2.3 Sedimentary Processes and Structures
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- Created by: 11pha
- Created on: 02-03-17 09:31
Weathering
the in situ chemical alteration and mechanical and biological breakdown of rocks by exposure to the atmosphere, water and organic matter
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Carbonation
the reation between carbonic acid and minerals
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Hydrolysis
the reation between minerals and water causing the minerals to decompose
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Exfoiliation
occurs when sheets of rock split off due to differential expansion and contraction of minerals during diurnal heating and cooling
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Frost shattering
caused by the expansion of freezing water in fractures which forces rocks apart
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Pressure release
the expansion and fracturing of rock due to removal of overlying rocks
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Root action
causes the mechanical and chemical weathering of rocks by the wedging action of plant roots
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Burrowing
by invertebrate and vertebrate animals mixes and brings to the surface rock and soil particles. This facilitates weathering at greater depth, by providing access for atmospheric gases and water
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Erosion
the wearing away of the land surface and removal of sediment by means of transport
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Abrasion
wearing away of the Earth's surface by the wind, water or ice dragging sediment over or hurling it at a surface
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Attrition
wearing down of sedimentary grains due to collisions with other grains during transport
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Solution
transport of ions dissolved in water
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Suspension
the transport of material in water or air, without it touching the Earth's surface
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Saltation
the transport of material by bouncing
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Traction
the transport of material by rolling and sliding along a surface
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Roundness
defines the relationship of the outline of a grain to a circle. A grain with few sharp corners has a high degree of roundness
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Shape
the relationship of a grain to a sphere, rod, disc or blade
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Phi Scale
expresses the grain size of a logarithmic scale. Phi values increase arithmetically as the grain size decreases geometrically
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Grain Size
the average diameter of the grains of sediment being studied
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Sorting
the degree to which particles are the same size
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Clast
a rock fragment or grain resulting from the breakdown of larger rocks
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Pyroclast
fragment of rock from a volcanic explosion
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Bioclastic
a biologically formed sedimentary rock composed of fragmented organic material
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Mechanically Formed
the erosion, transport and deposition of clasts are by mechanical processes
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Chemically Formed
the weathering transport and deposition of these rocks is by chemical processes
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Biologically formed
organisms such as sea creatures or trees extract ions that are in solution in sea water or groundwater and turn them into organic tissue, such as shells or wood
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Fossils
the remains of an organism that lived more than 10000 years ago including skeletons, tracks, impressions, trails, borings and clasts
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Rudaceous
sedimentary rocks are those in which the grain size of clasts is greater than 2 mm
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Arenaceous
sedimentary rocks are those in which the grain size of clasts is 0.0625 to 2 mm
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Argillaceous
sedimentary rocks are those in which the grain size of casts is less than 0.0625 mm
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Texture
refers to the interrelationship of grains in a rock. Includes grain size, sorting, roundness, shape and packing of sedimentary grains
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Clay Minerals
a group of sub-microscopic platy aluminium silicates related to mica
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Plasticity
the ability of a materia to permanently change shape without fracturing
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Fissile
refers to the tendency of a rock to split into thin layers
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Matrix
the background material, consisting of small particles in which larger fragments occur
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Micrite
a microcrystalline calcite, a depositional matrix of lime mud
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Sparite
a coarse grained (>0.01 mm) crystalline calcite cement, formed after deposition
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Cement
a material that binds sedimentary grains together
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Paleocurrent indicator
a sedimentary structure that allows the direction of an ancient current to be deduced
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Palaeo-environment indicator
a sedimentary structure formed in specific environmental conditions in the ancient part
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Way Up Indicator
allows geologists to work out whether rocks are in their original orientation or whether they have been inverted by folding
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Diagenesis
all changes that take place in sediments at low temperature and pressure, at or near the Earth's surface
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Lithification
the process of changing unconsolidated sediment into rock
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Porosity
the colume occupied by spaces in between sedimentary grains. A reduction in porosity squeezes fluids from pore spaces
