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Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
Easc116 Ch. 6 - Sedimentary Rocks
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Easc116 Ch. 6 - Sedimentary Rocks

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  • 1. CH. 6 – SEDIMENTARY RX
  • 2. Sediment: - weathering products (gravel, sand, clay minerals) - chemical precipitates - organic remains
  • 3. Sedimentary Rocks “sedimentum” = “settling” Sediment settles out of wind or water - forms layers at the surface
  • 4. Importance of Sedimentary Rx 1) Form 75% of exposed rx at surface (outcrops) - compose only 5% of total crust 2) Contain clues to reconstruct past environments on Earth
  • 5. Importance of Sedimentary Rx 3) Fossil record 4) Economic value - coal, petroleum, construction
  • 6. Sedimentary Rx Classification 1) Detrital = weathering products (mechanical or chemical) Named based on particle size
  • 7. Detrital Sedimentary Rocks Particle Size Gravel Name Breccia (angular) Conglomerate (rounded)
  • 8. Detrital Sedimentary Rocks Particle Size Sand Name Quartz Sandstone (quartz sand) Arkose (K-spar)
  • 9. Detrital Sedimentary Rocks Particle Size Sand Name Graywacke (rock frags, mafic minerals)
  • 10. Detrital Sedimentary Rocks Particle Size Clay-size Name *Shale (clay minerals) *Shale is the most abundant detrital sedimentary rock
  • 11. Detrital Rock Process 1) Weathering 2) Erosion (transportation) 3) Deposition (sediment settles) 4) Lithification – turning sediment into rock (“lithos” = rock) (after sediment is buried)
  • 12. Types of Lithification Processes a) Compaction - most effective on fine-grained rx (ex: shale) Exception: St. Peters Sandstone Starved Rock State Park, IL
  • 13. Lithification Processes b) Cementation Minerals dissolved in groundwater precipitate around sediment Ex: silica, calcite, hematite
  • 14. Sedimentary Rx Classification 2) Chemical – named based on composition Ex: calcite = limestone halite = rock salt plant remains = coal
  • 15. Chemical Sedimentary Rocks a) Inorganic – formed by chemical reactions in environment Ex: evaporites – rock gypsum, rock salt Ex: Travertine (limestone)
  • 16. Inorganic Chemical Sed. Rx Calcite: *Limestone = mostly marine origin Travertine = speleothems Oolitic Limestone = tidal flats * Most abundant chemical sedimentary rock
  • 17. Inorganic Chemical Sed. Rx Silica (microcrystalline quartz): Varieties: chert agate
  • 18. Silica (microcrystalline quartz): Varieties: Jasper Petrified Wood
  • 19. Chemical Sedimentary Rx b) Organic (“biochemical”) Plant remains = coal Microscopic sea shells = chalk Broken sea shells = coquina limestone
  • 20. Detective Analogy Geologists are solving a mystery Scene of the Crime Clues Mystery Solved
  • 21. Mystery Solved (Sed. Rx) Depositional environment - any area on surface where sediment accumulates Ex:
  • 22. Principle of Uniformitarianism “Present is the key to the past” Study modern depositional environments for clues Ex: coquina limestone Ex: ripple marks
  • 23. Sedimentary Facies Cumulative physical characteristics of a sedimentary rock which indicates its depositional environment “Clues” in detective analogy
  • 24. Principle of Lateral Continuity Nicolaus Steno (1669) Sediment is accumulated to edge of its depositional environment
  • 25. Sedimentary Facies Note: At the same time, each environment (facies) is accumulating its own sediment and characteristics!
  • 26. Sedimentary Facies
  • 27. Clues 1) Sediment size Distance deposited from source area Large = (closer to, further from) Small = (closer to, further from)
  • 28. Clues (sediment size) High vs. low energy environment Large particles = (high, low) Ex: ___________ Small particles = (high, low) Ex: ___________
  • 29. Clues 2) Sediment shape Distance deposited from source area: close to or far from? angular = ______ rounded = ______
  • 30. Clues 3) Composition – minerals present Two most common minerals found in sedimentary rocks are _____ and ______ .
