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Sedimentary Rocks

Sedimentary Rocks. Chapter 6. What Are Sediments?. Loose particulate material In order of decreasing size. Sources of Sediments. 1. From weathering & erosion 2. From chemical precipitation. What Happens to Sediments. 1. transported by: Water. Ice. Wind. Gravity.

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Sedimentary Rocks

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  1. Sedimentary Rocks Chapter 6

  2. What Are Sediments? • Loose particulate material • In order of decreasing size

  3. Sources of Sediments 1. From weathering & erosion 2. From chemical precipitation

  4. What Happens to Sediments 1. transported by: • Water. • Ice. • Wind. • Gravity. • Most sediment is buried and converted to sedimentary rock.

  5. What Happens to Sediments 2. Deposited by • Rivers • Wind • Glaciers • Other water • When the transportation vector has run out of energy, the sediments are deposited (dropped).

  6. River Sorting- Transporting & Depositing Headwaters Mouth Grade = change in elevation/length

  7. Principle of Original Horizontality Most sedimentary layers of rock are deposited in a horizontal position, with older rocks laid down first

  8. Lithification Sediment becomes sedimentary rock through lithification, which involves: • Compaction • Cementation • Recrystallization (of carbonate sediment) • Ex: sand Remember that SiO2 is released into groundwater from the chemical weathering of quartz and feldspars.

  9. 3 Classes of Sedimentary Rock Clastic - fragments of rock debris produced by physical weathering. Ex. Sand & clay. Chemical - sediment precipitates from solution in water. Ex. Calcium carbonate & salt. Biogenic (organic) - sediment composed of the fossilized remains. Ex. Coal, oil, & natural gas. Chemical

  10. Clastic Sedimentary Rock • From the weathering of other rocks – broken texture • Clasts (larger pieces, such as sand or gravel) • Matrix (mud or fine-grained sediment surrounding the clasts) • Cement (the glue that holds it all together), such as: • calcite • iron oxide • silica

  11. Gravel Clastic Rocks • If rounded clasts = conglomerate • If angular clasts = breccia

  12. Sand Clastic Rocks Different Sandstones based on dominate grains • quartz grains = quartz sandstone • feldspar grains = arkose • sand-sized rock fragment grains = graywacke

  13. Silt Clastic Rocks • Siltstone - Grain size 1/256 to 1/16 mm (gritty)

  14. Clay Clastic Rocks • Grains less than 1/256 mm (smooth) • Shale (if fissile – splits) • Kaolinite (if massive)also called Claystone • Note: Mud is technically a mixture of silt and clay. (Mudstone)

  15. Chemical Sedimentary Rocks Chemicals removed from seawater and made into rocks by chemical processes, or with help of biological processes (such as shell growth). 3 types • Evaporites • Carbonates • Siliceous

  16. Chemical Evaporites From the evaporation of water (usually seawater). • Rock salt - composed of halite (NaCl). • Rock gypsum - composed of gypsum (CaSO4.2H20) • Travertine- composed of calcium carbonate (CaCO3), and therefore, also technically a carbonate rock

  17. Chemical Carbonates • Formed through both chemical & biochemical processes. • Include the limestones (many types) • Two minerals are dominant: • Calcite (CaCO3) • Dolomite (CaMg(CO3)2)

  18. Chemical Siliceous Dominated by silica (SiO2). • From diatoms, radiolarians, or sponges. • Diatomite - looks like chalk, but doesn’t fizz in acid. Made of diatoms. Also referred to as Diatomaceous Earth. • Chert - Massive and hard, microcrystalline quartz. May be dark or light in color. Often replaces limestone. Does not fizz in acid.

  19. Biogenic (Organic) Sedimentary Rocks Coals • organic matter (plants). • Increasing depth of burial (temperature and pressure): • Peat (porous, brownish plant fragments) • Lignite (crumbly and black) • Bituminous(dull to shiny and black; sooty; layers may be visible) • Anthracite(extremely shiny and black; low density; not sooty

  20. Formations from Sediments • Large enough to be recognized. • Ex.- haystack rock, sand dunes, delicate arch, balanced rock

  21. Sedimentary Environments (Sinks) Places where sediments accumulate and sedimentary rocks form 3 Major Groups • Continental • Marine • Transitional

  22. Terrestrial Environments • Aluvial Fan • Braided stream • Lakes • Rivers • Levees • Swamps • Deserts • Glacial

  23. Marine Environments Seas & oceans • Continental shelf • Continental slope and rise (deep sea fans) • Abyssal plain • Reefs

  24. Transitional Environments between the land and the sea.

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