The ProterozoicThe Proterozoic

Sub DivisionsSub Divisions

►NeoproterozoicNeoproterozoic 1.0-0.544 b.y1.0-0.544 b.y

►MesoproterozoicMesoproterozoic 1.6- 1b.y.1.6- 1b.y.

►PaleoproterozoicPaleoproterozoic 2.5-1.6 b.y.2.5-1.6 b.y.

Laurentia: Proterozoic N. Laurentia: Proterozoic N. AmericaAmerica

► Six ElementsSix Elements SuperiorSuperior SlaveSlave HearneHearne RaeRae WyomingWyoming NainNain

Laurentia: Proterozoic N. Laurentia: Proterozoic N. AmericaAmerica

►During Proterozoic the six elements (or During Proterozoic the six elements (or provinces) are welded together during provinces) are welded together during orogenicorogenic episodes episodes

►This period of continental welding This period of continental welding ended by 1.7byaended by 1.7bya

►Extensive accretion of continental Extensive accretion of continental margin (2.3-0.9bya)margin (2.3-0.9bya)

Plate tectonics in the Plate tectonics in the ProterozoicProterozoic

►Rapid lateral motionRapid lateral motion Vigorous subduction/orogenyVigorous subduction/orogeny

►Extensive RiftingExtensive Rifting►Rapid sea-floor spreadingRapid sea-floor spreading

Paleoproterozic EventsPaleoproterozic Events

►Wopmay OrogenyWopmay Orogeny Western Margin of the Slave Western Margin of the Slave

provinceprovince►Evidence of opening of an ocean Evidence of opening of an ocean

basinbasin►Sedimentation along the new Sedimentation along the new

continental margincontinental margin►Closure of the ocean basinClosure of the ocean basinWilson CycleWilson Cycle

Depositional ZonesDepositional Zones

►Eastern zone of ocean basin (next to Eastern zone of ocean basin (next to Slave) Slave) Coastal Region Coastal Region

►Quartz sandstoneQuartz sandstone►Shallow marine environmentShallow marine environment►Over time Sandstone metamorphosed to Quartzite. Over time Sandstone metamorphosed to Quartzite.

Also contained massive Also contained massive stromatolitesstromatolites (now (now dolomitic)dolomitic)

This is the Rocknest FormationThis is the Rocknest Formation Western ZoneWestern Zone

►Continental Shelf depositsContinental Shelf deposits Deep water turbiditesDeep water turbidites

Evidence of Wilson CycleEvidence of Wilson Cycle

►Numerous tensional faultsNumerous tensional faults►Alluvial Fan and Fluvial depositsAlluvial Fan and Fluvial deposits►As the ocean widened the As the ocean widened the

western edge of the province western edge of the province became passive margin with two became passive margin with two parallel zones of depositionparallel zones of deposition

Closure of the ocean basinClosure of the ocean basin

►As westward edge of Slave subducted As westward edge of Slave subducted the continental shelf buckled the continental shelf buckled downward.downward.

►As depth increased:As depth increased: Carbonate deposition endedCarbonate deposition ended Accumulation of deep water clastics beganAccumulation of deep water clastics began

►Subsequent collisional forces caused Subsequent collisional forces caused additional folding and faulting.additional folding and faulting.

AulacogensAulacogens

►Aulacogens are inactive rifts of a radiating Aulacogens are inactive rifts of a radiating three-rift system that develops over areas three-rift system that develops over areas of crust that are being upliftedof crust that are being uplifted

Forming an AulacogenForming an Aulacogen

As the crust begins to bulge it breaks to As the crust begins to bulge it breaks to form the three rift zonesform the three rift zones

Forming an AulacogenForming an Aulacogen

► Two arms fill with Two arms fill with water to form water to form oceansoceans

► The third, failed, The third, failed, arm trends inlandarm trends inland

ExamplesExamples

Can you identify any modern Aulacogens on the world map?

