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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)
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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. 16
Middle Jurassic Earth History, Ch. 17
Ft. Dodge Formation Earth History, Ch. 16
Jurassic rocksof midcontinent Earth History, Ch. 16
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 Earth History, Ch. 16
Cardiff Giant Sold for $37,500 and then put on display Earth History, Ch. 16
“There’s a sucker born every minute” (David Hannum) P.T. Barnum’s fake of a fake Earth History, Ch. 17
Cretaceous World 65 • 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 Cretaceous System Mesozoic Era 142 Jurassic System 206 Triassic System 251 Earth History, Ch. 17
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 Earth History, Ch. 17
Angiosperm diversification Earth History, Ch. 17
Rudist reef Earth History, Ch. 17
Tyrannosaurus rex Earth History, Ch. 17
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……… Earth History, Ch. 17
Dinosaur bone structure Earth History, Ch. 17
Sue!! Earth History, Ch. 17
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 Earth History, Ch. 17
End-Cretaceous mass extinction • Cause is controversial • Asteroid impact • Volcanism (Deccan Traps, India) Earth History, Ch. 17
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 Earth History, Ch. 17
Iridium layer at Gubbio, Italy Earth History, Ch. 17
Mineral evidence Iridium layer near Drumheller in southern Alberta, Canada Earth History, Ch. 17
Mineral evidence microspherules shocked quartz Earth History, Ch. 17
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 Earth History, Ch. 17
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 Lab exam“What is it?” Earth History, Ch. 17
Chicxulub crater Earth History, Ch. 17
Radar image of Chicxulub crater Earth History, Ch. 17
Chicxulub crater Gravity survey data trajectory Earth History, Ch. 17
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
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
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 Earth History, Ch. 17
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 Earth History, Ch. 17
Early Triassic Earth History, Ch. 17
Late Triassic Earth History, Ch. 17
Early Jurassic Earth History, Ch. 17
Middle Jurassic Earth History, Ch. 17
Late Jurassic Earth History, Ch. 17
Early Cretaceous Earth History, Ch. 17
Late early Cretaceous Earth History, Ch. 17
Late Cretaceous Earth History, Ch. 17
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
Western U.S.orogenies Earth History, Ch. 17
Sevier Orogeny Nevadan Orogeny Earth History, Ch. 17
