• ATLAS INDEX

Carbonate Rock Classification

Components

Carbonate Particles

Non Skeletal Grains
  • Peloids
  • Coated grains
    • Ooids
    • Oncoids
    • Cortoids and micrite coated grains (micrite envelopes)
    • Pisoids
  • Aggregate grains
  • Intraclasts
  • Extraclasts/Lithoclasts
Skeletal grains

Carbonate mud matrix

Silt and clay-grade carbonate minerals (calcite, aragonite) as interstitial sediment between the grains (Wright, 1992). It appears dark in transmitted light due to the fine grain size. Previous authors have used different terms and crystal-size ranges to define the carbonate mud matrix.

Micrite

Microcrystalline carbonates

  • < 4 μm (Folk, 1959, 1962; Tucker, 1981)
  • < 20 μm (Dunham, 1962)
Lime mud/Carbonate mud/Calci-mud

Microcrystalline carbonate matrix

  • < 62 μm (Neumann and Land, 1975)
  • < 62 μm (Wright, 1992)

Carbonate precipitates

Chemical (abiotic/physico-chemical or biogenic) carbonate precipitates from aqueous solution.

Syn-depositional

Automicrite/Clotted peloidal micrite

Microcrystalline carbonate precipitated in situ (abiotic or biologically induced/influenced by microbial mats) as micrite or micritic peloids embedded in microsparite (clotted peloidal micrite)

Diagenetic

Cement/Sparite

Crystals of calcite and aragonite > than 62 μm (they can vary in size and shape) that appear hyaline/transparent in transmitted light. Crystal fabric and mineralogical composition are indicative of diagenetic environments (marine, meteoric, burial).

Microsparite/ Neomorphic microsparite

Primary precipitate or due to neomorphic recrystallization of micrite

  • 4-30 μm (Folk, 1959, 1962)
  • 5-50 μm (Bathurst, 1975)
  • 5-15 μm (Tucker, 1981)
Dolomite

Replacive dolomite crystals over calcite or dolomite cement varying in size and shape according to the diagenetic environment. Rare primary dolomite.

Non carbonate grains

  • Quartz
  • Feldspars
  • Extraclasts

Authigenic minerals

  • Glaucony
  • Pyrite
  • Phosphates
  • Evaporites (Gypsum, Anhydrite, Halite)

Porosity

Unfilled Open space volume

Primary depositional
  • Intergranular/Interparticle
  • Intragranular/Intraparticle
  • Intercrystalline
  • Growth Framework
  • Shelter
  • Fenestral
Secondary diagenetic
  • Dissolution related (mouldic, bio-mouldic, oo-moludic, vugs, karst/caves)
  • Fractures and fissures
  • Intercrystalline

Sources of carbonate mud matrix (calci-mud < 62 µm)

Shallow water (Recent)
  • Mostly aragonite, less High Mg Calcite (HMC)
  • Green algae break-down (aragonite)
  • Direct precipitation in the water column (abiotic and/or whitings/picoplankton; aragonite, HMC)
  • Abrasion/bioerosion of skeletal and non skeletal grains (aragonite, HMC, LMC)
Deep water (Recent)
  • Mostly Low Mg Calcite (LMC)
  • Calcareous nannoplankton (LMC)
  • Planktonic foraminifers (LMC)
  • Resedimented from shallow water (aragonite, HMC, LMC)

 

MudMatrix

 

1.1A_2 grains