| DRI | 2007 News Releases | ||||
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~ for immediate release news release May 25, 2007 All DRI News Releases are available at: http://news.dri.edu/ Revolutionary Namib Desert sand dune study reveals new information on dune age, structure and sheds new light on past climate change Article in GSA's online journal GEOLOGY this month
Reno, Nev.—Linear sand dunes, like those found in the Namib Desert in southwestern Africa, are the
most widespread type of desert sand dune around the world, and move over time as if alive—stretching farther
in long lines as winds blow across the desert, piling more sand on them. Until recently, insufficient data led
to challenges with determining the age of these sand dunes, as well as how they were formed. DRI's Dr. Nick
Lancaster, with colleagues Dr. Geoff Duller of the University of Aberystwyth and Dr. Charlie Bristow of the
University of London, used ground penetrating radar and optically stimulated luminescence dating to dig deep inside
the dunes to reconstruct the sedimentary layers and to solve the mystery of their age. The results, which
appear in an article in the new issue of the journal "Geology," are monumental: the dunes were younger
than expected; there was firm evidence of lateral migration—or shifting sideways—of linear dunes; and
they were constructed by winds from different directions than previously thought. The results have important
implications for understanding how all these ancient sand dunes formed, whether they were formed long ago during
the Jurassic Period (206 to 144 million years ago) such as the Navajo Sandstone, or in the last 5,000 years like
those in the Namib Desert. WHAT IS GROUND PENETRATING RADAR (GPR)? A GPR system, as shown above in the first
picture, sends electromagnetic signals down below the ground that are then reflected back through the sediment. How
the signals respond depends on the size of the sand and its moisture content, and sends back signals to a computer
allowing researchers to create an image of the sedimentary structure in the sand dune. WHAT IS OPTICALLY STIMULATED LUMINESCENCE (OSL) DATING? OSL dating is a method that measures the amount of light released when a grain of sand is exposed to a controlled source of light in a laboratory. Using it, researchers can determine the ages of ancient earthquakes and volcanic eruptions, or discover when climate shifts changed a forest or grassland into a sea of sand. With luminescence dating, researchers can determine the ages of many materials that are too old for the radiocarbon dating technique (older than 55,000 years) or do not contain organic material (like sand dunes). It measures the time elapsed since sand grains were last exposed to sunlight.
A cross section of the Namib dune showing the age of the sand. "Using GPR allowed us to pick out sedimentary units, or layers formed over time with different wind
direction," Lancaster said. "The resulting images showed us that the winds during the Jurassic
Period were different than we thought. The unique combination of the GPR with the luminescence dating study
provided a clear picture of how the dunes developed over thousands of years, and even revealed a break in the
migration of the dune, leading us to ask what happened with the wind regime and whether there was some significant
climate change, such as increased rainfall." ABOUT DRI: A nonprofit, statewide division of the Nevada System of Higher Education, or NSHE, DRI pursues a full-time program of basic and applied environmental research on a local, national, and international scale. More than 500 full- and part-time scientists, technicians, and support staff conduct more than 300 research projects at DRI annually. DRI generates $50 million in total revenue consisting predominately of competitively won research contracts and grants. The State of Nevada provides critical funding in support of DRI's administration, operations, and maintenance through the NSHE education budget. While DRI’s portion of the NSHE budget is approximately one percent, the institute leverages these funds to enhance its competitiveness. |
