Historical Geology 102
Proterozoic Eon


Proterozoic Eon

2.5 b.y. - 542 m.y. ago
42% of the Earth's history.
Major tectonic events center around continued accretion of continental landmasses into large continents.
Evolution of eukaryotic cells and metazoans

Early Proterozoic

Orogenies in North America
8 major Archean-aged crustal blocks: Hearne, Nain, Penokean, Rae, Slave, Superior, Wopmay, and Wyoming.
Collisions between these blocks resulted in orogenic (mountain building) events. - continent-continent collisions

Wopmay Orogeny

Evidence indicates that this area initially opened to form an ocean.
Faulting, sedimentary and igneous rocks all indicate that divergence initially formed a rift valley.
Continued spreading resulted in the development of a passive margin.
- Passive Margin - plate margin along which there is no tectonic activity.
Shallow marine deposits form on the continental shelf.
Oceanic crust is formed due to continued divergence. (ophiolite sequence - oceanic crustal rocks).
Divergence stops, then reverses direction.
Subduction zone develops as the western margin of the Slave plate (oceanic crust) is subducted beneath an eastward moving plate.
Collision occurs between two continental land masses - results in the Wopmay orogeny.

Trans-Hudson Orogeny

Similar to Wopmay Orogeny but with one important difference.
Initial rifting separates the Superior region from the rest of the continent.
Passive margin eventually develops with sedimentation along the continentalshelf.
Ocean crust forms as divergence continues.
Divergence stops and the Superior plate reverses direction.
Ocean basin closes, with subduction zone forming as the oceanic crust is subducted beneath the continent.
Volcanic arc develops.
Collision of the Superior and Wyoming plates with the Hearne plate results in mountain building.

Glaciation

First major period of glaciation occurs in the Early Proterozoic

Banded Iron Formations

Sedimentary beds composed of alternating layers of chert and iron, plus other sediments.

Red Beds

Continental sedimentary deposits of red-colored sandstones and shales.

Yavapai, Mazatzal, Central Plains Orogeny

Between 1.8 and 1.6 b.y. a series of collisions of volcanic arcs with the growing continent.
Lower most rocks in the Grand Canyon were formed during these events.

Middle Proterozoic

Grenville Orogeny

Occurred between 1.3 and 0.9 b.y. ago along eastern margin of NorthAmerica.
Deformation extending from southwest U.S. through Greenland into Scandinavia.
Collision with another continental plate resulted in extensive mountain building and deformation.

Mid-Continent Rift

Occurred at the same time as the Grenville Orogeny.
Interior of North America began rifting.
Rifting occurred from NE Kansas up through Lake Superior, then down through Michigan to Ohio.
Thick accumulations of basalt lava flows in central rift zone, and clastic sediments along rift margins.

Evolution of Eukaryotes

Eukaryote cells evolve in the Middle Proterozoic
Eukaryotes contain a true nucleus enclosed within a nuclear membrane and well-defined chromozones.
- sexual reproduction
Most eukaryotes are aerobic - require oxygen (O2)

Late Proterozoic

Late Proterozoic Paleogeography

Glaciation

Major event of the Late Proterozoic.
Glacial deposits found in Utah, Greenland, Africa and South America.

Evolution of Metazoans

Metazoans are multicellular organisms.
May have evolved 1.9-1.8 b.y. ago?
Clear evidence of metazoans is found by 0.9 b.y. ago.
Ediacaran fossils (Scene from the end of the Proterozoic)