Geology Reference
In-Depth Information
move from the equator toward the poles.) However, other scientists think that during
the Jurassic period (the warmest part of the Mesozoic), average temperatures were al-
most the same all over the globe.
Creating the mountains of North America
All over the world, continental landmasses were changing in size and shape as the con-
tinents of Pangaea moved apart. I focus here on just the changes in North America.
The eastern portions of North America, specifically the Appalachian Mountains, had
already formed by the start of the Mesozoic era. During the Mesozoic, North America ex-
perienced a series of mountain-building episodes, or
orogenies,
along its western coast.
The first of these is called the
Cordilleranorogeny
and created the Sierra Nevada and
Rocky Mountains. As the North American continental plate and the ancient Farallon
Plate moved toward each other, the Farallon Plate subducted (a process I explain in
Chapter 9), and volcanoes were formed along the plate boundary. (Only a small piece of
the Farallon Plate now remains and is called the
Juan de Fuca Plate.
It's located off the
northwest coast of the United States.) These volcanoes formed an island arc that was
eventually
accreted
(added) to the western coast of the North American continent.
Meanwhile, the previously formed Appalachian Mountains were eroding, moving sedi-
ments westward to settle across the continent at the bottom of a shallow sea called the
Sundance Sea
that covered what is now the central part of North America.
By the end of the Mesozoic, the Sundance Sea was a waterway crossing the continent
from north to south called the
intercontinental seaway
(see Figure 20-2). The sediments
deposited in the intercontinental seaway were washed down, forming what is now called
the Gulf of Mexico.
Figure 20-2:
North
America during the
Mesozoic era.
