Ch. 16 — Review

1. Ch. 16 — Review • Early Mesozoic life • Recovery from the end-Permian mass extinction • Dominance of mollusks on the sea floor • Appearance of swimming reptiles • Dominance of gymnosperms on land • Appearance of dinosaurs • Appearance of birds Earth History, Ch. 16

2. Today’s outline • Early Mesozoic paleogeography • Pangaea during the Triassic • The break-up of Pangaea • Jurassic paleogeography • The end-Triassic mass extinction • Jurassic rocks in Iowa Earth History, Ch. 16

3. Triassic paleogeography • Pangaea existed as a single supercontinent at beginning of Mesozoic time • Sea level was relatively low, exposing a huge land area • Tethys Ocean began to form • An arm of the sea that projected into what is now the Mediterranean region Earth History, Ch. 16

4. Earth History, Ch. 16

5. Triassic paleobiogeography • Distinct floras developed in various portions of Pangaea • Gondwanaland (southern temperate flora) • Euramerica (low latitude, warm and arid flora) • Siberian (northern temperate flora) • Marine bivalve Claraia was globally distributed around the margins of Pangaea • Terrestrial therapsid Lystrosaurus was widely distributed throughout Pangaea land areas • Evidence that all land areas were connected Earth History, Ch. 16

6. Break-up of Pangaea • Tethys seaway continued to deepen and extend westward throughout Mesozoic time • Rifting between northern Africa and southern Europe (Triassic time) • Rifting between North America and South America, and between North America and Africa (Jurassic time) • Incipient rift basins were periodically flooded by shallow seas • Evaporite deposition in proto-Mediterranean, proto-Gulf of Mexico, proto-South Atlantic Earth History, Ch. 16

7. Earth History, Ch. 16

8. Early Mesozoic evaporite basins Earth History, Ch. 16

9. Jurassic evaporites in Gulf of Mexico • “Louann Salt” underlies almost entire floor of Gulf of Mexico • Under burial conditions, evaporite rocks behave like ductile plastics—they flow • Salt domes and salt rafts create spectacular traps for hydrocarbons Earth History, Ch. 16

10. Gulf of Mexico Salt domes Earth History, Ch. 16

11. end-Triassic mass extinction Earth History, Ch. 16

12. end-Triassic mass extinction • Approx. 20% of marine families were eliminated • Extinction of conodonts, placodont reptiles • Great reduction in bivalves, ammonoids, plesiosaurs, ichthyosaurs (all rebounded) • Cause is poorly understood Earth History, Ch. 16

13. 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

14. Ft. Dodge Formation Earth History, Ch. 16

15. Jurassic rocksof midcontinent Earth History, Ch. 16

16. Cardiff Giant Earth History, Ch. 16

17. Cardiff Giant • Man-like figure carved into 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