F2 - Surface and Internal Processes of the Rock Cycle - Key Idea 1 Flashcards
What is weathering?
The breakdown of rock in situ (no movement)
What are the three types of weathering?
Physical - Freeze Thaw, Insolation
Chemical - Carbonation, Oxidation, Hydrolysis
Biological - Chemical and Physical types
Freeze Thaw
Need - Water, fluctuating temperatures of below and above 0’C, precipitation/rainfall, joints in the rock, repeated action
Location - Scotland
Product - Scree/Lithic fragments
Process:
- water gets into joints in the rock after it is precipitated down
- when the temperature falls below 0* the water freezes and expands by ~9%
- this causing pressure to build which forces the joint apart, the temperature increases again and the ice melts
- this process is repeated until the piece of rock breaks off
Insolation (onion skin)
Need - Largely fluctuating hot and cold weather (no fixed temp), repeated action, joints in the rock
Location - South Africa
Product - Scree/Lithic fragments
Process:
- the temperature rises during the day and causes the rock to get very hot and expand
- at night the temperature dramatically drops and causes the rock to get cold therefore the rock contracts
- this is repeated and causes the rock to get weaker, joints then start to appear
- rocks begin to peel off/break off due to the weakened state of the rock
Carbonation
Need - Limestone, rock made out of Calcium Carbonate (Calcite CaCO3), carbonic acid, joints in rock
Oxidation
Hydrolysis
Biological- Physical
Biological-Chemical
Erosion
The break down of rocks during or due to transportation (movement)
Movement is caused by: rivers, wind, oceans/seas, gravity, and ice
Abrasion
Grains rub on the channel or on other grains
Attrition
Grains bump into each other or the channel
Corrosion
Where limestone dissolves due to coming into contact with an acid ????
Transportation
The movement of sediment (the products of weathering and erosion)
Traction
Grains are in constact contact with the bed
Round in shape - roll
Long in shape - slide
Resistant/new minerals
Saltation
Grains sometimes in contact with the bed sometimes not
They bounce
Resistant/new minerals
Suspension
Grains never in contact with the bed
They hang in the transporting mode
Resistant/new minerals
Solution
Dissolved in the transport mode e.g. water
Ions in solution
Movement and changes
The sediments follow the direction of the current
Movement of the sediments is dependent on the: size of the grains, the density of the grains and the velocity of the current
Decrease in current - t to deposited, sa to t, su to sa, so stays the same/slows down with the current
Increase in current - t to sa, sa to su, su+so just move quicker (but size doesn’t change)
Seposition
Evaporates
Estuary
Sedimentary rock descriptions
Size (grains)
Shape (grains)
Sorting
Colour
Composition
Cement/Matrix
Size (grains)
Size of the average grain
You need a description and measurement
Coarse (mm, cm), medium (um), fine (<187um)
High energy (little transport and erosion) ———> low energy (lots of transport and erosion)
All medium grains are sandstones
Anything to fine to see is made of clay minerals
Shape (grains)
Very well rounded - lots of transport and erosion
Rounded
Sub-rounded
Sub-angular
Angular
Very angular - little transport and erosion
Sorting
How similar the grain sizes are to each other
Very well sorted ( all roughly the same size) - long transport and lots of erosion
Well sorted
Moderately sorted
Poorly sorted
Very poorly sorted (lots of different sizes) - short transport and little erosion
Colour
Can’t say grey or dark/light grey
Can say blue grey or dark/light blue grey
You need a colour as well as grey if you say grey
Composition
The percentage of the minerals + etc within the rock
Cement/Matrix
Foramtion
Conglomerate
Size - coarse/small pebbles to large pebbles, 7mm-29mm (size depends on example given)
Shape - rounded
Sorting - very poorly sorted
Colour - beige grey
Composition - lithic fragments ?%
Cement/Matrix - sand matrix but also a calcite cement
Breccia is the same apart from the shape where the grains would be angular instead of round
Orthoquartzite Desert Sandstone
Size - coarse 1mm or 750um (size depends on example given, very fine ODS is 375um, very coarse ODS is 1500um/1.5mm)
Shape - very well rounded
Sorting - very well sorted
Colour - brick red
Composition - quartz 90%, orthoclase 5% (white), lithic fragments 5% (black)
Cement/Matrix - hematite and quartz cement (red and hard)
Shale - and easy example even though it looks hard
Size - fine <187um
Shape - too fine to see (clay minerals are long and thin/Lath shaped so could say this)
Sorting - very well sorted
Colour - dark blue grey
Composition- clay minerals 100%
Cement/Matrix - none
Sedimentary Environments - Deserts
Arid (dry)
Playa lake
Wadi
Alluvial fan
Sand dunes
Playa lake
Low energy
Ions in solution
- evaporation due to heat and wind
- salts precipitate in order of solubility
• calcite - bottom and side
• gypsum - side and top
• halite
• bittern salts
Playa lake - sedimentary rock
Mudstone - laminations and desiccation cracks
• size - fine <187um
• shape - too fine to see/lath shaped
• sorting - very well sorted
• composition - 100% clay minerals
• colour - red/brown
• cement/matrix - none
Desiccation cracks
Sand dunes
Aeolian (wind)
Medium energy
Sand dune - sedimentary rock
Orthoquartzite desert sandstone - cross bedding and asymmetrical ripples
• size - medium 0.5-1.5mm
• shape - very well rounded
• sorting - very well sorted
• composition - 90% quartz, 5% orthoclase, 5% lithic fragments
• colour - brick red
• cement/matrix - hematite cement
Grains are frosted by attrition - dull/pitted surface
Cross bedding
Asymmetrical ripples
Laminations
Wadi
