the mesozoic - this old earth

The Mesozoic

Wednesday, November 30, 11

Periods of the Mesozoic

Triassic- First period of the Mesozoic eraJurassicCretaceous- Last period of the Mesozoic era


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- early 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 MesozoicK/T Boundary

Marks the border between the Cretaceous (K) and the Tertiary (beginning of current era-Cenozoic)


Composition of the KT Boundary

Tektites and shock quartz


Composition of the KT BoundaryIn 1980 a team of researches published an elemental analysis of the K/T boundary that showed high levels of the element iridium.

Since then these same results have been shown in multiple locations around the world


What Caused the K/T boundary?

All the evidence points to a meteorite impact. The problem is where is the crater

Meteor Crater Arizona


Locating the Crater


the mesozoic - this old earth

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