Wednesday, May 4, 2011

Paleogeography of the Monument in the late Cretaceous (by Matt Selman)

Snow College students and BLM field staff descend to a dig site in Grand Staircase-Escalante National Monument.

The Grand Staircase-Escalante National Monument has, in recent years, become a major national destination for scientists studying the life-forms of the late Cretaceous period. Teams from around Utah and the United States make yearly pilgrimages to the monument to explore its fossilized floodplains, river channels, and coastal lagoons in search of the animals that lived and died in what was an incredibly lush tropical area, now transformed into high desert and badlands topography.
Erosional forms on Horse Mountain.

As different as the climate of the period was from that of the present day, so was the geography markedly dissimilar. Cretaceous North America was the site of a vast, shallow sea known as the Interior Cretaceous Seaway. At its height in the Middle Cretaceous, the seaway’s western boundary devoured the eastern third of what is now Utah. By the Late Cretaceous, the shoreline receded to the east, leaving a damp coastal plain running through the center of present-day Utah.
Top: Dr. Alan Titus discusses the distribution of fossils within the Kaiparowits formation.
Bottom: Scott Richardson of the BLM descends to a dig site in the northern part of the Monument.

At the same time, a significant mountain-building event occurred in the region. The Sevier Orogeny created a chain of mountains running longitudinally from modern-day Mexico up into Canada. As quickly as these mountains were uplifted, the forces of erosion began to work on them, creating great river channels flowing down into the receding interior sea.

Hadrosaur humerus (top) and velociraptor claw (bottom), both deposited in prehistoric floodplain sediments.

This geography, along with the climate of the period--both of which are immensely different from that of today--created the conditions which allowed flora and fauna to flourish, and their remains to be relatively well preserved in the sedimentary deposits of rivers (flowing down and east from the Sevier mountains), floodplains, and the shores of the Interior Cretaceous Seaway.
Returning to camp.

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