Lecture 15 Mountain Building in Western North America in the Mesozoic
Focus Question:
What are the major geologic features of western North America formed in
Mesozoic time?
1.
Today we
will look at the FOUR mountain building events occurring in Mesozoic North
America
a.
Sonoman Orogeny-Triassic
b.
Nevadan Orogeny-Jurassic
c.
Sevier Orogeny-Cretaceous
d.
Laramide Orogeny-Late Cretaceous and into
Cenozoic time
2.
Triassic-Sonoman
Orogeny
a.
Microcontinent
“Sonomia” collided with North America as
ocean lithosphere subducted
b.
Sediments from descending ocean lithospheric
plate formed “Golconda terrrane”
c.
Sonomia today includes part of Oregon and
northern California
3
Jurassic-Nevadan
Orogeny
a.
Ocean
lithospheric plate subducted under North American continent.
b.
Subducting
plate melted, rising magma formed large batholiths, Sierra Nevadas
c.
Trench area-elongate basin-is the Great Valley of
California
4.
Cretaceous-Sevier
Orogeny
a.
Continued
subduction of ocean lithospheric plate under North America
b.
Entire Cordilleran mountain chain undergoing
uplift-note how volcanic activity spreads eastward.
c.
Eastward spread is hypothesized to have occurred
as descending slab changes angle to more shallow descent
5.
Shallow
seaway through midcontinent begins, starting in the North,
spreads south.
a.
In Late
Cretaceous, seaway reaches Gulf of Mexico
b.
Cretaceous Interior Seaway was shallow-no more
than 600 feet deep
c.
Made western portion of North America into a
long, North-South, mountainous island.
6.
Big Bend
National Park, Texas is an example of Cretaceous paleoenvironment on the edge of
the Cretaceous Interior Seaway
a.
Rio
Grande River has cut through these Cretaceous limestone and coastal sedimentary
rocks
b.
Large Pterosaurs, sauropods, giant crocodiles are
Cretaceous fossils
c.
Fluctuations in inland sea level show as facies
changes
7.
The
Cretaceous Period is the youngest and last period of the Mesozoic Era (remember,
there are three periods: Triassic,
Jurassic, and Cretaceous). Pangaea
had completely fragmented by late Cretaceous time, with the exception of
Antarctica and Australia, which were still linked.
Click on this
http://jan.ucc.nau.edu/~rcb7/90moll.jpg
to see the Cretaceous globe.
Things to note:
a.
Tethys
Seaway, shallow, subtropical seaway about where the modern Mediterranean is
today. The great petroleum reserves
of the Persian Gulf and Middle East are the legacy effect of those organic rich,
shallow seas.
b.
Note that Australia and Antarctica are still
linked.
c.
Note the position of India.
The lithospheric plate with India will move northward to collide with
Eurasia, forming the Himalayan Mountains, in early Cenozoic time.
d.
Note the
enormous seaway that flooded the North American continent from Alaska to the
Gulf of Mexico. This is the
Cretaceous Interior Seaway, which formed in mid-late Cretaceous time.
8.
Features
of the Cretaceous World
a.
Warmer
world than today
b.
Higher sea level than today – highest of
Phanerozoic time
c.
Long period of stability in the magnetic
field-most of the Cretaceous is “normal”.
d.
Rapid sea floor spreading (you can see that from
the fragmenting of Pangaea)
e.
Ocean
circulation weakened-low oxygen in the deep ocean
9.
Latest
Cretaceous and into Cenozoic Era-Laramide Orogeny – more uplift in the
Cordilleran range
10. Next Lecture-The End Cretaceous Extinction Event
