GEOL 102 UNLV Lecture 15 - Proterozoic Eon

Evidence of rise of oxygen at Early Paleoproterozoic

• oxidized Fe & Mn mineral deposits

• detrital uraninite & pryrite

• Paleosols

• Red Beds

• Sulfur Isotopes

• Eukaryotes

What eras are in the Proterozoic Eon?

• Neoproterozoic

• Mesoproterozoic

• Paleoproterozoic

First supercontinent

Nuna or "'Columbia”

What tectonic activity occurred during the Paleoproterozoic?

• Continental growth around Archean Shields through orogeny

• birth and death of a short-lived ocean to the west of the Slave Province of the Canadian Shield

• dolostone and interbedded shales

• intensive folding due to eat-west crustal shortening and accretion during the orogenic phase of development of the Wopmay orogen

• some rifted valleys aborted and failed to become oceans (aulacogens)

The Grenville orogeny

eastern North America; 1.1 Ga; thought to be the orogeny that formed Rodinia

When was the assembly and breakup of Rodinia?

Assembly: 1000-800 Ma; Breakup: 800-600 Ma

Rodinia

Neoproterozoic supercontinent that existed between 1000-700 Ma when all continents collided together (the supercontinent before Pangea)

The Gowganda tillite

in the Lake Huron region is the earliest known evidence of glaciation

Proterozoic CO2 level

lower than the Archean, but still much higher than today’s level

Proterozoic O2 level

higher than the Archean but lower than today’s level

Proterozoic Hydrosphere

• paleoproterozoic & archean: abundant

• mesoproterozoic: locally abundant

• neoproteroøic: rare except immediately after Neoproterozoic glaciations

• ocean was highly supersatured ith regard to CaCO3 in the Archean through Mesoproterozoic

What happened in the biosphere in the Proterozoic Eon?

• diversification of Cyanobacteria

• abundance of stromatolites

• mesoproterozoic - neoproterozoic Eukaryotes

• neoproterozoic multicellular algae

• animals: animal embryos (adult form not found)

• edicaran animal fossils:

  • acanthomorphic (spiny) acritarchs

  • soft body imprints

    • 550 Ma, post snowball

    • some think they are algae

• animal fossils (first known calcium carbonate shell-bearing fossils

• trace fossils

  • mobile animals instead of detrital feeding organisms

  • high oxygen demands

General Summary: Lithosphere

• continental growth by orogeny

• Nuna & Rodinia

General Summary: Atmosphere

• generally low O2 level but BIF largely disappeared after

  • reappeared sometime during snowball Earth

General Summary: Hydrosphere

• generally high CO2 level and seafloor aragonite crystal fan precipitation

• suggests CaCO3 supersaturation in the ocean

General Summary: Climate

• Gowganda glaciation: first known snowball Earth

  • not first glacial record

• Neoproterozoic Glaciations: snowball Earth

  • widespread glacial diamictites

  • multiple ice ages before animal fossils

  • low latitude glaciation

  • are glacial diamictites synchronous?

General Summary: Biosphere

• continuing success of cyanobacteria and stromatolites

• first appearance of eukaryotes about 2.1 Ga

• Many algal groups appear

• animals appear in late Neoproterozoic after severe snowball Earth glaciations