mesozoic geology. introduction the mesozoic began 248 mya and ended 65 mya –three periods -...
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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
1. The Breakup of Pangaea1. The Breakup of Pangaea• The movement of continents
during and after the breakup affected global climates
• Sea-level changes due MOR heating and growth, then cooling
Pangaea - Early TriassicPangaea - Early TriassicPangaea ran from pole to pole andstraddled the equator.The Panthalassa Ocean allowed equatorial waters to warm polar lands.
The East coast indent is called the “Tethys Sea”
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
Latest Jurassic – Early CretaceousLatest Jurassic – Early Cretaceous
Atlantic Connected with TethysAfrica rotation closes Tethys
Mesozoic Global Climates
• Carbonates (for example the stable Carbonates (for example the stable isotope ratio isotope ratio C)C)reveal large reveal large concentrations of carbon dioxide concentrations of carbon dioxide present in the Mesozoic atmosphere. present in the Mesozoic atmosphere.
• This suggests a greenhouse climate. This suggests a greenhouse climate.
• No glaciers, no coal, so CONo glaciers, no coal, so CO22 abundant. abundant.
• Greenhouse gasses pass sunlight which Greenhouse gasses pass sunlight which hits the land and sea. Re-radiate heat hits the land and sea. Re-radiate heat (IR)(IR)
• Greenhouse gasses hold the heat, not Greenhouse gasses hold the heat, not
lost to space as quicklylost to space as quickly. . Warmer Warmer
equilibriumequilibrium..
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 : Cretaceous : global rise in sea level global rise in sea level until 75 -70 mya, vast MORuntil 75 -70 mya, vast MOR
• Jurassic: Jurassic: –Atlantic opens E, Atlantic opens E, –began building the Cordillera W,began building the Cordillera W,– Gulf of Mexico begins to form and Gulf of Mexico begins to form and
experiences evaporite depositionexperiences evaporite deposition
• Late Triassic: Begin rifting in EastLate Triassic: Begin rifting in EastStart hereStart here
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
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 Basin
Lots 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 tilt sedimentsConcentrate petroleum
Discussion: Petroleum exploration around salt domesSquint: The Petroleum is in the bright spots, at the boundary of the salt and pushed up sediment. Tells us where to look, saves money, lowers cost of fuel.
Next: Western North AmericaNext: Western North AmericaTectonicsTectonics
• Building the western margin of North America and the Cordillera
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.
Exercise: Arrange the following terranes by oldest to youngest time of accretion onto the west coast: Alexander, Cache Creek, Chugach, Eastern, Stikine, Taku, Tracy Arm, Wrangellia, Yukon-Takana
Western RegionWestern Region• Cordilleran Orogeny
– Laramide – Vertical blocks-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
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
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 until 70mya, thins 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
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 SlopeUntil 70 mya
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 SS is bottom right
Navaho S
S
Fox Hills SS
Dakota SandstoneDakota Sandstone
Early Cretaceous shallow sea sediments gently folded by Sevier Orogeny.
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?
PierreShale
75 mya Regression75 mya RegressionMesa Verde Sandstones over Mancos Shale: Mesa Verde Sandstones over Mancos Shale: Coarsening UpwardCoarsening Upward