AS Sedimentary Rocks

Question 1

Weathering

Answer 1

the in situ chemical alteration and mechanical and biological breakdown of rocks by exposure to the atmosphere, water and organic matter.

Question 2

Carbonation

Answer 2

the reaction between carbonic acid and minerals.

Question 3

Hydrolysis

Answer 3

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

Question 4

Exfoliation

Answer 4

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

Question 5

Frost shattering

Answer 5

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

Question 6

Pressure release

Answer 6

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

Question 7

Root action

Answer 7

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

Question 8

Burrowing

Answer 8

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.

Question 9

Erosion

Answer 9

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

Question 10

Abrasion

Answer 10

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.

Question 11

Attrition

Answer 11

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

Question 12

Mineralogical maturity

Answer 12

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

Question 13

Solution

Answer 13

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

Question 14

Traction

Answer 14

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

Question 15

Saltation

Answer 15

the transport of material by bouncing.

Question 16

Suspension

Answer 16

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

Question 17

Roundness

Answer 17

defines the relationship of the outline of a grain to a circle. A grain with few sharp corners has a high degree of roundness.

Question 18

Shape

Answer 18

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

Question 19

Phi scale

Answer 19

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

Question 20

Textural maturity

Answer 20

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

Question 21

Sorting

Answer 21

the degree to which particles are the same size.

Question 22

Mechanically formed

Answer 22

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

Question 23

Siliciclastic rocks

Answer 23

form from sediments composed of silicate minerals and rock fragments.

Question 24

Matrix

Answer 24

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

Question 25

Clay minerals

Answer 25

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

Question 26

Plasticity

Answer 26

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

Question 27

Fissile

Answer 27

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

Question 28

Ooliths

Answer 28

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

Question 29

Micrite

Answer 29

a microcrystalline calcite, a depositional matrix of lime mud.

Question 30

Sparite

Answer 30

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

Question 31

Cement

Answer 31

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

Question 32

Pellets

Answer 32

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

Question 33

Diagenesis

Answer 33

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

Question 34

Lithification

Answer 34

the process of changing unconsolidated sediment into rock.

Question 35

Pressure dissolution

Answer 35

(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.

Question 36

Porosity

Answer 36

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

Question 37

Peat

Answer 37

partly decomposed plant remains with high water content.

Question 38

Coal

Answer 38

a carbon-rich rock formed from fossil plant remains.

Question 39

Permeability

Answer 39

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