Phanerozoic Eon: 542 - 0 Ma

Mesozoic Era: 252 - 65 Ma

Period	Range (Ma)
Cretaceous	145.5 - 65.5
Jurassic	199.6 - 145.5
Triassic	252.3 - 201.5

(Triassic boundary dates new as of 2010: previous calculations were 251.0 and 199.6 Ma).

Paleogeography and Geology of the Triassic:
The Sonoman Orogeny is still underway (collision of Sonomia and western North America).

Abundant redbeds in many parts of the world.(New Red Sandstone in Britain; Karoo Supergroup (actually a Permo-Jurassic unit) in southern Africa; Moenkopi through Chinle Formation in southwestern U.S., etc.). Once thought to indicate worldwide dry conditions, but now seen as product of a couple of other factors:

• Megamonsoons: configuration of Tethys centered on the equator allowed for much stronger seasonality of dry and rain moving onto and away from land.
• The "Coal Gap": nearly no coal or other organic rich terrestrial beds in Lower and Middle Triassic deposits. May be due to loss of major coal-forming organisms, but paleosol mineralogy suggests low oxygen levels. If charcoalification is a necessary precursor for coal formation, perhaps low oxygen level inhibited charcoalification and hence no coal.

Collision of North and South China blocks with Siberian coast completes Pangaea.

Appalachians and other mid-Pangaean mountains worn down until low ridge.

During latest Triassic: rifting in mid-Pangaea (between North America + Europe and Africa).

• Produces large-scale volcanism: the Central Atlantic Magmatic Province (or CAMP)
• Fault basins up and down rift: the Newark Supergroup of eastern North America
• Birth of the Atlantic Ocean
• Likely the trigger for the Triassic-Jurassic Extinction Event

Paleogeography and Geology of the Jurassic:
Continued rifting and volcanism along Central Atlantic margin (including the Palisades of New York, New Jersey, and southern New England); the Newark Supergroup development continues. Extensive evaporite deposits.

Continued evidence of arid conditions in many parts of the world during the Early Jurassic (Glen Canyon Group of American Southwest, etc.).

During Middle Jurassic, major global transgressions and return to calcite sea conditions. Europe flooded, development of European Archipelago.

As Atlantic grows:

• Pangaea splits into Gondwana and Laurasia (Laurentia + Baltica + Siberia + Kazakhstania + North China + South China)
• In latest Jurassic: beginning of rifting of Africa from South America (beginnings of South Atlantic) and from Indomadagascar (beginnings of Indian Ocean)
• By latest Jurassic, wide enough separation to allow beginnings of trans-equatorial circulation
• Beginning of the Coastal Plain sedimentation along eastern North America and Gulf Coast

In Middle-Late Jurassic, development of ongoing "Andean"-style subduction along Pacific coastline of North America. Foreland periodically flooded and emergent.

During Late Jurassic, Nevadan Orogeny:

• A large accretionary wedge, the Franciscan Ophiolite & Mélange, is thrust up onto western North America
• Fold and thrust belt pushes up the plutons of the ancestral Sierra Nevada
• Molasse from this event forms huge clastic wedge from Montana to Arizona and as far east as South Dakota and Oklahoma: the Morrison Formation

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Last modified: 14 January 2011