Trans-Hudson OrogenyTrans-Hudson Orogeny

► N and W side of N and W side of Superior ProvinceSuperior Province

► Records Wilson CycleRecords Wilson Cycle► Joins Hearne and Joins Hearne and

Wyoming Wyoming Severe folding and Severe folding and

metamorphism during metamorphism during closure of wilson closure of wilson cycle welded the cycle welded the Superior plate to the Superior plate to the Wyoming and HearneWyoming and Hearne

Paleoproterozoic Ice AgePaleoproterozoic Ice Age

►Superior Province 2.6-2.1 bySuperior Province 2.6-2.1 by►Gowgonda FormationGowgonda Formation

Notable for conglomerates and laminated Notable for conglomerates and laminated mudstonesmudstones►Laminations represent repeated summer and Laminations represent repeated summer and

winter sediment layers (called winter sediment layers (called varvesvarves))►In Gowgonda Formation varves alternate with In Gowgonda Formation varves alternate with

tillitestillites

►Formation lies above 2.6 by crystalline Formation lies above 2.6 by crystalline rock and is intruded by 2.1 by igneous rock and is intruded by 2.1 by igneous rocks rocks

Labrador TroughLabrador Trough

► Curved track on east Curved track on east side of Superior side of Superior ProvinceProvince Records yet another Records yet another

Wilson CycleWilson Cycle During closing phase During closing phase

eastern zone eastern zone underwent intense underwent intense folding, thrust faulting, folding, thrust faulting, and metamorphism- and metamorphism- known as Hudsonian known as Hudsonian OrogenyOrogeny

Mesoproterozoic Mesoproterozoic

►Hudsonian Orogeny serves as the Hudsonian Orogeny serves as the event that separates paleoproterozoic event that separates paleoproterozoic from mesoproterozoicfrom mesoproterozoic

Keweenawan SequenceKeweenawan Sequence

► Rocks rest on crystalline or Rocks rest on crystalline or animikiananimikian stratastrata

► Extend for hundreds of kilometers from Extend for hundreds of kilometers from Lake Superior regionLake Superior region

► Consist of Quartz sandstone, arkoses, Consist of Quartz sandstone, arkoses, conglomerates, as well as basaltic conglomerates, as well as basaltic volcanics.volcanics. The lava flows are well known for their The lava flows are well known for their

content of native copper.content of native copper.

Keweenawan SequenceKeweenawan Sequence

► In some areas lava flows accumulated to a In some areas lava flows accumulated to a thickness of several kilometers.thickness of several kilometers.

► Although this seems like a lot of lava, most of Although this seems like a lot of lava, most of the magma remained underground forming the the magma remained underground forming the Duluth GabbroDuluth Gabbro (12kmX160km)(12kmX160km) What is most basaltic magma/lava What is most basaltic magma/lava

associated with?associated with?► Large amounts of mafic magma typically Large amounts of mafic magma typically

signals the presence of a riftsignals the presence of a rift Had the rift continued, the eastern US would Had the rift continued, the eastern US would

have drifted awayhave drifted away

The Grenville ProvinceThe Grenville Province

► Exposures extend from Labrador to Lake Exposures extend from Labrador to Lake Huron. However, region actually extends Huron. However, region actually extends down eastern US and westward into Texas.down eastern US and westward into Texas.

► Consist of carbonates and sandstones that Consist of carbonates and sandstones that have been deformed, metamorphosed, and have been deformed, metamorphosed, and intruded.intruded.

The Grenville ProvinceThe Grenville Province

►Deformation occurred 1.2-1.0 bya Deformation occurred 1.2-1.0 bya during the during the Grenville OrogenyGrenville Orogeny.. (the (the beginnings of the Appalachians)beginnings of the Appalachians)

Only one part of a series of continental Only one part of a series of continental collisions involved in the formation ofcollisions involved in the formation of the the supercontinentsupercontinent RodiniaRodinia

RodiniaRodinia

NeoproterozoicNeoproterozoic

►Rodinia was assembled by 1.0 bya, Rodinia was assembled by 1.0 bya, however, by 750mya it began to split however, by 750mya it began to split apartapart

►During this time the proto-pacific During this time the proto-pacific ocean (ocean (PanthalassaPanthalassa) was created west ) was created west of N. Americaof N. America

Proterozoic Ice HouseProterozoic Ice House

►Neoproterozoic rocks on all Neoproterozoic rocks on all continents, except India and continents, except India and Siberia, show Siberia, show glacial glacial striationsstriations..

► Tillites and varves can also be Tillites and varves can also be found found Evidence is so prevalent, geologist Evidence is so prevalent, geologist

refer to our planet during this time refer to our planet during this time as “as “Snowball EarthSnowball Earth””►Formally this time is called the Formally this time is called the

Varangian GlaciationVarangian Glaciation

RodiniaRodinia

What could have cause this?What could have cause this?

►Plate tectonicsPlate tectonics Most land masses located at low or mid Most land masses located at low or mid

lattitudeslattitudes►Land is much more reflective than waterLand is much more reflective than water►As glaciers formed land became even more As glaciers formed land became even more

reflectivereflective

►AtmosphericAtmospheric Loss of Carbon DioxideLoss of Carbon Dioxide During this time fungi, lichens and vascular During this time fungi, lichens and vascular

plants were present.plants were present.

