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Written by Brooks Britt
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Monday, 11 June 2007 |
 In the last decade an array of new dinosaurs have been recovered from the Lower Cretaceous Cedar Mountain Formation in Utah. The formation contains as many as three distinct faunas but due to a lack of recognizable volcanic ash beds (except at the top of the formation) the absolute ages for the lower two faunas remained a mystery. To determine the ages of these faunas we utilized detrital zircon crystals – zircons reworked from volcanic ash beds and incorporated into sandstones and silty mudstones. After crushing the rocks and recovering the zircons, BYU geology students travel to George Gehrels geochronology lab at the University of Arizona where they use a laser and mass spectrometer to obtain uranium-lead ages. The results have exceeded our expectations. The base of the Cedar Mountain and most diverse dinosaur fauna (Utahraptor, Falcarius, Gastonia, and several sauropod genera) dates to 124 Ma and the middle fauna (giant nodosaurs and ankylosaurs and a brachiosaurid sauropod) dates to about 116 Ma.
The uppermost fauna was previously dated to 99 Ma by others, including Bart Kowallis. Thus the Cedar Mountain Formations spans 24 Ma – a large chunk of time for a single formation. We are now expanding the project by collecting a large number of samples from the top of the Morrison, through the entire Cedar Mountain and Dakota Sandstone formations at four widely spaced localities in Utah. We hope to use ages from these samples to unravel the Early Cretaceous tectonic history of Utah. Our geochronology team includes students Darrin Burton, Adam McKean, Garrett Schwanke, and Sarah Seeley plus faculty members Britt, Kowallis, and Christiansen and George Gehrels of the University of Arizona. The preliminary results of this project have been presented by these students at three two regional and one national GSA meetings. The students are part of BYU’s mentoring project.
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Last Updated ( Wednesday, 10 September 2008 )
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