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Mesozoic Geology

Mesozoic Geology. Introduction. The Mesozoic began 248 mya and ended 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

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Mesozoic Geology

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  1. Mesozoic Geology

  2. Introduction • The Mesozoic began 248 mya and ended 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

  3. Tectonism and Sedimentation Seaway drains

  4. 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

  5. Pangaea - Early Triassic Pangaea ran from pole to pole and straddled the equator. The Panthalassa Ocean allowed equatorial waters to warm polar lands. The East coast indent is called the “Tethys Sea” Tethys Panthalassa Panthalassa

  6. Late Triassic – Rifting E Orogeny W We will consider mostly North America for this lecture Orogeny Rift Better look at Tethys

  7. Pangaea – Early Jurassic

  8. E Jurassic – Atlantic Rift Shallow Note offshore Terranes

  9. E Jurassic – Another Look Orogeny New Sea Wrangellia

  10. Pangaea: mid-Jurassic

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

  12. Tethys Atlantic

  13. Late K – Epeiric Sea until 70 mya

  14. Mesozoic Global Climates • Carbonates (for example the stable isotope ratio d13C)reveal large concentrations of carbon dioxide present in the Mesozoic atmosphere. • This suggests a greenhouse climate. • No glaciers, no coal, so CO2 abundant. • 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.

  15. 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

  16. 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 Start here

  17. 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 nonmarine sediment plus dikes and sills • eroded to a flat plain by the Cretaceous

  18. Mesozoic rift basins Kean University

  19. Structure of the Newark basin Note how faulting offsets sedimentation

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

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

  22. 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 Does this cross-section show a transgression or regression?

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

  24. Discussion: Petroleum exploration around salt domes Squint: The Petroleum is in the bright spots, at the boundary of the salt and pushed up sediment. Tells us where to look, saves money, lowers cost of fuel.

  25. Next: Western North AmericaTectonics • Building the western margin of North America and the Cordillera

  26. 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 this map. Exercise: Arrange the following terranes by oldest to youngest time of accretion onto the west coast: Alexander,Cache Creek, Chugach,Eastern, Stikine, Taku, Tracy Arm,Wrangellia, Yukon-Takana

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

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

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

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

  31. Buoyant Subduction Laramide Orogeny Vertical block uplift Normal, thin-skinned Now we understand weird looking Tetons Approaching Continent pushes accretionary wedge sediments into forearc sediments

  32. Sevier thin-skinned deformation Using the layer colored sky blue, look at the faults. Is the hanging wall mostly up or down? What kind of faults are these?

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

  34. let’s look down here

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

  36. Next: Mesozoic Sedimentation on the Craton • Cretaceous • extensive marine deposition until 70mya, thins to the east • Jurassic • clean cross-bedded sandstones • marine sediments in the Sundance Sea • Triassic • shallow-water marine clastics • red beds Foreland Basin!

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

  38. 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

  39. Triassic caliche paleosol- Nova Sc. Source of carbonates for d13C measurements. Results suggest high CO2 in atmosphere Similar in Newark Supergroup

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

  41. Sedimentation Seaway drains Evaporites

  42. Jurassic Eolian sandstone Navaho SS, S. Utah

  43. 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 Apatosaurus, also Stegosaurus, carnivore Allosaurus

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

  45. Giant sauropod and Allosaurus bones, Mossison Fm., DNM, Vernal Utah

  46. Late Cretaceous really big epeiric sea Dinosaurs on the North Slope Until 70 mya Land Land

  47. Did the Sevier Orogenic Belt form before or after the Navaho SS, lower left? Did the Sevier Orogenic Belt form before or after the Fox Hills SS, upper right? Fox Hills SS Western Interior Seaway Regression Western Interior Seaway Transgression Navaho SS Dakota SS is bottom right

  48. Dakota Sandstone Early Cretaceous shallow sea sediments gently folded by Sevier Orogeny.

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