Transcript The Mesozoic Era

The Mesozoic Era
Geology 103
Key theme: Pangea breaks up
• Process will take
150 my and will
extend into the
Cenozoic
• Laurentia/Baltica
and
Australia/Antarctica
are still joined at
the end of the
Mesozoic
After the Permian extinction…
Life came back in 10 to 20 million years. No tabulate or rugose
corals, so reefs were made of different organisms. Many niches on
land were repopulated by much different creatures.
Angiosperms appear in the Cretaceous
• Angiosperm plants are those that have flowers
• Major change in plant life – insects are now the pollinators
• These are generally broad-leaf plants
Diversification of Reptiles
Marine Reptiles
Ichthyosaurs
Flying Reptiles
Pterosaurs
The Dinosaurs
Saurischian
Ornithischian
Reptiles gain flight in Triassic
• Pteranodon – much different wing structure and
musculature than modern flying mammals like bats,
or even non-mammals like birds.
The Dinosaurs
Approximately 700 species in 300 genera
Mostly warm-blooded (homeostatic)
Rapid metabolism; prey-predator ratio; many blood vessels
pores in the bones
Reproduction and Habits
Nesting behavior and social behavior (herds)
Characteristics
Eoraptor earliest thecodont (“socket-teeth”), related to
crocodiles
Sauropods long necks and large body quadrupeds;
Ornithopods are bipedal herbivores (Camptosaurus);
Stegosaurs and Ceratopians are quadruped herbivores
Extinctions: Late Jurassic-Early Cretaceous, and, of course, End
Cretaceous
The Dinosaurs: Middle Triassic
Differences based on pelvic bone
arrangement: Late Triassic Evolution
Saurischian
“Lizard-hipped”, earliest group
Similar to thecodonts
Theropods (carnivorous dinosaurs)
Prosauropods (herbivores)
Sauropods (large herbivores)
Ornithischian
“Bird-hipped”, herbivorous dinosaurs
evolved from Prosauropods
True birds appear in the Jurassic
• Archaeopteryx is the first
recognized bird
• Most specimens are from
the Solnhofen lagenstatten
in Germany
• True feathers, wishbone
• However, this creature was
descended from one clade
of coelurosaurian
theropods; a different clade
is believed to be the lineage
for birds
True mammals appear in the Triassic
• Evolved from a lineage of
mammal-like reptiles
• Hair, mammary glands
homeostasis (= “warmblooded”, though some of
the dinosaurs may have
been)
The mammals
Mammal-like reptiles therapsids (cynodonts)
Early Triassic: small cynodont gave raise to medium-size carnivores
and herbivores that are ancestral to mammals
Late Triassic: a small cynodont gave rise to the earliest mammal, the
morganucodontids
Most Triassic and Jurassic mammals were insectivores and very small
About twelve inches long; less than 2 kg
Key point: warm climate is the driver of
biodiversity/distribution in Mesozoic
Keep an eye on: Tethys Sea
Opens from east in Permian, greatest extent in Jurassic, closes from
west in Cretaceous
Triassic Period
First large rifts in
Pangea appear
Characterized
worldwide by:
Nonmarine red beds
Arkosic sandstones
Lake shales
All these are
deposited at the rift
margins
Rifts will become
modern oceans
Absaroka transgression is ending
Mountains of Taconic orogeny
erode into newly-forming rift
basins (circled area is New
England, arrows show
direction of transport)
PALISADES SILL, NJ
Evidence of rifting of Atlantic Ocean
The “fall line”
Interesting
aspect of
eroding the
Taconic: the
Cretaceous
sediment is
eroded back
on US east
coast rivers
until it gets to
Taconic
crystalline
rocks –
waterfalls are
formed
Red beds
• Red beds are
sandstones, siltstones
and shales that are,
well, “red” due to iron
oxide which was formed
either due to erosion of
red soils or exposure of
iron-rich sediments to
oxygen
Gulf of Mexico opens (restricted basin)
• Restricted basin means that
marine waters evaporate
and leave lots of salt
• Tropical marine water also
is quite bioproductive –
organisms get trapped in
salt and eventually turn into
petroleum (oil and gas)
• Salt domes here protect the
oil and therefore are
exploited
Sonoma orogeny ends on US west coast
Subduction zone switches from westward dipping to eastward
dipping – finally, denser oceanic seafloor to the west – all these
mountains are gone, except for basin sediments
Evidence of terrane accretion during the
Nevadan orogeny
Deformed bedded cherts of the Franciscan Fm., CA – the blue area on
the map
End of Triassic map
Mass extinction at the end of the Triassic –
the least understood of the “Big Five”
Causes of the end of Triassic mass extinction
Not really known, but may have to do with the end of the Absaroka
transgression (sea level was falling through the Triassic) and the
huge volumes of ocean floor basalt erupted when the Americas
rifted from Africa/Europe.
