Earth History GEOL 2110

The Mesozoic EraCretaceous Trangression

And Mesozoic Life

Major Concepts• A major transgression in the Cretaceous created a Great

Interior Seaway where great accumulation of marine and non-marine sediment were deposited in the Great Plains

• Climate in the Cretaceous was uniformly warm due to a lack of polar ice caps, an abundance of water surface, large volcanic eruptions

• After the Permo-Triassic extinction, radiation of marine life was driven by reactions of species to predatation.

• Synapsid reptiles of the Triassic gave way to dinosaurs during the Jurassic and Cretaceous

• Flowering plants (angiosperms) bloomed in the mid-Cretaceous and supplied a rapidly reproducing supply of food to the dinosaurs

• The mass extinction at the end of the Cretaceous was not as abrupt as first described, suggesting a non-impact cause

Events of the Mesozoic Era

Great Inland SeawayThe Last Epicontinental Sea

Cretaceous Seaway Rock Types

Alluvial Fan Conglomerate

Deltaic SS and Coal

Deltaic SS and Marine Shale

Black Shale

Chalk Carbonate

Cretaceous Chalk DepositsAccumulation of Carbonate Micro-organism

Calcareous ooze

White Cliffs of Dover Carbonate Ooze

Carb

onat

e M

icro

foss

ils

NiobraraChalk of Nebraska

Deposits along the Eastern Shore of the Cretaceous Seaway

Lignite and Fine Sandstone

Weathered Archean Gneiss

Cretaceous PaleoclimateUnlike the Permian, globe

seemed uniformly warmHumid (rare evaporites)No glacial depositsExtensive water coverage promoted solar heating

Cretaceous Black ShalesEvidence of Uniformly Warm Ocean Waters

Organic –rich muds due to : - Rapid deposition of C- Rapid mud deposition- O-poor deep waters* * Oxygen is more soluble in cold water leading to vigorous circulation of cold, dense oxygenated water in the deep ocean when temperature is strongly zoned. Not the case when oceans are uniformly warm

Pierre Shale

Mesozoic Marine Life

After the Permo-Triassic ExtinctionBryozoans, Brachiopods, Rugose and Tabulate Coral, and Crinoids give way to: Bivalves, Gastropods, Mollusks, Modern Coral Crustaceans, Cephlapods, Echoniderms, Diverse Fish and Swimming Reptiles

PREDATOR-PREY RELATIONS RULE THE SEAS

Mesozoic Marine LifeBivalves Dominate

Rudistid clams

Inoceramids

Mesozoic Marine LifeAmmonites – the index fossil of the Mesozoic

Mesozoic Marine LifeMicro-organisms

Calcereous ForaminferaSiliceous Diatoms

Coccoliths

Mesozoic Marine LifeMososaurs, plesiosaurs, teleost fish, ammonites, turtles ----

Mesozoic Land LifeThe Land Before Time

Flowering Plants Evolve

Rapid regeneration provided ample food supply for dinosaurs

Pollinating insects (moths and bees) become important partners

The Cretaceous-Tertiary Extinction~ half of life is exterminated

Evidence for a Meteor ImpactVolcanic Glass Spherules

Shocked Quartz

Cretaceous Volcanism

Ontang–Java Oceanic Plateau

Deccan Flood Basalts

Summary of the Mesozoic

Next Lecture

The Cenozoic Era

The Modern World EmergesTectonics