Sediment DepositionSediment Deposition

►During this period extensive layers of During this period extensive layers of limestone were deposited.limestone were deposited.

If Limestones are typically If Limestones are typically associated with relatively warm associated with relatively warm seas how could this be possible?seas how could this be possible?

The Fossil RecordThe Fossil Record

► Inherited Archean LifeInherited Archean Life Photosynthetic cyanobacteria Photosynthetic cyanobacteria

(oxygenated)(oxygenated) anaerobic prokaryotesanaerobic prokaryotes

► StromatolitesStromatolites► molecular fossilsmolecular fossils

Heliotropic Heliotropic StromatolitesStromatolites

► Sine-wave growth Sine-wave growth form=yearly cyclesform=yearly cycles

► Laminar Laminar structure=daily structure=daily growth phasegrowth phase

► Bitten Springs Fm., Bitten Springs Fm., Australia (850 my)Australia (850 my) Anabaria juvensis Anabaria juvensis

(Stromatolite)(Stromatolite) 435 435

laminae/cycle=laminae/cycle=435 435 days/yeardays/year

EukaryotesEukaryotes

► Record of large cells: 1.6-1.4 b.y to presentRecord of large cells: 1.6-1.4 b.y to present► SteranesSteranes: molecular fossils: molecular fossils► AcritarchsAcritarchs (Planktonic Algae; Skiagia) (Planktonic Algae; Skiagia)

Max age 1.6 b.y.Max age 1.6 b.y. Fossil sites; Russia, California, AustraliaFossil sites; Russia, California, Australia

► Eukaryotic ProtozoansEukaryotic Protozoans: Vase-shaped fossils : Vase-shaped fossils from Spitsbergen and Arizonafrom Spitsbergen and Arizona

► MetazoansMetazoans Australia: Ediacara HillsAustralia: Ediacara Hills China: Doushantuo Formation (~570 m.y.)China: Doushantuo Formation (~570 m.y.) Russia: White Sea coast (~550 m.y.)Russia: White Sea coast (~550 m.y.)

Some may not have modern equivalentsSome may not have modern equivalents

Body and trace fossil Body and trace fossil MetazoansMetazoans

► Cloudina: 3cm, tube dwelling wormCloudina: 3cm, tube dwelling worm► EdiacaranEdiacaran trace fossils trace fossils

Cyclomedusa: discoidal (Jellyfish ?)Cyclomedusa: discoidal (Jellyfish ?) Tribrachidium: circular (unknown)Tribrachidium: circular (unknown) Charniodiscus: Frond shape (Sea pen)Charniodiscus: Frond shape (Sea pen) Dicksonia: ovate-shape (Flatworm)Dicksonia: ovate-shape (Flatworm) Spriggia: Elongate (Annelid)Spriggia: Elongate (Annelid)

EdiacaranEdiacaran

Fossil ExpansionsFossil Expansions

► Mesoproterozoic (1.4 b.y. ago) EukaryotesMesoproterozoic (1.4 b.y. ago) Eukaryotes► Neoproterozoic (0.6 b.y. ago) MetazoansNeoproterozoic (0.6 b.y. ago) Metazoans

► Proterozoic Prokaryotes (Gunflint Proterozoic Prokaryotes (Gunflint Fossils, 1.9b.y.)Fossils, 1.9b.y.)► Gunflintia: unbranched filament (algae)Gunflintia: unbranched filament (algae)► Animikiea: fine filament (algae)Animikiea: fine filament (algae)► Eostrion: Dawnstar (bacterium)Eostrion: Dawnstar (bacterium)► kakabekia: plumose form (unknown)kakabekia: plumose form (unknown)

Changing EnvironmentChanging Environment

► Free Oxygen begins to Accumulate in Free Oxygen begins to Accumulate in atmosphere (2.0 b.y. ago)atmosphere (2.0 b.y. ago)

► Oxygen increases sporadically as CO2 Oxygen increases sporadically as CO2 level decrease (1.0 b.y.)level decrease (1.0 b.y.)

► Oxygen rises to 3-10% of current level Oxygen rises to 3-10% of current level (0.6 b.y. ago)(0.6 b.y. ago)

► Wide variety of climatesWide variety of climates Hot, dry (evaporates)Hot, dry (evaporates) Tropical (algae reefs)Tropical (algae reefs) Ice Ages (glacial deposits)Ice Ages (glacial deposits) Warm, tropical (Carbonates)Warm, tropical (Carbonates)