Chapter 3- Sedimentary Rocks and Processes Flashcards
Weathering
in situ breakdown of rocks by exposure to the atmosphere, water, and organic matter. Can be chemical, physical or biological
carbonation
calcite + carbonic acid -> calcium + hydrogen carbonate ions in solution / CaCO3 + H2CO3 -> Ca2+ + 2HCO3 -
Hydrolysis
the reactions between minerals and water, causing the minerals to decompose
exfoliation
occurs when sheets of rock split off due to differential expansion and contraction of minerals during diurnal heating and cooling
frost shattering
caused by expansion of freezing water in fractures which forces rocks apart
pressure release
caused by expansion and fracturing of rock due to removal of overlying rock
clast
fragment of broken rock created by mechanical weathering and/or erosion
root action
causes mechanical and chemical weathering of rocks by the wedging action of plant roots
burrowing
burrowing animals mix and bring rock and soil particles to the surface, facilitates weathering at greater depth
erosion
the wearing away of a land surface and removal of sediment by means of transport
abrasion
the wearing away of the land surface
Attrition
wearing down of sedimentary grains due to collisions with each other during transport
Mineralogical maturity
a measure of the extent to which minerals have been destroyed by weathering and attrition
solution
transport of ions dissolved in water, commonly K, Ca and Na
Traction
transport of a material by rolling and sliding along a surface
Saltation
transport of material by bouncing
suspension
transport of a mineral by water or air without it touching the Earth’s surface
Roundness
defines the relationship of the outline of the grain to the shape of a circle
shape
describes the relationship of a grain to the shape of a sphere, rod, disc, or blade
phi scale
expresses grain size on a logarithmic scale. Phi increases arithmetically as the grain size decreases geometrically
textural maturity
a measure of the extent to which a sediment is well sorted and well rounded
sorting
the degree to which particles in a sediment are the same size
coefficient of sorting (p)
p= phi 84 - phi16 / 2
Rock: coarse grained/rudaceous, siliciclastic, angular clasts, poorly sorted, set in a matrix
breccia- form as scree, alluvial fans, wadi deposits and volcanic/pyroclastic breccia
Rock: coarse grained/rudaceous siliciclastic rock, rounded clasts, poorly sorted, may be set in a mineral cement
Conglomerate, beach and river channel deposits
Rock: 0.0625-2mm/arenaceous, mainly comprised of quartz but can include mica and feldspar
sandstone, any environment
Rock: over 90% quartz, well sorted and rounded grains, white grey in colour, little to no unstable minerals
orthoquartzite, beach and shallow marine deposits
Rocks: grains around 1mm, red in colour, well sorted and rounded, high sphericity, quartz and iron oxide
desert sandstone, commonly form in arid environments
Rock: medium to coarse grained, at least 25% feldspar, pink, moderately sorted and rounded
Arkose, alluvial fan, arid environments
Rock: fine to coarse grains, dark coloured, poorly sorted, angular clasts, 155 clay matrix
Greywacke
Rock: fine/argillaceous, plastic and mouldable, may be high in organic content making it darker, clay minerals
Clay
Rock: dark grey, fine grained siliciclastic, clay minerals, no preferred alignment, no plasticity
mudstone
Rock: dark coloured, fine grained siliciclastic, distinctive layers due to alignment of minerals, fissile, brittle, impermeable
shale
Mechanically formed
sedimentary rocks result from processes pf erosion, transport, and depositon of clasts
siliciclastic rocks
rocks formed from sediments composed of silicate minerals and rock fragments
matrix
background material of small grains in which the larger grains occur
clay minerals
a group of sub-microscopic platy aluminium silicates related to mica
plasticity
ability of a material to permanently change shape without fracturing
fissile
refers to tendency of a rock to split into thin layers
rudaceous
sedimentary rocks with grain size of clasts bigger than 2mm
arenaceous
sedimentary rocks with grain size between 0.0625-2mm
agrillaceous
sedimentary rocks with grain size smaller than 0.0625mm
texture
refers to the relationship between grains in a rock, including size, shape, sorting, roundness and packing of sedimentary grains
fossil
remains of an organism that lived more than 10.000 years ago, includes skeletons, tracks, impressions, borings, and casts
Chemical limestone
formed from precipitation of CaCO3 from sea water
biological limestone
formed from organic remains ie shell fragments
Ooliths
