Petrologi 8-sedimen

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Petrologi 8-sedimen

  1. 1. Semester 2, 2007-2008 petrologi 2 SKS teori 1 SKS praktikum by: hill. gendoet hartono Senin, jam 09.50 – 10.40 jam 10.45 – 11.35
  2. 2. Sedimentary Rocks Batuan Sedimen
  3. 3. Sediments and Sedimentary Rocks Rock Cycle
  4. 4. What is a sedimentary rock? • Sedimentary rocks result from mechanical and chemical weathering • Comprise ~ 5% of Earth’s upper crust • About 75% of exposed rocks • Contain evidence of past environments • Record how sediment is transported • Often contain fossils
  5. 5. Fossil Fish - 50 Million Year Old Lakes in southern Wyoming These fish tell us the Wyoming climate 50 million years ago. Sedimentary Rock made of fine-grained mudstone.
  6. 6. Overview ► sediment production ► types of sediment and sedimentary rocks ► sediment transport and deposition ► depositional systems ► stratigraphic architecture and basins ► chrono-, bio-, chemo-, and sequence stratigraphy ► Earth history
  7. 7. Sedimentary rocks are the creation product of the creation, transport, deposition, and diagenesis of detritus and solutes solutes derived from preexisting rocks.
  8. 8. Steps Involved in Formation of Clastic Sedimentary Rock Weathering Erosion Transport Deposition Lithification --Compaction --Cementation
  9. 9. Weathering
  10. 10. Steep terrain accelerates erosion
  11. 11. Turbidity Currents
  12. 12. Ions weather out of rock, are transported by groundwater to sediment layers below 6_11 Ions transported to lake or Water enters pore ocean spaces between sediment grains Ion-rich groundwater Dissolved ions precipitate to form cement between sediment grains
  13. 13.  Diagenesis includes:  Recrystallization – growth of stable minerals from less stable ones  Lithification – loose sediment is transformed into solid rock by compaction and cementation Natural cements: calcite, silica, and iron oxide. Formed from ions in solution in water.
  14. 14. ► Diagenesis – chemical and physical changes that take place after sediments are deposited ► Diagenesis varies with composition
  15. 15. Lithification ► Compaction: As more sediments are piled on top, compaction drives out the excess water. ► Cementation: Precipitation of chemicals dissolved in water binds grains of a sediment together. ► Remember where the dissolved chemicals come from?
  16. 16. Compaction and Cementation of Clastic Sediment into Rock Overburden Sediment Compaction Cementation
  17. 17. Lithification and compaction of shale NB volume loss during compaction
  18. 18. ► Source area - the locality from which the sediment was derived: factors used to evaluate source area include rock type, environment of deposition, direction (paleocurrents) and distance from source area
  19. 19. ► Depositional environment – where sediment is deposited. It can be determined by looking at sedimentary structures (including fossils), the bed shape and vertical sequences within the sedimentary layers, and grain composition
  20. 20. Sedimentary environments & plate tectonic settings Convergent boundaries – coarse-grained clastic sediments with abundant volcaniclastic and felsic material
  21. 21. Sedimentary environments & plate tectonic settings Divergent boundaries - thick wedges of gravel and coarse sand along margins,with lake bed deposits and associated evaporite rocks possible in bottoms of rift valleys
  22. 22. What is the economic importance of sedimentary rocks? ► They are important for economic reasons Remember this because they contain when we talk about ►Coal ►Petroleum and natural gas correlation. Note how beds pinch out or are offset by faults ►Iron, aluminum, uranium and manganese ►Geologists use them to read Earth’s history
  23. 23. SEDIMENTARY ROCKS ► WEATHERING PROCESSES BREAK ROCK INTO PIECES, SEDIMENT, READY FOR TRANSPORTATION DEPOSITION BURIAL LITHIFICATION INTO NEW ROCKS.
  24. 24. CLASSIFYING SEDIMENTARY ROCKS ► ► ► ► THREE SOURCES Detrital (or clastic) sediment is composed of transported solid fragments (or detritus) of pre-existing igneous, sedimentary or metamorphic rocks Chemical sediment forms from previously dissolved minerals that either precipitated from solution in water , or were extracted from water by living organisms Organic sedimentary rock consisting mainly of plant remains
