Proterozoic Eon: 2.5 - 0.542 Ga

Era	Range
Neoproterozoic	1000 - 542 Ma
Mesoproterozoic	1.6 - 1.0 Ga
Paleoproterozoic	2.5 - 1.6 Ga

• Clear evidence of "modern-style" (continent-scale) plate tectonics
• Decrease in abundance of komatiites & greenstone belts
• HUGE deposits of Banded Iron Formations during 1rst half of Paleoproterozoic
• Complex unicellular, and first multicellular life
• Indications of higher levels of oxygen

The 2.5 Ga boundary is somewhat arbitrary: shift from "Archean" to "Proterozoic"-style crust begins at 2.95 Ga in southern Africa, but not until 2.6 in North Ameirca, and after 2.45 in some other regions.

Lithologies of the Proterozoic:

• Stromatolites VERY abundant throughout
• BIFs VERY abundant during first half of Paleoproterozoic (92% of all BIFs deposited from 2.5-2.0 Ga); reappear in brief intervals associated with Neoproterozoic superglaciation
• Rare greenstone belts
• Paleoproterozoic glacial deposits:
  • Some of the oldest known tillites deposited on striations is Gowganda Formation (c. 2.3 Ga, Great Lakes region, Canada)
  • Possible older one at 2.7 Ga in Bruce Formation of Ontario
  • Also, some carbon isotope evidence for large scale glaciation in Paleoproterozoic
• Last of the detrital uranite & pyrite at 2.3 Ga
• First red beds (arkoses, reddish shales, etc.) at 2.0-1.8 Ga

Paleoproterozoic saw the suturing together of many small Archean cratons to form much larger continents: the formation of the large cratons of today:

• Kenoran Orogeny:
  • Archean-Proterozoic boundary
  • Evidenced only by granitic intrusives into granitoid-greenstone complex in Superior Province (an Archean craton), Canada
  • Oldest known evidence of major orogeny
• Wopmay Orogeny:
  • In Slave Province (an Archean craton), Canada
  • Oldest well-studied modern style orogeny with passive margin -> flysch -> molasse -> passive margin sequence
  • Caused by collision of Slave Province with some other craton, 2.0 Ga

Recent work has suggested the followin Paleoproterozoic continents and supercontinents had formed by accretion and suturing of Archean provinces:

• 2.5 Ga: Arctica (perhaps associated with the Kenoran orogeny?): various northern and central Canadian, Greenland, and Siberian cratons
• 2.1 Ga: Baltica, northwestern Europe
• 2.0 Ga: Atlantica: various cratons in modern South America and Africa, later incorporated into western Gondwana
• 1.8 Ga: Laurentia: the core of North America and Greenland
• 1.6 Ga: Nena/Nuna/Columbia, fusion of Laurentia, Siberia, and Baltica (forshadowing later Laurussia and Laurasia).
• Many other cratons established during this Era

The Paleoproterozoic Era has recently been subdivided into the Siderian ("iron", after banded iron: 2.50 - 2.30 Ga), Rhyacian ("streams of lava": 2.30 - 2.05 Ga), Orosirian ("mountain building": 2.05 - 1.80 Ga), and Statherian ("stabilization": 1.80 - 1.60 Ga) Periods. The boundaries are arbitrarily defined, but their names are derived from prominent geologic processes occurring at that time.

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Last modified: 10 January 2008