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Last Time

Last Time. We ended our discussion of the Paleozoic with the greatest recorded mass extinction to affect Earth. This occurred at the end of the Permian about 90% of all marine invertebrate species extinct

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Last Time

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  1. Last Time • We ended our discussion of the Paleozoic with the greatest recorded mass extinction to affect Earth. This occurred at the end of the Permian • about 90% of all marine invertebrate species extinct • Rugose and tabulate corals, many bryozoan and brachiopod orders, and trilobites did not survive the end of the Permian • causes for this have been speculated to be: • reduction in marine shelf as Pangaea formed • global drop in sea level due to glaciation • reduction in marine shelf due to regression • climatic changes HOWEVER

  2. Stable Isotope ratios for Carbon d13C • There are two stable isotopes of carbon that are routinely measured in fossils. • The standard carbon isotope ratios in calcite are from belemnites in the Pee Dee Formation (abbreviated as PDB “Pee Dee Belemnite”). • The process of photosynthesis favors the lighter form of carbon in plant tissue. AT THE BOUNDARY: • “… it appears that a significant portion of the land plants burned; this would have released a great deal of light carbon into the atmosphere” • http://www.acad.carleton.edu/curricular/GEOL/DaveSTELLA/Carbon/c_isotope_models.htm

  3. 65.7 mya another mass extinction Cretaceous 144 – about 65 mya Jurassic 208-144 mya Triassic 248-208 mya About 248 to 245 mya Depends on method Mesozoic Geology Pangaea

  4. Introduction • The Mesozoic began 248 mya and ended about 65 mya • Three periods - Triassic, Jurassic, Cretaceous • breakup of Pangaea was the major geologic event • tectonism and sedimentation are used to classify the Mesozoic in N. America • Note the overlap in three styles of Cordilleran Orogeny

  5. Tectonism and Sedimentation Seaway drains

  6. 1. The Breakup of Pangaea • The movement of continents during and after the breakup affected global climates • Sea-level changes due MOR heating and growth, then cooling

  7. Pangaea - Early Triassic Pole to pole and straddled equator Panthalassa Ocean E. coast indent is “Tethys Sea” Tethys Panthalassa Panthalassa

  8. Late Triassic – Rifting E Orogeny W We will consider mostly North America for this lecture Orogeny Rift Tethys Equator to Pole current gyres Better look at Tethys

  9. Pangaea – Early Jurassic

  10. E Jurassic – Atlantic Rift Shallow Note offshore Terranes

  11. E Jurassic – Another Look Orogeny New Sea Wrangellia

  12. Pangaea: mid-Jurassic North Atlantic opens, India and Antarctica-Australia leave Gondwana

  13. Latest Jurassic – Early Cretaceous Atlantic Connected with Tethys Africa rotation closes Tethys

  14. Tethys Atlantic

  15. Late K – Epeiric Sea until 70 mya Mid-Atlantic Ridge huge and fast NOTE the Farallon and Pacific plates

  16. Mesozoic Global Climates • Carbonates (via the stable isotope index d13C)reveal large concentrations of carbon dioxide present in the Mesozoic atmosphere. • This suggests a greenhouse climate. • No glaciers so CO2 abundant. • There is some coal due interior seas and transgressions and regressions) • Greenhouse gasses pass sunlight which hits the land and sea. Re-radiate heat (IR) • Greenhouse gasses hold the heat, not lost to space as quickly. Warmer equilibrium. Conifers, Cycads

  17. Global Climates in the Mesozoic • Mesozoic climates were more equable than today, lacked the strong north-south climate zones. • Mesozoic plant fossils indicate subtropical conditions in high latitude locations • Seasonal differences were monsoonal Cycads

  18. Next: Mesozoic Tectonics NA • Cretaceous : global rise in sea level until 75 -70 mya, vast MOR • Jurassic: • Atlantic opens E, • began building the Cordillera W, • Gulf of Mexico begins to form and experiences evaporite deposition • Late Triassic: Begin rifting in East

  19. Late Triassic: Rifting opens the Atlantic • The Newark Supergroup documents the rifting of Pangaea to form the Atlantic • Early Triassic saw coarse detrital sediments deposited from the erosion of Appalachian highlands • fault-block basins developed as N. America separated from Africa and filled with non-marine sediment plus lava flows, dikes and sills • East side eroded to a flat plane by Cretaceous

  20. Mesozoic rift basins Kean University

  21. Structure of the Newark basin Recall radial cracks due swelling and uplift. We live on the western side. Note dominant block orientation. Other side is in Morocco; most face toward the West Note how faulting offsets sedimentation

  22. Lake cycles, East Berlin formation Laterites Monsoonal Dry Wet cycle Lake Alternating wet and dry climate due 21000y Milankovitch cycle of tilt axis wobble Also 100,000 year cycles due to orbit eccentricity

  23. E. Jurassic Gulf Coast Evaporites 200 mya is just outside our door Restricted Basin Lots of evaporation

  24. Gulf Coastal Region • First, as continents separate, restricted basin, thick evaporites formed in the Gulf • Normal marine deposition returned to the Gulf by Late Jurassic, with transgressions and regressions • thousand of meters of sediments were deposited over the salt Remember: “The facies follow the shoreline shifts” Does this cross-section show a transgression or regression?

