The mountain belts of the Cordilleran of North America, the Andean of
South America, and the Tethyan of Africa-Eurasia contained thick marine
deposits of Triassic age.The Cordilleran and Andean belts were created by the
collision of east-Pacific plates with the continental margins of the American
plates formed when Pangaea rifted apart. The Tethyan belt formed when
Africa collided with Eurasia, raising the Alps, which contain an abundant fos-
sil-bearing Triassic section. The Tethys Sea, located in the tropics during the
Triassic, contained widespread coral reefs that uplifted to form the Dolomites
and Alps during the collision of Africa and Eurasia in the Cenozoic.
During the Triassic, when North America was still part of Pangaea and the
ocean began in present-day Nevada, an ancient major river system called the
Chinle flowed through western United States.The source of the Chinle was the
highlands of Texas, known as the Amarillo-Wichita Uplift. From there it flowed
westward across northern New Mexico and southern Utah. It emptied into the
sea at central Nevada. Sedimentary rocks of the Chinle Formation produced
important uranium ore deposits responsible for the uranium boom of the Amer-
ican West beginning in the 1950s. Eventually, the Texas highlands eroded down
to plains, and Pangaea drifted away from the equator into the drier midlatitudes.
By the time North America separated from the other continents around 200 mil-
lion years ago, the great Chinle River was drying up.
Late in the Triassic, an inland sea began to flow into the west-central
portions of North America. Accumulations of marine sediments eroded from
the Cordilleran highlands to the west,often referred to as the ancestral Rock-
ies.They were deposited onto the terrestrial redbeds of the Colorado Plateau.
Important reserves of phosphate used for fertilizers were precipitated in the
late Permian and early Triassic in Idaho and adjacent states. Huge sedimentary
deposits of iron were also laid down. The ore-bearing rocks of the Clinton
Iron Formation, the chief iron producer in the Appalachian region from
Alabama to New York, were deposited during this time.
Evaporite accumulation peaked during the Tr iassic, when the superconti-
nent Pangaea was just beginning to rift apart. Evaporite deposits form when
shallow brine pools replenished by seawater evaporate. Few evaporite deposits
date beyond 800 million years ago, however, probably because most of the salt
was buried or recycled into the sea. Ancient evaporite deposits exist as far north
as the Arctic regions. These indicate that either these areas were once closer to
the equator or the global climate was considerably warmer in the past.
TRIASSIC BASALTS
Over the last 250 million years, 11 episodes of massive flood basalt volcanism have
occurred worldwide (Fig. 143 and Table 9). They were relatively short-lived
TRIASSIC DINOSAURS