1. Reminders Lab exam next Tuesday Open lab today and Monday
Earth History, Ch. 16

2. Early Mesozoic Era Jurassic System Triassic System 142 Late
Jurassic System named
in early 1900’s for classic
exposures in the Alps.
Triassic System named
in 1834 by von Alberti
in Germany. Triassic is
bounded by mass extinc-
tions above and below.
Jurassic
System
Middle
Early
206
Late
Triassic
System
Middle
Early
251
Earth History, Ch. 16

3. Early Mesozoic marine life
End-Permian mass extinction wiped out:
Corals, fusulinids, blastoids, trilobites, most crinoids, most brachiopods, most bryozoans
Paleozoic invertebrate faunas were dominated by sessile, filter-feeding organisms
End-Permian mass extinction caused a complete reorganization of marine communities
Earth History, Ch. 16

4. Sepkoski’s three faunas (marine invertebrates)
mostly active grazers
and carnivores
mostly sessile
filter-feeders
Earth History, Ch. 16

5. Triassic hexacorals Hexacorals probably are not
related to Paleozoic corals,
but evolved indepently from
sea anemonies.
Explosive adaptive radiation
started in late Triassic time.
Earth History, Ch. 16

6. Pelagic organisms Calcareous nannoplankton Ammonoids and belemnoid
Earth History, Ch. 16

7. Early Mesozoic marine vertebrates
Swimming reptiles diversified in Triassic time
Nothosaurs (seal-like)
Placodonts (turtle-like)
Plesiosaurs (giant “Nessie-like”, up to 40 feet long)
Ichthyosaurs (dolphin-like)
Crocodiles
Earth History, Ch. 16

8. Nothosaur
Earth History, Ch. 16

9. Placodont
Earth History, Ch. 16

10. Plesiosaurs
Earth History, Ch. 16

11. Ichthyosaur
Earth History, Ch. 16

12. Early Mesozoic terrestrial animals
Therapsids (primitive synapsids) barely survived end-Permian mass extinction
Then gave rise to true mammals in late Triassic time
Earliest mammals were small and inconspicuous
No larger than a house cat
Earth History, Ch. 16

13. Earth History, Ch. 16

14. Origin of the dinosaurs
Thecodonts were small early Triassic reptiles that gave rise to earliest dinosaurs
Early dinosaurs were small, but by end of Triassic some reached up to 20 feet in length
By early Jurassic time, many kinds of huge dinosaurs existed
Earth History, Ch. 16

15. Thecodonts and early mammal
Earth History, Ch. 16

16. Earth History, Ch. 16

17. Allosaurus (Jurassic)
Earth History, Ch. 16

18. thecodont
Earth History, Ch. 16

19. Dinosaur pelvises Saurischian pelvis Ornithischian pelvis
Earth History, Ch. 16

20. Saurischian pelvis
Ornithischian pelvis
Earth History, Ch. 16

21. Saurischian pelvis and legs (compared with modern bird)
Earth History, Ch. 16

22. Jurassic dinosaurs
Morrison Formation (extends from Montana to New Mexico) has best assemblage of Jurassic dinosaurs in world
Dinosaur “Bone Wars”
Cope vs. Marsh feud
Gun battles and railroad cars full of bones!!
Earth History, Ch. 16

23. “Bone Wars”
Earth History, Ch. 16

24. Morrison Formation
Earth History, Ch. 16

25. Earliest vertebrate flight
Pterosaurs (late Triassic reptiles) were earliest flying vertebrates
Probably clumsy upon take-off and landing, but well suited for soaring through the air
Earth History, Ch. 16

26. Earliest birds
First true birds appeared in late Jurassic time (evolved from saurischian dinosaurs)
Earth History, Ch. 16

27. Archaeopteryx from Solnhofen Limestone (Germany)
Earth History, Ch. 16

28. World’s smallest dinosaur
Earth History, Ch. 16

29. Today’s outline Early stages in break-up of Pangaea
Early Mesozoic geology of eastern and western North America
Earth History, Ch. 16

30. Permian
Tethys Ocean
Pangaea
Earth History, Ch. 16

31. Early stages in the break-up of Pangaea
Westward expansion of Tethys seaway
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

32. Rift/Drift Sequence of events
Break-up of a continent follows a predictable sequence of events
Rifting, accompanied by block-faulting, volcanism, non-marine sedimentation
Flooding by shallow marine waters (with periodic evaporation)
Establishment of fully marine conditions
Earth History, Ch. 16

33. Earth History, Ch. 16

34. Modern analog
East Africa rift valley and Red Sea area is a modern example of continental break-up
Earth History, Ch. 16

35. Break-up of Pangaea 3 4 1 2
Earth History, Ch. 16

36. Triassic
Earth History, Ch. 16

37. Early Jurassic
Earth History, Ch. 16

38. Middle Jurassic
Earth History, Ch. 16

39. Late Jurassic
Earth History, Ch. 16

40. Earth History, Ch. 16

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

42. 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

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

44. Eastern U.S. rift basins
Appalachian Mountains were eroding during early Triassic time
Rifting (break-up of Pangaea) reached eastern North America by late Triassic-early Jurassic time
Normal faults (extensional) created deep basins that received thick deposits of non-marine sediments
Newark Supergroup: 6 km thick
Earth History, Ch. 16

45. Late Triassic– Early Jurassic rift basins
Earth History, Ch. 16

46. Newark Basin Mafic intrusives (dikes and sills) Tr-Jr non-marine
eroded
Appalachians
Mafic intrusives (dikes and sills)
Earth History, Ch. 16

47. Palisades sill (across Hudson River from New York City)
Earth History, Ch. 16

48. Triassic
Earth History, Ch. 16

49. Early Jurassic
Earth History, Ch. 16

50. Middle Jurassic
Earth History, Ch. 16

51. Late Jurassic
Earth History, Ch. 16

52. Western U.S. accreted terranes
Continental growth by accretion began in Paleozoic time
Antler orogeny (Devonian-Mississippian)
Klamath island arc
Accretion of microplates and island arc terranes continued throughout Mesozoic time
Earth History, Ch. 16

53. Sonoma Orogeny
Early Triassic accretion of Golconda arc and Sonomia microcontinent to western North America
Present-day western Nevada, northern California, southeastern Oregon
Earth History, Ch. 16

54. Sonoma orogeny
Earth History, Ch. 16

55. Western accreted terranes
Early Triassic
(Sonoma)
Earth History, Ch. 16

56. Nevadan Orogeny: Continued accretion
Beginning in middle Triassic time, and continuing through late Jurassic time, exotic terranes repeatedly were accreted to western North America
Franciscan and Great Valley sequences (California)
Stikine terrane et al. (Canada–Alaska)
Earth History, Ch. 16

57. Western accreted terranes
Late Jurassic
(Nevadan)
Earth History, Ch. 16

58. 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

59. Earth History, Ch. 16

60. early Late Jurassic
Earth History, Ch. 16

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

62. Jurassic rocks of midcontinent
Earth History, Ch. 16

63. Cardiff Giant
Earth History, Ch. 16

64. 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