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 HOWEVERclimatic changes HOWEVER

Stable Isotope ratios for Carbon  13C 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” aveSTELLA/Carbon/c_isotope_models.htmhttp:// aveSTELLA/Carbon/c_isotope_models.htm

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

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

Tectonism and Sedimentation Seaway drains

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

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

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

Pangaea – Early Jurassic

E Jurassic – Atlantic Rift Shallow Note offshore Terranes

E Jurassic – Another Look Wrangellia Orogeny New Sea

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

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

Atlantic Tethys

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

Mesozoic Global Climates Carbonates (via the stable isotope index  C) reveal large concentrations of carbon dioxide present in the Mesozoic atmosphere.Carbonates (via the stable isotope index  C) reveal large concentrations of carbon dioxide present in the Mesozoic atmosphere. This suggests a greenhouse climate.This suggests a greenhouse climate. No glaciers so CO 2 abundant.No glaciers so CO 2 abundant. There is some coal due interior seas and transgressions and regressions)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 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.Greenhouse gasses hold the heat, not lost to space as quickly. Warmer equilibrium. Conifers, Cycads

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

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

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

Mesozoic rift basins Kean University

Structure of the Newark basin Note how faulting offsets sedimentation 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

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 Wet cycle Lake Dry Laterites Monsoonal

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

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 Does this cross-section show a transgression or regression? Remember: “The facies follow the shoreline shifts”

Gulf Coast continental margin Rising Salt Domes tilt sediments Concentrate petroleum

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

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

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

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

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

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

Sevier thin-skinned deformation

Competent (resistant to flow)

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

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

Now let’s look down here

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

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

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

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

Triassic caliche paleosol- Nova Sc. Source of carbonates for  13C measurements. Results suggest high CO 2 in atmosphere Similar in Newark Supergroup Same Caliche found when our new gym was built Same Laterites found in our stream

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

Sedimentation Seaway drains Evaporites

Jurassic Eolian sandstone Navaho SS, S. Utah

Jurassic Morrison Formation Stream Deposits, huge sauropods Camarasaurus, also Stegosaurus, carnivore Allosaurushuge sauropods Camarasaurus, also Stegosaurus, carnivore Allosaurus Paul Olsen's Dinosaur Course

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

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

Western Interior Seaway Transgression Western Interior Seaway Regression 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? Dakota SS Navaho SS Fox Hills SS Morrison Fm.

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

Then, at my, Regression

Western Interior Seaway Transgression Western Interior Seaway Regression In Montana the sequence is similar. Above the marine Pierre Shale (ammonites) and Claggett Sandstone (nearshore and beach) is the Late Cretaceous Judith River Fm. containing dinosaur bones and conifers in stream deposits. Is this sequence a transgression or a regression?

75 mya Regression Mesa Verde Sandstones over Mancos Shale: Coarsening Upward

K-T Boundary

Dust cloud Plants need light Herbivores eat plants Carnivores eat herbivores Survivors can sleep through it. Uh, oh. That can’ t be good.

End of Mesozoic Geology