Chapter 7 - The Proterozoic Eon

I.	Proterozoic subdivisions
	A.  Neoproterozoic:  1.0 - 0.57 b.y.a.
	B.  Mesoproterozoic: 1.6-1.0 b.y.a.
	C.  Paleoproterozoic:  2.5 - 1.6 b.y.a.

II.	Laurentia - Proterozoic North America
	A.  Elements:  Superior, Slave Hearne, Rae, Wyoming and Nain
	B.  Orogenic welding:  Joining elements
	C.  Period of welding:  2.0 - 1.7 b.y.a.
	D.  Accretion of continental margin (2.3 - 0.9 b.y.a.)
	E.  Plate tectonic characteristics
	    1.  Rapid lateral motion
	    2.  Vigorous subduction and orogeny
	    3.  Extensive rifting
	    4.  Rapid sea floor spreading

III.  Paleoproterozoic events:  Laurentia
	A.  Formation of Wopmay orogen
	B.  Development of Wilson cycle (open and close of ocean)
	C.  Development of continental margin (Rocknest Fm.)
	D.  Development of Aulacogens (3 arm rift)
	    1.  Two arms form oceans
	    2.  Third arm fails to become an ocean, fills with terrestrial sediment
	E.  Formation of Trans-Hudson Orogen
	    1.  N and W sides of Superior province
	    2.  Records Wilson cycle
	    3.  Joins Hearne and Wyoming terraines
	F.  Ice Age (Superior Province, Gowganda Fm. 2.6 - 2.1 b.y.a.)
	    1.  Conglomerates (tillites)
	    2.  Laminated mudstones (glacial lakes)
	G.  Formation of Animikie Group (Superior Province)
	    1.  Bonanza iron ores (banded iron formations)
	    2.  Gunflint Chert (cyanobacteria, prokaryotes)
	H.  Formation of Labrador Trough
	    1.  Curved tract on east side of Superior Province
	    2.  Records Wilson cycle
	    3.  Stratigraphy:  East versus west
		a.  east:  Tholeiitic (sea floor) basalt's
		b.  west:  Sandstone's, dolostones, banded iron formation
	    4.  Structure
		a.  east:  Folding and metamorphism
		b.  west:  Thrust faulting
	    5.  Hudsonian Orogeny:  Close of trough and end of Paleoproterozoic

IV.	Mesoproterozoic events:  Laurentia
	A.  Deposition of Keweenawan Sequence (Superior Province)
	    1.  Above Archean granite and gneiss and Paleoproterozoic Animikian rocks
	    2.  Clean sandstone and vesicular basalt's
	    3.  Lava's several 1000 m thick with abundant copper deposits (in vesicles)
	B.  Rift and intrusion of Duluth (mafic) Complex
	    1.  Rifting:  1.2 - 1.0 b.y.a
	    2.  Tensional faulting, then intrusion
	    3.  Funnel shaped Duluth Complex intrusion
		a.  gabbro in graded layers
		b.  dimensions:  12 km x 160 km
	C.  Development of Grenville Province:  Eastern Canada to Alabama, then to
 Texas
	    1.  Age 1.2 - 1.0 b.y.a.
	    2.  Metamorphosed carbonates and sandstone's, intruded by igneous bodies
	    3.  Overturned folds with NE axis orientation
	    4.  Models for development
		a.  plate tectonics (Wilson cycle)
		b.  intra-plate deformation
	D.  Events in western Laurentia
	    1.  Wyoming terrain collided with 1 or more island arcs (1.8 - 1.6 b.y.a.)
	    2.  Yavapai-Mazatzal terrain collision (1.8-1.7 b.y.a.; mylonite/breccia zone in
    		WY - CO)
	    3.  Magmatism episode 1.5 - 1.4 b.y.a (anorogenic plutons)
	    4.  Widespread rifting (1.4 - 0.85 b.y.a)
		a.  Uinta Series (UT)
		b.  Pahrump Group (CA)
		c.  Belt Supergroup (MT, ID, BC; 12 km thick)
	    5.  Mazatzal orogeny (1.4 - 1.3 b.y.a.)
		a.  Vishnu Schist (Grand Canyon, AZ)
		b.  Zoroaster Granite (Grand Canyon, AZ)
6.  Development of N-S passive margin:  Deposition of Grand Canyon
    Supergroup

