1. WEATHERING (2 basic types; chemical and physical)
- Factors controlling weathering rates

• Rock Properties- differential solubility of minerals; chemically stable minerals (ie. quartz) weather very slowly. Structural weaknesses (fractures, layering) promotes rapid physical and chemical weathering.
• Climate- rainfall and temperature. Hot and rainy climates (tropics) accelerates chemical weathering; cold and arid climates physical will still be appreciable.
• Soil development- presence of soils promotes weathering by retaining water and has bacteria, vegetation, and organisms that produce acids.
• Exposure duration- longer exposure times cause increases weathering

- Chemical Weathering

• Feldspar breakdown: (hydration process; production of clay minerals; release of K+ and dissolved SiO2; reaction representative of most silicates)

• Oxidation of Fe: (oxidation process; production of iron oxide minerals; hematite)

iron pyroxene + oxygen >>>>>>>>   hematite + dissolved silica
4FeSiO₃        +   O₂      >>>>>>>>   Fe₂O₃   +  4SiO₂

• Dissolution of carbonates:
calcite     +   carbonic acid    >>>>>>>>   dissolved calcium    +    dissolved bicarbonate ion
CaCO₃   +        H2CO₃        >>>>>>>>             Ca²⁺            +           2HCO₃^-
 
• Relative Stability of Minerals to chemical weathering: dependent on the solubility (amount of mineral dissolved in H2O at the saturation point). Stability of minerals can be expressed as the opposite of Bowen's Reaction Series.

- Physical Weathering (dominant process in arid/cold climates). Natural zones of weakness (fractures; joints, bedding, foliation) are attacked by:

• Frost- or Ice-wedging: splitting by freeze-thaw cycles in cold climates.
• Organisms (tree roots, lichens, algae, bacteria): physically push apart rocks.
• Alternating hot-cold cycles: cyclic expansion-contraction in arid climates.

2. SOILS (products of chemical and physical weathering; important natural resource)
- Basic Soil Profile

• A-horizon: includes the uppermost organic-rich topsoil layer and a lower leached zone of rich in clay and insoluble minerals.
• B-horizon: has little organic matter; dissolved minerals from A-horizon precipitate.
• C-horizon: slightly altered and cracked bedrock with clay from chemical weathering

• Wet Tropical climate - Laterites, thick masses of Al- and Fe-hydroxides; important source of aluminum ore (bauxite). Deforestation and erosion strips thin topsoil and leaves infertile layers exposed.
• Dry climate - Pedocals, thin A-horizon; thick B-horizon with calcite nodules.
• Temperate, humid climate - Pedalfers, thick organic-rich A-horizon; typical profile.

Prof. Gorring
GEOS 112 PHYSICAL GEOLOGY
Sept. 24, 1998

1.  Important Component of the Rock Cycle
-processes: transportation, deposition, burial, lithification (diagenesis)
 

2. Types of Sediment

• -clastic (detrital) = solid grains or fragments of rock; derived from physical weathering
• chemical = dissolved ions in river, lake, or ocean water; derived from chemical weathering
• bioclastic (biogenic) =  particles that are biological produced; skeletal fragments, shells

3. Processes occuring during transport

• transport by currents of air, water, or ice.
• relationship between current strength and density, sediment particle size, leads to sorting.
• physical weathering during transport leads to size reduction and rounding.

4. Depositional Environments
- has unique geological processes and environmental conditions; closely related to tectonic settings and climate.

• Continental: diverse settings depending fluid media and climate(alluvial, desert, lake, glacial).
• Shoreline: mostly depends on waves, tides, and currents interacting with shoreline; abundant organisms (tidal, delta, beach).
• Marine: diverse settings mostly dependent on water chemistry and T, current velocity and water depth. (shelf, slope, deep sea, shallow tropical)

5. Sedimentary structures
-bedding, cross-bedding, graded bedding, ripples, mud-cracks, bioturbation, bedding sequences. Help to intrepret paleo-environments of deposition and ultimately Earth's history.
 

6. Burial, Diagenesis, and Lithification
- Thick piles of sediments can accumulate in sedimentary basins; burial causes diagenesis - physical and chemical changes that occur during transformation from sediment to rock; occurs at low T (150°C). Compaction; cementation; lithification.