  • 31. Variety of minerals: Ex: quartz, K-spar, plagioclase feldspar, mafic minerals, rock fragments - very little chemical weathering - indicates rapid deposition close to source area Ex: arkose in alluvial fan
  • 32. One mineral composition: Well-sorted - sediment traveled far from source area Ex: Quartz sandstone, shale
  • 33. Clues 4) Sedimentary Structures - features produced in sediment BEFORE it’s lithified
  • 34. Sedimentary Structures a) Bedding – layering w/in rock Bedding plane – flat surfaces along which rx tend to break or separate - separates different episodes of deposition
  • 35. Bedding i) Laminar bedding – horizontal layers - usually deposited in calm energy environment Ex: shale, some sandstones
  • 36. Bedding ii) Graded bedding – sorted by size - occurs w/sudden decrease in velocity Ex: turbidity currents, alluvial fans
  • 37. Bedding iii) Cross-bedding (Figure 6.22) - layers are angled in sets - occurs with change of current direction (either wind or water)
  • 38. Sedimentary Structures b) Ripple marks - wave action moves sediment - shallow water
  • 39. Types of Ripple Marks i) Asymmetrical - also called “current ripple marks” - used to determine paleocurrent directions
  • 40. Types of Ripple Marks ii) Oscillation (symmetrical) - wave action is back and forth - usually indicates shallow lagoon environment
  • 41. Sedimentary Structures c) Mudcracks Environmental conditions: a) b) Ex:
  • 42. Sedimentary Structures d) Trace Fossils Any evidence an organism was in the environment but no physical remains of the organism exist
  • 43. Trace Fossils Examples: i) Footprints ii) Coprolites iii) Bioturbation
  • 44. Clues 5) Fossils – evidence of prehistoric life Fossil record is incomplete - shows remarkable pattern of change from simple to complex life forms
  • 45. Steps to becoming a fossil Step 1: Death Step 2: Hard parts – bones, teeth, shells (Who you are!) Step 3: Rapid burial (Where you die!) Step 4: Time (prehistoric)
  • 46. Fossils Fossil record biased towards marine environment - abundant life in oceans - many critters have hard parts - lots of sediment for quick burial
  • 47. Fossils Good evidence for reconstructing past environments Ex: Beach sandstone vs. desert sandstone
  • 48. Clues 6) Color Black or green = unoxidized iron - lack of oxygen in environment Ex: deep ocean, deep lake, swamp
  • 49. Color Red = oxidized iron Ex: river floodplain, tidal flats, desert deposits Green/purple = volcanic ash mixed in with sediment
  • 50. Clues 7) Geometry of rock unit - shape & thickness of rock unit Ex: beach sandstone vs. desert sandstone
  • 51. Depositional Environments Handout
  • 52. Lithofacies map For a particular moment in geologic time, rocks indicate the landscape 1) Map out the areas where each rock type is found & draw boundaries
  • 53. Lithofacies map 2) Look at the lithologies (rock types) & compare them to: - nearby rx - geometry of rock unit 3) Determine the original depositional environment
  • 54. Cyclothems Cyclical alternations of lithologies deposited as shorelines shift
  • 55. Sedimentary Facies
  • 56. Stratigraphic Sequences 1) Transgressions - sea level rises Strat column changes vertically from coarser sediment to finer sediment “Fining-upward” sequence
  • 57. Stratigraphic Sequences 2) Regressions – sea level drops Strat column changes vertically from finer sediment to coarser sediment “Coarsening-upward” sequence
  • 58. Color Red = oxidized iron Ex: river floodplain, tidal flats, desert deposits Green/purple = volcanic ash mixed in with sediment

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