ocr geology a level sedimentary rocks and processes

• what is weathering

  breakdown on rocks in situ. chemical, biological, and mechanical
• what is carbonation process

  carbon dioxide in rains and reacts with soil to create carbonic acid.calcite +carbonic acid=calcium+hydrogen carbonate ions in a solution.mainly affects limestone leaves clay residue behind
• what are the different types of weathering

  chemical-carbonation,hydrolysismechanical-exfoliation,frost shattering,pressure releasebiological-root action,burrowing
• what is hydrolysis

  reaction between water and silicate minerals. sped up if water contains carbonic acid.
• what is exfoliation

  heat expands rock bu they contract at night. eventually weakens rock and causes it to break off.
• what is frost shattering

  water enters cracks in rock. freezes and expands at night. melts and contracts in day. more water gets in and process repeats until rock is eventually pushed off and called scree
• what is pressure release

  surface rock being eroded away, causing rock below to have less pressure on top and expand. as they expand, the rock fractures
• what is root action

  tree roots grow along bedding planes which break rock apart
• what is burrowing

  animals that burrow pushes rocks to surface it is then weathered as it is on the surface
• what is erosion

  wearing away of rock through a medium
• what is abrasion


  sediment being hit against as large surafce
• what is attrition

  wearing down of sediment due to collisions with other sediment
• what is solution

  transport of particles dissolved within the water
• what is traction

  rolling large sediment across the floor
• what is saltation,

  bouncing material down the river bed
• what is suspension

  transport of material without it touching the floor
• what are the six types of grain shape/roundness

  very angular,angular,sub angular,sub rounded,rounded, and well rounded
• what are the sediment size names

  clay,silt,sand(very fine), sand(fine), sand(medium),sand(coarse,sand(very course), gravel, pebble, cobble, boulder
• what is sorting

  the degree in which particles are the same sizecan show hoe rocks were transported
• what does mechanically formed mean

  sedimentary rocks result from the processes of erosion,transport, and deposition of clasts
• what are siliciclastic rocks

  form from sediments composed of silicate minerals and rock fragments
• what is a matrix

  background material of small grains in which larger grains occur
• what is plasticity

  the ability of a material to permanently change shape without fracturing
• what does fissile mean

  the ability for rocks to split into thin layers
• what is breccia

  a course grained siliciclastic rock. angular clasts. poorly sorted. usually form as scree.

  
• what is roundness

  relationship of the rock shape to a circle
• what is a rocks shape

  defines the relationship of the outside of a grain to the shape scale
• what is a phi scale

  expresses grain size on a logarithmic scale
• what is textural maturity

  a measure of the extent to which a sediment is well sorted and well rounded
• what is a conglomerate

  coarse grained siliclastic rock. rounded clasts. poorly sorted. commonly found at beach/river channel deposits

  
• what are sandstones

  grain size between 00625-2mmfound is nearly all sedimentary environmentsmainly made from quartz.

  
• what is orthoquartzite

  quart grains cemented together by quartz cement, white/grey in colour. well rounded and well sorted. found in beach deposits

  
• what is desert sandstone

  red in colour due to oxidisation. very well sorted, very well rounded. coarse sand size. high sphericity. form in arid environments, as wind blown sands

  
• what is arkose

  medium to course grained sandstone. mainly quartz and feldspar. usually found in alluvial fan environments. moderately sorted. sub-angular/sub rounded.

  
• what is greywacke

  sandstone that is fine to course grain size. dark coloured. poorly sorted. angular/sub angular clasts. show graded bedding and deposited in turbidity currents.
• what are ooliths

  spherical grains showing concentric banding of carbonate material

  
• what is diagenesis

  all the changes that take place in sediments at low temperature and pressure, very close to surface.
• what is lithification

  the process of changing sediment into rock
• what is pressure dissoloution


  occurs where pressure causes minerals to dissolve
• what is porosity

  the volume occupied by spaces in between sedimentary grains.