Late+Mesozoic[1]

Late+Mesozoic[1] - The Cretaceous World Cretaceous Period...

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Unformatted text preview: The Cretaceous World Cretaceous Period 66.3 Million years 145 Million years Life of the Cretaceous • Diversity • Plankton • Ammonoids and belemnoids persisted Life of the Cretaceous • Teleost fish - Dominant modern group - Specialized fins - Symmetric tail - Short Jaws Life of the Cretaceous • Marine reptiles still important – Mosasaurs • Up to 15 m in length – Marine turtles Life of the Cretaceous • Foraminifera – Many modern benthic foraminifera originated • Encrusting Bryozoan – Cheilostomes • Burrowing bivalve mollusks • Gastropod Mollusks • Crabs Life of the Cretaceous • Surface-dwelling bivalve mollusks – Rudists – Formed large tropical reefs • Up to 1 m height • Predators led to reduction in brachiopods and stalked crinoids Life of the Cretaceous • Flowering Plants – Angiosperms appear • Flowering plants • Hardwood trees – Increase in complexity and form – Gymnosperms still dominant Life of the Cretaceous • Vertebrate faunas – Community analogous to modern African savannah – Duck-billed dinosaurs Life of the Cretaceous • Tyrannosaurus rex • Flying vertebrates – Reptiles – Birds Life of the Cretaceous • Terrestrial crocodiles – up to 15 m in length Life of the Cretaceous • Mammal evolution – – – – Pointed teeth Endothermic Large brains Suckled their young – Rear feet for grasping • Tree climbing Life of the Cretaceous • Purgatorius – Rat-like mammal Paleogeography • Most continents were isolated • Seas opened: – South Atlantic; Gulf of Mexico; Caribbean Sea • Mid-Cretaceous sea level high – Tethys Seaway Paleogeography • Period of high sea level – Associated with rapid sea floor spreading – Long period without reversal Paleogeography • Oceans stagnated – Epicontinental black muds when seas spilled over – Normally thin oxygen poor zone expanded Paleogeography • High latitudes were warm – 50°F / 10°C – Dinosaurs near south pole • Late Cretaceous polar cooling – Some extinctions • Rudists Mass Extinction Event • • • • • Meteor Impact (quick) Gradual rise in temperature (gradual) Disease Ice Age Evolution- birds Cretaceous Mass Extinction • • • • • Dinosaurs Ammonoids Mosasaurs and other marine reptiles Reductions in gymnosperms and angiosperms 90% calcareous nannoplanton and foraminifera went extinct Meteor Impact Theory • Nobel laureate Luis Alvarez, his geologist son Walter Alvarez, nuclear chemist Frank Asaro, and paleontologist Helen Michael (on left, from right to left) 1980 • Levels of Iridium at Mesozoic (K/T) boundary • Terminal Cretaceous iridium anomaly • Drumheller, near Alberta, Canada Meteor Impact Simulation • 150-300 km crater • Meteor 6-15 km in diameter The Impact • Chicxulub Crater – Gravity anomalies • Striated dolomite from the blast impact The Impact • Microspherules – Wyoming Tectonic Events inWestern U.S. • Cordilleran Mountain Building – Continued Franciscan subduction • Sevier Orogeny Tectonic Events in Western U.S. • Subduction angle shifted – Volcanism farther inland • Idaho and Nevada Tectonic Events-Western U.S. • Mowry Sea – Oil shale – By late Cretaceous it extended to Gulf of Mexico • Cretaceous Interior Seaway • Bounded by barrier island and alluvial fans closest to mountains Tectonic Events in Western U.S. • Mountain building generated sediments – Conglomerate sediments – Greater subsidence in the western reaches Tectonic Events in Western U.S. • Upper Cretaceous seaway – Transgression followed by regression Tectonic Events in Eastern U.S. • Formation of the continental shelf – Accumulated sediments in rift basins – Overlain by Jurassic carbonates – Siliclastic sediments Chalks of Europe • Late Cretaceous – Region was flooded – High rates of carbonate accumulation – 15 cm/year • White Cliffs of Dover • Denmark ...
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