THE EARLY MESOZOIC

• Middle Life

• Intermediate Evolutionary Forms

• “The Age of Reptiles”

• Dinosaurs ruled the Earth

• Evolution of Birds, Mammals and Flowering Plants

• 182 million years

The Early Mesozoic• Triassic- Tri or Three

– Friedrich August von Alberti– Unit between Zechstein and Lias Limestones of Germany– Red non-marine sandstones-Marine Muschelkalk-Red non-marine marls

and clay

• Jurassic– Highly fossiliferous, ammonites– Alexandre von Humboldt> Jura-kalk-stein, 1799– Jura Mountains: France & Switzerland

• 85 my

PANGEA

Paleogeography

• Continental fragmentation> Rifting

• Break-up occurred in Late Triassic

• Northern hemisphere rifted from southern and then east rifted from west producing many blocks

• In the Jurassic, Gulf of Mexico continued to open

•East Coast of the US•Rifting >Atlantic Ocean•Fault-block basins alongthe east coast from NovaScotia to S. Carolina•Triassic Redbeds and Basalts•The Newark Supergroup

•Fluvial & Lacustrine Redbeds•Sills and Dikes• Vertebrate Footprints

PALISADES SILL

Three-toed Dinosaur Footprint- Newark Supergroup

GULF of MEXICO- Evaporite sequences of the Jurassic depositedin the initial rift sequenceThe salt domes can be as high as 20km and have 2km diametersSalt rises due to low densityThese diapirs are good oil traps in Texas and Louisiana

Tectonic History

• Cordilleran Orogenic Belt– Western North America-South America– 300-1000km wide– Terrane accretion

• Wrangelia Traveled 5000KM

– Jurassic to today

Middle Triassic Sonoman OrogenyEarly Jurassic Nevadan OrogenySuturing of Exotic terranes to western US

Deformed Bedded Cherts of the Franciscan Fm., CA

Orogenic events created igneousplutonic intrusions, batholiths,like the Sierra Nevada Batholithand the Idaho Batholith

Sierra Nevada Batholith

Yosemite

NEOPROTEROZOIC TO CENOZOIC TRANSGRESSIONS AND REGRESSIONS OBSERVED

ON THE CRATON

Variable sea level represented sequences of sediments bounded by unconformities on all of the cratons -

Regression, very low sea levelduring the TriassicZuni Transgression in Jurassic through Cretaceous, very high sea level

Early Jurassic of the Western US

Chinle Fm. Petrified Forest

Petrified National Forest

Eolian Cross Bedding in the Early Jurassic Navajo Sandstone

Economic Minerals: Carnotite, Uranium Ore

Regular Echinoid Cidaris Irregular Echinoid Hemiaster

Rapid Radiation of Mesozoic Sea Urchins

Ceratitic Ammonoid from theTriassic

Radiation of the AmmonoidsBest Index Fossils for the Jurassic

Diversification of ReptilesMarine Reptiles

IchthyosaursFlying Reptiles

PterosaursThe Dinosaurs Pelvic Bone Arrangement

SaurischianOrnithischian

Saurischian

Ornithischian

The Dinosaurs: Middle TriassicDifferences Based on Pelvic Bone Arrangement:

Late Triassic Evolution

• Saurischian– Lizard Hipped, earliest group– Similar to thecodonts– Theropods (carnivorous dinosaurs); Prosauropods

(herbivores); Sauropods (large herbivores)

• Ornithischian– Bird Hipped, differentiated– Herbivorous dinosaurs evolved from Prosauropods

Carnivorous vs. Herbivorous

• Carnivores– large head compared to body– Tyrannosaurus velocity 60km/hr

• Herbivores– small head compared to body– Apatosaurus velocity 10-12km/hr

Herrerasaurus: one of the oldestDinosaurs from the Triassic

Coelophysis: Theropod, carnivorousDinosaur

Plateosaurus: Late TriassicSauropod ancestor

The Sauropods: Largest of theDinosaurs

The Dinosaurs• Approximately 700 species in 300 genera

• Warm Blooded– Rapid metabolism; prey-predator ratio; many blood vessels pores in the bones

• Reproduction and Habits– Nesting behavior and social behavior (herds)

• Characteristics– Eoraptor earliest thecodont; sauropods long necks and large body

quadrupeds; Ornithopods are bi-pedal herbivores (Camptosaurus); Stegosaurs and Ceratopians are quadruped herbivores

• Extinction>Late Jurassic-Early Cretaceous/End K

Mammals

• Mammal-like reptiles therapsids (cynodonts)

• Early Triassic small cynodont gave raise to medium size carnivores and herbivores that are ancestral to mammals

• Late Triassic a small cynodont gave rise to the earliest mammal the morganucodontids

