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SEDIMENTARY ROCKS

SEDIMENTARY ROCKS. A Brief Review. THERE ARE 4 BASIC COMPONENTS OF SEDIMENTARY ROCKS. sediments & sed. rocks are usually described according to 4 basic components : a. grains (larger particles) b. matrix (fines) c. pores (air, H 2 O, oil, gas)

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SEDIMENTARY ROCKS

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  1. SEDIMENTARY ROCKS A Brief Review

  2. THERE ARE 4 BASIC COMPONENTS OF SEDIMENTARY ROCKS • sediments & sed. rocks are usually described according to 4 basic components: • a. grains (larger particles) • b. matrix (fines) • c. pores (air, H2O, oil, gas) • d. cement (usually post-depositional) grains pores cement matrix

  3. CLASSIFICATION OF SEDIMENTARY ROCKS • Classified as either: • Detrital = composed of broken fragments & weathering products of other rocks &/or minerals • Shales • Sandstones • conglomerates • Chemical = composed of minerals precipitated from water solutions • Inorganic (direct ppt) • evaporites like rock salt which is halite • some cherts, such as at Ross Creek • Organic (indirect ppt) • fossiliferous limestones (organisms secrete CaCO3, not seawater) • some cherts (with silica skeletons of micro-organisms, diatoms)

  4. DETRITAL SEDIMENT GRAIN SIZES • Grain-size is the primary basis of distinguishing different kinds of detrital sedimentary rocks:

  5. CLASSIFICATION OF DETRITAL SEDIMENTARY ROCKS

  6. CONGLOMERATE • Cemented sedimentary rock whose grain-size diameters are greater than 2 mm • Four categories: • 2-4 mm = granule conglomerate • 4-64 mm = pebble " • 64-256 mm = cobble " • >256 mm = boulder " • Cements vary. Common ones are: • calcite (calcium carbonate) • quartz (silicon dioxide) • hematite (iron oxide)

  7. CONGLOMERATE • Conglomerates are common in continental stream channel deposits

  8. BRECCIA • A conglomerate whose grains are angular

  9. SANDSTONE • Grain size = 1/16th mm to 2 mm • Cements vary, commonly: calcite quartz or iron oxides • Quartz sandstone = quartz grains predominate • Arkose • rich in feldspar grains • pink or red colour from feldspars • Graywacke • >15% clay matrix • gray to black colour • lots of feldspar & rock fragments

  10. SILTSTONE • Grain size: • less than fine sand (<1/16th mm) • larger than clay sizes (<1/256th mm) • feels "gritty between your teeth :( • Quartz dominates • Structures: • finely laminated • rippled • cross-bedded

  11. SHALE • Subparallel parting splits into thin layers • Clay and silt sizes dominate • Clay minerals dominate • Colours vary: • Grey (contains organic matter) • Black: • may be rich in organic matter • some associated with coals • Red (contains iron oxides) • Preserves fossils well

  12. CLASSIFICATION OF CHEMICAL SEDIMENTARY ROCKS

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