The Mesozoic
• Breakup of Pangea
– Rifting
• Western Mountain Building
• High S/L in Cretaceous
• Marine Revolution
• Dinosaurs
• K/T boundary event
Breakup of Pangea
• Why did Pangea break apart?
• Triassic Rifting and rift basins
• What does the breakup do?
– Mesozoic Tectonics
• West Coast - passive to active margin
The Triassic World
• East Coast = rift basin
• West Coast = island arcs
• Colder, dry climate
• Low global sea level
• Fluvial deposits and evaporites
– Red beds
The Jurassic World
• Early Jurassic - the Navajo Desert
• Late Jurassic - the Sundance Sea
– Carbonates and evaporites
Western Mountain Building
• The Cordilleran
– Very complex history
• Very wide mountain belt formed from multiple events
• Problems:
– Compressional tectonics, but no continental collision
– Compression and uplifts - inboard on the continent
Western Mountain Building
• Triassic - Late Cretaceous - Andean Arc
• Sonomian Orogeny - Sierra Nevada
– Triassic through Middle Jurassic
• Nevadan Orogeny - docking of microcontinents
– Late Jurassic - Early Cretaceous
Western Mountain Building
• Cordillera foreland basin - Late Jurassic and Early Cretaceous
• Morrison Formation
Western Mountain Building
• Sevier orogeny - Late Cretaceous
– Volcanic arc shifts eastward
– Massive backarc thrusting - fold and thrust belt
• Problem: where did the inboard compression come from?
– Change in subduction angle
Western Mountain Building
• Laramide Orogeny - Late Cretaceous to Eocene
– Final phase of Cordilleran Mountain building
• Uplifts and broad anticlinal folding
– Doesn’t fit any present tectonic model
The Cretaceous World
• 100 my ago - highest global sea level
• Why?
• High rates of sea floor spreading
• Western Interior Seaway
The Cretaceous World
• High global temperatures and CO2
• No ice caps
• Cyclic sedimentation - Cretaceous Cyclothems
• How?
• Sandstone-shale couplets
• Limestone-marl couplets
The Mesozoic Marine Revolution
• Diversification following Permian mass extinction
• New groups dominate
• Mobile molluscs, arthropods, echinoderms
• Why might mobility be important
• Modern corals and rudist reefs
The Dinosaurs
• First appeared in the Triassic - synapsids
• What were the dinosaurs?
- terrestrial reptiles
- one of the most successful groups of organisms that have ever lived
The Dinosaurs
• How are they related to the other reptiles?
• one of the distinguishing features = stance
The Dinosaurs
• What are the major groups?
• the “lizard hip” and “bird hip” dinosaurs
K/T Mass Extinction
• What happened to the dinosaurs?
• Asteroid Impact?
• Volcanism
• Many questions remain
K/T Mass Extinction
• Asteroid Impact => evidence
• the crater site
• iridium
• ”shocked quartz”
• spherules