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Identification and Classification of Sedimentary Rocks PowerPoint PPT Presentation


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Identification and Classification of Sedimentary Rocks. Terrigenous Clastic Sediments and Rocks. No “Simple” Classification Scheme. Folk. FICHTER. Nichols. Descriptive Textural Classification: Ternary Plots (see appendix B in Fichter and Poche ) of

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Identification and Classification of Sedimentary Rocks

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Identification and Classification of Sedimentary Rocks

Terrigenous Clastic Sediments and Rocks


No “Simple” Classification Scheme

Folk

FICHTER

Nichols


Descriptive Textural Classification:

Ternary Plots (see appendix B in Fichter and Poche) of

G (gravel >2mm) - S (2mm>sand> 0.063mm)- M (mud<0.063mm)

significance of gravel (>30%) min. transport energy

or

S (sand) - C (clay<0.004mm)- S (0.063mm>silt> 0.004mm)

Wacke??!!

Siliciclastic Rock Classification: Texture


Textural Nomenclature – TC’s

Nichols, Fig. 2.5, p. 9


Classification of Mudrocks


Classification of Gravel/CGL


Siliciclastic Rock Classification

  • Mineralogical Classification/terminology

    • Sand ----------->Arenites

    • CGL------------->Rudites

    • MDST----------->Lutites

      textural term mineralogical term

  • Arenite (& Rudite) Petrology, Why?

    • Ease of analysis and sampling

    • Composition can be interpreted


Mineralogical ClassificationSandstone Architecture

  • F-M-C-P

    • Framework Grains

      • > 0.05mm (particulate residues; larger than coarse-grained silt)

    • Detrital Matrix

      • < 0.05mm (clay, qtz, flds, -CO3, organics, oxides) chemical weathering products

    • Cement

      • post-depositional orthochemical components; ppt from circulating pore fluids (qtz,-CO3, clay, fldsp, oxides, zeolite, salts)

    • Pores;

      • Primary (up to ~40%) or 2ndary due to leaching/dissolution


Mineralogical ClassificationSandstone Architecture

  • Framework Grains:

    • relative abundance a function of mineral grain

      Availability, Chemical Stability, Mechanical Durability

  • Anything Possible, most common:

    • Qtz :

      • mono, poly, ign, meta, qtzite, chert, volc, etc; mech & chem stable, abundant

    • Feldspar:

      • K-spar (sandine, microcline), Plag (Na-Ca), stains (Amaranth soln), abundance and mechanical stability (variable)

    • Rock Fragments:

      • all kinds (including limestone/dolomite RF’s) ; abundant, variable stability


Mineralogical Classification ofSandstone Architecture

  • Carbonate cement (calcite, dolomite, ankerite, siderite)

  • Clay minerals (kaolinite, illite)

  • Quartz

  • Feldspar (albite)

  • Zeolite

  • Authigenic Components


Pores


Mineralogical ClassificationPrimary Sandstone Architecture

  • Framework Grains

    • Accessory Minerals:

      • Mica

      • ZTR; zircon, tourmaline, rutile: stable heavies

      • Unstable heavies: Amph, Pyx, Chl, Garn, Epid

      • carbonate allochems

      • non-detrital/orthochem; glauconite (iron-rich clay after fecal pellets) and phosphate (colophane, apatite); unusual oceanographic conditions


Data Plots and Sandstone Classification

  • TC’s with >50% grains & > 0.05mm

    • Arenites Ternary Diagram Q - F - R(L)

      • Q= mono and polycrystalline (not chert) quartz

      • F= monocrystalline feldspar

      • R (L)= rock (or lithic) fragments

        Normalized, 3 phase classification: Q=q/q+f+r; F=f/q+f+r; R=r/q+f+r


Data Plots and Sandstone Classification

  • Normalized, 3 phase classification

    • Q= q/q+f+r

    • F= f/q+f+r

    • R= r/q+f+r

  • 7 types of “normal” Arenites

    • others = “mineral” arenite, i.e. mica-arenite, magnetite-arenite


Sandstone Classification

  • Complete Arenite name (Folk,Andrews, and Lewis, 1970):

    • (sorting term),

    • (size term):

    • (cement),

    • (prominent non-detrital grain type),

    • (prominent detrital acc grain type),

    • (named arenite)

      e.g Moderately Sorted, Medium-grained:

      Calcite Cemented, Glauconitic, Micaceous, Quartz Arenite

Fichter and Poche


Interpretation of Sandstone Composition:

  • MATURITY –

    • a relative measure of how extensively and thoroughly a sediment (sand size and larger) has been weathered, transported and reworked toward its ultimate end product, quartz sand.


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