THE NEW RED SANDSTONE
The Triassic witnessed the complete retreat of marine waters from the land as
the continents continued to rise. Abundant terrestrial redbeds and thick beds
of gypsum and salt were deposited in the abandoned basins. Also, the amount
of land covered with deserts was much greater in the Triassic than today.This
is indicated by a preponderance of red rocks composed of terrestrial sand-
stones and shales exposed in the mountains and canyons in the western
United States.Terrestrial redbeds covered a region from Nova Scotia to South
Carolina and the Colorado Plateau (Fig. 142).
Redbeds are also common in Europe, where in northwestern England
they are particularly well developed. Over northern and western Europe, the
terrestrial redbeds are characterized by a nearly fossil-free sequence called
the New Red Sandstone, named for a sedimentary formation in Scotland
famous for its dinosaur footprints. The unit shows a continuous gradation
from Permian to Triassic in the region, with no clear demarcation between
the two periods.
The wide occurrences of red sediments probably resulted from massive
accumulations of iron supplied by onethe most intense intervals of igneous
activity the world has ever known. Air trapped in ancient tree sap suggests a
greater abundance of atmospheric oxygen, which oxidized the iron to form
the mineral hematite, named so because of its blood red color.Figure 142
Downwarping of the
Pierce Canyon redbeds
along the north margin of
Nash Draw, Eddy
County, New Mexico.
(Photo by J. D.Vine,
courtesy USGS)
Historical Geology