Last TimeLast Time• We ended our discussion of the Paleozoic with

the greatest recorded mass extinction to affect Earth. This occurred at the end of the Permian– about 90% of all marine invertebrate species extinct– Rugose and tabulate corals, many bryozoan and brachiopod

orders, and trilobites did not survive the end of the Permian– causes for this have been speculated to be:

• reduction in marine shelf as Pangaea formed• global drop in sea level due to glaciation• reduction in marine shelf due to regression

• climatic changes HOWEVERHOWEVER

Stable Isotope ratios for Carbon Stable Isotope ratios for Carbon 13C13C• There are two stable isotopes of carbon that are

routinely measured in fossils.• The standard carbon isotope ratios in calcite are

from belemnites in the Pee Dee Formation (abbreviated as PDB “Pee Dee Belemnite”).

• The process of photosynthesis favors the lighter form of carbon in plant tissue. AT THE BOUNDARY:

• “… it appears that a significant portion of the land plants burned; this would have released a great deal of light carbon into the atmosphere”

• http://www.acad.carleton.edu/curricular/GEOL/DaveSTELLA/Carbon/c_isotope_models.htm

Mesozoic GeologyMesozoic Geology

65.7 mya another mass extinctionCretaceous 144 – about 65 myaJurassic 208-144 myaTriassic 248-208 myaAbout 248 to 245 myaDepends on method

Pangaea

IntroductionIntroduction• The Mesozoic began 248 mya and

ended about 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 TriassicPole to pole andstraddled equatorPanthalassa OceanE. coast indent is “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

Tethys

Equator to Polecurrentgyres

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

North Atlantic opens, India and Antarctica-Australia leave Gondwana

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 myaMid-Atlantic Ridge huge and fast

NOTE the Farallon and Pacific plates

Mesozoic Global Climates• Carbonates (via the stable isotope index Carbonates (via the stable isotope index

C)C)reveal large concentrations of carbon reveal large concentrations of carbon dioxide present in the Mesozoic atmosphere. dioxide present in the Mesozoic atmosphere.

• This suggests a greenhouse climate. This suggests a greenhouse climate.

• No glaciers so CONo glaciers so CO22 abundant. abundant.

• There is some coal due interior seas and There is some coal due interior seas and transgressions and regressions)transgressions and regressions)

• Greenhouse gasses pass sunlight which hits the Greenhouse gasses pass sunlight which hits the land and sea. Re-radiate heat (IR)land and sea. Re-radiate heat (IR)

• Greenhouse gasses hold the heat, not lost to Greenhouse gasses hold the heat, not lost to

space as quicklyspace as quickly. . Warmer equilibriumWarmer equilibrium..

Conifers, Cycads

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 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 non-marine sediment plus lava flows, dikes and sills

– East side eroded to a flat plane by

Cretaceous

Mesozoic rift basinsMesozoic rift basins

Kean University

Structure of the Newark basinStructure of the Newark basin

Note how faulting offsets sedimentation

Recall radial cracks due swelling and uplift. We live on the western side. Note dominant block orientation. Other side is in Morocco; most face toward the West

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

Wet cycle Lake

Dry

LateritesMonsoonal

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 over the salt

Does this cross-section showa transgression or regression?

Remember: “The facies follow the shoreline shifts”

Gulf Coast continental marginGulf Coast continental margin

Rising Salt Domes tilt sedimentsConcentrate petroleum

Next: Western North America TectonicsNext: Western North America Tectonics• 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 their order, and the metamorphic ages of their suture zones

Western RegionWestern Region• Cordilleran Orogeny

– YOUNGEST – Laramide – Vertical blocks-built the

present day Rockies late K-Tertiary– Sevier – J thrust faulting to the east– Nevadan – mid J to mid K batholith

intrusion in the Sierra Nevada and elsewhere on the western edge

– OLDEST

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

Mid J to mid K Nevadan Batholiths

Westward subduction zones stopped when continentalcrust arrived.

Nevadan Orogeny east subduction Farallon

Sonoma began late Permian.It continued into the Early Triassic

Barbs show dip of fault

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 (due Wrangellia docking?)Later moved by transform fault?

Thin-skinned tectonics

K-T Laramide Continental OverideBouyant Subduction

Sevier thin-skinned deformationSevier thin-skinned deformation

Competent (resistant to flow)

Sevier thrust beltSevier thrust beltPrecambrian and/or Paleozoic Sediments

thrust over younger Mesozoic rocks

Buoyant Subduction Laramide OrogenyBuoyant Subduction Laramide Orogeny

Normal, thin-skinned

Vertical block uplift

Approaching Continent pushesaccretionary wedge sediments

into forearc sediments

Subduction Zone overrun by fast drifting continental plate

Now 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 (dunes)– 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

Same Caliche found when our new gym was built

Same Laterites found in our stream

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 Camarasaurus, 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 SlopeAlaska’s Jurassic Park

Alaska dinosaurs

Western Interior Seaway Transgression

Western Interior Seaway Regression

Did the Sevier Orogenic Belt form before or after the Navaho SS, purple, lowest left?

Did the Sevier Orogenic Belt form before or after the Fox Hills SS, red uppermost right?

Dakota SS

Navaho S

S

Fox Hills SS

Morrison Fm.

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

Dust cloudPlants need lightHerbivores eat plantsCarnivores eat herbivoresSurvivors can sleep through it.

Uh, oh. That can’ t be good.

End of Mesozoic Geology