early mesozoic of iowa
DESCRIPTION
Early Mesozoic of Iowa. No Triassic rocks in Iowa (surface or subsurface) Jurassic rocks crop out in vicinity of Ft. Dodge (Webster County) Ft. Dodge Formation is gypsum deposit (evaporite) Iowa is 2 nd largest gypsum producing state in U.S. (1.65 million tons/year) - PowerPoint PPT PresentationTRANSCRIPT
Earth History, Ch. 16 1
Early Mesozoic of Iowa• No Triassic rocks in Iowa (surface or
subsurface)• Jurassic rocks crop out in vicinity of Ft.
Dodge (Webster County)– Ft. Dodge Formation is gypsum deposit
(evaporite)– Iowa is 2nd largest gypsum producing state in
U.S. (1.65 million tons/year)– Same age as dinosaur-bearing Morrison
Formation to the west
Earth History, Ch. 17 2
MiddleJurassic
Earth History, Ch. 16 3
Ft. Dodge Formation
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Jurassic rocksof midcontinent
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Cardiff Giant
• Man-like figure carved from Ft. Dodge gypsum
• 10’ 4.5” long, 3’ wide, 2990 pounds
• Cooked up as a hoax in 1866 by George Hull (visiting his sister in Ackley, Iowa)
• Now preserved in Cooperstown, New York
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Cardiff Giant
Sold for $37,500 and then put on display
Earth History, Ch. 17 9P.T. Barnum’s fake of a fake
“There’s a sucker born every minute” (David Hannum)
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Cretaceous World• Cretaceous System
was named in 1822 for deposits that are “chalky” in many parts of the world
• Duration of Cretaceous Period is longer than any other
142
206
65
251
CretaceousSystem
TriassicSystem
JurassicSystemM
esoz
oic
Era
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Rise of the angiosperms
• Gymnosperms continued to dominate terrestrial floras in Cretaceous (just as in Triassic and Jurassic)
• Angiosperms initial appearance was in middle Cretaceous time– Double-fertilization and enclosed seeds
– Flowers (for attracting insects)
– Co-evolution wih insects
– Faster reproductive cycles
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Angiosperm diversification
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Rudist reef
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Tyrannosaurus rex
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Warm-blooded Dinosaurs?
• Evidence in support of endothermy– Cretaceous dinos lived in high latitudes– Birds are endothermic, and birds are highly
specialized dinosaurs– Dinosaur bone structure resembles that in
endothermic mammals• Haversian canals
• But………
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Dinosaur bone structure
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Sue!!
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End-Cretaceous mass extinction
• Geologically instantaneous • Non-avian Dinosaurs, mosasaurs,
plesiosaurs, rudists and ammonoids were totally eliminated
• Angiosperms and gymnosperms suffered big hits
• 90% of the species of calcareous nannoplankton and planktonic foraminifers were wiped out
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End-Cretaceous mass extinction
• Cause is controversial– Asteroid impact– Volcanism (Deccan Traps, India)
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End-Cretaceous mass extinction
• Mineral evidence for asteroid impact:– Iridium anomaly at top of Cretaceous in both marine
and terrestrial rocks• Iridium is rare on Earth, but abundant in meteorites
– Shocked quartz grains• Welded planar fractures due to enormous pressure
– Microspherules• Liquefied droplets of molten rock that cool rapidly
– Microscopic diamonds• Again, high pressure minerals
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Iridium layer at Gubbio, Italy
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Mineral evidenceIridium layer nearDrumheller insouthern Alberta,Canada
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Mineral evidence
microspherulesshocked quartz
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End-Cretaceous mass extinction
• Further evidence for asteroid impact:– The crater itself has been discovered in the Gulf
of Mexico, just offshore Yucatan Peninsula
• Chicxulub crater– Central cavity (60 miles in diameter)– Outer ring (120 miles in diameter)– Magma that cooled after impact is dated at 65 ±
0.4 Ma, exactly same as end-Cretaceous boundary
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Lab exam“What is it?”• Plants
– Ferns– Sphenopsids– Lycopsids
• Protists– Fusulinids
• Echinoderms– Crinoids– Blastoids
• Mollusks– Pelecypods
– Gastropods
– Ammonoids• Goniatitic suture
• Ceratitic suture
• Ammonitic suture
– Belemnites
• Cnidarians (corals)– Rugose
– Tabulate
– Scleractinian
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Chicxulub crater
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Radar image of Chicxulub crater
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Chicxulub crater
Gravity surveydata
trajectory
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Effects of the impact
• Perpetual darkness from atmospheric dust• Short-term global refrigeration from dust
and aerosol particles (like “nuclear winter”)• Acid rain from sulfur dioxide and water in
atmosphere• Wildfires, especially in North America• Long-term global warming from aerosols
that stayed in atmosphere
Earth History, Ch. 17 36
Aftermath
• Although angiosperms suffered loss of diversity, they recovered to become the dominant flora
• With dinosaurs out of the way, mammals diversified spectacularly in post-extinction Cenozoic Era
Earth History, Ch. 17 37
Continued break-up of Pangaea
• Remember: Pangaea began to break up during early Mesozoic– Triassic rifting between N. Africa and S.
Europe – Jurassic rifting between N. America and S.
America; between N. America and Africa– But, Gondwanaland remained intact
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Cretaceous paleogeography
• By late Cretaceous time:– South America, Africa and India had become
discrete entities– Only Australia and Antarctica remained
attached to one another– Greenland split from North America– Sea-level nearly at an all-time high
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Early Triassic
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Late Triassic
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Early Jurassic
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Middle Jurassic
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Late Jurassic
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Early Cretaceous
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Late early Cretaceous
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Late Cretaceous
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Cretaceous geology ofNorth America
• East coast, now a passive continental margin, was mostly quiet
• West coast, a convergent margin, continued to experience mountain building– Sevier orogeny produced folding and thrusting
as far east as Wyoming; igneous activity in California, Nevada, Idaho, and farther north
Earth History, Ch. 17 49
Western U.S.orogenies
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Sevier Orogeny
Nevadan Orogeny
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Cretaceous geology ofNorth America
• Interior seaway developed when continent was flooded: Arctic Ocean joined with Gulf of Mexico
• Late Cretaceous rocks of interior seaway are cyclic deposits produced by oscillation of shoreline– Nearshore sand facies
– Shallow marine shale facies
– Offshore chalk facies
Earth History, Ch. 17 52
Late Cretaceous cyclic deposits
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Rememberthis?
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