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Sedimentary Rocks and Sedimentary Environments

Sedimentary Rocks and Sedimentary Environments. So, what do we get from weathering?. Big rocks break into smaller rocks and grains Clast is a general term (fine material = sediment ) If still large enough, clasts may contain more than one mineral

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Sedimentary Rocks and Sedimentary Environments

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  1. Sedimentary RocksandSedimentary Environments

  2. So, what do we get from weathering? • Big rocks break into smaller rocks and grains • Clast is a general term (fine material = sediment) • If still large enough, clasts may contain more than one mineral • Small clasts are generally only one mineral cobbles sand grains Size of clasts

  3. Clast Size: terms • Clay (refers to a specific mineral that is often very fine grained, AND to any very fine grains) • Silt – almost all quartz • Sand – quartz with some other minerals • Pebbles – variable mineralogy • Cobbles – variable mineralogy • Boulders –variable mineralogy Size of clasts

  4. So, what do we get from weathering? • Some minerals are not very stable • They may dissolve • Or break down to form other minerals • Oxidation => “rusty” red minerals • Hydrolysis => clay minerals oxidation clay Composition

  5. Goldich’s weathering series Composition

  6. Big picture

  7. Stream load

  8. Settling velocity low energy high energy

  9. Big picture (continued) weathering and erosion clastic material dissolved material biological material transportation deposition gravity chem. precipitation lithification

  10. The book sort of combines chemical and biological

  11. The most common sedimentary minerals in clastic rocks Quartz Clay Why? Quartz grains in a sandstone 2 mm Shales are almost entirely made of Clay, but the grains are too small To see

  12. Olivine beach - Hawaii

  13. What kind of sediment collects . . . • On mountain sides • Near glaciers • In sand dunes • Along rivers • In lakes • At deltas • On beaches • In lagoons • In wetlands • Near reefs Oysters, Mancos Shale

  14. Kinds of sedimentary rocks rock salt • Clastic • Chemical • Biological sandstone limestone

  15. Kinds of sedimentary rocks rock salt • Clastic • Chemical • Biological sandstone limestone

  16. Deposition in layers • Bed – relatively uniform layer E.g., “the limestone bed” • Strata – an identifiable layer May be smaller than a “bed” • Formation – a rock stratigraphic unit that has particular characteristics that allow it to be identified in different places. May not be completely homogeneous

  17. Grand Canyon

  18. Grand Canyon Rim

  19. Supai Group

  20. “Massive” layers

  21. “Interbedded” layers

  22. “Laminated” rocks

  23. Examples of sedimentary rocks • Breccia • Conglomerate • Sandstone • Shale, etc • Carbonate • Evaporite Almost all clastic material Generally little clastic material

  24. Carbonate rocks • Called limestone or dolostone • Or, generically, just limestone • Most form by precipitation of calcium carbonate from seawater • Generally in moderate to deep ocean basins • A few are freshwater • Some are reef deposits (organic) • Some contain clastic components

  25. Evaporite rocks • From by evaporation of ocean waters • Gypsum => gyp rock • Halite => rock salt

  26. Examples of sedimentary rocks • Clastic Sedimentary Rocks • Breccia • Conglomerate • Sandstone • Shale, etc • Chemical Sedimentary Rocks • Carbonate • Evaporite

  27. Kinds of Sedimentary Rocks • Clastic • Chemical • Biological coal coquina

  28. Kinds of Sedimentary Rocks • 1. Clastic rocks shale conglomerate sandstone

  29. Kinds of Sedimentary Rocks • 1. Clastic rocks • 2. Chemical sedimentary rocks Limestone with fossils evaporite evaporite Rock salt Gyp rock

  30. Salt flats Halite deposits

  31. Gypsum precipitates Gypsum in red soil

  32. Kinds of Sedimentary Rocks lignite (coal) • 1. Clastic rocks • 2. Chemical sedimentary rocks • 3. Biological sedimentary rocks anthracite (coal) Coquina = “beach rock” Limestone (petrified reef)

  33. Examples of sedimentary rocks • Clastic Sedimentary Rocks • Breccia • Conglomerate • Sandstone • Shale, etc • Chemical Sedimentary Rocks • Carbonate • Evaporite • Biological Sedimentary Rocks • Coal • Coquina Named according to grain size and shape Named according to composition

  34. Why do we have different kinds of sedimentary rocks on top of each other? • Change in the environment of deposition • = a facies change

  35. Transgression and regression • Transgression = increase in ocean depth • Regression = decrease in ocean depth

  36. (relative) sea level changes • Due to climate change • Uplift of continents • Downdropping of continents • Depth of water may change • Areas may become dry land • Dry land may flood

  37. Sedimentary facies • Facies = environment of deposition • Different kinds of sediment deposited in different places at the same time

  38. Characteristics of different facies

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