Petrologi 8-sedimen

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Transcript of Petrologi 8-sedimen

  • 1. Semester 2, 2007-2008petrologi 2 SKS teori 1 SKS praktikum by: hill. gendoet hartono Senin, jam 09.50 10.40 jam 10.45 11.35

2. Sedimentary Rocks Batuan Sedimen 3. Sediments and Sedimentary RocksRock Cycle 4. What is a sedimentary rock? Sedimentary rocks result from mechanical and chemical weathering Comprise ~ 5% of Earths upper crust About 75% of exposed rocks Contain evidence of past environments Record how sediment is transported Often contain fossils 5. Fossil Fish - 50 Million Year Old Lakes in southern WyomingThese fish tell us the Wyoming climate 50 million years ago.Sedimentary Rock made of fine-grained mudstone. 6. Overview sediment production types of sediment and sedimentaryrocks sediment transport and deposition depositional systems stratigraphic architecture and basins chrono-, bio-, chemo-, and sequence stratigraphy Earth history 7. Sedimentary rocks are the creation product of the creation, transport, deposition, and diagenesis of detritus and solutes solutes derived from preexisting rocks. 8. Steps Involved in Formation of Clastic Sedimentary Rock Weathering Erosion Transport Deposition Lithification --Compaction --Cementation 9. Weathering 10. Steep terrain accelerates erosion 11. Turbidity Currents 12. Ions weather out of rock, are transported by groundwater to sediment layers below6_11Ions transported to lake or Water enters pore ocean spaces between sediment grainsIon-rich groundwaterDissolved ions precipitate to form cement between sediment grains 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. Diagenesis chemical and physical changesthat take place after sediments are deposited Diagenesis varies with composition 15. Lithification Compaction: As more sediments are piled ontop, 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. Compaction and Cementation of Clastic Sediment into Rock OverburdenSedimentCompactionCementation 17. Lithification and compaction of shaleNB volume loss during compaction 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. 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. Sedimentary environments & plate tectonic settings Convergent boundaries coarse-grained clastic sediments with abundant volcaniclastic and felsic material 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. 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 gascorrelation. Note how beds pinch out or are offset by faultsIron, aluminum, uranium and manganeseGeologists use them to read Earths history 23. SEDIMENTARY ROCKS WEATHERING PROCESSES BREAKROCK INTO PIECES, SEDIMENT, READY FOR TRANSPORTATION DEPOSITION BURIAL LITHIFICATION INTO NEW ROCKS. 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. CLASTIC SEDIMENTARY ROCKS CLASSIFIED ON GRAIN OR PARTICLE SIZE Shales: finest-grained Sandstones: medium-grained Conglomerates Breccias: coarse-grained 26. SHALES SHALES:finest-grained composed of very small particles (from 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. CONGLOMERATES BRECCIAS CONGLOMERATESAND 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. CHEMICAL SEDIMENTARY ROCKS TWO CATEGORIES: INORGANIC CHEMICAL SEDIMENTARY ORGANIC CHEMICAL SEDIMENTARY 30. INORGANIC CHEMICAL SEDIMENTARY ROCKS Formed when dissolved products ofchemical 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. INORGANIC - LIMESTONES Limestones- account for 10% - 15% of allsedimentary rocks formed from Calcite or Calcium Carbonate (CaCO3).Formed as pure carbonate muds accumulate on the sea floorAlso 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. ORGANIC LIMESTONES Formed with calcite from marine environment: CaCO 3 shells and internal/external skeletons of marine animalsCoquina - 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. 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. SEDIMENTARY ENVIRONMENTS Lakes Lagoons Rivers Oceanbottoms Estuaries Salt Flats Playas Glacial environments 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 rockCompaction - 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.