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Chapter 23Chapter 23Mesozoic Earth HistoryMesozoic Earth HistoryMostly Physical EventsMostly Physical Events
IntroductionIntroduction• The Mesozoic began 248 mya and
ended 65 mya– Three periods - Triassic, Jurassic,
Cretaceous– breakup of Pangaea was the major
geologic event– tectonism and sedimentation are used
to classify the Mesozoic in N. America– Note the overlap in three styles of
Cordilleran Orogeny
Tectonism and SedimentationTectonism and Sedimentation
Seaway drains
1. The Breakup of Pangaea1. The Breakup of Pangaea• The movement of continents during
and after the breakup affected global climate and oceanic regimes as well as that of individual continents– ocean basins were created or closed
before new mountain ranges were built– sea-level changes
Pangaea - Early TriassicPangaea - Early TriassicPole to pole andstraddled equatorPanthalassa OceanE. coast indent is “Tethys Sea”northern coast was the southern coastline of EurAsiaSouthern coast N coasts of Ind Arabia, AustraliaMany mountain ranges;topography controls climates & sedimentation
Panthalassa
PanthalassaTethys
Late Triassic – Rifting E Orogeny WLate Triassic – Rifting E Orogeny W
Rift
Orogeny
Better look at Tethys
We will consider mostly North America for this lecture
Pangaea – Early JurassicPangaea – Early Jurassic
E Jurassic – Atlantic Rift ShallowE Jurassic – Atlantic Rift Shallow
Note offshore Terranes
E Jurassic – Another LookE Jurassic – Another Look
Wrangellia
Orogeny
New Sea
Pangaea – JurassicPangaea – Jurassic
Late Jurassic – Early CretaceousLate Jurassic – Early Cretaceous
Atlantic Connected with TethysAfrica rotation closes Tethys
Atlantic
Tethys
Late K – Epeiric Sea until 70 myaLate K – Epeiric Sea until 70 mya
Mesozoic Global ClimatesMesozoic Global Climates• Carbonates (for example the stable isotope
index C)reveal large concentrations of carbon dioxide present in the Mesozoic atmosphere.
• This suggests a greenhouse climate.
• No glaciers, no coal, so CO2 abundant.
• Greenhouse gasses pass sunlight which hits the land and sea. Re-radiate heat (IR)
• Greenhouse gasses hold the heat, not lost to space as quickly. Warmer equilibrium.
Global Climates in the MesozoicGlobal Climates in the Mesozoic
Mesozoic climates were more equable than today, lacked the strong north-south climate zones.
Mesozoic plant fossils indicate subtropical conditions in high latitude locations
Seasonal differences were monsoonal
Cycads
Next: Mesozoic Tectonics NANext: Mesozoic Tectonics NA
• Cretaceous : global rise in sea level until 75 -70 mya, vast MOR
• Jurassic: –Atlantic opens E, –began building the Cordillera W,– Gulf of Mexico begins to form and
experiences evaporite deposition
• Late Triassic: Begin rifting in East
Late Triassic: Rifting opens the AtlanticLate Triassic: Rifting opens the Atlantic
• The Newark Supergroup documents the rifting of Pangaea to form the Atlantic
• Early Triassic saw coarse detrital sediments deposited from the erosion of Appalachian highlands– fault-block basins developed as N. America
separated from Africa and filled with nonmarine sediment plus dikes and sills
– eroded to a flat plain by the Cretaceous
Mesozoic rift basinsMesozoic rift basins
Kean University
Structure of the Newark basinStructure of the Newark basin
Note how faulting follows sedimentation
Lake cycles, East Berlin formationLake cycles, East Berlin formation
Alternating wet and dry climatedue 21000y Milankovitch cycle of tilt axis wobbleAlso 100,000 year cycles due to orbit eccentricity
E. Jurassic Gulf Coast EvaporitesE. Jurassic Gulf Coast Evaporites
200 mya is just outside our door
Restricted BasinLots of evaporation
Gulf Coastal RegionGulf Coastal Region• First, as continents separate, restricted basin, thick evaporites
formed in the Gulf• Normal marine deposition returned to the Gulf by Late Jurassic, with
transgressions and regressions – thousand of meters of sediments were deposited
Does this cross-section showa transgression or regression?
Gulf Coast continental marginGulf Coast continental margin
Rising Salt Domes
http://www-erl.mit.edu/~jfrank/pubBioPage/work/lu06_timeReversal.pdf
Discussion: Petroleum exploration around salt domes
Next: Western North AmericaNext: Western North AmericaTectonicsTectonics
• Building the western margin of North America and the Cordillera
Western RegionWestern Region• Cordilleran Orogeny
– Laramide - built the present day Rockies K-Tertiary
– Sevier – J-K thrust faulting to the east
– Nevadan - Jurassic batholith intrusion in the Sierra Nevada and elsewhere on the western edge
Displaced terranes – Western CordilleraDisplaced terranes – Western Cordillera
These terranes overlap in age but have different rock types, paleolatitudes and fossils. However, we can deduce when they accreted from this map.