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Peat
partly decomposed plant remains with high water content
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Coal
carbon-rich rock formed from fossil plant remains
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Permeability
the ability of a rock to allow fluids such as water to pass through it
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Till
a poorly sorted sediment ranging from boulders to clay size, deposited from ice and not reworked by water
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Erratics
clasts of a different rock type from that found locally and therefore transported from another area
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Flucio-glacial deposits
sediments produced by meltwater streams flowing from a glacier
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Varves
fine grained banded deposits from glacial lakes containing coarses pale material deposited in summer and finer dark material deposited in winter
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Upward fining
describes a series of layers in whhich average grain size decreases upwards as energy decreases
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Channel Lag
coarse grained sediment deposit left in a channel after finer grained particles have been transported away
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Point Bar
a deposit of sand or coarser grained sediments on the inside of a meander bend
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Flood Plain
flat land adjacent to a river over which it spreads when in flood
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Flash Flood
a brief but very high energy flow of water over a surface or down a river channel, usually caused by heavy rain
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Wadi
a river channel in a hot desert region in which flow may occur very occasionally
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Playa Lakes
a temporary lake formed by storm run-off in deserts having inland drainage
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Evaporites
sedimentart rocks resulting from the exaporation of saline water
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Foresets
sedimentart rocks resulting from the exaporation of saline water
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Bottomsets
the lowest horizontal layers of a delta, commonly consisting of shales
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Cyclotherm
represents layers repeated due to cyclic sedimentation
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Bioturbation
the distance of sediment by the activities of organisms
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Seat Earth
a sandy or clay-rich fossil soil found beneath a coal seam. It represents the soil in which coal forming plants grew and frequently contains carbonised traces of plant roots
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Distributary
a stream channel that takes water away from the main stream channel
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Topsets
the uppermost horizontal layers of a delta commonly consisting of channel sandstones, coal and seat earth
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Spring Tides
the tides with the greates range, and occur about every two weeks
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Tidal range
the vertical difference in height between extreme high and extreme low water
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Littoral Zone
the area between extreme low and extreme high water of the spring tide
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Rip Current
a narrow fast current flowing seaward, away from the coastline
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Transgression
occurs where the sea spreads over the land
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Glauconite
a green-coloured mineral formed on continental shelves
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Resgression
occurs where the sea retreats from the land
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Macrofossil
fossil large enough to be visible
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Microfossil
a fossil that is less than 1 mm and can only be seen with a lens or microscope
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Detrital
describes fragments derived from the mechanical weathering of rocks
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Taslus
mass of coarse rock fragments accumulating at the foot of a slope
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Supersaturated
a solution that contains more dissolved substance than does a saturated solution
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Brine
a concentrated solution of salts formed by partial evaporation of sea water
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Barred Basin
a bay partly isolated from the open ocean by a bar
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Turbidity Current
a high velocity current that flows down a gentle gradients because the sediment dispersed within it makes it denser than sea water
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Turbidite
a upward fining deposit of greywacke deposited from a turbidity current
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Bourma Sequence
an idealised sequence of sediments and sedimentary structures seen in a trubidite deposit
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Plankton
minute organisms living in the surface layers of the ocean, transported by currents
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Diatom
a planktonic plant that secretes siliceous material
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Radiolara
planktonic animals with a siliceous test
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Calcareous ooze
pelagic clay containing >30% biogenic skeletal material made of calcite
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Siliceous ooze
pelagiv clay containing >30% biogenic skeletal material made of silica
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Carbonate compensation depth
the depth in the oceans at which the rate of solution of solid CaCO3 equals the rate of supply
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Other cards in this set
Card 2
Front
Carbonation
Back
the reation between carbonic acid and minerals
Card 3
Front
Hydrolysis
Back
Card 4
Front
Exfoiliation
Back
Card 5
Front
Frost shattering
Back
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