Eighth Edition
by Harold L. Levin

Chapter 15 - page 2

Cenozoic Events

Paleogeography and Plate Tectonics

During the Cenozoic, the Atlantic and Indian Oceans widened, and the continents moved to their current positions.
Half of the present ocean crust has formed at the mid-ocean ridges since the beginning of the Cenozoic.

           
Position of the continents during the Eocene, about 50 million years ago.
Note that Antarctica and Australia are still connected.
India has not yet collided with Asia.
North and South America are not yet connected.
South America is connected or nearly connected with Antarctica.
Compare the highlighted areas with those on the globe below.

           
Position of the continents today (plotted on the same projection).
Compare the positions of Australia and India with the image above.
Antarctica has completely separated from neighboring continents, and is now completely surrounded by ocean.
Antarctica is also centered on the South Pole.

As the North American plate moved westward (accompanying the widening of the Atlantic Ocean), subduction of ocean crust and accretion of exotic terranes occurred along its western edge.

           
            Exotic terranes along the western edge of North America.

Eventually, the western edge of the North American plate came into contact with the northwestward-moving Pacific Plate, forming the San Andreas Fault system.

Tectonic and Paleographic Changes and Their Effects on Climate

Orogenic and volcanic activity were intense along the western edge of the North and South American plates, and caused the formation of the Isthmus of Panama, a land bridge linking North and South America. This land bridge blocked the westward flow of the North Atlantic Current. The current was deflected to the north (turning to the right, as a result of the Coriolis Effect), and formed the Gulf Stream.

The Gulf Stream transported warm water northward and resulted in bringing warmer climates to northwestern Europe. (It also supplied warm, moist air toward the North Pole, which would ultimately result in precipitation which helped build the glacial ice sheets.)

The land bridge between North and South America provided a path for plant, animal, and human migration between the Americas.

Several major tectonic changes occurred. The changes involving Antarctica affected climate.

1. Most dramatic Cenozoic tectonic event = Collision of Africa and India with Eurasia, forming the Alps and Himalayas.
   Tethys Sea deposits were deformed into mountain ranges.

2. Important continental breakups:
1. North Atlantic rift separated Greenland from Scandinavia, and severed the land connection between Europe and North America.


2. Australia separated from Antarctica by the Oligocene, about 30 m.y. ago. Circumpolar currents isolated Antarctica from warmer waters. Led to cooling of Antarctica. Cold, dense ocean waters around Antarctica drifted northward along ocean floor, contributing to global cooling and eventually the Ice Age.


3. Rifting occurred between Africa and Arabia, associated with a branch of the Indian Ocean. This formed the Red Sea and the Gulf of Aden.

Continental interiors were well above sea level and not flooded by epicontinental seas during the Cenozoic. Marine transgressions were limited.

Overall cooling trend during the Cenozoic.
Tropical and subtropical plants were replaced by temperate plants, such as grasses. Tropical plants retreated toward the equator.