Arrange the following terranes by oldest to youngest time of accretion onto the west coast: Alexander, Cache Creek, Chugach, Stikine, Taku, Tracy Arm, Wrangellia,
Details, but you don't need them to do this problem
Western Margin during OrogensWestern Margin during Orogens
Sonomia docking Late Pm –Early Triassic
North America drifting west due opening of Atlantic
Late Triassic on, eastwardsubduction of Farallon oceaniccrust continues Cordilleran Orogeny
Late J Early K Nevadan Batholiths
Westward subduction zones stopped when continentalcrust arrived.
Nevadan Orogeny east subduction Farallon
Remember the late Permian Sonoma?It continued into the Early Triassic
Sierra Nevada MountainsSierra Nevada MountainsNevadan Orogeny:Subduction formed batholith cores of
continental volcanic arc once as tall as Andes
Mesozoic orogenic eventsMesozoic orogenic events
Cretaceous Sevier Wrangellia docking?Later moved by transform fault?
Thin-skinned tectonics
K-T Laramide Continental OverideBouyant Subduction
Buoyant Subduction Laramide OrogenyBuoyant Subduction Laramide Orogeny
Normal, thin-skinned
Vertical block uplift
Approaching Continent pushesaccretionary wedge sediments
into forearc sediments
Now we understand weird looking Tetons
Sevier thin-skinned deformationSevier thin-skinned deformation
Using the layer colored sky blue, look at the faults.Is the hanging wall mostly up or down? What kind of faults are these?
Sevier thrust beltSevier thrust beltPrecambrian and/or Paleozoic Sediments
thrust over younger Mesozoic rocks
let’s look down here
Look in detail at western plate marginLook in detail at western plate margin
Franciscan Range, Great Valley Group, and Sierra Nevada Volcanics and Plutonics
This area has much simpler geology
Next: Mesozoic Sedimentation on the CratonNext: Mesozoic Sedimentation on the Craton
• Cretaceous– extensive marine
deposition, thin to the east
• Jurassic– clean cross-bedded
sandstones– marine sediments in
the Sundance Sea
• Triassic– shallow-water marine
clastics– red beds
Foreland Basin!
North America - TriassicNorth America - Triassic
Chinle
Newark
Marine deposition limited to western margin
Note Equator
Volcanic Arc sends frequent ashfalls eastward
Pollen similar
Late Triassic Chinle Fm.Late Triassic Chinle Fm.Mudstones and Sandstones of stream deposits, volcanic ash, with fossil trees (the Petrified Forest!)Texas, New Mexico, northern Arizona, Nevada, Utah, and western Colorado Pollen studies show that the Chinle is the same age as early Newark Supergroup
http://en.wikipedia.org/wiki/Petrified_Forest_National_Park
Triassic caliche paleosol- Nova Sc.Triassic caliche paleosol- Nova Sc.Source of carbonates for 13C measurements. Results suggest high CO2 in atmosphere
Similar in Newark Supergroup
North America - Jurassic periodNorth America - Jurassic period
Zuni Transgression
Dry region in the rain
shadow of the beginning Nevadans
SedimentationSedimentation
Seaway drains
Evaporites
Jurassic Eolian sandstoneJurassic Eolian sandstone
Navaho SS, S. Utah
Jurassic Morrison FormationJurassic Morrison Formation
Stream Deposits, huge sauropods Apatosaurus, also Stegosaurus, carnivore Allosaurus
http://rainbow.ldgo.columbia.edu/courses/v1001/morisson14.html
Paul Olsen's Dinosaur Course
Fossils of Jurassic dinosaursFossils of Jurassic dinosaurs
Morrison Formation sandstones, DNM, Vernal, Utah
Late Cretaceous really big epeiric seaLate Cretaceous really big epeiric sea
Land
Land
Dinosaurs on the North SlopeScroll down, open Alaska’s Jurassic Park
http://www.blm.gov/ak/ak930/cultrl.html
Western Interior Seaway Transgression
Western Interior Seaway Regression
Did the Sevier Orogenic Belt form before or after the Navaho SS, lower left?
Did the Sevier Orogenic Belt form before or after the Fox Hills SS, upper right?
Dakota SandstoneDakota Sandstone
Early Cretaceous shallow sea sediments gently folded by Sevier Orogeny.
Then, at 75-70 my, RegressionThen, at 75-70 my, Regression
Western Interior Seaway Transgression
Western Interior Seaway Regression
In Montana the sequence is similar. Above the marine Pierre Shale (ammonites) and Claggett Sandstone (nearshore and beach) is the Late Cretaceous Judith River Fm. containing dinosaur bones and conifers in stream deposits. Is this sequence a transgression or a regression?
75 mya Regression75 mya RegressionMesa Verde Sandstones over Mancos Shale: Mesa Verde Sandstones over Mancos Shale: Coarsening UpwardCoarsening Upward
K-T BoundaryK-T Boundary
End of Mesozoic Geology