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Terrigenous Sediments. Weathering. Sediment Production and Weathering. Sedimentary Cycle Components of the Sedimentary Cycle Weathering Physical Types Chemical Types Products clays. Sedimentary Cycle. Rock Cycle Sedimentary Cycle Mass movement (non- sedimentary)

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Terrigenous Sediments

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sediment production and weathering
Sediment Production and Weathering
  • Sedimentary Cycle
    • Components of the Sedimentary Cycle
  • Weathering
    • Physical
      • Types
    • Chemical
      • Types
      • Products
        • clays
sedimentary cycle
Sedimentary Cycle
  • Rock Cycle
    • Sedimentary Cycle
    • Mass movement (non- sedimentary)
  • Components of Sediment Cycle
    • Weathering
    • Erosion
    • Transportation
    • Deposition
    • Lithification
    • Uplift
    • Weathering again
components of sediment cycle
Components of Sediment Cycle
  • Weathering
    • Processes which break down rock at the E’s surface to form discrete particles
  • Erosion
    • Processes which remove newly formed sediment from bedrock
  • Transportation
    • Gravity driven (creep, mass flow, glaciers, rivers)
    • Segregates/ sorts the weathering products
  • Deposition
    • Energy is exhausted
  • Lithification
    • Compaction, cementation
physical weathering
Physical Weathering
    • Mechanical fraction of the rock
    • Aids in Chemical weathering
    • Works best in cold, dry, high relief
    • Producesmineralogically immature particulate material
physical weathering and sediment production
Physical Weathering and Sediment Production
  • Physical weathering is a function of:
    • Climate
      • Temperature
      • Precipitation
      • Vegetation
    • Slope Angle (gravity)
    • Area
physical weathering mechanisms
Physical Weathering Mechanisms
  • Freeze-thaw/ frost- wedging (ice expands)
  • Daily heating/ cooling (deserts, maybe)
  • Plant Roots (expand cracks)
  • Crystallization of salts (salts expand)
  • Release of overburden pressure
    • Erosion or melting of thick glaciers
  • Volume changes as primary (original minerals) are converted to clay minerals (secondary)
physical weathering10
  • Insolation
    • Large diurnal temperature variations
      • Hot arid climates: Mohave
        • Spring 48°F; to 92°F; Summer 71°F to 108°F
        • Fall 59°F to 100°F, Winter temperature 41°F to 68°F
    • Expansion/ contraction due to temperature change
      • Minerals respond differently, aids in generating stress
      • If it’s rapid, can crack the rock
        • Rocks can pop and crack after sun sets (cooling)
physical weathering11
Physical Weathering
  • Volume changes from hydration/ dehydration
    • Alternating wet and dry seasons
    • Clays, lightly indurated shales expand with water
    • Upon dehydration, shrinkage cracks develop
      • Increases permeability to aid in chemical weathering
      • Reduces rock strength
physical weathering12
Physical Weathering
  • Stress Release of overburden
    • At depth, rocks are compressed by overburden
      • Elastic-- returns to original size after compression
    • With weathering, erosion of overburden, rock expands
      • Can fracture
      • Creep can aid fracturing
    • Fractures impacted by other weathering processes
  • Sheeting
  • Exfoliation domes
stress release
Stress Release

