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Physical Geology Review

Physical Geology Review. the expanse of material is vast!. Internal Structure of the Earth granitic/basaltic. crust = 0-40 km; mantle = 40-2900 km; outer core (liquid) = 2900-5200 km; inner core = 5200-6400 km. from: www.usgs.gov. Guidelines for Structural Analysis. reference frame

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Physical Geology Review

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  1. Physical Geology Review the expanse of material is vast!

  2. Internal Structure of the Earthgranitic/basaltic crust = 0-40 km; mantle = 40-2900 km; outer core (liquid) = 2900-5200 km; inner core = 5200-6400 km from: www.usgs.gov

  3. Guidelines for Structural Analysis • reference frame • law of original horizontality (rocks deposited on nominally horizontal surfaces) • law of superposition (deposition of new layers are on top of old layers) • stratigraphic continuity (deposits tend to be continuous laterally, or discontinuous strata that lie in the same plane are equivalent in time) • nature of contacts • stratigraphic (bedding or unconformities) • intrusive (igneous or sedimentary) • tectonic (fractures/faults)

  4. Basic Principles • principle of superposition • younger rocks are deposited on top of older rocks

  5. Basic Principles • law of original horizontality • all sediments originally laid down in horizontal layers Grand Canyon, Arizona

  6. Basic Principles • law of original horizontality • non-horizontal bedding implies some sort of deformation The Alps of Sisteron, France

  7. Interpreting Field Data • strike and dip measurements • topography following geologic structure • geologic cross-sections

  8. “Undeformed”, horizontal rock Cedar Point, UT

  9. Horizontal Bedding in Sedimentary Rocks younger • original horizontality • lateral continuity • superposition older

  10. Strike and Dip

  11. Looking in strike direction,dip is angle from horizontal arrow pointing down dip

  12. Interpreting Field Data • strike and dip = attitude of planes (beds, fractures, ...) • strike is intersection of plane with horizontal • dip is angle between plane and horizontal

  13. Vertical BedsMiocene Monterey Fm., California coastLaminated bedding with selective dolomitization (yellow beds) 1 meter

  14. Horizontal is reference frame North is reference direction Strike is intersection between plane and horizontal Orientation of Planes (strike) • 3d block diagram

  15. Orientation of Planes (dip) • vertical cross-section view strike dip angle Dip is inclination of plane from horizontal, measured in vertical plane perpendicular to strike

  16. Folds and Faults - folds are evidence of ductile rock deformation - faults represent brittle rock deformation

  17. Monocline on the San Juan River, Utah

  18. Lateral Continuity (or lack thereof!)

  19. Fault Faults • vertical cross-section view dip angle Hanging Wall Footwall

  20. Fault Faults • 3d block diagram Hanging Wall Footwall

  21. Hanging Wall Footwall Dip-Slip (Normal)

  22. Hanging Wall Footwall Dip-Slip (Normal) horizontal stretching = extension vertical thinning

  23. Hanging Wall Footwall Dip-Slip (Reverse)

  24. Hanging Wall Footwall Dip-Slip (Reverse) horizontal shortening = contraction, vertical thickening

  25. Hanging Wall Footwall Strike-Slip strike-slip faults are typically vertical, but they can be dipping like this one

  26. Hanging Wall Footwall Strike-Slip (right-lateral) as you step across the fault, the block you are stepping onto moves to the right

  27. Hanging Wall Footwall Strike-Slip (left-lateral) as you step across the fault, the block you are stepping onto moves to the left

  28. Hanging Wall Footwall Oblique-Slip

  29. Hanging Wall Footwall Oblique-Slip both strike-slip and dip-slip

  30. Fault Plane Bedding Normal Fault with Basin Shaped Fold in Hanging Wall shear sense = normal Foot Wall Hanging Wall Slip vector

  31. Fault drag & shale smear

  32. Strike-slip fault and Drag folding

  33. Slickensides = shear

  34. Reverse Fault in Core

  35. Geologic Cross-section B A B A Cross-section view Map view

  36. Fracture Types • shear failure – faults • relative displacement is parallel to fracture face = shearing mode • tensile failure – joints, veins, dikes • a fracture with relative displacement perpendicular to fracture face = opening mode

  37. Joint are “just” cracks….(looking at dip slopes) orientation changes from bed to bed

  38. Joints(looking at bed scarps)

  39. A Joint filled with minerals = vein Ouachita Mtns., Arkansas Bristol Channel, UK

  40. A “Joint” filled with magma = dike Mt. Moran, Grand Tetons, WY

  41. Famous Fractures in the Movies The Middle East? hardly! from Transformers

  42. How about New Mexico? propagating dike volcanic source curving path to line up with earth stresses Volcanic Neck and Igneous Dike:Shiprock dike volcanicsource

  43. Igneous Rock Features from Press and Siever, Understanding Earth

  44. Other Geomorphic Features

  45. Glacial Moraine & U-shaped Valley

  46. Glacial Moraine

  47. Immature River – Steep, V-shaped Canyons Yellowstone River

  48. Mature, meandering river (Yellowstone River)

  49. High energy rivers – heavy sediment load channel cut & fill, graded bedding braided stream

  50. Alluvial fan

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