The age of Utah’s Navajo Sandstone

ANNOUNCEMENTS

Adapted from a release prepared by the Geological Society of America. Find the original here.

The real Jurassic Park was as an ancient landscape home to a vast desert covered mostly in sand dunes as far as the eye could see, where dinosaurs and small mammals roamed southern Utah. The iconic Navajo Sandstone is known for its beautiful red and tan crossbedded sandstones that grace many of the national parks and monuments in the southwest U.S., particularly in Arches, Canyonlands, Capitol Reef and Zion national parks. The sands were deposited in dunes within the largest known sand sea (also called an erg) in Earth’s history during the Early Jurassic. These deposits show a record of desertification—the process by which fertile lands become desert. How did this landscape lose its water bodies, vegetation, and animals? How long did desertification take to happen? How long did it last? What amount of time is actually represented by these deposits? Many questions are unanswered due to the lack of age constraints in these sediments.

A study in Geology, by researchers including University of Utah distinguished professor Marjorie Chan, determined numerical ages from several calcium carbonate rock layers representing lake deposits that once occupied interdune areas and served as watering holes for a variety of dinosaurs and small theraspids (relatives of mammals). These carbonates yielded ages of around 195-200 million years. These age dates show that eastern Utah parts of the Navajo desert are much older than previously thought and, together with age dates from Arizona, show that the giant sand sea become younger to the south. The lake and associated spring deposits also show this vast desert, at times, had a wetter climate and more active water cycle than had been previously assumed. This work demonstrates that the desertification process is complex, and that age dates from carbonates and correlation of rock layers will help answer major questions of how desertification takes place in continental interiors.