Chapter 3- Sedimentary Rocks and Processes Flashcards
(126 cards)
1
Q
Weathering
A
in situ breakdown of rocks by exposure to the atmosphere, water, and organic matter. Can be chemical, physical or biological
2
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carbonation
A
calcite + carbonic acid -> calcium + hydrogen carbonate ions in solution / CaCO3 + H2CO3 -> Ca2+ + 2HCO3 -
3
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Hydrolysis
A
the reactions between minerals and water, causing the minerals to decompose
4
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exfoliation
A
occurs when sheets of rock split off due to differential expansion and contraction of minerals during diurnal heating and cooling
5
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frost shattering
A
caused by expansion of freezing water in fractures which forces rocks apart
6
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pressure release
A
caused by expansion and fracturing of rock due to removal of overlying rock
7
Q
clast
A
fragment of broken rock created by mechanical weathering and/or erosion
8
Q
root action
A
causes mechanical and chemical weathering of rocks by the wedging action of plant roots
9
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burrowing
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burrowing animals mix and bring rock and soil particles to the surface, facilitates weathering at greater depth
10
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erosion
A
the wearing away of a land surface and removal of sediment by means of transport
11
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abrasion
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the wearing away of the land surface
12
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Attrition
A
wearing down of sedimentary grains due to collisions with each other during transport
13
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Mineralogical maturity
A
a measure of the extent to which minerals have been destroyed by weathering and attrition
14
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solution
A
transport of ions dissolved in water, commonly K, Ca and Na
15
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Traction
A
transport of a material by rolling and sliding along a surface
16
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Saltation
A
transport of material by bouncing
17
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suspension
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transport of a mineral by water or air without it touching the Earth’s surface
18
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Roundness
A
defines the relationship of the outline of the grain to the shape of a circle
19
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shape
A
describes the relationship of a grain to the shape of a sphere, rod, disc, or blade
20
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phi scale
A
expresses grain size on a logarithmic scale. Phi increases arithmetically as the grain size decreases geometrically
21
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textural maturity
A
a measure of the extent to which a sediment is well sorted and well rounded
22
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sorting
A
the degree to which particles in a sediment are the same size
23
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coefficient of sorting (p)
A
p= phi 84 - phi16 / 2
24
Q
Rock: coarse grained/rudaceous, siliciclastic, angular clasts, poorly sorted, set in a matrix
A
breccia- form as scree, alluvial fans, wadi deposits and volcanic/pyroclastic breccia
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Rock: coarse grained/rudaceous siliciclastic rock, rounded clasts, poorly sorted, may be set in a mineral cement
Conglomerate, beach and river channel deposits
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Rock: 0.0625-2mm/arenaceous, mainly comprised of quartz but can include mica and feldspar
sandstone, any environment
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Rock: over 90% quartz, well sorted and rounded grains, white grey in colour, little to no unstable minerals
orthoquartzite, beach and shallow marine deposits
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Rocks: grains around 1mm, red in colour, well sorted and rounded, high sphericity, quartz and iron oxide
desert sandstone, commonly form in arid environments
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Rock: medium to coarse grained, at least 25% feldspar, pink, moderately sorted and rounded
Arkose, alluvial fan, arid environments
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Rock: fine to coarse grains, dark coloured, poorly sorted, angular clasts, 155 clay matrix
Greywacke
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Rock: fine/argillaceous, plastic and mouldable, may be high in organic content making it darker, clay minerals
Clay
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Rock: dark grey, fine grained siliciclastic, clay minerals, no preferred alignment, no plasticity
mudstone
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Rock: dark coloured, fine grained siliciclastic, distinctive layers due to alignment of minerals, fissile, brittle, impermeable
shale
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Mechanically formed
sedimentary rocks result from processes pf erosion, transport, and depositon of clasts
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siliciclastic rocks
rocks formed from sediments composed of silicate minerals and rock fragments
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matrix
background material of small grains in which the larger grains occur
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clay minerals
a group of sub-microscopic platy aluminium silicates related to mica
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plasticity
ability of a material to permanently change shape without fracturing
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fissile
refers to tendency of a rock to split into thin layers
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rudaceous
sedimentary rocks with grain size of clasts bigger than 2mm
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arenaceous
sedimentary rocks with grain size between 0.0625-2mm
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agrillaceous
sedimentary rocks with grain size smaller than 0.0625mm
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texture
refers to the relationship between grains in a rock, including size, shape, sorting, roundness and packing of sedimentary grains
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fossil
remains of an organism that lived more than 10.000 years ago, includes skeletons, tracks, impressions, borings, and casts
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Chemical limestone
formed from precipitation of CaCO3 from sea water
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biological limestone
formed from organic remains ie shell fragments
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Ooliths
spherical grains showing concentric banding of carbonate material, less than 2mm in diameter
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pisoliths
ooliths that are bigger than 2mm in diamter
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micrite
a microcrystalline calcite, a depositional matrix of lime mud
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sparite
a coarse grained crystalline calcite cement, formed after deposition
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cement
minerals precipitated between grains in sedimentary rocks binding them together
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pellets
carbonate materials excreted by animals. lack concentric structure, usually 0.04-0.08 mm in diameter
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interclasts
grains formed by erosion of material within a basin of deposition
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Mudstone (dunham clas)
mud supported, less than 10% grains
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Wackestone (dunham clas)
mud supported, more than 10% grains
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Packstone (dunham clas)
grain supported, contains mud
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grainstone (sunham clas)
grain supported, lacks mud
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Diagenesis
all changes that take place in sediments at low temperatures and pressures near the earth's surface
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Lithification
the process of changing unconsolidated sediment into rock
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pressure dissolution/solution / chemical compaction
when minerals dissolve as a result of applied pressure, leads to a reduction of volume in the rock
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porosity
the volume of the rock occupied by spaces between sedimentary grains. A reduction in porosity squeezes fluid from the 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
ability of a rock to allow fluids to pass through it
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Compaction
