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Geology AS > AS Sedimentary Rocks > Flashcards

AS Sedimentary Rocks Flashcards

1
Q

Weathering

A

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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2
Q

Carbonation

A

the reaction between carbonic acid and minerals.

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3
Q

Hydrolysis

A

is the reaction between minerals and water, causing the minerals to decompose.

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4
Q

Exfoliation

A

occurs when sheets of rock split off due to differential expansion and contraction of minerals, during diurnal heating and cooling.

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5
Q

Frost shattering

A

caused by the expansion of freezing water in fractures, which forces rocks apart.

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6
Q

Pressure release

A

caused by the expansion and fracturing of rock due to removal of overlying rock.

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7
Q

Root action

A

causes the mechanical and chemical weathering of rocks by the wedging action of plant roots.

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8
Q

Burrowing

A

by invertebrate and vertebrate animals mixes and brings rock and soil particles to the surface. This facilitates weathering at greater depth, by providing access for atmospheric gases and water.

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9
Q

Erosion

A

the wearing away of the land surface and removal of sediment by means of transport.

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10
Q

Abrasion

A

the wearing away of the Earth’s surface by the action of wind, water or ice dragging sediment over or hurling it at a surface.

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11
Q

Attrition

A

the wearing down of sedimentary grains due to collisions with other grains during transport.

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12
Q

Mineralogical maturity

A

a measure of the extent to which minerals have been destroyed by weathering and attrition.

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13
Q

Solution

A

the transport of ions dissolved in water, particularly K, Ca and Na.

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14
Q

Traction

A

the transport of material by rolling and sliding along a surface.

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15
Q

Saltation

A

the transport of material by bouncing.

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16
Q

Suspension

A

the transport of material in water or air, without it touching the Earth’s surface.

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17
Q

Roundness

A

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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18
Q

Shape

A

defines the relationship of a grain to a sphere, rod, disc or blade.

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19
Q

Phi scale

A

expresses grain size on a logarithmic scale. Phi values increase arithmetically as the grain size decreases geometrically.

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20
Q

Textural maturity

A

a measure of the extent to which a sediment is well sorted and well rounded.

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21
Q

Sorting

A

the degree to which particles are the same size.

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22
Q

Mechanically formed

A

sedimentary rocks result from the processes of erosion, transport and deposition of clasts.

23
Q

Siliciclastic rocks

A

form from sediments composed of silicate minerals and rock fragments.

24
Q

Matrix

A

the background material of small grains in which larger grains occur.

25
Q

Clay minerals

A

a group of sub-microscopic platy aluminium silicates related to mica.

26
Q

Plasticity

A

the ability of a material to permanently change shape without fracturing.

27
Q

Fissile

A

refers to the tendency of a rock to split into thin layers.

28
Q

Ooliths

A

spherical grains showing concentric banding of carbonate material. These are less than 2 mm in diameter, if larger they are called pisoliths.

29
Q

Micrite

A

a microcrystalline calcite, a depositional matrix of lime mud.

30
Q

Sparite

A

a coarse grained (>0.01 mm) crystalline calcite cement, formed after deposition.

31
Q

Cement

A

the minerals precipitated between grains in sedimentary rocks binding them together.

32
Q

Pellets

A

are carbonate material excreted by animals. They lack concentric structures and are normally 0.04 to 0.08mm diameter.

33
Q

Diagenesis

A

all the changes that take place in sediments at low temperature and pressure, at or near to the Earth’s surface.

34
Q

Lithification

A

the process of changing unconsolidated sediment into rock.

35
Q

Pressure dissolution

A

(sometimes called pressure solution) occurs where minerals dissolve as the result of applied pressure. Because pressure dissolution leads to a reduction of volume of the rock in which it occurs, it is also called chemical compaction.

36
Q

Porosity

A

the volume occupied by spaces in between sedimentary grains. A reduction in porosity squeezes fluids from pore spaces.

37
Q

Peat

A

partly decomposed plant remains with high water content.

38
Q

Coal

A

a carbon-rich rock formed from fossil plant remains.

39
Q

Permeability

A

is the ability of a rock to allow fluids such as water to pass through it.

40
Q

Breccia

A

A coarse, angular grained, poorly sorted siliciclastic sedimentary rock

41
Q

Conglomerate

A

A coarse, rounded grained, poorly sorted sedimentary rock

42
Q

Orthoquartzite

A

A coarse, well sorted, well-rounded sandstone, quartz grains with a quartz cement, >90% quartz

43
Q

desert sandstone

A

A coarse, well sorted, well rounded sandstone. Red in colour due to iron present around the grains, often an iron oxide cement

44
Q

Arkose

A

Medium to coarse grained sandstone that contains over 25% feldspar. Sub angular to sub rounded.

45
Q

Greywacke

A

Poorly sorted, angular sandstone, dark in colour. Contains some feldspar and clay in addition to quartz

46
Q

Clay

A

A fine grained, plastic siliciclastic rock, contains mostly clay minerals.

47
Q

Mudstone

A

A fine grained siliciclastic rock that contains clay, mica and quartz. No layers, not plastic.

48
Q

Shale

A

A fine grained, dark, siliciclastic rock that shows alignment of flat platy clay minerals, also contains some mica and quartz.

49
Q

Oolitic limestone

A

A limestone consisting of calcium carbonate ooliths, approximately 1mm in diameter, form in tropical seas. Held together by calcite cement

50
Q

Fossiliferous limestone

A

Limestone made up of a large proportion of fossils or fossil fragments held together with a calcite cement

51
Q

Chalk

A

A limestone composed of coccoliths, the calcareous skeletons of single celled algae

52
Q

Folk classification

A

A limestone classification based on the type of grains present and the cement. E.g. oo, intra, bio, pel, micrite, sparite

53
Q

Dunham classification

A

A limestone classification system based on texture and mud content:
<10% grains - Mudstone,
>10% grains - Wackstone.
Grains and mud - Packstone,
Grains, lacks mud - Grainstone

54
Q

Difference between a matrix and a cement

A

A matrix is small background grains holding larger grains together whereas a cement is minerals precipitated out of groundwater that holds grains together

Geology AS (10 decks)

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