Post on 14-Dec-2015
GL4 E1GL4 E1
Key Idea 2 b iiiKey Idea 2 b iii SEDIMENTARY ROCKS SEDIMENTARY ROCKS The mineralogy and texture of The mineralogy and texture of
sedimentary rocks are controlled by sedimentary rocks are controlled by processes of weathering, erosion and processes of weathering, erosion and depositiondeposition
GL4 E1 KI2 b (iii) DepositionGL4 E1 KI2 b (iii) Deposition
DEPOSITION, selectively concentrates DEPOSITION, selectively concentrates products in particular environments – products in particular environments – grain size related to energy of grain size related to energy of depositional environment; dominance depositional environment; dominance of quartz and muscovite in coarse of quartz and muscovite in coarse fraction and clay minerals in fine fraction and clay minerals in fine fraction; flocculation; precipitation; fraction; flocculation; precipitation; concentration of biogenic material in concentration of biogenic material in particular environmentsparticular environments
What is deposition?What is deposition? Transporting agents can only carry Transporting agents can only carry
sediment when they have energysediment when they have energy When energy is reduced, some of load When energy is reduced, some of load
must be dropped (deposited)must be dropped (deposited)
Energy lost all of a sudden = load Energy lost all of a sudden = load dumped, no sortingdumped, no sorting
Energy lost gradually = load gradually Energy lost gradually = load gradually dumped, largest particles first then dumped, largest particles first then smaller (graded bedding)smaller (graded bedding)
Grain size/energy currentGrain size/energy current
Big link between these!Big link between these! Hence the grain sizes found in a rock Hence the grain sizes found in a rock
tell us the energy current which tell us the energy current which existed just before it was depositedexisted just before it was deposited
Depositional environmentsDepositional environments River flowing into a lakeRiver flowing into a lake Precipitation from Precipitation from
evaporation of sea waterevaporation of sea water Glacier meltingGlacier melting River flood plainRiver flood plain BeachBeach Estuary deltaEstuary delta SeabedSeabed Desert Desert
River depositionRiver depositionProfile along a river from source to mouthSource
Mouth
Particles deposited here are large and irregular and consist of a variety of lithologies, including the least resistant
Particles deposited here are mid-sized and of intermediate sphericity, and include resistant and non-resistant lithologies
Particles deposited here are small and nearly spherical, and consist mainly of the most resistant lithologies
The effects of siltation in rivers The effects of siltation in rivers and streamsand streams
Siltation is a leading pollution problem. Over the short term: silt can kill fish, destroy spawning beds, increase water turbidity (and reduce rates of photosynthesis).Over the long term: unchecked siltation can alter habitat and affect aquatic life.
Credit: U.S. Geological Survey
Average annual concentrations of suspended sediment, nitrogen, and
phosphorus input into the reservoir system and output to the Chesapeake Bay.
RiversRivers Flowing water (current flow depends on Flowing water (current flow depends on
gradient)gradient) Deposition in lower course of riverDeposition in lower course of river Meanders (outside = erosion; inside = Meanders (outside = erosion; inside =
deposition)deposition) Levees and flood plain – “flood dumping”Levees and flood plain – “flood dumping” Alluvial fans (change in slope Alluvial fans (change in slope energy energy
change)change) Deltas (build out into still body of water – Deltas (build out into still body of water –
prograde)prograde)
River deposition featuresRiver deposition features
AsymmetricAsymmetric ripple ripple marksmarks
Cross laminationCross lamination Point bar depositsPoint bar deposits (Alignment due to (Alignment due to
river flow)river flow) Gradual rounding Gradual rounding
of fragments of fragments downriverdownriver
Credit: British Geological Survey
DesertDesert Aeolian (wind) transportAeolian (wind) transport Small range of grain sizes Small range of grain sizes
transported (~ 0.3mm)transported (~ 0.3mm) Frosted grains (wind blasted)Frosted grains (wind blasted)
Credit: U.S. Geological Survey
Desert deposition featuresDesert deposition features Large scale cross beddingLarge scale cross bedding Red colour (oxidised iron matrix)Red colour (oxidised iron matrix) Flash floods bring in larger materialFlash floods bring in larger material Lakes dried up quickly – evaporation Lakes dried up quickly – evaporation
features (eg. mud cracks)features (eg. mud cracks)
Credit: British Geological Survey Credit: British Geological Survey
Land environmentLand environment
