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Sedimentation and Sedimentary Rocks

Sedimentation and Sedimentary Rocks. GLY 2010 - Summer 2014 - Lecture 10. Sediment. Unconsolidated material that accumulates at the earth’s surface Minerals and organic remains of plants and animals are the major components of soil. Sedimentary Rock.

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Sedimentation and Sedimentary Rocks

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  1. Sedimentation and Sedimentary Rocks GLY 2010 - Summer 2014 - Lecture 10

  2. Sediment • Unconsolidated material that accumulates at the earth’s surface • Minerals and organic remains of plants and animals are the major components of soil

  3. Sedimentary Rock • As sediment accumulates, pressure, and often temperature, increases • Changes occur which convert the sediment from unconsolidated form to a consolidated form, sedimentary rock • Sedimentary rock makes up 5% of the crust of the earth, but accounts for 75% of the rock exposed at the surface

  4. Importance of Sedimentary Rock • Provide clues to the earth’s past – examples: • Including erosion of mountain ranges • Transgressions of the sea over the land

  5. Fossils • Often contain fossils, which provide clues to: • Types of life living in the past • The environment they lived in

  6. Types of Sediment • Detrital • Chemical • Biogenic

  7. Sediment Transport • Water, glaciers, or wind moves the sediment from high elevations to lower elevations, where it may accumulate • Annual transport of detrital sediments to the oceans is about 10 billion tons • During transportation, sediment size is often reduced

  8. Transport of Sediment By rivers By glaciers

  9. Formation of Detrital Rock • Deposition • Sorting • Shape

  10. Clastic Rock and Matrix

  11. Lithification • Literally means creation of stone • Involves three possible processes • Compaction • Cementation • Recrystallization

  12. Compaction • Fragments will be compacted by the weight of accumulating sediment • Air and water are expelled from spaces between grains

  13. Cementation • Dissolved substances in water may precipitate solids which act as cements

  14. Recrystallization • Unstable minerals may reorganize due to heat, pressure, and fluid interaction into more stable minerals • Process must occur at low temperatures • Ex: Aragonite  Calcite

  15. Sedimentary Structures • Bedding - sediments are ordinarily deposited in horizontal units called beds • Graded bedding • Cross-bedding

  16. Graded Bedding

  17. Graded Bedding Animation

  18. Cross Bedding Animation

  19. Cross-bedding, Zion National Park Photos: Duncan Heron

  20. Principle of Original Horizontality • Most sediments settle through bodies of water • They will be deposited in horizontal, or very nearly horizontal, layers • Beds which are not horizontal have often had their position changed by post-depositional processes

  21. Right Side Up • Beds may occasionally be completely overturned, so we need ways to tell if beds are right side up • Selected indicators: • Ripple Marks • Mudcracks • Raindrop impressions • Salt crystals

  22. Aeolian Ripple Marks • Aeolian (wind) ripples at White Sands, New Mexico (Photo Yamato Sato)

  23. Fossilized Ripple Marks • Parallel ripple marks preserved on a slab of sandstone • The rocks contain the fossilized remains of marine animals - these ripples were formed in shallow sea water by gentle currents • Fossilized ripple marks. Capitol Reef National Park, Utah

  24. Mudcracks

  25. Mudcracks Mudcracks form by desiccation of mud or clay

  26. Raindrop Impressions

  27. Salt Crystals • If the deposition occurs in the ocean, and the water is quite saline, salt crystals may precipitate and settle on the sediment

  28. Size Range of Detrital Particles • Clay < 0.004 millimeters • Silt 0.004 to 0.063 millimeters • Sand 0.063 to 2 millimeters • Granule 2 to 4 millimeters • Pebble 4 to 64 millimeters • Cobble 64 to 256 millimeters • Boulder >256 millimeters

  29. Sediment Types • Mud is composed of clay or silt • Sand is composed exclusively of sand sized particles • Gravel includes granules, pebbles, cobbles, and boulders

  30. Detrital Rock Types

  31. Shale

  32. Siltstone

  33. Sandstone with Silica Cement

  34. Sandstone with Hematite Cement

  35. Conglomerate

  36. Quartz Pebble Conglomerate

  37. Breccia

  38. Formation of Chemical Sedimentary Rocks • Precipitation is the process of converting materials dissolved in a fluid (water or air) to another form • Water dissolved in the atmosphere may precipitate as rain, or as some solid form such as snow, sleet, hail, etc • Solids dissolved in water precipitate as solids

  39. Saturated Solution • In order for precipitation to occur, the fluid must be saturated • A saturated solution holds as much as it can of a particular substance • A fluid may be saturated with respect to one substance (e.g. lime) and undersaturated with respect to another substance (e.g. halite)

  40. Chemical Precipitation • Solutions which are saturated, or slightly supersaturated, may spontaneously form crystals, which settle in the solution

  41. Biochemical Precipitation • Some organisms have the ability to concentrate an unsaturated solution internally to the point where precipitation occurs This fossiliferous limestone contains carbonate shells, produced by biochemical precipitation

  42. Evaporites • When saline solutions (sea-water) evaporate, a series of substances precipitate in a definite sequence, from the least to the most soluble • Sequence is: • Lime – a carbonate • Gypsum, a sulfate, precipitates second • Halite, common table salt, is next • Potassium and magnesium salts are last

  43. Bonneville Salt Flats

  44. Layered Gypsum

  45. Evaporite Nodules

  46. Chemical Sedimentary Rocks • Limestone is composed of calcium carbonate, CaCO3 • Dolostone is composed of dolomite, CaMg(CO3)2

  47. Oolitic Limestone • In warm, saturated, and highly energetic environments, lime may precipitate around tiny bits of suspended matter • They stick together to form an oolitic limestone, such as the Miami oolite formation

  48. Oolitic Limestone

  49. Biochemical Sedimentary Rock • Coral reefs • Coquina

  50. Ancient Marine Reef • El Capitan reef, Guadalupe Mountains National Park, formed as part of a very large reef complex during the Permian period

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