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Weathering and Erosion Formation of Sedimentary Rocks. Weathering – the physical breakdown ( disintegration ) and chemical alteration ( decomposition ) of rock at or near Earth’s surface Erosion – the physical removal of material by agents such as water, wind, ice, or gravity. insoluable. - PowerPoint PPT Presentation
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• Weathering – the physical breakdown (disintegration) and chemical alteration (decomposition) of rock at or near Earth’s surface
• Erosion – the physical removal of material by agents such as water, wind, ice, or gravity
Weathering and ErosionFormation of Sedimentary Rocks
insoluable
basalt(Mg,Fe)2SiO4 (Mg,Fe)SiO3 pyroxine
H4SiO4 in solution
Mg2+ in solution
Fe (III) hydroxide (insoluble, rust)
CaAl2Si2O8 Ca-feldspar and NaAlSi3O8 Na-Feldspar
Ca+2 in solution
Na+1 in solution
Al2Si2O5(OH)4 (insoluble, “clay”)
graniteSiO2 quartz
SiO2 (insoluble, “sand”)
CaAl2Si2O8 Ca-feldspar; NaAlSi3O8 Na-Feldspar KAlSi3O8 K-Feldspar
Ca+2 , Na+1, K+1 in solution
Al2Si2O5(OH)4 (insoluble, “clay”)
(Ca,Na)2(Mg,Fe,Al)5(Al,Si)8O22(OH)2 amphibole (and also mica)
Mg+2, Ca+2 , Na+1 in solution
Al2Si2O5(OH)4 (insoluble, “clay”)
Fe (III) hydroxide (insoluble, rust)
Climateand
Weathering
Hot and wet favors chemical
weathering
Cold and snowy favors
mechanial weathering
Differential Weathering and Erosion
creates topography
Slowly weathered and eroded - high
(Morningside Heights, Palisades, Ramapo Mountains)
Quickly weathered and eroded - low
(sediments beneath Hudson River and west of Palisades)
Residual topography
Hill formed by differential erosion
uplift erosion
Clastic Sediments and Clastic Sedimentary Rocks
A. Sediments
B. Sedimentary Rocks
Energy and Depositional Environment
Worldwide sediment yield of major drainage basins
Migrationof meanders
leads tocross-bedding
crossbed from fieldtrip
Cross-section of Deltanote that delta grows (progrades) towards sea
Hjulstrom Curve
Hjulstrom Curve
Pebbles and cobbles
Pebbles and cobbles: hard to get moving, an hard to keep moving
Hjulstrom Curve
SandSand: easy to get moving, a fairly easy to keep moving
Hjulstrom Curve
Silt and Clay
Silt and Clay: hard to get moving, but very easy to keep moving
Ocean Sediments
Part 1
Evapotite: common during with continental rifting
Fossil Fuels
Solid Earth System
petroleum
Organic-rich source rock, e.g. shale
Maturation through burial at the right temperature
Collection in a porous reservoir rock
Concentration in trap through buoyancy
Formation of Ores
Some unusual process must:
1) remove specific elements, compounds or minerals from ordinary rock,
2) transport these elements, compounds, or minerals
3) concentrate the elements, compounds, or minerals preferentially at one spot or zone where the transport stops.
the primary mechanisms for concentrating minerals into ores
involves either:
sorting by density
sorting by solubility.
Concentration through liquid immiscibilityLow T
Desirable element preferentially concentrated into low-volume melt
High T
Aqueous fluids in magmaAs magma cools, the volatiles (mostly water and carbon dioxide) that they contain can form super-critical fluids.
supercritical fluids are on the verge of making the phase transition from liquid to gas.
because of their extremely high temperature, many elements are soluble.
These fluids can concentrate copper, molybdenum, gold, tin, tungsten and lead.
The fluids from a large pluton can invade surrounding rocks, along cracks called hydrothermal veins).
Aqueous fluids from granitic magma have invaded surrounding rock
porphery copper ore
Mechanisms that involve oxidation state of the water
Ground water can carry dissolved materials. These can precipitate out of solution if the water becomes more or less oxidizing.
Example: uranium ore
soluable U6+ is produced during the weathering of igneous rocks.
U6+ was transported by groundwater until it encounters reducing conditions. It is reduced to U4+ and precipitates as uranium oxide.
Mineral Commodities
Solid Earth System
Geothermal Power
6.5 km – expensive but routine, areas of western US are hot
Solution to low permeabiliy
Artificially increase permeability by creating fractures
“Hydrofracture” … pressurize well until you crack the surrounding rock, routinely used in oil extraction, at least for small volumes of rock
Fresh Water
Possibly the most Limiting Resource
US Water Usage, billion gallons / day
IrrigationDomestic SupplyPublic Supply
Livestock & AquacultureIndustrialMining
Thermoelectric Power
800.627.3
3.414.91.2
135
Total 262
How much irrigation water does the world need?
2000 calories/day minimum
At 3 cal/liter
670 liters/day
6 billion people 365 days/year
= 1.46 1015 liters/year
= 14700 cubic kilometers per yearAbout 46,000 cu km available
Global impoundments of water8400 km3
Not much growth in last decade, except in Asia-Australia
Good luck with the final
best wishes for 2009