Sedimentary rocks

• Sedimentary rocks cover about 75% of the world's land area
• Most of the earth's energy resources such as coal and petroleum products are hosted by sedimentary deposits
• Sediments


  Loose, solid particles that originate by (1) weathering and erosion of pre-existing rocks, (2) precipitation of minerals dissolved in water or (3) remains of plants and animals

  
• Sedimentary rocks

  Rocks formed from (1) lithification of any type of sediment, (2) precipitation from solution and other chemical processes and (3) consolidation of the remains of plants and animals and other biologically aided processes

  
• Weathering


  Chemical alteration, physical, and biological breakdown of rocks during exposure to the atmosphere, hydrosphere, and biosphere

  
• Types of Weathering

  • Mechanical/Physical Weathering
  • Chemical Weathering
• Mechanical/Physical Weathering


  • Physical breakdown (disintegration) of rocks leading to changes in size, shape, roundness, etc. with no accompanying changes to the composition of the rock

  
• Types of Mechanical Weathering

  • Frost Wedging
  • Grinding/Rubbing/Abrasion
  • Heating and cooling
  • Wetting and drying
  • Organisms
  • Unloading (Sheeting)
• Chemical Weathering


  • Breakdown (decomposition) of minerals by chemical reactions with water, with chemicals dissolved in water, or with gases in the air
• Types of Chemical Weathering

  • Dissolution
  • Hydrolysis
  • Acidification
  • Hydration
  • Oxidation (and Reduction)
  • Ion-exchange
• Goldich Stability Series


  Describes the relative order or sequence in which silicate minerals weather, with minerals formed at high temperatures and pressures being least stable at the surface and weathering most quickly

  
• Weathering is usually a combination of physical and chemical processes
• Granite is usually composed of K-feldspar, quartz, and mica. Physical weathering will breakdown the granite into smaller individual quartz fragments while chemical weathering will convert K-feldspars and micas into clay minerals and ions
• olivine sands exist
• Although we separately discussed the two types of weathering, the breaking down of rocks most of the time is a combination of these two. Both types are responses to physical and chemical conditions experienced by the rocks in the earth's surface.

  
• Factors Controlling Weathering

  • Source Composition
  • Climate
  • Topographic Relief
• Source Composition


  Refers to composition of rock sources, their mineralogy, texture, and rock structure. Goldich stability demonstrates the relative resistance of minerals to weathering. Fine-grained rocks chemically decompose more readily than coarse-grained rocks. Rock structures contribute as possible pathways of weathering agents or as weak spots in the rock allowing differential weathering.

  
• Climate


  Precipitation governs the extent of hydrolysis, hydration, and dissolution. In warm, humid regions, weathering is generally more active than in cold dry regions. Large temperature fluctuations also aid in the effectiveness of ice-wedging and heating and cooling processes.
• Topographic Relief


  Relief influences the amount of rock exposed to the forces of weathering. Slope steepness controls the rate at which weathered products are eroded to be transported elsewhere. Flat slopes allow accumulation of weathered products while steep slopes easily transport them away.

  
• Main Products of Weathering

  • Soluble ions (e.g. Na+, Ca2+, Mg2+, K+)
  • Resistant minerals (e.g. quartz, oxides)
  • Clay minerals (e.g. kaolinite, montmorillonite)

  
• Soil


  Complex combination of rock/regolith (~45%), organic materials (5%), and spaces (~50%) filled with varying amounts of air and water
• Soil Texture Classification


  Based on the proportions of sand-, silt-, and clay-sized grains

  
• Soil Orders

  • Alfisol
  • Andisol
  • Aridosol
  • Entisol
  • Gelisol
  • Histosol
  • Inceptisol
  • Mollisol
  • Oxisol
  • Spodosol
  • Ultisol
  • Vertisol
• Sediments


  Loose, solid particles that originated by:

  1. Weathering and erosion of pre-existing rocks (of any type)

  2. Precipitation of minerals dissolved in water

  3. Remains of plants and animals

  
• Rocks

  • breccia
  • rock salt
  • bituminous coal
• Special Soil Terms

  • Pedocal (Ca-rich soil formed in arid - semi-arid regions)
  • Caliche (formed in dry climates where carbonates accumulate impervious layers of white CaCO3)
  • Pedalfer (Al and Fe-rich soil in temperate regions)
  • Laterite (soft-reddish gray soil in tropical regions)
• Processes consolidating sediments into rock bodies

  1. Weathering

  2. Erosion

  3. Transportation

  4. Deposition

  5. Diagenesis

  
• Physical/Mechanical Weathering

  Physical breakdown (disintegration) of rocks leading to changes in size, shape, roundness, etc with no accompanying changes in the composition of the rock
• Soil Profile

  • O Horizon (organic layer)
  • A Horizon (TOPSOIL, humus mixed with mineral particles)
  • E Horizon (ELUVIATION LAYER, sand and silt, leached)
  • B Horizon (SUBSOIL, clay and mineral deposits)
  • C Horizon (REGOLITH, slightly broken-up bedrock)
  • R Horizon (BEDROCK, unweathered rock layer)
• Chemical Weathering


  Breakdown (decomposition) of minerals by chemical reactions with water, chemicals dissolved in water, or with gases in the air
• Erosion


  Movement or rock and soil through different agents involving gravity, water, wind, ice, and organism
• In the Philippines, water (due to precipitation) and gravity (in mountainous regions) are the most dominant natural agents of erosion.
• Transportation


  Movement of eroded materials (sediments and dissolved ions) from their site of erosion to a site of deposition

  
• Dissolution

  Ionic crystals break down (dissociates) into ions in liquid
• Modes of Sediment Transportation


  • Solution
  • Suspension
  • Saltation
  • Traction

  
• Udden-Wentworth Classification

  Classifies sediments into three major types based on the average diameter: muds (<1/16 mm), sands (1/16 to 2mm), and gravels (> 2mm). Each group can be further classified.

  
• Dissolution examples


  • Salt in water
  • Carbonate rocks in karst topography
• Sorting


  Measure of the variation in grain sizes of sediments
• Hydrolysis


  Minerals react with water to form hydroxides
• Hydrolysis example


  • K-feldspar in granites turns into kaolinite