The Navajo sandstone is one of Utah’s most iconic rock formations, with its massive white-pink cliffs strikingly visible in Zion and other national parks and monuments. Deposited during the Jurassic time period, these sandstones tell us the story of a major turning point in Earth’s history when fertile lands turned into an immense desert – in a process called desertification.
“A lot of geology is looking at the landscape, it is sort of like reading a book. You look at the things around you and you get little clues. The more clues you get the more you are able to understand the story,” said Marjorie Chan, distinguished professor in the Geology and Geophysics department at the University of Utah.
Chan and colleagues obtained the first radiometric dates of the Navajo sandstone using carbonate deposits - also called limestone - that contained Uranium and Lead isotopes yielding dates around 200 and 195 million years ago, the oldest dates ever reported for this unit.
The carbonates themselves also reveal more about the environment during this time period.
“Those carbonate deposits tell us that there was standing water, and maybe those were the kind of watering holes that attracted animals like dinosaurs," Chan said. "There were also probably insects and burrowing organisms around. So actually, surprising for a desert, there may have been a significant amount of life around these watering holes."
Chan believes this research is a starting point to predict how futures landscape will be impacted by desertification.
“With global warming, it is inevitable that some regions more are going to become desert," she said. "Our study may actually encourage people to look at the question of how quickly desertification has happened in the past, what are some of the signs, how does life respond, what kind of communities are able to persist during the desertification. We can actually use some of the examples of the Navajo sandstone and try to project that into what could happen in the future."