V.	Neoproterozoic events:  Laurentia
	A.  Basin and shelf deposition around continent
	B.  Rifting and development of proto-Atlantic Ocean
	C.  Ice age:  240 million years duration

VI.	Proterozoic Global Events
	A.  Neoproterozoic paleogeography
	    1.  Rodinia:  Proto-Pangaea supercontinent
	    2.  Mirovia:  Global ocean
	B.  Baltic Shield deformation:  Part of Grenville Orogeny
	C.  Development of Angaran Shield (Siberia)
	    1.  Mobile belts on east and south (Urals and Himalayan rocks, respectively)
	    2.  Complex core of crystalline rock; multiple deformations
	    3.  Rhiphaen Rocks:  1.6 b.y.a. with abundant stromatolites
	    4.  Zone of soft body fossils:  Vendian System of Russia
	D.  Development of South American Shield
	    1.  Welding of 3 shields:  Guianan, Brazilian, and Patagonian
	    2.  3 fold stratigraphy:  Crystalline, volcanics, and sediments
	E.  Development of African Shield
    1.  Welding of 4 shields:  W. Africa, Angola-Kasar, Rhodesia-Transvaal,
    	Tanzania
	    2.  Deformation continued to 0.4 b.y.a.
	F.  Assemblage of Indian Shield
	    1.  Pilbara and Yilgarn shields welded to east side of Australian craton
	    2.  Stratigraphy of 1.5 b.y.a. duration
		a.  carbonates with stromatolites (oldest)
		b.  banded iron formations
		c.  glacial and lacustrine beds
		d.  Rawnsley Quartzite (soft body fossils)
	G.  Evolution of Antarctic shield

VII.  Fossil Record
	A.  Inherited Archean Life
	    1.  photosynthetic cyano-bacteria (oxygenated)
	    2.  anaerobic prokaryotes (anaerobic)
	    3.  stromatolites
	B.  Heliotropic stromatolites
	    1.  sine-wave growth form = yearly cycles
	    2.  laminar structure = daily growth phase
	    3.  Bitten Spring Fm., Australia (850 m.y.a.)
		a.  Anabaria juvensis (stromatolite)
		b.  435 laminae/cycle = 435 days/year
C.  Eukaryotes
	    1.  Record of large cells:  1.6 - 1.4 b.y.a. to present
	    2.  Actitarchs (planktonic algae; Skiagia)
		a.  maximum age:  1.6 b.y.a.
		b.  fossil sites:  Russia, California, Australia
	    3.  Eukaryotic protozoans:  Vase-shaped fossils from Spitsbergen and Arizona
	    4.  Modern equivalents of jellyfish and corals
	    5.  Some may not have modern equivalents
	D.  Body and Trace fossil metazoans
	    1.  Coludina: 3 cm, tube dwelling worm
	    2.  Ediacaran trace fossils (0.6-0.57 b.y.a.)
		a.  Cyclomedusa:  Discoidal (jellyfish?)
		b.  Tribrachidium:  Circular (unknown)
		c.  Charniodiscus:  Frond-shape (sea pen?)
		d.  Dicksonia:  Ovate-shape (flatworm?)
		e.  Spriggia:  Elongate (annelid?)
		f.  Kimberella:  Internal organs in a body cavity
	E.  Fossil "expansions"
	    1.  Mesoproterozoic (1.4 b.y.a.): Eukaryotes
	    2.  Neoproterozoic (0.6 b.y.a.):  Metazoans
	F.  Proterozoic Prokaryotes (Gunflint fossils, 0.9 b.y.a)
	    1.  Gunflinia - unbranched filament (algae?)
	    2.  Animikiea - fine filament (algae)
	    3.  Eoastrion - "downstar" (bacterium)
	    4.  Kakabekia - phimose form (unknown)
	    5.  Eospaera - sphere (unknown)

VIII.	Changing Environment
	A.  Free oxygen begins to accumulate in atmosphere (2.0 b.y.a.)
	B.  Oxygen increases sporadically as CO2 decreases (1.0 b.y.a.)
	C.  Oxygen rises to 3 to 10% of current level (0.6 b.y.a.)
	D.  Wide variety of climates
	    1.  hot dry (evaporites)
	    2.  tropical (algal reefs)
	    3.  ice ages (glacial deposits)
	    4.  warm, tropical (carbonates)