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

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