 | The idea to investigate the origin of Utah's desert sands was sparked during a departmental field trip in 2002 to Kolob Canyon in Zion National Park led by Professors Reiners and Brandon. The reddish Navajo sandstone, seen in the background, underlies much of the park. Zion is known for cliff-size exposures of ancient sand dunes, where the Navajo sandstone was deposited. |
Team traces Utah desert sand to Appalachian mountains
Using a novel dating technique, Yale geologists discovered that desert sands found in Utah actually originated in the Appalachian Mountains in eastern North America.
"This surprising finding suggests that an ancient westward-flowing river system transported sediment across the continent of North America during the Jurassic era, perhaps in a fashion similar to the Amazon in modern day South America, which carries material across the continent from the Andes," says Peter Reiners, assistant professor in the Department of Geology and Geophysics and co-author of the study published this month in the journal Geology.
During the Jurassic era, approximately 190 million years ago, a huge sand sea similar to today's Sahara desert covered much of the western United States. In southern Utah, these desert sands are exposed at Zion National Park in the Navajo Sandstone, a rock unit famous for its large fossil sand dunes visible in steep cliff exposures.
The tremendous amount of sediment preserved in the sand sea led the researchers to explore the origins of the sedimentary material. The idea for the study arose during a departmental field trip to Zion National Park during spring break 2002 and led by Reiners and Professor Mark Brandon. Zion is known for cliff size exposures of ancient sand dunes, where the Navajo sandstone was deposited. The field trip sparked the idea to use zircon dating to study the source of the Navajo sediment.
Reiners and Jeffrey Rahl, senior author of ,the study and a fifth-year graduate student at Yale, devised a new technique to provide a distinctive "fingerprint" of the original source of most of the sediment found within sedimentary rocks.
The researchers measured both crystallization ages and cooling ages in single sand grains composed of the mineral zircon. The crystallization age corresponds to the time a rock formed deep in the Earth, while the cooling age roughly corresponds to when a rock was eroded at the Earth's surface. Previous approaches have been restricted to the measurement of a single criterion.
"Together, these two ages provide a relatively precise constraint on the source of sediment," Rahl says. "The bulk of the zircons analyzed show a combination of crystallization and cooling ages that is consistent with an origin from only one place in North America: the Appalachian Mountains."
Co-authors included researchers from the Australian National University. The research was partially funded by the National Science Foundation and the Petroleum Research Fund of the American Chemical Society.
-- By Jacqueline Weaver
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