Mesozoic GeologyMesozoic Geology

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 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

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: mid-JurassicPangaea: mid-Jurassic

Latest Jurassic – Early CretaceousLatest 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 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

Mesozoic rift basinsMesozoic rift basins

Kean University

Structure of the Newark basinStructure of the Newark basin

Note how faulting offsets 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 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

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 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

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

Giant sauropod and Allosaurus bones,Mossison Fm., 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.

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?

PierreShale

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