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Chapter 8

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Chapter 8

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  1. Chapter 8 Sedimentary Rocks Part2 • Types of sedimentary rock • Sedimentary structures

  2. Sedimentary rocks Types of sedimentary rocks • Sediment originates from mechanical and/or chemical weathering • Rock types are based on the source of the material • Clastic rocks – transported sediment as solid particles • Chemical/Biochemical rocks – sediment that was once in solution

  3. Chapter 8 Sedimentary rocks • Clastic • sedimentary rocks • Size of clasts (particles) common name size Detrital rock • gravel bigger than 2 mm conglomerate • (1/10 inch) or breccia • sand sand-sized (1/16-2) sandstone • silt, clay very fine-grained (<1/16) shale, mudstone,siltstone See Table 8.3

  4. gravel sand silt clay conglomerate sandstone siltstone shale sediments sedimentary rocks

  5. Chapter 8 Sedimentary rocks • deposited in quiet (slow moving) water - deep ocean & continental slope - lakes - floodplains (siltstone) • Clastic sedimentary rocks • Siltstone, Mudstone & Shale • silt & clay-sized particles (clay, silt), particles too small to identify w/ eye • over 1/2 of all sedimentary rocks • shale beds often underlay groundwater conduits • shale may contains fossils, oily organics, breaks along bedding planes • raw material for brick, tile, pottery, china • shale+limestone= Portland cement Shale w/plant remains

  6. Chapter 8 Sedimentary rocks • Clastic sedimentary rocks • Sandstone • composed of sand grains • 2nd most abundant sedimentary rock • deposited by moderate currents: • - rivers & deltas • - beaches • - wind (sand dunes) • mostly quartz (strong & chemically stable, but may also contain volcanic rock) See Fig. 8.15 for major groups of sandstone

  7. Chapter 8 Sedimentary rocks • Clastic sedimentary rocks • Sandstone • sorting degree of similarity in particle size

  8. Chapter 8 Sedimentary rocks • Clastic sedimentary rocks • Sandstone • shape degree of roundedness

  9. Chapter 8 Sedimentary rocks • Clastic sedimentary rocks • Conglomerate • composed mostly of gravel • pebbles to boulders • poorly sorted • deposited by strong, turbulent currents: • - big flooding rivers • - steep streams (near mountains) • - glaciers

  10. Chapter 8 Sedimentary rocks • Clastic sedimentary rocks • Breccia • conglomerate with angular grains • didn’t travel far

  11. Chapter 8 Sedimentary rocks • Chemical • sedimentary rocks • derived from material carried in solution to lakes/seas • precipitation from solution to form “chemical sediments” • 2 types of precipitation • - chemical • - biochemical See Table 8.4

  12. Chapter 6 Sedimentary rocks • Chemical sedimentary rocks • Limestone • 10% of all sedimentary rocks (by volume) • most abundant chemical sedimentary rock • composed primarily of calcite (calcium carbonate CaCO3) • Marine biochemical limestones form as coral reefs, coquina (broken shells), and chalk (microscopic organisms) • Inorganic limestones include travertine (caves) and oolitic limestone (tropical beach environment) • Dolostone: dolomite=CaMg(CO3)2Typically formed secondarily from limestone

  13. Chapter 6 Sedimentary rocks • Chemical sedimentary rocks Organic rock of biochemical origin • coquina (rock of shell fragments): bioclastic

  14. Chapter 6 Sedimentary rocks • Chemical sedimentary rocks Fossiliferous limestone

  15. Coral reef Limestone cliff (Guadalupe Mountains Natl Park, TX)

  16. How to build a carbonate platform See Figure story 8.16

  17. How to build an atoll Darwin’s theory on atolls (1831) See Box 8.1

  18. Chapter 8 Sedimentary rocks Agate • Chemical sedimentary rocks • Common chemical sedimentary rocks • Chert • Made of microcrystalline silica (SiO2) • Varieties include flint and jasper (banded form is called agate)

  19. Chapter 8 Sedimentary rocks (a) calcite • Chemical sedimentary rocks • Evaporites • water evaporates and triggers the deposition of salts • sequence of precipitation: calcite (calcium carbonate), gypsum (calcium sulfate), rock salt (halite, NaCl); bitter salts (potassium and magnesium salts)

  20. Chapter 8 Sedimentary rocks Salt flats, Utah Death valley, Calif. • Chemical sedimentary rocks • Evaporites • water evaporates and triggers the deposition of salts • sequence of precipitation: carbonate, gypsum (calcium sulfate), rock salt (halite, NaCl); bitter salts (potassium and magnesium salts) • ancient seawater basins evaporated and deposited salt

  21. Chapter 8 Sedimentary rocks • Chemical sedimentary rocks • Evaporites- the story of the Mediterranean During the Miocene, lower sea level almost shut down the inflow of Atlantic surface water into the Mediterranean over the Strait of Gibraltar. Evaporation removed vast quantities of water and left behind evaporative sediments that underlay the sediments in the Mediterranean today. Fig. 8.19

  22. Chapter 8 Sedimentary rocks • Chemical sedimentary rocks • Coal • buried and compacted plant material • different kinds of coal, depending on formation process

  23. Sedimentary structures (Physical features) 1. Layers (bedding, or “strata”) 2. Cross-bedding 3. Graded beds 4. Ripple marks 5. Mud cracks

  24. Sedimentary structures (Physical features) 1. Layers (bedding, or “strata”) • deposited horizontally • each layer is unique • separated by bedding planes

  25. Sedimentary structures (Physical features) 2. Cross-bedding • tilted bedding • commonly ancient sand dunes • river deltas, flow channels

  26. particles within a layer • gradually change: • coarse at bottom • fine at top Sedimentary structures (Physical features) 3. Graded beds • rapid deposition from • water w/ varying sed. sizes Colorado River

  27. Sedimentary structures (Physical features) 4. Ripple marks • wavy surfaces in sand: current • ripple marks • tell direction of current because they are perpendicular to flow See Fig. 8.8

  28. Sedimentary structures (Physical features) 5. Mud cracks • sediment alternatively • wet/dry • shallow lakes, • desert basins • flood plains

  29. Some MC questions… Which of the following sets of processes is written in order of increasing temperature? A. sedimentation, metamorphism, diagenesis B. diagenesis, sedimentation, metamorphism C. sedimentation, diagenesis, metamorphism D. metamorphism, diagenesis, sedimentation

  30. Some MC questions… What type of sediments are accumulations of solid fragments produced by weathering? A. biochemical sediments B. chemical sediments C. clastic sediments D. all of the above

  31. Some MC questions… Which of the following statements about transportation of sediment is false? A. Smaller particles settle faster than larger particles. B. As a current slows, the largest particles start to settle. C. Faster currents carry larger particles than slower currents. D. Rivers and ocean currents move much more material than do air currents.

  32. Some MC questions… In what type of environment did the ripples depicted above most likely form? A. beach (waves) B. desert (wind) C. alluvial (stream) D. delta (river + tides)

  33. Some MC questions… Which of the following minerals is least likely to occur in a marine evaporite environment? A. calcite B. gypsum C. halite D. quartz