  25. Gulf Coast continental margin Rising Salt Domes tilt sediments Concentrate petroleum

  26. Next: Western North America Tectonics • Building the western margin of North America and the Cordillera

  27. Displaced terranes – Western Cordillera These terranes overlap in age but have different rock types, paleolatitudes and fossils. However, we can deduce when they accreted from their order, and the metamorphic ages of their suture zones

  28. Western Region • Cordilleran Orogeny • YOUNGEST • Laramide – Vertical blocks-built the present day Rockies late K-Tertiary • Sevier – J thrust faulting to the east • Nevadan – mid J to mid K batholith intrusion in the Sierra Nevada and elsewhere on the western edge • OLDEST

  29. Western Margin during Orogens North America drifting west due opening of Atlantic Barbs show dip of fault Westward subduction zones stopped when continental crust arrived. Late Triassic on, eastward subduction of Farallon oceanic crust continues Cordilleran Orogeny Mid J to mid K Nevadan Batholiths Sonoma began late Permian. It continued into the Early Triassic Nevadan Orogeny east subduction Farallon Sonomia docking Late Pm –Early Triassic

  30. Sierra Nevada Mountains Nevadan Orogeny: Subduction formed batholith cores of continental volcanic arc, once as tall as Andes

  31. Mesozoic orogenic events Thin-skinned tectonics Cretaceous Sevier (due Wrangellia docking?) Later moved by transform fault? K-T Laramide Continental Overide Bouyant Subduction

  32. Sevier thin-skinned deformation

  33. Competent (resistant to flow)

  34. Sevier thrust belt Precambrian and/or Paleozoic Sediments thrust over younger Mesozoic rocks

  35. Buoyant Subduction Laramide Orogeny Vertical block uplift Normal, thin-skinned Subduction Zone overrun by fast drifting continental plate Approaching Continent pushes accretionary wedge sediments into forearc sediments

  36. Now let’s look down here

  37. Look in detail at western plate margin This area has much simpler geology Franciscan Range, Great Valley Group, and Sierra Nevada Volcanics and Plutonics

  38. Next: Mesozoic Sedimentation on the Craton • Cretaceous • extensive marine deposition, thin to the east • Jurassic • clean cross-bedded sandstones (dunes) • marine sediments in the Sundance Sea • Triassic • shallow-water marine clastics • red beds Foreland Basin

  39. North America - Triassic Marine deposition limited to western margin Volcanic Arc sends frequent ashfalls eastward Newark Pollen similar Chinle Note Equator

  40. Late Triassic Chinle Fm. Mudstones and Sandstones of stream deposits, volcanic ash, with fossil trees (the Petrified Forest) Texas, New Mexico, northern Arizona, Nevada, Utah, and western Colorado Pollen studies show that the Chinle is the same age as early Newark Supergroup http://en.wikipedia.org/wiki/Petrified_Forest_National_Park

  41. Triassic caliche paleosol- Nova Sc. Source of carbonates for d13C measurements. Results suggest high CO2 in atmosphere Same Caliche found when our new gym was built Similar in Newark Supergroup Same Laterites found in our stream

  42. North America - Jurassic period Dry region in the rain shadow of the beginning Nevadans Zuni Transgression

  43. Sedimentation Seaway drains Evaporites

  44. Jurassic Eolian sandstone Navaho SS, S. Utah

  45. http://rainbow.ldgo.columbia.edu/courses/v1001/morisson14.htmlhttp://rainbow.ldgo.columbia.edu/courses/v1001/morisson14.html Jurassic Morrison Formation Paul Olsen's Dinosaur Course Stream Deposits, huge sauropods Camarasaurus, also Stegosaurus, carnivore Allosaurus

  46. Fossils of Jurassic dinosaurs Morrison Formation sandstones, DNM, Vernal, Utah

  47. Late Cretaceous really big epeiric sea Alaska dinosaurs Dinosaurs on the North Slope Alaska’s Jurassic Park Land Land

  48. Did the Sevier Orogenic Belt form before or after the Navaho SS, purple, lowest left? Did the Sevier Orogenic Belt form before or after the Fox Hills SS, red uppermost right? Fox Hills SS Western Interior Seaway Regression Western Interior Seaway Transgression Dakota SS Navaho SS Morrison Fm.

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