• Bounded at the base by the Permian extinction and at the top by another major extinction.

Terminal Triassic extinction included: 20% of all families, conodonts, placodont reptiles, many (bivalves, ammonoids, plesiosaurs, and icthyosaurs,

I. Paleogeography.

• Single large supercontinent through most of Period.
• Tethys (large equatorial embayment into Gondwanaland)
• Largely emergent, large arid regions, continental climate, widespread evaporites.

II. Regional Events.

• A. Atlantic Rift Basins.

• Development of long narrow depositional basins bounded by faults in the gentle Appalachian terrain (e. g. N.Y. to northern Virginia, central Conn.).
• Subsided through Early Jurassic with up to 6 km of sedimentation.
• Also found in Africa and S. America. with thick evaporites.
• These eastern U.S. rift basins associated with extension.
• Rift deposits= Newark Supergroup.
  
• B. Basaltic dikes and sills form in rift faults
• e.g. Palisades sill of Hudson Valley.
  
• C. Western N. America. Marine deposition mostly west of Colorado. Dominance of non-marine sedimentation.
• e.g. SW Utah.
• Navajo Ss., Desert Dunes, Jr, Zion
• Kayenta, Fluvial Deposits, Tr
• Wingate Ss., Desert Dunes, Tr
• Chinle River,Lake Deposits Tr
  
• D. Tectonics.
• Collision of Golconda arc (Sonoma Orogeny) in E. Triassic attaching a microcontinent ( SE Oregon, N. California, Nevada).
• mid Triassic western margin again rests along a subduction zone that ultimately extended from Alaska to Chile.

III. TRIASSIC OF THE WESTERN INTERIOR

• N. Dakota to Arizona (CO., WY.., Utah, N.D., S.D., N.M.)

• 1. Moenkopi Fm- (Early Triassic)
• red and chocolate brown mudstones (E. Tr.)
• local gypsum, halite, anhydrite in lagoons some lmst. in Arizona and Nevada.
• Low coastal plain, shallow lagoons, occasional minor transgressions from the west.
• Climate alternately warm and dry or warm and humid.
• Prominent in:
• Painted Desert Petrified Forest N. P. (east central Arizona)
• Grand Canyon N.P. (Northern Arizona)
• Zion N.P. (SW Utah)
• Canyonlands N.P. (SE Utah)
• Arches N.P. (SE Utah)
• *Rests unconformably upon Permian Kaibab Lmst.
  
• 2. Chinle Fm
• variegated colored mudstone and siltstone (L. Tr.)
• widely exposed on Colorado Plateau
• rich in fossil vertebrates contains Petrified Forest of Arizona with its fossil conifers, cycads and ferns.
• Further regression had left an immense alluvial plain in the Colorado Plateau area also with stream and swamp deposits.
• Increased volcanism to the west provided a source of silica for permineralization of fossil wood.
• Climate had become more humid.
• The basal member is the Shinarump Conglomerate (M. Triassic) Prominent in:
• Painted Desert Petrified Forest N. P. (east central Arizona)
• Zion N.P. (SW Utah)
• Canyonlands N.P. (SE Utah)
• Arches N.P. (SE Utah)
  
• 3. Wingate Fm
• White sandstones
• Canyonlands N.P. (SE Utah)
• Arches N.P. (SE Utah)
  
  B. Depositional environment

• broad, low, alluvial plain.
• Drained by slow rivers
• arid conditions evidenced by Moenkopi lagoons with salt, anhydrite, and gypsum formation.
  

IV. TRIASSIC-BIOLOGICAL EVENTS

• 1. Conifers and cycads dominant, flowering plants appear.
• 2. Ammonites recover from near extinction and become important guide fossils.
• 3. "Modern" corals (hexacorals) appear
• 4. First dinos appear. Many reptile types present. Amphibians continue to decrease in number, though some of the largest ones occurred during this period.
• 5. First true mammals appear in the upper Triassic. Small, shrew-like animals (insectivores).

I. Plate Tectonics and Paleogeography.

• Tethys (large equatorial embayment into Gondwanaland) propagated westward separating Gondwana and Laurasia landmasses.
• Gulf of Mexico began forming
• Gondwana continents remained attached to one another '
• America began breaking away from Africa in mid-Jurassic.

II. Regional Events.

A. Nevadan Orogeny.

• called Nevadan because it gave rise to the structure of the Sierra Nevada Mts. (uplifted in Pliocene-Pleistocene)
• great phase of batholith emplacement
• Klamath (N. California) to Baha (1000 miles)
• Coastal Range of British Columbia
• 1250 miles long by 35- 125 miles wide.
• not formed in a single phase but the main phase was during the Late Jurassic (10-15 m.y. duration) and spread eastward.
• many ore deposits formed associated with batholith emplacement
• Mother-Lode system of the Sierra Nevada-120 mi long
• Lead-zinc, mercury, copper and gold in British Columbia
• Franciscan Fm of California formed (Coastal Range) as a trench
• accretionary wedge (graywacke, black shale, sandstone, conglomerate, chert, pillow basalts).
• Great Valley Group
• shelf-slope fore-arc setting
• deep marine facies.
  
  B. Middle to Late Jurassic transgression

• vast Sundance Sea formed in western interior which later retreated as a consequence of clastic influx from rising highland to west.
  

III. JURASSIC OF THE WESTERN INTERIOR

Large exposures of the Jurassic occur in the western interior.
In contrast, none is exposed in the eastern U.S., except for upper Newark and Michigan basins with continental clastics.

A. Non-marine deposits

• 1. Massive sands [e.g. Navajo Sandstone, Zion N.P. (SW Utah)] recycled from continental interior and the Canadian Shield.
  
• 2. Large early Jurassic coastal desert
• dune deposits seen in:
• Zion Canyon, Utah
• Canyon de Chey
• Glen Canyon, Utah (Glen Canyon Group).
• In western Utah sands 2500' thick.

B. Marine Sedimentation

• Dominance of the Late Jurassic interior seaway called the Sundance Sea which extended from the Arctic to almost the Gulf of Mexico. Named after the Sundance Fm of the Black Hills, S. Dakota.
  
• Uncompahgre and Front Range uplifts now only low islands w/evaporite lagoons.
  
• Sundance Sea became restricted northward near the end of the period filling with clay, silt, and sandstone.
  
• Morrison Fm- mostly mudstone and siltstone (gray, green, red, maroon)
• Graveyard of Dinosaurs.
• Formed in region of Sundance Sea following its regression.
• Dinosaur National Monument (Vernal, Utah).
• Arches National Park (southeast Utah)

IV. JURASSIC-BIOLOGICAL EVENTS

• 1. Cycads are the dominant plants and conifers also common. Flowering plants still rare.
• 2. Ammonites very common.
• 3. Dinosaurs at peak abundance with hundreds of species. The largest dinos occurred near the end of the period.
• 4. Other major reptile groups include: ichthyosaurs and plesiosaurs in the sea, flying pterosaurs, turtles, crocodiles.
• 5. Several types of primitive mammals present but not common.