rock composed of pebbles, cobbles, and boulders; the lithified equivalent of gravel

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Sand

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A siliclastic sediment consisting of medium-sized particles, ranging from 0.062 to 2 mm diameter

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Sandstone

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The lithified equivalent of sand

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Silt

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A siliclastic sediment in which most of the particles are between 0.0039-0.062 mm in diameter

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Mud

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A fine-grained siliclatic sediment mixed with water, in which most of the particles are less than 0.062 mm in diameter

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Mudstone

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A blocky, poorly bedded, fine-grained sedimentary rock produced by the lithification of mud

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Shales

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A fine-grained sedimentary rock composed of silt plus a significant component of clay, which causes it to break readily along the bedding planes

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Clay

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A siliclatic sediment in which most of the particles are less than 0.0039 mm in diameter and which consist largely of clay minerals, the most abundant in fine-grained sedimentary rocks

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Claystones

Back 38

A sedimentary rock made up exclusively of clay-sized particles