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Identification and Classification of Sedimentary Rocks

Identification and Classification of Sedimentary Rocks

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Identification and Classification of Sedimentary Rocks

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  1. Identification and Classification of Sedimentary Rocks Terrigenous Clastic Sediments and Rocks

  2. No “Simple” Classification Scheme Folk FICHTER Nichols

  3. 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

  4. Textural Nomenclature – TC’s Nichols, Fig. 2.5, p. 9

  5. Classification of Mudrocks

  6. Classification of Gravel/CGL

  7. 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

  8. 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

  9. 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

  10. Mineralogical Classification ofSandstone Architecture • Carbonate cement (calcite, dolomite, ankerite, siderite) • Clay minerals (kaolinite, illite) • Quartz • Feldspar (albite) • Zeolite • Authigenic Components

  11. Pores

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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.