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Mesozoic Earth History

The Mesozoic Era 251-66 MYA

Breakup of PangeaChanges in air and oceanic currentsEvolution of new terrestrial and marine lifeOpening of the Atlantic Ocean BasinRocky MountainsSalt depositsBatholiths with ore deposits

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Breakup of Pangea

Rifting between Laurasia and Gondwanda – TriassicRifting of North America from South America – Late Triassic –JurassicAustralia/Antarctica separate from South America/Africa – Late Triassic-JurassicIndia separates from Gondwana –Late Triassic-Jurassic

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Breakup of Pangea - continued

South America separates from Africa – Jurassic - CretaceousAustralia and Antarctica split –CretaceousIndia travels to Equator -CretaceousGreenland becomes independent landmass – Cretaceous - Cenozoic

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Evaporite Deposits form in early Mesozoic

Narrow basins

Near Equator

High heat flow

Oceans and Seaways

Tethys Ocean begins to close in Jurassic – continues through CretaceousAtlantic Ocean opens - Cretaceous

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Effects of Pangea Breakup on Global Climate Patterns

Pangea was mostly aridLarge continental land massSurrounded by mountain rangesEvidence = evaporites, sand dunes and red beds

Some humid regions in Triassic;Evidence= coal deposits

High latitudes like Scottish peat bogsSome humid regions around Tethys seaway as it opened (warm, monsoons)

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Permian – Guadalupe Mountains

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Permian Guadalupe Mtns

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Triassic Marginal Marine

Coal

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Effects of Pangea Breakup on Global Climate Patterns and Ocean Circulation

Temperature gradientDifference in temperature between poles and tropicsAffects speed of atmospheric and oceanic circulation (steeper gradient, faster circulation)Oceans absorb 90% sun’s heat; continents only 50% or lessOcean dominated = warmer

Effects of Pangea Breakup on Global Climate Patterns and Ocean Circulation

Steeper thermal gradient as continents moved northwardOceans and atmosphere accelerated circulationSeasonality increases on landWarm water from Tethys circulation kept climate equable worldwide through CretaceousIn general, circulation patterns more complex as Mesozoic progressed.

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Mesozoic History of North America

Early Triassic – Same as Permian – connected to Pangea

East Appalacian Mountain BeltWest Cordilleran mobile beltSuturing of volcanic island arc –Sonoma orogeny

Late Triassic – JurassicN. America begins to separate from AfricaFault block and igneous activity in AppalaciansN. America separates from South AmericaGulf of Mexico fills with evaporitesMajor Mountain building resulting in Sierra Nevada and Rocky Mountains – Cordilleran orogeny

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Mesozoic History of North America

Cretaceous rise of sea levelMarine deposition over most of N. American CordilleranAbsaroka Sequence; Zuni Sequence

Regional Mesozoic History – Eastern North America

Early Triassic – Uplifted Appalacians erode to low hillsLate Triassic – uplift and fault block basins from rifting (breakup of Pangea)

Deposition in non-marine basins of Newark Group –many dinosaur footprintsIgneous activity – lava flows and intrusions

Palasades sill

Jurassic and Early Cretaceous – ErosionCretaceous –Re-elevation of Appalacians; creation of Atlantic Coastal plain sediments

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Association of Rifting with Normal Faults

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Palasades Sill

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Regional Mesozoic History – Gulf Coastal Region

Late Triassic-Early Jurassic Gulf began as N. America separated from S. America

Shallow, restricted basinFilled with evaporitesLater associated with petroleum accumulation

Late Jurassic – normal marineTransgression and regressionDeep sedimentary pile

Cretaceous seaway to Arctic OceanExtensive reefs composed of bivalve, rudists – became reservoirs for oil

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Regional Mesozoic History – Western Region

Permian-TriassicWestern island arc formedSubduction of oceanic plate beneath island arcThrusting of Island arc eastward against craton = Sonoma OrogenySuturing of island arc terrane to western edge of N. America

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Regional Mesozoic History – Western Region

Late TriassicSubduction Zone to the west where N. America overrides Farallon Plate

Middle to Late JurassicTwo subduction zones dipping in opposite directionsN. America overrides Farallon Plate eliminating the westward subductionzone

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Regional Mesozoic History – Western Region

Late Jurassic – CenozoicFranciscan Complex

Chaotic mixture of rock typesRepresent continental shelf, slope, deep-sea environment rocks all brought together in a trench, partly subducted, then squeezed against N. America

Great Valley GroupSedimentary rocks of the Continental shelf, slope collecting at same time as FranciscanNow in thrust fault relationship with Franciscan

Franciscan Formation/Group

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Great Valley Group

Thin turbidites of Great Valley Group

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Regional Mesozoic History – Western Region

Orogenies of the Western RegionNevadan

Granitic masses beneath N. America became the batholiths of the Sierra Nevada, Southern California, Idaho, and Coast RangeContemporaneous with Franciscan/Great ValleyChange from high angle to low angle subduction moved plutonism and volcanism to the east

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Orogenies of the Western Region

Sevier OrogenyNumerous overlapping thrust faultsMoved blocks of older strata over youngerMountains of Montana to Western Canada

Laramide OrogenyDeveloped east of the SevierRocky Mountains – mostly Cenozoic

Mesozoic Sedimentation

Triassic of the western continental shelf

Shallow marine sandstone, shale and limestoneRegression to erosion and red beds

Moenkopi Formation –tracks and fossil amphibians and reptilesShinarump conglomerateChinle Formation – petrified forest and fossil amphibians, phytosaurs, small dinosaurs

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Mesozoic Sedimentation

JurassicCross-bedded sandstones from dunesWingate SandstoneNavajo Sandstone – prominentSundance Sea produced Sundance FormationMountain building shed sediments eastward and Sundance Sea northwardMorrison Formation - Dinosaurs

Mesozoic Sedimentation

CretaceousEarly to mid-Cretaceous transgression led to mid continental seawayBlack ShalesSevier orogenic belt fed sediments to interiorAs regression took place coal bodies formed

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Accretion of Terranes

TerranesSmall accreted lithospheric blocks that are clearly of foreign originDiffer from surrounding blocks and cratons

Fossil contentStructural trendsStratigraphyPaleomagnetic properties

Almost certainly of foreign origin carried for many miles as continental or other plate fragments

Terranes

Composed of Volcanic island arcsOceanic ridge fragments (ophiolites)SeamountsHot spot tracksFragments of continents

ExamplesWrangellia terranes (continent)Klamath Mountains (island arc)

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Mesozoic Mineral Resources

Coal – Rocky Mtns.Petroleum of Persian Gulf and Gulf of MexicoUranium of Mid Continent N. AmericaDiamonds of S. AfricaGold of the Mother LodeCopper of N. and S. America