• Most Triassic and Jurassic mammals were insectivores and very small

Archaeopteryx: Jurassic Bird or Feathered Dinosaurfrom the Solnhofen Fm. Of GermanyBirds arose from coelosaurs in the Jurassic.Early birds differed from dinosaurs in feathers and a wishboneTeeth were lost in all birds before the end of the Cretaceous and the tail was shortenedThe pelvic structure was first similar to other theropods (saurischians)but later through parallel evolution shifted to an ornithischian form

Climates• Warming trend which reached a maximum in the Late

Jurassic and Cretaceous

• Variable and cooler temperatures since Late Cretaceous

• Abundant redbeds, evaporites and carbonates

• Warmer mid latitude and high latitude rainfall as evidenced by coal deposits for a mild polar condition

• Oxygen levels were low during Triassic (15%) and rose to 25% then lowering to 21% by the Late Jurassic

The Cretaceous

Terrain Cretace, France

Creta: Chalk (Latin)

J.J. d’Omalius d’Halloy (1822)/ Conybeare & Phillips (1822)

144 my to 66.4 my

Chalk: White Cliff along the Dorset Coast of Southern EnglandClose-up of chalk with flint (chert) nodules

Higher CO2 from rifting higher productivity of phytoplankton(coccolithosphorids), chalk deposits and higher O2

Cretaceous• 70 my• Sea level higher>> epeiric seas• Divergence of planktic organisms• Large coal and oil deposits• Atlantic continued to open• Tethys closed• India migrated northward• 3rd largest mass extinction K/T

Paleogeography

• Tectonic events

– Rifting between Africa-S. America; • India-Antarctica/Australia; • Britain-New Foundland; • Madagascar-Africa

– Collisions Sevier and Laramide orogeny in western US

Cordilleran Orogenic System• Terrane accretion• Subduction• Intense deformation• Fold-thrust belts• Plutonism & Volcanism• Sevier Orogeny

– 130-80 my

• Laramide Orogeny– 80-50 my

Cross-section indicating major tectonic features presentin the Cretaceous across the western US

Melange Fold/Thrust Belt

Sevier type deformation consisting of thrust faults

Highest stand of sea-level280m above currentAtlantic coastal plainsubsidingFlorida was a shallowsubmarine carbonate bank

Black shales: carbonaceousmatter from unoxidizedphytoplankton due to lackof polar cold water circulation

Diagrams indicating how rapid sea-floor spreading cancause displacement of water onto continents

Area of outcrop of Cretaceous limestone and marl in the Atlanticand Gulf Coast Coastal Plain

Fall Line

Cretaceous Climates

• Warm tropical climates

• Shallow seas, carbonates

• Coal, bauxite evidence of humid conditions

• Tropical and subtropical climates extended from 45oN to 70oS

• Polar regions mild

• Widespread reefs (Rudists and Corals)

• Oxygen levels 30% to 35%

Warm Climates

• Decrease reflection of sunlight by high stands of sea levels– water absorbs more heat

• Paleogeographic changes- – changes in currents due to plate tectonics,

circumequatorial current

• Increase CO2 in the atmosphere released by mantle plumes, greenhouse effect

Economic Deposits

• Oil, Gas and Coal

• Oil– Phytoplankton-biologic material-source beds– Heat-converts to hydrocarbons– Permeable beds- reservoir– Geologic traps-impermeable beds

Cretaceous Life

• Marine Communities– Pelagic diversification of planktic coccoliths,

forams, diatoms and dinoflagellates; – Nektics ray-fin fishes (Teleost), ammonoids,

plesiosaurs, ichthyosaurs, mosasaurs– Benthic forams, major expansion of filter and

deposit feeders

• Terrestrial Communities– Appearance of angiosperms– Coevolution of pollinating insects

Extinctions

• K/T Boundary

• Dinosaurs, pterosaurs, many marsupial mammals became extinct

• Extinction for terrestrial organisms only 15%

• Marine extinctions at the generic level 70%

• All ammonites, rudists, marine reptiles

Causes of Extinction at the K/T Boundary

• Sea Level changes

• Temperature changes

• Increased seasonality

• Changes in plant distribution and extinction

• Increased competition with mammals

• Bolide collision

Impact Theory• Iridium Anomaly

– clay around K/T enriched in Ir

• Spherules– glass beads, felsic, melting of crustal rocks

• Soot– carbonaceous particles, wildfires

• Shocked Quartz– lamelle > high pressure shock wave

• Stishovite– high pressure form of quartz

Shocked Quartz

Iridium-rich clay layerGubbio, ItalyCretaceous

Tertiary

Occurences of Iridium-rich sediments at the K/T

Meteor Crater, AZ30m bolideExcavated 1.2km crater

Phobos, a Martian moon about 20km diameter

Location of Chicxulub structure

Volcanic Model

• Iridium as aerosol from volcanism

• Large eruption of flood basalts– Deccan Plateau– Periodicity of 30 my of basalts coincide with

extinction peaks

• Sulfates >> acid rain > pH

• Cooling due to erupted ash

Erupted at 66 my3 periods each lasting50,000-100,000 yrsMillions of cubic kilometersof magma