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Paleoenvironment of Utah: Fading the Mists of Time

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1 Paleoenvironment of Utah: Fading the Mists of Time

2 Late Permian Pangea Supercontinent Laurasia and Gondwanaland
Tethys Sea Cutler and Kaibab Limestone NA Southwest Far different oceanic and atmospheric circulation, arid climate in Utah Cold high latitudes Tropical Tethys Sea, with rice and diverse fauna Vast stretches of lowland on Pangea had homogeneous floras and faunas, low diversity of land reptiles, cosmopolitan marine species, gymnosperm forests-complex and diverse ferns and conifers

3 Permo-Triassic Extinction
Most devasting mass extinction – 90-95% of marine species died out 75% of vertebrate families went extinct, synapsids heavily hit Casualites: Trilobites, Tabulate and Rugose Corals, Pareiasaurs, Cordaites Causes: Many! Severe climatic fluctuations, Siberian traps, Oceanic Overturn Seen at Capital Reef NP Cordaites: mangrove-like swamp trees Traps: sulfates into atmosphere, decrease global temps Then warming Oceanic overturn=hypercapnia, carbon-dioxide had accumulated = poisoning

4 Triassic Pangea begins to break up
Adaptive radiation of flora and fauna Archosauromorphs become dominant vertebrates Utah = 5-10 degrees North of the Equator NA Southwest Life began to rediversify after the great Permo-Triassic extinction and warm-water faunas spread across Tethys. Similar to Permian – Pangea –begins to split Late Triassic, due to rifting in eastern NA, Europe and North America, leading to North Atlantic Ocean The supercontinent of Pangea, mostly assembled by the Triassic, allowed land animals to migrate from the South Pole to the North Pole—tetrapods disperse widely (faunas similar worldwide) 

5 Triassic Early (240 Ma): Moenkopi Shinarump Conglomerate
Early: A broad fluvial and shallow marine depositional system (the Moenkopi Formation) covers much of the southern Western Interior. -fossil ripples, playa deposits=ephemeral lakes Late: The Chinle fluvial system covers much of the Western Interior. Chinle rivers are sourced in remnant highlands of the Appalachian Mountain system. Late (215 Ma): Chinle Upper Triassic

6 Triassic Paleoclimate
Globally warmer by 6˚C, with little latitudinal variation No polar ice caps Climatic Shift from warm and moist to hot and dry Large landmass = interior continental desert with high seasonality Poles instead warm and moist…more ideal climate Much of the rainfall was predominantly convective in character, often focused over the oceans and leaving major desert expanses on the continental areas. Yellow=evaporite red=calcrete Red-bed sandstones and evaporites Utah: semiarid to subhumid climate Paleosols of Moenkopi record MAP mm and MAT 13-23˚C  desert shrub or dry woodlands Paleosols of Lower Chinle record MAP mm, but up to 1400mm and MAT 18˚C  open forest (Petrified Forest) Paleosols of Upper Chinle record MAP mm and MAT 29˚C  desert shrub or dry woodlands

7 Triassic Flora and Fauna
Massospondylus Cycad Flora: seed ferns, cycads, conifers Fauna: Archosauria: Dinosaurs! Climatic warming mirrored in floral and faunal turnovers Plants of this age include: precursors of the Ginkgo tree and Maidenhair fern, cycads with pollen bearing cones, and early conifers. Archosauria = Triassic laid foundations for radiation of dinosaurs, pterosaurs (winged reptiles), and crocodiles (ultimately birds) Due to shift in climate to warmer conditions: S. Hemisphere Seed ferns replaced by Northern-style confer-dominated floras = dominant herbivores died out, replaced by first herbivorous dinosaurs Coelophysis was a long-necked, bipedal, carnivorous dinosaur of the late Triassic. a herding theropod About 9 ft (3 m) long, it was light, fast, and agile. From western USA. Massospondylus was an early herbivore about 13 feet (4 m) long and 3 feet (1 m) tall. It had a long neck, very long tail, a small head, peg-like teeth, and large, five-fingered hands with a large thumb claw. Massospondylus may have been able to use its hand for grasping in addition to walking. Ceolophysis

8 Jurassic Pangea breaks up into North America, Eurasia, and Gondwana as the North Atlantic Sea opens Tethys Sea closed Spread of Dinosaurs NA Southwest

9 Jurassic Navajo Sandstone  Widespread Coastal Dunes
Great Navajo “sand sea” spreads across interior of Western North America. Epicontinental seaway present = Some shallow marine excursions Late Jurassic uplift to the West causes stream direction to reverse, expanding deposition of dinosaur fossil-bearing Morrison Fm Namibian Desert, SW Africa

10 Jurassic Paleoclimate
Globally warm and moist climate, prevailing up to the polar regions Southwestern North America: Arid Coastal Desert Ferns and subtropical varieties found as far north as 60 degrees – rich floras in Greenland and Antarctica Green=coal, blue=bauxite Thicknesses of annual depositional cycles within the Navajo Sandstone indicate strong near-equatorial, north-westerly winds Mountains to the West enhanced wind strength, and cast a rain shadow, allowing active dunes to extend very close to the palaeoequator.

11 Jurassic Flora and Fauna
Conifers: most diverse, majority of tall trees Cycads, tree ferns and gingkos Age of Dinosaurs Pterosaurs First mammals Gingko=living fossil, only extant member of group huge Diplodocus and the meat-eating Allosaurus. Stegosaurus had stiff bony plates along its back. Camptosaurus (plant-eating and beaked) could walk on its two hind legs. Gingko Morganucodon

12 Cretaceous Break-up of Pangea into present day continents complete
Dinosaurs continue terrestrial dominance Radiation of Angiosperms NA Southwest Near Price Southern Atlantic ocean open, australia and antarctica still attached

13 Cretaceous Mancos Shale  Marine shale, overlain by shallow marine sandstones and fluvial deposits. The Western Interior is the site of an encroaching epicontinental seaway from the north. Mountain building orogenies to the West

14 Cretaceous Paleoclimate
Globally warm and moist climate – Tropics 9-12˚C warmer than today, Deep Ocean 15-20˚ warmer than today Increased Sea level = Epiconinental Seaways Extensive tropical ocean stabilized global climate, gentle temperature laditudinal gradient Weaker global winds

15 Cretaceous Flora and Fauna
Angiosperms diversify, dominant Late Cretaceous – coevolution with insects Age of Dinosaurs Birds Hadrosaurs, t-rex, triceratops Cret. Angio. Include magnolia, beech, fig, willow, palm

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