  25. 25. CLASTIC SEDIMENTARY ROCKS CLASSIFIED ON GRAIN OR PARTICLE SIZE ► Shales: finest-grained ► Sandstones: medium-grained ► Conglomerates – Breccias: coarse-grained
  26. 26. SHALES ► SHALES: finest-grained – composed of very small particles (from <0.004-0.063 mm)  50% of all sedimentary rocks are Shales  Consist largely of Clay minerals  Subcategories: Claystones; Siltstones; Mudstones  Economic value: building material; china and ceramics; spark plug housings
  27. 27. SANDSTONES ► SANDSTONES: medium-grained; particle-size (0.063-2 mm) ► 25% of all sedimentary rocks fall into this category ► Three major kinds of Sandstone, based on mineral composition and appearance:    Quartz Arenite: >90% quartz grains Arkoses : more Feldspar minerals Graywackes :quartz and feldspar grains, and volcanics ► Economic value: glass; natural reservoirs for oil, gas, and groundwater
  28. 28. CONGLOMERATES BRECCIAS ► CONGLOMERATES AND BRECCIAS : ► The coarsest of all the detrital sedimentary rocks ► Composed of particles >2 mm in diameter  Conglomerate - the particles are rounded  Breccia - the particles are angular
  29. 29. CHEMICAL SEDIMENTARY ROCKS ► TWO CATEGORIES:  INORGANIC CHEMICAL SEDIMENTARY  ORGANIC CHEMICAL SEDIMENTARY
  30. 30. INORGANIC CHEMICAL SEDIMENTARY ROCKS ► Formed when dissolved products of chemical weathering precipitate from solution ► Most common types:  Inorganic limestones and cherts: precipitates directly from seawater and fresh water  Evaporites: precipitates when ion-rich water evaporates  Dolostones: Origin is still in debate
  31. 31. INORGANIC - LIMESTONES ► Limestones - account for 10% - 15% of all sedimentary rocks formed from Calcite or Calcium Carbonate (CaCO3). ► Formed as pure carbonate muds accumulate on the sea floor ► Also formed on land:  Tufa - a soft spongy inorganic limestone that forms where underground water surfaces  Travertine - forms in caves when droplets of carbonate-rich water on the ceiling, walls and floors precipitate a carbonate rock
  32. 32. ORGANIC LIMESTONES ► Formed with calcite from marine environment: CaCO 3 shells and internal/external skeletons of marine animals ► Coquina - “crushed” shell fragments cemented with CaCO3 Chalk - made from billions of microscopic carbonate-secreting organisms Coral Reefs - Formed from the skeletons of millions of tiny invertebrate animals who secrete a calcite-rich material. Live “condo” style while algae acts as the cement to create the large structures called “reefs”. Organic Chert - formed when silica-secreting microscopic marine organisms die (radiolaria {single-celled animals} and diatoms {skeletons of singled-celled plants}) Flint - an example of an Organic Chert ► ► ► ► ►
  33. 33. ORGANIC SEDIMENTARY ROCKS ► ► Coal - Organic sedimentary rock consisting mainly of plant remains Formation:  Burial of decaying vegetation;  Increasing pressure from the overlying layers expels water, CO2 and other gases;  Carbon accumulates. ► ► ► ► Peat - formed early in the process, when the original plant structure can still be distinguished. Lignite - a more hardened form of Peat Bituminous - more pressure and more heat produce this moderately hard coal. Anthracite - the hardest coal - formed from metamorphic processes under extreme heat and pressure - Hard - Shiny - the most desired as an energy resource.
  34. 34. SEDIMENTARY ENVIRONMENTS ► Lakes ► Lagoons ► Rivers ► Ocean bottoms ► Estuaries ► Salt Flats ► Playas ► Glacial environments
  35. 35. SEDIMENTARY PROCESSES ► LITHIFICATION : ► As sediment is buried several kilometers beneath the surface, heated from below, pressure from overlying layers and chemically-active water converts the loose sediment into solid sedimentary rock ► Compaction - volume of a sediment is reduced by application of pressure Cementation - sediment grains are bound to each other by materials originally dissolved during chemical weathering of preexisting rocks ►  typical chemicals include silica and calcium carbonate.

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