Lecture 16  The End Cretaceous extinction event

Focus Question-What are the proposed causes of the Cretaceous-Paleogene extinction event?

1.        The global extinction event that marks the end of the Cretaceous and the end of the Mesozoic is a famous one.  The extinction event included:

a.        Dinosaurs, Pterosaurs, Marine Reptiles

b.      Most surface ocean plankton

c.       Many tropical and subtropical plants and animals.

2.        Today, we will look at the two current hypotheses on the causes of the Cretaceous-Paleogene Extinction event.  To do this, we will focus on two very different areas of the world-

a.        The Meteorite Crater known as the Chicxulub Crater, on the edge of the Yucatan Peninsula

b.      The Deccan Traps flood basalts, located in western India

3.        What defines the global Cretaceous-Paleogene boundary? 

a.        A boundary clay with a spike of the heavy metal Iridium

b.      A lot of carbon-12

c.       The mass extinction of about 90% of surface ocean plankton

4.        Kinds of evidence can we look for to indicate the occurrence of a meteorite impact?

a.        A crater

b.      Pieces of meteorites

c.       Microspherules-tiny drops of glass and melted rock from the impact

d.      “shocked” quartz-quartz grains that have a warped crystal structure from pressure wave of impact

e.      Iridium-a heavy metal associated with meteorites, but rare in the Earth’s crust.

5.        The Chicxulub crater-edge of Yucatan Peninsula

a.       Crater is about 250 km in diameter

b.      Radiometric dates are 65 million yrs ago

6.        The Deccan Trap Flood Basalts, western India

a.       Erupted when India was located in southern Indian Ocean, approximately where Reunion Island is today

b.      Located over a “hotspot” mantle plume that produced a flood basalt similar to Siberian Traps of the Permian

c.        Duration of eruptions less than 1 million years

d.      Radiometric age is slightly older, about 65.7 million years, but error bars put it in the 65 my range

7.        Both of these events were significant problems for global climate. 

a.        Surface ocean plankton show severe extinctions-up to 90% in the tropics

b.      Many species of large vertebrates, both marine and terrestrial, become extinct

c.       Numerous species in tropical reef communities become extinct

d.      Large amount of carbon-12 is measured in marine sediments, indicates plankton that photosynthesize were not there to take up carbon-12

e.       Suggests cooling in tropics, breakdown of foodweb

8.        Roadtrip-where can we go to see the Cretaceous-Paleogene boundary in the U.S.?  We can see this in the Badlands National Park, South Dakota

a.        Cretaceous Interior Seaway sediments and Paleogene sediments exposed

b.      Boundary can be distinctly identified by fossils, iridium and characteristic clay deposit

9.        It seems that the Cretaceous-Paleogene extinction event was driven by either or more likely both of these severe events in Earth’s history-the Chicxulub impact and the Deccan Traps flood basalts.  Note that this is the third big flood basalt – extinction record co-occurrence (We saw these in the Permian-Triassic extinction events and the Triassic-Jurassic  extinction events). 

10.   Next lecture, Cenozoic Mountain Building and the Yellowstone Hotspot Trail