spherical grains showing concentric banding of carbonate material, less than 2mm in diameter
pisoliths
ooliths that are bigger than 2mm in diamter
micrite
a microcrystalline calcite, a depositional matrix of lime mud
sparite
a coarse grained crystalline calcite cement, formed after deposition
cement
minerals precipitated between grains in sedimentary rocks binding them together
pellets
carbonate materials excreted by animals. lack concentric structure, usually 0.04-0.08 mm in diameter
interclasts
grains formed by erosion of material within a basin of deposition
Mudstone (dunham clas)
mud supported, less than 10% grains
Wackestone (dunham clas)
mud supported, more than 10% grains
Packstone (dunham clas)
grain supported, contains mud
grainstone (sunham clas)
grain supported, lacks mud
Diagenesis
all changes that take place in sediments at low temperatures and pressures near the earth’s surface
Lithification
the process of changing unconsolidated sediment into rock
pressure dissolution/solution / chemical compaction
when minerals dissolve as a result of applied pressure, leads to a reduction of volume in the rock
porosity
the volume of the rock occupied by spaces between sedimentary grains. A reduction in porosity squeezes fluid from the pore spaces
Peat
partly decomposed plant remains with high water content
coal
carbon rich rock formed from fossil plant remains
permeability
ability of a rock to allow fluids to pass through it
Compaction
load pressure acting vertically causes the sediments to become more closely packed, reducing the porosity of the rock
Cementation
minerals are precipitated from ground water to fill the pore spaces of rocks
most common cementing minerals (4)
quartz, calcite, iron minerals, clay minerals
Lignite
type of coal with a relatively high water content, brown and crumbly with woody material
bituminous coal
coal with a relatively high carbon content, black in colour with bright and dull layers
anthracite
coal with very high carbon content, hard with a metallic lustre
facies
all characteristics of a sedimentary rock that come from it’s environment of deposition
lithofacies
includes physical and chemical characteristics of a rock
biofacies
include palaeontological characteristics of a rock
facies assossiation
describes a group of sedimentary facies that occur together and typically represent one depositional environment
Uniformitarianism
‘the present is the key to the past’
striations
scratches formed by rocks carried in moving ice. they can be used to tell the direction of movement of ancient ice sheets
tillite
rock formed from very poorly sorted and varied material dropped by the ice
Varves
annual lake clays and silts in distinctive thin layers
Fluvio glacial sands and gravels
sediements produced by meltwater streams flowing from a glacier
Polymictic conglomerate
coarse grained sedimentary rock containing clasts of many different rock types
oligomictic conglomerate
a coarse grained sedimentary rock containing clasts of a few different rock types
monomictic conglomerate
a coarse grained sedimentary rock containing clasts of a single rock type
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
littoral zone
area between the extreme high and extreme low water of spring tides
Characteristics of river transport
sorting by size, sub-mature
characteristics of wind transport
very small size range, mineralogically mature
Characteristics of glacial transport
very poorly sorted, long axes parallel to direction of movement
characteristics of shallow marine environments
reverse sorting by size, deposits contain more resistant grains
Palaeo-environmental indicator
a sedimentary structure formed in a specific environmental condition in the ancient past
palaeocurrent indicator
sedimentary structure that allows the direction of an ancient current to be deduced
way-up structures
structure that allows geologists to determine if the rock is in it’s original orientation
Cross bedding
within the bed, way up and palaeocurrent indicator, typically indicates large scale desert dunes
Graded bedding
within the bed, way up structure, can indicate turbidite deposits
imbricate structure
within the bed, palaeo-current, indicates river channels
salt pseudomorphs
within the bed, doesn’t show way up or palaeocurrent, indicates an environment of arid evaporation
Ripple marks
on the bedding plane, way up indicator, asymmetrical can be used for palaeo-current, indicates beach, shallow seas or dunes
desiccation cracks
on bedding plane, way up structure, indicates environment of arid evaporation
flute casts
on bedding plane, way up structure and palaeocurrent, indicates turbidite deposits on deep ocean floor