Mainly erosional, not depositionalMainly erosional, not depositional Swamp landsSwamp lands Glacial depositionGlacial deposition
Land depositional featuresLand depositional features Glaciers – erratics, drumlins, Glaciers – erratics, drumlins,
till/boulder clay, outwash sands and till/boulder clay, outwash sands and gravelsgravels
Swamps – coal depositsSwamps – coal deposits
Pleistocene glacial deposits,Thurstaston, Wirral
Sea/coastsSea/coasts
Storm beach – high energy sea (large Storm beach – high energy sea (large fragments)fragments)
Wave action/long shore drift – rolling Wave action/long shore drift – rolling of particles – roundingof particles – rounding
Lagoons – conditions more still, and Lagoons – conditions more still, and may also be evaporationmay also be evaporation
Limestone reefsLimestone reefs Turbidity currentsTurbidity currents
Sea/coast deposition Sea/coast deposition featuresfeatures
Graded beddingGraded bedding Finest laminations far offshore, Finest laminations far offshore,
clay/shale depositionclay/shale deposition
Credit: British Geological SurveyCredit: British Geological Survey
Other featuresOther features Sole marks/groove casts – Sole marks/groove casts –
pebbles/animals bouncing on a pebbles/animals bouncing on a sediment surface, marks left infilled sediment surface, marks left infilled by sediment deposited on topby sediment deposited on top
Scour marks/flute casts – erosion of Scour marks/flute casts – erosion of surface by current, infilledsurface by current, infilled
Flame structures/mud volcanoes – Flame structures/mud volcanoes – sand deposited on top of mud, sand sand deposited on top of mud, sand weighs down and mud erupts up weighs down and mud erupts up through sand layerthrough sand layer
What else?What else?
dominance of quartz and muscovite dominance of quartz and muscovite in coarse fraction and clay minerals in coarse fraction and clay minerals in fine fraction; in fine fraction;
Go back to Bowen’s reaction series Go back to Bowen’s reaction series for the reason why quartz is for the reason why quartz is resistant/survivesresistant/survives
Clay minerals from broken down Clay minerals from broken down feldsparfeldspar
FlocculationFlocculation Fine particles begin to stick Fine particles begin to stick
together (due to addition of a together (due to addition of a catalyst – e.g. when freshwater catalyst – e.g. when freshwater meets saltwater in an estuary)meets saltwater in an estuary)
Flocs are heavy so sinkFlocs are heavy so sink
EvaporatesEvaporates
Salt waterSalt water High temperatures, little rainfallHigh temperatures, little rainfall Calcium carbonate first to precipitate Calcium carbonate first to precipitate
(least soluble)(least soluble) In shallow lagoons the following can In shallow lagoons the following can
precipitate after limestone:precipitate after limestone: Gypsum CaSOGypsum CaSO44.2H.2H22O (must lose 80% of O (must lose 80% of
water for this to occur)water for this to occur) Then Halite (NaCl) (90% water gone)Then Halite (NaCl) (90% water gone) Finally potassium and magnesium saltsFinally potassium and magnesium salts
LimestoneLimestone
Calcium carbonateCalcium carbonate Reef structures (calcium carbonate Reef structures (calcium carbonate
built by shelled creatures)built by shelled creatures) Lagoons behind reef collect fine Lagoons behind reef collect fine
calcium “muds”calcium “muds”
Evaporates 2Evaporates 2
300cm depth of seawater yields just 300cm depth of seawater yields just 5cm of salts5cm of salts
Calculate how much water was Calculate how much water was evaporated to form the Stassfurt evaporated to form the Stassfurt sequence in Germany which is sequence in Germany which is 1000m thick1000m thick
Right, the maths bit!!Right, the maths bit!!
1000m x 100cm = 100,000cm1000m x 100cm = 100,000cm 100,000cm 100,000cm ÷÷5cm = 20,000 units5cm = 20,000 units 20,000 units each of 3m of water20,000 units each of 3m of water
= = 60,000m of sea water60,000m of sea water
= 60km of sea depth= 60km of sea depth
Is this feasible?????Is this feasible?????
How deep are our oceans?How deep are our oceans?
Seas aren’t deep enough!Seas aren’t deep enough!
Refill/top-up theory – sea basin (like Refill/top-up theory – sea basin (like the Mediterranean) evaporates and the Mediterranean) evaporates and then is refilledthen is refilled
Carbonate Compensation DepthCarbonate Compensation Depth
Carbonate dissolves when water is Carbonate dissolves when water is deeper than 4km deeper than 4km
Concentration of biogenic Concentration of biogenic materialmaterial
Only in selected environmentsOnly in selected environments Trees (coal) – swamps (and delta tops), Trees (coal) – swamps (and delta tops),
rapid burial essential (to preserve rapid burial essential (to preserve material by excluding oxygen to stop material by excluding oxygen to stop biogenic material rotting)biogenic material rotting)
Credit: British Geological Survey