Reminders
• Lab exam next Tuesday
– Open lab today and Monday
Earth History, Ch. 16
1
Early Mesozoic Era
142
Late
Jurassic System named
in early 1900’s for classic
exposures in the Alps.
Middle
Triassic System named
Early
in 1834 by von Alberti
206
in Germany. Triassic is
Late
bounded by mass extincMiddle
tions above and below.
251
Early
Earth History, Ch. 16
Jurassic
System
Triassic
System
2
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
3
Sepkoski’s three faunas
(marine invertebrates)
mostly active grazers
and carnivores
mostly sessile
filter-feeders
Earth History, Ch. 16
4
Triassic hexacorals
Hexacorals probably are not
related to Paleozoic corals,
but evolved indepently from
sea anemonies.
Explosive adaptive radiation
started in late Triassic time.
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Pelagic organisms
Calcareous
nannoplankton
Ammonoids and belemnoid
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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
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Nothosaur
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Placodont
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Plesiosaurs
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Ichthyosaur
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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
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Earth History, Ch. 16
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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
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Thecodonts and early mammal
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16
Allosaurus
(Jurassic)
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thecodont
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Dinosaur pelvises
Saurischian pelvis
Ornithischian pelvis
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Saurischian pelvis
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Ornithischian pelvis
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Saurischian
pelvis and legs
(compared with
modern bird)
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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!!
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“Bone Wars”
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Morrison Formation
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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
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Earliest birds
• First true birds appeared
in late Jurassic time
(evolved from saurischian
dinosaurs)
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Archaeopteryx from Solnhofen
Limestone (Germany)
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World’s smallest dinosaur
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Today’s outline
• Early stages in break-up of Pangaea
• Early Mesozoic geology of eastern and
western North America
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Permian
Tethys Ocean
Pangaea
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Early stages in the
break-up of Pangaea
•
Westward expansion of Tethys seaway
1. Rifting between northern Africa and southern
Europe (Triassic time)
2. 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, protoGulf of Mexico, proto-South Atlantic
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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
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Modern analog
• East Africa rift valley and Red Sea area is a
modern example of continental break-up
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Break-up of Pangaea
3
4
1
2
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Triassic
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Early Jurassic
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Middle Jurassic
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Late Jurassic
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Early Mesozoic evaporite basins
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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
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Gulf of Mexico Salt domes
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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
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Late Triassic–
Early Jurassic rift basins
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Newark Basin
Tr-Jr non-marine
eroded
Appalachians
Mafic intrusives (dikes and sills)
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Palisades sill
(across Hudson River from New York City)
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Triassic
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Early Jurassic
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Middle Jurassic
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Late Jurassic
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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
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Sonoma Orogeny
• Early Triassic accretion of Golconda arc
and Sonomia microcontinent to western
North America
– Present-day western Nevada, northern
California, southeastern Oregon
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Sonoma orogeny
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Western
accreted terranes
Early Triassic
(Sonoma)
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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)
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Western
accreted terranes
Late Jurassic
(Nevadan)
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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
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early Late Jurassic
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Ft. Dodge Formation
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Jurassic rocks
of midcontinent
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Cardiff Giant
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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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