Paleoenvironment of Utah:
Fading the Mists of Time
Late Permian
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Pangea Supercontinent
Laurasia and Gondwanaland
Tethys Sea
Cutler and Kaibab Limestone
NA Southwest
Permo-Triassic Extinction
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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
Triassic
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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
Triassic
Early (240 Ma):
 Moenkopi
 Shinarump Conglomerate
Late (215 Ma):
 Chinle
 Upper Triassic
Triassic Paleoclimate
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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
Utah: semiarid to subhumid climate
Paleosols of Moenkopi record MAP 300-400mm and MAT 13-23˚C  desert
shrub or dry woodlands
Paleosols of Lower Chinle record MAP 700-900mm, but up to 1400mm and
MAT 18˚C  open forest (Petrified Forest)
Paleosols of Upper Chinle record MAP 400-600mm and MAT 29˚C  desert
shrub or dry woodlands
Triassic Flora and Fauna
Massospondylus
Cycad
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Ceolophysis
Flora: seed ferns, cycads,
conifers
Fauna: Archosauria:
Dinosaurs!
Climatic warming
mirrored in floral and
faunal turnovers
Jurassic
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Pangea breaks up into North America, Eurasia, and
Gondwana as the North Atlantic Sea opens
Tethys Sea closed
Spread of Dinosaurs
NA Southwest
Jurassic
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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
Jurassic Paleoclimate
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Globally warm and moist
climate, prevailing up to
the polar regions
Southwestern North
America: Arid Coastal
Desert
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.
Jurassic Flora and Fauna
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Conifers: most
diverse, majority
of tall trees
Cycads, tree ferns
and gingkos
Age of Dinosaurs
Pterosaurs
First mammals
Gingko
Morganucodon
Cretaceous
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Break-up of Pangea into present day continents
complete
Dinosaurs continue terrestrial dominance
Radiation of Angiosperms
NA Southwest
Cretaceous
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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
Cretaceous Paleoclimate
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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
Cretaceous
Flora and Fauna
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Angiosperms diversify,
dominant Late Cretaceous
– coevolution with insects
Age of Dinosaurs
Birds