Themes of the Day:

• Basins Wrap-up
• Weathering Review
• Soils & Paleosols

Depositional Basins

• Preservation Potential - with age, by tectonic setting
• Sea Level fluctuations
• US Latitude through Time
• Tectonic Settings of Deposition
• Classification of Sedimentary Basins - See Table 11-3, 11-4
• Basin Examples
  • Bay of Bengal
  • Atlantic Rift Basins
  • Eastern US Rift Basins
  • Accretionary Wedge
  • Subduction Zone Cross Section
  • Aleutian Arc - Intraarc Basins
  • Backarc Basins
  • Appalachian Clastic Wedge
  • Central US Basins
  • North American Intracratonic Basins
• Climate and Continental Drift

Physical (Mechanical) Weathering

• Physical force breaks material into smaller fragments
• Examples:
  • Frost Wedging (ice expands 9% on freezing)
  • Abrasion (fluvial, aeolian, surf zone, glacial, etc.)
  • Biological (burrowing and tree roots)
  • Exfoliation
• Most effective with steep slopes (rugged topography)
• Gravity is the ultimate driving force (for most)

Chemical Weathering

• Most effective in hot, wet climates
• Products of Weathering are both solids (clastic sediments) and dissolved in H₂O (chemical sediments)
• Four basic types of chemical reactions:
  • Oxidation (ex. 4Fe₃O₄ + O₂ = 6Fe₂O₃) Figures 7.8, 7.9
  • Dissolution (ex. NaCl + H₂O = Na⁺ + Cl^- + H₂O)
  • Acid Reaction (Carbonation) (ex. CO₂ + H₂O = H₂CO₃ = H⁺ + (HCO₃)^-
    H⁺ + (HCO₃)^- + CaCO₃ = Ca²⁺ + 2(HCO₃)^-) Figure 7.7
  • Hydrolysis (ex. Fe₂O₃ + H₂O = 2FeO(OH))
• Feldspar Breakdown
• Kaolinite Clay
• Muscovite/Illite
• Example: Carbon Cycle - Role of Bicarbonate
• Stability of Minerals during Chemical Weathering

Soils & Paleosols

• Solubility of cations and anionic complexes - See Table 12-1
• Modern Soil Horizons
• Criteria for Recognizing Paleosols - See Table 12-2
• Eocene Calcrete
• Solubility of chemical species as a function of pH
• Modern Silcrete
• Silcrete Thin Section
• Paleosol Features
• Badlands Paleosols