•Sedimentary Rocks Flashcards
What is weathering?
The disintegration or decomposition of insitu rock at or near the earth’s surface by mechanical breakdown and chemical alteration
What is mechanical/ physical weathering?
The in situ disintegration of rock due to the development of stress within the rock caused by changing weather
What is chemical weathering?
The decomposition of rock due to the chemical reaction of rock minerals with weakly acidic rock
What is frost weathering?
What rocks are affected?
What are the products?
Caused by the expansion of ice within rock. Water freezes into ice causing a 10% volume increase which causes stress
Happens in all rock but especially in porous and fractured rock
Created frost shattered, angular rock degree called scree or talus
What is insolation weathering?
What rocks are affected?
What are the products?
Caused by the daily expansion of rock exposed to the suns heat
Happens in all rock but especially those with dark colours
Angular rock debree fragments called scree or talus
What is hydrolysis?
What rocks are affected?
What are the products?
Water reacts with Feldspar and causes decomposition
Affects any rock containing Feldspar e.g Granite
Creates Clay and Salt
What is carbonation?
What rocks are affected?
What are the products?
Water reacts with limestone and causes the limestone to change into soluble calcium bicarbonate
Affects limestone
Creates calcium bicarbonate (shells)
What is oxidation?
What rocks are affected?
What are the products?
Minerals containing Fe react with oxygen and turn into ferrous iron oxide I.e rust
Affects all rock containing iron ( mafic)
Created rust
What is solution weathering?
What rocks are affected?
What are the products?
Rocks dissolve in the prescence of water
Affect natural salts and limestone
Creates salt
What is erosion?
The wearing down of transported debris because of inter-particle collisions
What is traction?
rounded particles are rolled by force of flowing water
What is saltation?
Series of hops caused by a sudden increase in energy (flat)
What is flocculation?
Salt in sea water ensures electrical charge causing clay particles attracting them together so they become bigger and sink
Grain sizes
Coarse >2mm
Medium 0.06- 2mm
Fine <0.06
Sorting
Poorly sorted
Moderately well sorted
Well sorted
Powers roundness chart
Very angular Angular Sub angular Sub rounded Rounded Well rounded
Cements
Iron oxide= red= desert
Calcite= fizzes= beach from shells
Silica= grey/yellow= river environments
Conglomerate
Coarse
Poorly sorted
Sub angular/ sub rounded
Shingle beach
Sand
Breccia
Coarse
Poor
Sub angular/ angular
Alluvial fan
Sand and large particles
Greywacke (sandstone)
Fine- medium
Moderate
Sub-rounded
Undersea Mudflow
Turbidity currents
Mudmatrix and sand
Arkose (sandstone)
Medium-coarse
Moderate
Sub-angular
Flood plane
Braided river
Quartz and feldspar
Orthoquartzite (sandstone)
Medium grained
Well sorted
Rounded
Sand beach
Quartz
Bioclastic limestone
Medium-coarse
Poorly sorted
Warm tropical seas and beaches
Fossilised shells
Mixture mud
Sparry calcite crystals
Chalk
Fine grain
Well sorted
Warm
Deep sea
Still water
Cocolith (zoo plankton)
Micrite mud
Oolitic limestone
Medium grained
Well sorted
Tropical beaches
Wave action moved a shell or sand nucleus over the beach micrite mud sticks to it
Ooliths
Soft micrite mud
Sparry calcite crystals
Normal bedding
Layer caused by a single pulse of sedimentation
Less than 1cm thick is called a laminae
Separated by lamination planes
Ripples and dunes
<10cm ripples
>10cm dunes
Asymmetric
Cross bedding
Inclined foreset beds
Climbing ripples
> 5m deserts
0.5-5m shallow marine
0.1-0.5m rivers
<0.1 beach
Lee
Stoss
Foreset
Graded bedding
Decrease in grain size from bottom upwards
Rapid deposition
Dessication cracks
Surface of sediment drys, contracts and cracks
Polygonal pattern
Sole structures
Convex irregularities found on the underside of a bed of sandstone
Flute cast
Bulges that occur on the base of turbidite deposits
Turbidity current of up to 100mph creates a blast wave and scours out the soft sea bed
The scouts are infilled by sand/mud
Tool marks
Impact scares created by hard tools (stone or fossil fragments) as it is swept over soft sediment.
Turbidity current of up to 30mph carrying a shell that creates an impact impression or tool mark which is then infilled
What is a groove Mark?
A linear ridge on the base of a sandstone bed that if formed by the infilling of a groove cut into underlying rock
Turbidity current of up to 100mph carrying a large stone digs into the soft sediment
Cuts a groove into the sediment which is later infilled
Load cast
Bulbous loves that penetrate downwards into the rock. Heavier saturated sand sinks into soft rock beneath
Creates flame structures
What is a mature rock?
Stable rock that has undergone chemical breakdown during transportation
What is an immature rock?
A rock that was deposited before weathering and erosion so contains unstable components such as rocks containing feldspars
Shale
Fine grained
Well sorted
Shape- N/A
Deep sea
