Diagenesis

1
Diagenesis

• Process of turning sediments into sedimentary
  rocks ? water-rock interactions precipitating
  minerals
• Water is pores of sediments
• fresh muds can be gt80 water
• Water can be trapped at time of deposition,
  transported in, or evolved from dehydration
  reactions of hydrous minerals
• Also can be significant organic matter
• Drive redox reactions reduce Fe3, Mn4, SO42-

2
Diagenesis

• Muds are compacted to shales water is expelled,
  though up to 30 H2O can remain associated with
  clays even at 1 km depth
• Minerals from water and changing conditions ?
  clays, sulfides, siicates, carbonates

3
Clay Geochemistry

• Clays can have significant chemical substitution,
  they undergo phase transitions as diagenesis
  proceeds
• Illites ? Smectites in shales for example
• Al2Si4O10(OH)2nH2O KAlSi3O8 ?
  KAl2(AlSi3)O10(OH2) 4 SiO2(aq) n H2O

4
Sandstone Diagenesis

• Sandy sediments have high permeability, meaning
  water flows through them faster
• The water brings ions, precipitation of calcite
  and silica occurs WHY?
• These minerals cement the sediments
• Silica becomes a more important cementing
  material at high T
• Pressurized pockets can become more concentrated,
  when the pressure is released they are instantly
  supersaturated

5
Carbonate Diagenesis

• Aragonite and Mg-rich calcite are the major
  phases associated with shallow sedimentary
  carbonates
• Dolomite problem Dolomite is not the first thing
  to form typically from a water, why are units of
  calcite so extensively dolomitized?
• Reaction requires a higher Mg/Ca ratio
  occurring perhaps in sabka (supratidal pools)
  environments, or at seawater-meteoric water
  interfaces where calcite is undersaturated but
  dolomite is supersaturated

6

• How do these ions get to these places and form
  cement?
• Transport through water
• Diffusion and advection account for the movement
  of ions

7
Soil

• soil - (i) The unconsolidated mineral or organic
  material on the immediate surface of the earth
  that serves as a natural medium for the growth of
  land plants. (ii) The unconsolidated mineral or
  organic matter on the surface of the earth that
  has been subjected to and shows effects of
  genetic and environmental factors of climate
  (including water and temperature effects), and
  macro- and microorganisms, conditioned by relief,
  acting on parent material over a period of time.
  A product-soil differs from the material from
  which it is derived in many physical, chemical,
  biological, and morphological properties and
  characteristics.

8
Soil stratigraphy

• Soil layers, or Horizons, lettered
  O?A?E?B?C?R
• O organic layer plant fibers, high organics,
  leafy
• A topsoil minerals organics
• E leached layer minerals leached, low
  organics
• B accumulation zone leached and carried down,
  lots of clays
• C Parent material partially weather original
  minerals
• R bedrock

9
Soil Components

• Soil fabric spatial arrangement of these things
• Liquid 1-35
• Chelates organics that bond metals strongly,
  solubilizing them (bidentate or polydentate 2
  or 2 bonds to the metal)
• Equilibrium description?

• Minerals
• Organic Material
• Microorganisms
• Plants
• Gas CO2, CH4, H2S, etc.
• Water

10
Chelators

• These are key organic compounds which
  SIGNIFICANTLY affect how much metals get into
  water and how they can be transported
• Cu solubility
• Cu2 EDTA ? Cu(EDTA) log K 18
• 2Cu O2- Cu2O log K -15