terrigenous sediments l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Terrigenous Sediments PowerPoint Presentation
Download Presentation
Terrigenous Sediments

Loading in 2 Seconds...

play fullscreen
1 / 41

Terrigenous Sediments - PowerPoint PPT Presentation


  • 183 Views
  • Uploaded on

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)

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Terrigenous Sediments' - hasad


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
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
  • RETAINS CHARACTERISTICS OF ORIGINAL ROCK
    • 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
PhysicalWeathering
  • 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

Phyllosilicates

Si2O5

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

sheets

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
weathering
Weathering
  • 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
erosion
Erosion
  • Water
    • ? environments
  • Wind
    • Sandblasting
transportation
Transportation
  • 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)