Steven Marshak

chemical weathering
Chemical Weathering
  • Meachanical weathering produces sediments
    • Quartz: 25 - 50% of igneous rock
      • Beach sands: 50 - 99% quartz
      • Limestones and evaporites
chemical weathering17
Chemical Weathering
  • Destruction of rock by solution
    • Therefore dependent upon water (not frozen)
      • Water itself only really dissolves evaporites
      • Needs acid!
      • Groundwater is acidic
        • Carbonic acid (CO2 from atmosphere)
        • Humic acids (from soils)
    • Usually accompanies mechanical weathering
chemical weathering18
Chemical Weathering
  • Rock broken down into three main constituents
    • Residua
      • Often quartz rich
      • Feldspar and mica dependent upon weathering
    • Solutes (end up in ocean!)
      • Na, K (other alkali metals- base soluble in water)
      • REE, Ca, Mg, Sr
    • Newly formed minerals
      • Clays (hydrated aluminosilicates)
      • Classification on basis of combination with Ca, K, Mg, Fe
chemical weathering20
Chemical Weathering
  • Volumetrically, most significant process in the production of sediments
    • Chemical alteration (reaction) under at surface Conditions:
      • low temperature (slow reaction rates)
      • abundant water
      • high Eh (oxidizing conditions)
      • generally low pH (acidic conditions; especially in the presence of decaying vegetation)
chemical weathering21
Chemical Weathering
  • Sequence of Rock Weathering
    • Relative mobility of main rock- forming elements
      • decreases from Ca and Na, to Mg, Si, Fe and Al.
    • Rocks undergoing weathering
      • Depleted in Ca, Na, Mg
      • Enriched in Fe- oxides, Al, Si
    • Particulates produced in reverse of Bowen’s reaction series
chemical weathering22
Chemical weathering
  • Sequence
    • Early: particulates are produced and altered
      • Mafic minerals (olivine, amphibole, pyroxene) form chlorite clays (Fe-, Mg- rich)
      • Feldspars produce smectites, illites, kaolins
    • Clays are flushed out as colloidal clay particles
      • Some stay to form residuum
      • Mg-, Ca- bearing minerals removed if weathering continues
    • Ultimately, rock residuum is just Q (if present in parent) + kaolin, bauxite, and limonite
      • requires warm humid climate, slow erosion
types of chemical weathering
Types of Chemical Weathering
  • Hydrolysis
  • Oxidation
  • Solution
types of chemical weathering25
Types of Chemical Weathering
  • Hydrolysis
    • hydrogen ion (H+) combines with silicate group

Mg2SiO4 + 4H20 ---> 2Mg++  + 4OH- + H4SiO4

(olivine, unstable protolith mineral)(hydroxyl) + (silicic acid)

      • reaction raises pH, and
      • releases silicic acid (a weak acid)
    • In the presence of dissolved CO2 ( increased conc. by 10x to 100x) of biogenic origin
    • production of carbonic acid (2H2CO3) drives reaction to the right
types of chemical weathering26
Types of Chemical Weathering
  • Oxidation
    • Loss of an electron with positive increase in valence (charge).
    • Due to the presence of an oxidant which is Reduced (gain of an electron) with negative increase of valence.
  • Most metals immediately oxidize in the presence of Oxygen (the most famous surface oxidant) especially:
    • Fe++--->Fe+++, Mn++---> Mn+4, S--->S+6 (SO4--).
types of chemical weathering27
Types of Chemical Weathering
  • Common sequential reactions in the surface weathering environment
    • Hydrolysis + Oxidation

Hydrolysis: liberates metal cations:

Fe2SiO4 + 4H2CO3(aq) ---> 2Fe++  + 4HCO3- +H4SiO4

(olivine, fayalite)

Oxidation: reprecipitates oxides:

2Fe++  + 4HCO3- + 1/2O2 +2H2O --> Fe2O3 + 4H2CO3

                                  hematite or amorphous iron oxide

types of chemical weathering28
Types of Chemical Weathering
  • Solution
    • ionization of ionically bonded metal cations (Ca++, Na+, Mg++, K+) by dipolar water molecule.