Jurassic Period
Beginning of Zuni
transgression
On US mainland,
epeiric Sundance
Sea in Canada; due
to low sea levels,
significant
nonmarine sand
and silt deposition
– Morrison Fm in
northern US is a
good source of
dinosaur bones
Nevada orogeny is responsible for
emplacement of many batholiths
Obduction
occurs when
low-density
rocks ride
up over the
other plate
at a
subduction
zone
Jurassic age batholiths
• All that remains of the Nevadan
orogeny are these batholiths
which have been obducted (in
some cases) on the North
American plate
Early Jurassic of the western US
Chinle Formation at Petrified Forest
National Park, Arizona
Cretaceous Period
“Creta” means chalk
Reflects the Zuni
transgression;
worldwide warm
seas that allows
coccolithophores to
thrive and their
shells to deposit
and form chalk
Rudist (bivalve)
reefs are now oil
and gas traps
During the Cretaceous…
Sea level were higher; epeiric seas covered continents
Divergence of planktic organisms led to large coal and oil deposits
The Atlantic Ocean continued to open while the Tethys Ocean closed
India migrated northward
Oxygen levels neared 35% (modern = 21%); polar areas are warm
Why was the Cretaceous warm?
The deep ocean
was much warmer
than today. This
implies that more
hot rocks were
making up the sea
floor – greater sea
floor spreading!
This may have
been caused by
increased mantle
plume activity
Coccoliths
A coccolithophore is a calcium
carbonate-secreting green algae. Its
shell comprises round coccolith
plates, whose function is not well
understood. First appearing in the
Traissic, coccolithophores are an
important part of how calcium is
cycled to and from organisms.
Rudist bivalves formed reefs – went extinct
at K/T boundary
Which leaves the niche wide open for the scleractinian corals
Sevier (130-80 My) and Laramide (80-50 My)
orogenies
Both orogenies are
due to the subduction
of the Farallon Plate;
the difference is
timing (Sevier came
first) and the angle of
subduction
All that remains of the
Sevier are folds and
thrusts in Nevada and
Utah; Laramide are
the Colorado Plateau
and some of the
southern Rocky
Mountains
Cretaceous/Tertiary (K/T) boundary: the
second largest extinction in the record
Causes of the K/T extinction event ––
Chicxulub impact
Stratigraphy of an impact
Evidence for impact
Iridium is an
extremely rare
metal on the Earth’s
surface – some
asteroids (via
meteorites) have
high concentrations
of iridium. This
iridium “spike” seen
in Montana is seen
worldwide.
Further evidence for impact
Spherules
glass beads, felsic, melting of
crustal rocks
Soot
carbonaceous particles, wildfires
Shocked Quartz
Contains lamelle (little lines),
evidence of a high pressure shock
wave
Stishovite
high pressure form of quartz
Shocked Quartz
Causes of the K/T extinction event ––
Deccan traps (2nd largest flood basalt)
Some magma sources are
contain high concentrations of
iridium.
Ammonites and nautiloids flourish in the
oceans – ammonites go extinct at the K/T
boundary, nautiloids survive
The reason for this is unclear
In fact, only 15% of terrestrial genera go extinct, while 70% of
marine genera do
At the end of the Cretaceous