THE EARLY MESOZOIC
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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 along
the east coast from Nova
Scotia to S. Carolina
•Triassic Redbeds and
Basalts
•The Newark Supergroup
•Fluvial & Lacustrine
Red
beds
•Sills and Dikes
• Vertebrate Footprints
PALISADES SILL
Three-toed Dinosaur Footprint- Newark Supergroup
GULF of MEXICO- Evaporite sequences of the Jurassic deposited
in the initial rift sequence
The salt domes can be as high as 20km and have 2km diameters
Salt rises due to low density
These 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 Orogeny
Early Jurassic Nevadan Orogeny
Suturing of Exotic terranes to western US
Deformed Bedded Cherts of the Franciscan Fm., CA
Orogenic events created igneous
plutonic intrusions, batholiths,
like the Sierra Nevada Batholith
and 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 level
during the Triassic
Zuni 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 the
Triassic
Radiation of the Ammonoids
Best Index Fossils for the Jurassic
Diversification of Reptiles
Marine Reptiles
Ichthyosaurs
Flying Reptiles
Pterosaurs
The Dinosaurs
Pelvic Bone Arrangement
Saurischian
Ornithischian
Saurischian
Ornithischian
The Dinosaurs: Middle Triassic
Differences 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 oldest
Dinosaurs from the Triassic
Plateosaurus: Late Triassic
Sauropod ancestor
Coelophysis: Theropod, carnivorous
The Sauropods: Largest of the
Dinosaur
Dinosaurs
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 Dinosaur
from the Solnhofen Fm. Of Germany
Birds arose from coelosaurs in the Jurassic.
Early birds differed from dinosaurs in feathers and a wishbone
Teeth were lost in all birds before the end of the Cretaceous and the tail
was shortened
The 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 England
Close-up of chalk with flint (chert) nodules
Higher CO2 from rifting higher productivity of
phytoplankton
(coccolithosphorids), chalk deposits and higher O2
Cretaceous
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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
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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 present
in the Cretaceous across the western US
Melange
Fold/Thrust Belt
Sevier type deformation consisting of thrust faults
Highest stand of sea-level
280m above current
Atlantic coastal plain
subsiding
Florida was a shallow
submarine carbonate bank
Black shales: carbonaceous
matter from unoxidized
phytoplankton due to lack
of polar cold water
circulation
Diagrams indicating how rapid sea-floor spreading can
cause displacement of water onto continents
Fall Line
Area of outcrop of Cretaceous limestone and marl in the Atlantic
and Gulf Coast Coastal Plain
Cretaceous Climates
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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
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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
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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
Occurences of Iridium-rich sediments at
the K/T
Shocked Quartz
Tertiary
Cretaceous
Iridiumrich clay
layer
Gubbio,
Italy
Location of Chicxulub structure
Meteor Crater, AZ
30m bolide
Excavated 1.2km crater
Phobos, a Martian moon about 20km diameter
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 my
3 periods each lasting
50,000-100,000 yrs
Millions of cubic kilometers
of magma