Belt/Purcell SupergroupOldest Rocks resting on NW Basement Rock

Glacier National Park

Extent of the Belt/Purcell

Rocks

A-4

(from Burchfiel, Cowan, and Davis, 1992)

Belt-AgeRocks

A-5

(from Winston, 1971)

Belt Thickness

A-5

East(Montana)

West(Idaho)

15-20 km

Rock Types

1. Shalesa) Redb) Green

2. Sandstones

3. Limestones

4. Diabase Intrusions(Type of mafic igneous rockbetween a basalt & gabbro)

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Belt Supergroup - Glacier National Park, Montana (Linda Kah).

Belt Structures - Shales/Sandstone

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• Laminations• Mudcracks• Ripples• Raindrop

Impressions• Salt Crystal

Impressions

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Belt Structures - Limestones

• StomatolitesQuickTime™ and aTIFF (Uncompressed) decompressor

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Modern Stromatolites

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Shallow Marine - Intertidal Zone

Sediment Source:

East & West

A-4

(from Burchfiel, Cowan, and Davis, 1992)

Age of the Belt

Youngest Basement Rock - 1,576±13 Myrs

Basalt on top = 750 to 830 Myrs

Bel

tS

uper

grou

p

Age:Between about

1,500 & 800 Myrs

Intrusiuons: ca. 1,200 MyrsMostly between

1,500 &1,200 Myrs ?

Interpretations

• Red Shale• Green Shale• Sandstone• Limestone• Stomatolites• Laminations• Mudcracks• Ripples• Salt Crystals• Western Source• Diabase Intrusions

• Quiet: Land/shallow ocean• Quiet: Deeper ocean• Beach/river• Shallow tropical ocean• Shallow tropical ocean• Quiet water / no animals• Arid land surface• Intertidal zone/beach• Salty Water• Land to the west• Hot spot / Divergent zone

Interpretations - Big Picture

1. Marine Embayment

2. Salty Lake

3. Inland Sea caused by Rifting

A-4

Continental Rift

ModernInland Seas

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Black Sea

Caspian Sea

Did the Belt Rifted Apart?

East(Montana)

West

BeltSupergroup

Where did it go?

Fault Bounded

The World about 800 Myrs

Montana(Belt)

New York

A-6

Rodinia“Motherland”

A-7

RodiniaRifts

(750 Myrs)

Montana

New York

Rifts to form the (pre-Pacific) PanthalassaOcean

Rifts to form the (pre-Atlantic) Iapetus Ocean

Rifting of Rodinia

As Rift Spread ApartSeiments Accumulate on the

Margin of North America

Windermere Supergroup(750-540 Myrs)

Extent of the Windermere

Rocks

A-4

(from Burchfiel, Cowan, and Davis, 1992)

Windermere-Aged(750-550 Myrs)

Rocks

A-5

(from Winston, 1971)

Windermere: Toby Formation

Tillite

Late Proterozoic Ice Age

Major“Ice Ages”

in Earth History

1

2

3

4

5A-8

Glacial Evidence forlate Proterozoic Ice Age

A-8

SnowballEarth?

Post-RiftingWest Coast Became a Passive Margin

750 to 200 Myrs Ago

B-5

NorthAmerica

Ocean

Continental ShelfSediments

Direction of Plate Motion

A-6

Belt Supergroup

WindermereSupergroup

Continental ShelfDeposits