Weathering and sedimentary environments

Carbonation

C02 reacts with rain water to produce carbonic acid

Hydrolysis

The chemical breakdown of a compound due to reaction with water

Spheroidal weathering

Water enters natural joints in the rock and weathers the corners to become rounded

Oxidation

Iron rich minerals incorporate oxygen atoms into their structures

Freeze thaw weathering

Repeated freezing and expanding, melting and contracting over many years

Insolation

The expansion and contraction of rock due to the sun

Exfoliation

Pressure reduces as rocks are uplifted forming cracks parallel to the exposed surfaces

Abrasion

The grinding away of rock by other rock particles

Attrition

Wearing down due to collisions

Suspension

Transport in water

Saltation

Transport by bouncing. Pebbles and small stones

Traction

Transport by rolling and sliding. Large rocks and boulders

Products of weathering (4)

rock fragments, unreactive quartz grains, clay minerals, ions in solution

Mature sediments, eg. sandstone (5)

well sorted, rounded, fine grains, long transport, high energy

Immature sediments, eg. breccia (5)

poorly sorted, angular, coarse grains, short transport, low energy

Wadi channel - flash flood channel, eg. conglomerate (5)

high energy for short periods, coarse grained, poorly sorted, angular, immature

Alluvial fan - fan shaped deposit, eg. arose (5)

high energy for short periods, coarse grained, poorly sorted, angular, immature

Aeolian dunes, eg. desert sandstone (5)

long transport, fine grained, well sorted, rounded, mature

Playa lake - temporary lake (2)

High evaporation rates, ions in solution condense and precipitate out least soluble first

Pediment - loose material weathered by insolation, eg. breccia (6)

fallen by gravity, no transport, coarse grained, angular, poorly sorted, immature

How is carbonate mud (micrite) formed

Forms from the recrystallisation of carbonate mud during diagenesis or when calcium carbonate is precipitated as fine grains

Where does carbonate mud (micrite) form

Forms in calm waters where the grains can settle

How does oolitic limestone form

Forms when calcium carbonate is deposited on the surface of sand grains then rolled around by waves

Where does oolitic limestone form

Forms in warm shallow waters with high tidal activity

How is a reef limestone formed

Formed by chemical sedimentary processes such as precipitation

Point bar

sediment deposited on the inside of a meander where energy is low

Sorting of a point bar

Moderately well sorted, sub rounded, micaceous limestone

River cliffs

erosion occurs on the outside bend of a meander where energy is high

Channel lag

Coarse grained sediment left in a channel after finer grained particles have been transported away