Presentation on theme: "North American Geological History. Proterozoic – Cambrian Cordillera Proterozoic: Cambrian – Ordovician: Major rifting in Southern California (and presumably."— Presentation transcript:
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. Passive margin in West; intracratonic seas over the Grand Canyon
Cambrian- Ordovician craton Cambrian Ordovician Widespread shoreline facies (quartz-rich sandstones) with tidal features; closeness of Moon meant gigantic tides over huge regions on flat craton. Widespread carbonates indicate almost all of continent underwater with little land to erode and produce sediment (except to the East).
So what did we figure out about the East Coast so far? Proterozoic: Cambrian: Ordovician: suture zone, rifting passive margin subduction island arc (Japan-like) hits North America It hits an irregular coastline at an angle, causing a complex collision that happens at different times in different places.
OK, on to the rest of the Paleozoic Silurian: Devonian: Miss/Penn: Permian: passive margin collision of continental fragment with North America – Avalonia: Acadian Orogeny Acadian mountains shed sediment into the interior of the continent collision of North America with Africa and Europe assembles 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
Let’s look at the formation and breakup of Pangaea over time… 9rk
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 big changes in shoreline
What do larger sea level changes do? 5dw
So looking at the whole Paleozoic… Let’s watch the movie all the way from Cambrian on… yJu3DA
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? Rift valley followed by passive margin
Mesozoic-Cenozoic Craton Back to the movie to watch what happens 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 to Triassic exotic terranes So what kind of plate boundary must the Cordillera be during this time? Subduction Zone with lots of collisions (smaller and larger suture events)
Paleozoic-Triassic 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 Cordillera Jurassic – well developed subduction complex like the Andes
S gr2.jpg el/g148_f09/lecture_notes/nort h_coast/berryessa_cut.jpg Franciscan melange Great Valley forearc turbidites
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 We’ll do this by looking at the animations available at: wnload_Page.html#WNATectGeolHist
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