load pressure acting vertically causes the sediments to become more closely packed, reducing the porosity of the rock
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Cementation
minerals are precipitated from ground water to fill the pore spaces of rocks
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most common cementing minerals (4)
quartz, calcite, iron minerals, clay minerals
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Lignite
type of coal with a relatively high water content, brown and crumbly with woody material
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bituminous coal
coal with a relatively high carbon content, black in colour with bright and dull layers
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anthracite
coal with very high carbon content, hard with a metallic lustre
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facies
all characteristics of a sedimentary rock that come from it's environment of deposition
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lithofacies
includes physical and chemical characteristics of a rock
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biofacies
include palaeontological characteristics of a rock
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facies assossiation
describes a group of sedimentary facies that occur together and typically represent one depositional environment
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Uniformitarianism
'the present is the key to the past'
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striations
scratches formed by rocks carried in moving ice. they can be used to tell the direction of movement of ancient ice sheets
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tillite
rock formed from very poorly sorted and varied material dropped by the ice
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Varves
annual lake clays and silts in distinctive thin layers
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Fluvio glacial sands and gravels
sediements produced by meltwater streams flowing from a glacier
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Polymictic conglomerate
coarse grained sedimentary rock containing clasts of many different rock types
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oligomictic conglomerate
a coarse grained sedimentary rock containing clasts of a few different rock types
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monomictic conglomerate
a coarse grained sedimentary rock containing clasts of a single rock type
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till fabric analysis
a method of tracing the former movement direction of ice by taking compass bearings on the long axes of large clasts in till deposits
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littoral zone
area between the extreme high and extreme low water of spring tides
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Characteristics of river transport
sorting by size, sub-mature
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characteristics of wind transport
very small size range, mineralogically mature
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Characteristics of glacial transport
very poorly sorted, long axes parallel to direction of movement
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characteristics of shallow marine environments
reverse sorting by size, deposits contain more resistant grains
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Palaeo-environmental indicator
a sedimentary structure formed in a specific environmental condition in the ancient past
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palaeocurrent indicator
sedimentary structure that allows the direction of an ancient current to be deduced
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way-up structures
structure that allows geologists to determine if the rock is in it's original orientation
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Cross bedding
within the bed, way up and palaeocurrent indicator, typically indicates large scale desert dunes
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Graded bedding
within the bed, way up structure, can indicate turbidite deposits
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imbricate structure
within the bed, palaeo-current, indicates river channels
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salt pseudomorphs
within the bed, doesn't show way up or palaeocurrent, indicates an environment of arid evaporation
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Ripple marks
on the bedding plane, way up indicator, asymmetrical can be used for palaeo-current, indicates beach, shallow seas or dunes
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desiccation cracks
on bedding plane, way up structure, indicates environment of arid evaporation
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flute casts
on bedding plane, way up structure and palaeocurrent, indicates turbidite deposits on deep ocean floor
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point bar
deposits of sand or coarser grained sediments inside the meander
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channel lag
coarse grained sediment left in the channel after finer grained sediments have been transported away
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flood plain
flat land adjacent to a river over which it spreads when in flood
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upward fining
describes a series of layers where grain size decreases upwards as energy decreases
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Products of sedimentation in a fluvial depositional environment
alluvial fan breccias/conglomerates, channel conglomerates and sandstones in meandering and braided rivers, flood plain clays and silts
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characteristics of ancient river deposits
limited lateral extent, lignite plant fossils in sandstones but lack of other fossils, mix of conglomerates, sandstones, and shales together
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flash floods
brief but very high energy flows of water over a surface or down a river channel, usually caused by heavy rainfall
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wadis
river channel deposits in hot desert regions in which flow may occur very occasionally
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playa lakes
temporary lakes formed by storm run off in deserts having inland drainage
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evaporites
sedimentary rocks resulting from evaporation of saline water
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Products of deposition in a hot desert environment
wadi conglomerates, alluvial fan arkose, aeolian sandstones, playa lake evaporites
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Evaporite minerals (most to least soluble) (5)
K minerals, ie sylvite
halite
anhydrite
gypsum
calcite
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characteristics of ancient desert deposits
red colour formed by iron oxide, well sorted and well rounded sandstones with large scale cross bedding, evaporites and clays formed in playa lakes, dessication cracks and salt pseudomorphs
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spring tides
the tides with the greatest range, occur every two weeks
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longshore drift
combination of littoral drift and beach drift
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glauconite
green-coloured mineral, iron and potassium silicate of the mica group, formed on continental shelves
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transgression
occurs when the sea spreads over the land
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regression
occurs when the sea retreats from the land
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characteristics of ancient shallow sea deposits
beds of well sorted and rounded sandstone with symmetrical ripple marks or small-scale cross-bedding, shales with abundant fossils, lateral variation as sediments are laid down at the same time on the continental shelf
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macrofossils
fossils large enough to be visible to the naked eye
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microfossils
usually less than 1mm, can only be seen with a microscope
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detrial
fragments derivied from mechanical weathering of rocks
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cryptocrystalline
material that's too fine grained for individual crystals to be distinguished using a petrological microscope
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radiolaria
planktonic animals with a siliceous test
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test
hard shell of some planktonic animals
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calcareous ooze
pelagic clay containing more than 30% biogenic skeletal material CaCo3/calcium carbonate
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characteristics of deposits in an ancient marine carbonate environment
composition of calcium carbonate, abundant fossils in most limestones, light colour due to lack of terrigenous sediment
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