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