north american geological history
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North American Geological History. Proterozoic – Cambrian Cordillera. Proterozoic: Cambrian – Ordovician:. Major rifting in Southern California (and presumably north and south along a now hard-to-find ancient continental edge. Failed rifting in Grand Canyon region. - PowerPoint PPT PresentationTRANSCRIPT
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=2y43-yJu3DA
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 pull-
apart basins that produce oil• North America arches up, water drains off the
Atlantic and Gulf Coast