The Mesozoic

Periods of the Mesozoic ► Triassic ► Jurassic ► Cretaceous

Breakup of Pangaea ► ► Stage one (Triassic)   Rifting and volcanism, normal faulting   Tensional stresses separate N. America from Gondwanaland   Similarly, Mexico from S. America   Sea floor generated during opening of ocean

Breakup of Pangaea ► Stage two (Triassic-Jurassic)  Rifting of narrow Oceans between S. Africa and Antarctica, Africa and India  Massive outpouring of basaltic lavas (7 million km2)

Breakup of Pangaea ► Stage three (Jurassic-Cretaceous)  Atlantic Ocean rift extended northward  Clockwise rotation of Eurasia  Closing of eastern Tethys Sea (Mediterranean)  S. America-Africa split apart  Australia-Antarctica remain intact  Eastern N. America and Greenland remain intact

Post Mesozoic Breakup ► Stage four  N. America and Eurasia split completely  Antarctica and Australia split

Mesozoic history of N. America ► Eastern and Southern areas  Triassic and Jurassic ► Normal fault bounded basin develop due to rifting (Nova Scotia to North Carolina)  Troughs filled with terrestrial sediments and volcanics  Newark Group (upper Triassic-lower Jurassic)  Palisades Sill of NJ and NY (190mya)

Triassic and Jurassic ► Development of Gulf of Mexico  Occupied areas opening south of Appalachian- Ouachita folded mountains  Filled with Upper Triassic-Lower Jurassic salts and evaporates (indicating previous arid condition); over 1000m deposited (origin of Gulf Coast salt domes)

Cretaceous ► Flooding of coastal lowlands due to high sea levels ► Atlantic and Gulf Coast plains inundated as they acted as subsiding shelves ► Thick delta, barrier island, shelf and reef deposits ► Florida: Shallow submarine bank for limestones ► Reefs made of Rudistid bivalves rimmed Gulf Coastal area ► Extensive chalk deposits due to massive production of calcerous plankton  Rifting and ocean opening on eastern side leads to closure and compression on western side

Western Areas ► Triassic  Accretionary tectonics- Characteristic of west coast subduction ► Steeply dipping subduction zone ► Volcanic Arcs and micro-continents carried to western margin ► Massive accretion by subduction (including volcanics) ► Tectonic collage of displaced terrain 70% of total western accretion

Cordilleran Region ► Western belt- Volcanics and siliceous deposits ► Eastern belt- stable interior sediments

Sonoma Orogeny (Permian- Triassic, Nevada) ► Island arc collided with western margin ► Then a west dipping subduction zone ► Added 300km new area to west ► Massive thrust faulting

Eastern Belt deposition ► Sandstones and limestones (shallow marine, 1000m in Idaho) ► Lower Triassic red bed facies farther east ► Upper Triassic sediments mostly from rivers (flowed west over area)  Upper Triassic- Jurassic Stratigraphy: Moenkopi fm, Shinarup Fm., Navajo Sandstone, Wingate Sandstone

Jurassic-Early Tertiary ► Nevadan Orogeny (eastward shift in orogenic effect)  Formation of Convergent mélange deposits  Franciscan belt of California (classic mélange)  Great volumes of granodiorite intruded: Sierra Nevada, Idaho, and coastal range batholiths

Sevier Orogeny (middle Jurassic- earliest Tertiary) ► Precedes batholith intrusion ► basement-involved tectonics: multiple imbricated thrust faults (low angle) ► Mainly seen in NV, UT and MT  Most famous thrust fault: Lewis Thrust (65km displacement)

Jurassic and Cretaceous Sedimentation  Navajo Sandstone (Lower Jurassic): Clean recycled eolian sands deposited in coastal dune and shoreline environments  Sundance Formation (Middle Jurassic) Famous for fossil reptiles deposits of the Sundance Sea  Morris Formation (Upper Jurassic) Swampy plain deposits formed as Sundance Sea retreated upon rising Cordilleran  Early Cretaceous Seaway: marine intrusion leaving deposits south from Arctic ocean to Gulf of Mexico

End of the Mesozoic ► K/T Boundary  Marks the border between the Cretaceous (K) and the Tertiary (beginning of current era-Cenozoic)