H2O + CaCO3 --> Ca++ + CO3= + H2O

    • Produces the metal cations common in natural waters
types of chemical weathering29
Types of Chemical Weathering
  • Ions in Solution
    • Ions introduced into the surface and ground water by chemical degradation of surface exposed rock-forming minerals
      • congruentsolution: only ions in solution
      • incongruent: ions in solution + new mineral phase
    • Elements with preference to ionic bonding are generally most soluble
types of chemical weathering30
Types of Chemical Weathering
  • Limiting Factors:
    • Water
      • facilitates most weathering reactions
    • Sufficient Activation Energy (Temperature)
      • initiates chemical reactions
    • Long residence time in the soil horizon
      • access to checmial weathering
      • minimal physical weathering
products of chemical weathering
Products of Chemical Weathering
  • Insitu Minerals (minerals formed in place)
    • Clay Minerals : hydrous Alumino-silicate minerals (phylosilicates;)
  • Oxides
    • Hemitie - iron oxide
    • goetite/limonite - iron hydroxide
    • pyrolusite - mangenese oxide
    • gibbsite - aluminum hydroxide
  • Amorphous Silica
    • product of hydrolysis reactions of silicate minerals (see above)
generalized chemical weathering
Generalized Chemical Weathering
  • Temperate Climates

3KAlSi3O8 + 2H+ + 12H2O --> KAlSi3O10(OH)2 + 6H4SiO4 + K+

(K-feldspar)          (mica/illite) (silicic acid)

  • Temperate Humid Climates:

2KAlSi3O8 + 2H+ + 3H2O --> 3Al2Si2O5(OH)4 + K+

(K-feldspar)                          (kaolinite)

  • Humid Tropical Climate:

Al2Si2O5(OH)4 + 5H2O --> 2Al(OH)3 + 2K+ + 4H4SiO4

(kaolinite) (gibbsite)

clays important chemical weathering products
Clays: Important Chemical Weathering Products
  • Clay Mineral Species are a function of
    • environmental conditions at the site of weathering
    • available cations produced by chemical degradation
sheet silicates the mica s and clay minerals
Mica and clay minerals are Phyllosilicates

Sheet or layered silicates with

Two dimensional polymerization of silica tetrahedra

Common structure is a Si205 layer

Sheet Silicates: the Mica's and Clay Minerals



sheets of silica tetrahedra

structure of phyllosilicates
Structure of Phyllosilicates
  • Octahedral layer
    • Layer of octahedral coordinated
      • magnesium (brucite layer) or
      • Aluminum (gibbsite layer)
    • Makes up the other basic structural unit

Kaolinite: Al2Si2O5(OH)4

1:1 tetrahedral – octahedral


the major clay mineral groups
The Major Clay Mineral Groups
  • Kaolinite group:
    • 1:1 TO clay minerals
  • Mica (illite) group:
    • 2:1 TOT clay minerals
    • Expandible clays:
      • Smectite- montmorillonite complex 2:1 clay minerals
  • Chlorite
    • Fe- and Mg-rich TOT clays
chemical weathering products
As the age of sedimentary rocks increases clay mineral assemblages in the subsurface transform through diagenesis to illite + chlorite

Clay mineral assemblages in the subsurface provide an indication of the time/temperature conditions experienced (enjoyed???) during burial

Chemical Weathering Products
biological weathering
Biological Weathering
  • Breakdown of rock by organic processes
    • Biochemical solution
      • bacteria
      • humic acids (rotting organic matter)
    • Physical fracturing
      • Tree roots
      • Burrowing (promotes chemical weathering)
        • Worms ingest up to 1 mm diameter, can reduce size
        • Up to 107 earthworms/km2 ; around since Precambrian
        • Bring 104 km (0.5 cm) of soil to surface
  • Product
    • soil
  • Products
    • Solute
      • Soluble fraction of rocks which are carried in water
    • Residua
      • Insoluble products of weathering
        • Boulder to colloidal clay
        • Colloid
          • Substance made up of very small, insoluble nondiffusable particles that remain in suspension
  • Water
    • ? environments
  • Wind
    • Sandblasting
  • Agents vary in effectiveness at sorting
  • Gravity, ice (avalanches, glaciers)
    • Competent to transport ALL weathering products
    • Inefficient at segregation
  • Water
    • Competent to carry material in solution
    • Less efficient transport residua (?boulders)
  • Wind
    • Highly selective (< 0.35 mm)
      • Medium- fine sands (saltation)
      • Silty loess (suspension)