Transcript North American History Powerpoint

North American Geological
History
So what did we figure out about the East
Coast so far?
• Proterozoic: suture zone, rifting
• Cambrian: passive margin
• Ordovician: subduction complex (Japan-like)
hits North America
OK, on to the rest of the Paleozoic
• Silurian: passive margin
• Devonian: collision of continental fragment
with North America – Avalonia: Acadian
Orogeny
• Miss/Penn: Acadian mountains shed sediment
into the interior of the continent
• Permian:collision with Africa and Europe
makes Pangaea
Pangaea
• The Permian collision was only a piece of the
formation of a supercontinent called Pangaea
http://3dparks.wr.usgs.gov/nyc/images/fig83.jpg
How do we know Pangaea existed and
finished forming in the Permian?
• Age patterns on ocean floor (reflected in
magnetic stripes
http://sos.noaa.gov/ge/land/sea_floor_age/topo/4096.png
How do we know Pangaea existed and
finished forming in the Permian?
• Age patterns on ocean floor (reflected in
magnetic stripes
• Mountain belts /terranes that run from one
continent to another
• Climate belts that run from one continent to
another
• Fossils
http://www.mrsciguy.com/sciimages/fossil_record.gif
How do we know Pangaea existed and
finished forming in the Permian?
• Age patterns on ocean floor (reflected in
magnetic stripes
• Mountain belts /terranes that run from one
continent to another
• Climate belts that run from one continent to
another
• Fossils
• Glaciation
Meanwhile, back on the craton…
• Cambrian: lots of sandstones, limestone –
some land to erode to make sand
• Ordovician: lots of limestone, whole continent
is covered in water – no land eroding to make
sediment
• Silurian - Devonian: evaporites in Michigan
Basin because reefs around the edge restrict
circulation
Middle Paleozoic Michigan
Basin
Reefs around the edge, salty water in the middle
Late Paleozoic craton
• Remember what happened in the
Appalachians?
• As the big mountains started to go up, the sea
drained off the continent
• More terrestrial deposits, including
widespread coal swamps
http://www.museum.state.il.us/exhibits/changes/htmls/tropical/upland_emerges.html
Cyclothems
• Repeating sequences of sedimentary rocks
that go from non-marine to marine
• Repeat tens to hundreds of times.
http://www.isgs.uiuc.edu/maps-data-pub/publications/geonotes/geonote2.shtml
Cyclothems
• Repeating sequences of sedimentary rocks
that go from non-marine to marine
• Repeat tens to hundreds of times.
• What caused the many repetitions?
– Deltas growing off the rising Appalachian
mountains
– Small changes in sea level across a low-lying area
can cause changes
So what happened to Pangaea?
• Triassic Rocks of East Coast:
– Red sandstones and shales, red conglomerates
and breccias
– Basalts
– Normal faults
– What happened?
• Age of the Atlantic Ocean floor
Then what happened to Pangaea?
• Breaks up in Triassic: normal faults, basalt,
redbeds
• Atlantic Ocean forms
• Atlantic grows wider throughout the Mesozoic
and Cenozoic
• So what tectonic facies has the East Coast
been throughout this time?
And on the craton…
• Let’s watch the movie all the way from
Cambrian on…
• http://www.youtube.com/watch?v=2y43yJu3DA
Mesozoic-Cenozoic Craton
• Triassic: craton dry – very little rock
• Jurassic: mostly dry, little deposition in Gulf
Coast
• Cretaceous: Great Cretaceous seaway cuts NA
in half – marine rocks on west edge of craton.
Paleozoic Cordillera
• Paleozoic – subduction zone with many
collisions of small things – island arcs,
continental fragments – builds the NA
continent wider
• Orogenies: Antler, Sevier
• Accreted terranes have ophiolites in between
them
Jurassic-Cretaceous
• Foothills: now-metamorphosed volcaniclastic
sedimentary rocks.
– Andesitic bits
– Graded greywackes
– Cherts
• Coast Range:
– Great Valley Sequence:
• Graded greywackes, laminated shales
– Franciscan Formation:
• Greenschist with blueschist, basalt and marble
inclusions
So what is it?
Cretaceous change
• Great Valley sediments contain granite bits by
mid-late Cretaceous – what does it mean?
• Pause of 10 million years – no volcanoes in
Western US
• Volcanoes pop up in Colorado – what
happened?
Cretaceous time
• Western volcanoes shut down, and the
subduction mountains erode away• Great Valley deep water rocks contain bits of
granite from the magma chamber
• 10 million years later – volcanoes start
erupting in Colorado
• Low angle subduction moves the volcanoes of
the subduction zone far inland from the
trench
Cenozoic complications
• Subduction of a diverging boundary
• San Andreas Fault forms
• Tensional tectonics across the Basin and Range –
stretches to twice its width and creates fault
block mountains
• Colorado Plateau rises intact
• Santa Barbara block spins around opening pullapart basins that produce oil
• North America arches up, water drains off the
Atlantic and Gulf Coast