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)
2
SiO
4
(Mg,Fe)SiO
3 pyroxine
H
4
SiO
4 in solution
Mg 2+ in solution
Fe (III) hydroxide (insoluble, rust)
CaAl
2
Si
2
O
8
Ca-feldspar and NaAlSi
3
O
8
Na-Feldspar
Ca +2 in solution
Na +1 in solution
Al
2
Si
2
O
5
(OH)
4
(insoluble, “clay”)

SiO
2 quartz
SiO
2
(insoluble, “sand”) granite
CaAl
2
Si
2
O
8
Ca-feldspar; NaAlSi
3
O
8
Na-Feldspar KAlSi
3
O
8
K-Feldspar
Ca +2 , Na +1 , K +1 in solution
Al
2
Si
2
O
5
(OH)
4
(insoluble, “clay”)
(Ca,Na)
2
(Mg,Fe,Al)
5
(Al,Si)
8
O
22
(OH)
2 amphibole (and also mica)
Mg +2 , Ca +2 , Na +1 in solution
Al
2
Si
2
O
5
(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

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

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 U 6+ is produced during the weathering of igneous rocks.
U 6+ was transported by groundwater until it encounters reducing conditions. It is reduced to
U 4+ and precipitates as uranium oxide.

Mineral Commodities
Solid Earth System

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

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  10 15 liters/year
= 14700 cubic kilometers per year
About 46,000 cu km available

Global impoundments of water
8400 km 3
Not much growth in last decade, except in Asia-
Australia

Good luck with the final best wishes for 2009