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

How do we know Pangaea existed and finished forming in the Permian? Age patterns on ocean floor (reflected in magnetic stripes

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

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

Cyclothems Repeating sequences of sedimentary rocks that go from non-marine to marine Repeat tens to hundreds of times.

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… 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