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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
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”)
granite
SiO2 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)
Climate
and
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)
uplift
erosion
Hill formed by
differential erosion
Residual
topography
Clastic Sediments
and Clastic Sedimentary Rocks
A. Sediments
B. Sedimentary Rocks
Energy and Depositional Environment
Worldwide sediment yield of
major drainage basins
crossbed from fieldtrip
Migration
of meanders
leads to
cross-bedding
Cross-section of Delta
note that delta grows (progrades) towards sea
Hjulstrom Curve
Hjulstrom Curve
Pebbles and cobbles: hard to
get moving, an hard to keep
moving
Pebbles and
cobbles
Hjulstrom Curve
Sand
Sand: 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 immiscibility
High T
Low T
Desirable element preferentially concentrated into
low-volume melt
Aqueous fluids in magma
As 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
Public Supply
Domestic Supply
27.3
0.6
Irrigation
Livestock & Aquaculture
Industrial
Mining
80
3.4
14.9
1.2
Thermoelectric Power
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 year
About 46,000 cu km available
Global
impoundments of
water
8400 km3
Not much growth
in last decade,
except in AsiaAustralia
Good luck with the final
best wishes for 2009