Eighth Edition
by Harold L. Levin

Chapter 13 - page 1

Mesozoic Events

Introduction

Mesozoic Era = 251 to 65.5 million years ago.

Name Mesozoic means "middle life"

The Mesozoic Era consists of three periods:

1. Triassic (Oldest. Lasted about 51 million years)
2. Jurassic (Lasted about 55 million years)
3. Cretaceous (Youngest. Lasted about 80 million years)

The Mesozoic Era followed the extinction of Paleozoic organisms. Mesozoic rocks contain the remains of organisms that are more advanced than those in the Paleozoic, but not as modern as those living today. Two new vertebrate classes appeared: birds and mammals.

The Mesozoic Era lasted approximately 186 million years, and ended with an extinction event in which the dinosaurs met their demise.

Paleogeography

The ancient geographic arrangement of the continents is referred to as paleogeography ("ancient geography").

At the beginning of the Mesozoic, all of the continents were assembled into a supercontinent, Pangea.

Pangea = "all land"

Pangea formed in the Late Paleozoic by the collision and joining of all of the continents to form a single landmass surrounded by a vast ocean.

 
Global paleogeography near the end of the Paleozoic Era.

In the equatorial area to the east, between Africa and Europe, and between India and Asia, was an embayment called the Tethys Sea.

The climate became arid; evaporites (E) were deposited.

In the Mesozoic, Pangea began to break up. Pangea began to break up into two separate land masses; the northern continents, Laurasia, and the southern continents, Gondwana. Laurasia began to break up, with Laurentia (North America) and Baltica (Europe) separating from each other.

Paleogeographic reconstruction showing the beginning of the breakup of Pangea, about 180 m.y. ago.

The breakup occurred in four stages:

1. Rifting and volcanism along normal faults in the Triassic, resulting in the separation of North America (Laurasia) from Gondwanaland.
   Normal faulting in eastern North America, accompanied by the intrusion of dikes along fractures or cracks, along with lava flows and vent eruptions.
   Atlantic Ocean opened and widened through the extrusion of oceanic basalts.
   Note: The continents did not split along the places that marked their previous edges. The old suture (or "seam") between North America and Africa lies in southern Georgia. When Africa pulled away, it left a sliver of the African continent attached to the southeastern U.S.
2. Rifting and separation of Africa, India, and Antarctica.
   Large volumes of basalt were extruded.
3. The Atlantic rift extended northward, Eurasia moved clockwise (to the south), partially closing the Tethys Sea.
   South America began to split from Africa by the Late Jurassic, and completely separated by the Late Cretaceous.
   Australia remained connected with Antarctica.
   India was moving northward toward Asia.
   Greenland began to separate from Europe (Baltica), but remained attached to North America (Laurentia).
4. After the Mesozoic, the breakup of Pangea continued.
   North America (Laurentia) separated from Eurasia (Baltica) along the North Atlantic rift.
   Antarctica and Australia separated about 45 m.y. ago.

The total time for the fragmentation of Pangea was about 150 m.y.