Geology Reference
In-Depth Information
Sevier and
Laramide
mountain
building
Lowlands
Alluvial
plain
Carbonate
bottom
Land
Mountains
Epeiric sea
Deep ocean
Figure 22.6 Cretaceous Paleogeography of North America
slope, and deep-sea environments were brought together in
a submarine trench when North America overrode the sub-
ducting Farallon plate (
The general term Cordilleran orogeny is applied to
the mountain-building activity that began during the Ju-
rassic and continued into the Cenozoic (
Figure 22.10).
The Franciscan Complex and the Great Valley Group ,
which lies east of it, were both squeezed against the edge of
the North American craton as a result of subduction of the
Farallon plate beneath the North America plate. The Fran-
ciscan Complex and the Great Valley Group are currently
separated from each other by a major thrust fault. The Great
Valley Group consists of more than 16,000 m of conglom-
erates, sandstones, siltstones, and shales that were deposited
on the continental shelf and slope at the same time that the
Francisan deposits were accumulating in the submarine
trench (Figure 22.10).
Figure 22.11).
The Cordilleran orogeny consisted of a series of individual
mountain-building events that occurred in different regions
at different times, but overlapped to some extent. Most of
this Cordilleran orogenic activity is related to the continued
westward movement of the North American plate as it over-
rode the Farallon plate and its history is highly complex.
The fi rst phase of the Cordilleran orogeny, the Nevadan
orogeny (Figure 22.11), began during the Late Jurassic and
continued into the Cretaceous as large volumes of granitic
magma were generated at depth beneath the western edge
of North America. These granitic masses were emplaced as
 
Search WWH ::




Custom Search