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Utah’s redrock may have changed global climate

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04.12.2003

The Navajo Sandstone -- one of the brightly colored rock formations that comprise southern Utah’s famous redrock -- is exposed in the cliffs at Zion National Park, the Petrified Dunes at Arches National Park and in many parts of Capitol Reef National Park.

Now, a new study from the University of Utah concludes that bleaching patterns in the Navajo Sandstone suggest the rock formation once may have harbored vast amounts of hydrocarbons, likely natural gas (methane). And when the once-buried sandstone was exposed and started eroding roughly 6 million years ago, the gas would have been released to the atmosphere. Because methane is a so-called "greenhouse gas," the release of large quantities to the atmosphere may have warmed Earth’s ancient climate.

The study was published in the December 2003 issue of the journal Geology by Brenda Beitler, a University of Utah doctoral student in geology. A summary of that study is reproduced below. It was part of a news release issued by the Geological Society of America outlining contents of the December issue of Geology.


Bleaching of Jurassic Navajo Sandstone on Colorado Plateau Laramide highs: Evidence of exhumed hydrocarbon supergiants? Brenda Beitler, University of Utah, Department of Geology and Geophysics, Salt Lake City, UT 84112-0111, U.S.A.; et al. Pages 1041-1044.
Spectacular color variations in the Jurassic Navajo Sandstone in southern Utah have long attracted the attention of geologists and laypersons alike. In this paper, we explain the cause of the color variations and discuss the implications. The Navajo Sandstone is perhaps the largest eolian (sand dune) complex on Earth, past or present. Abrupt red-white color transitions are believed to be the result of reducing fluids, likely gas hydrocarbons, flowing through the sandstone pores and removing the red pigment.

Field mapping and analysis of satellite imagery indicate both stratigraphic and structural control on where fluids have left the sandstone "bleached." The most extensive regional bleaching occurs on eroded crests of broad asymmetrical uplifts produced during Laramide deformation (Cretaceous-Tertiary age). Alteration patterns suggest that the faults that core these uplifts were carriers for hydrocarbons and brought the buoyant bleaching fluids to the crests of the anticlines where they bleached the sandstone in both structural and stratigraphic traps.

The extent of bleaching indicates that the Navajo Sandstone may have been one of the largest hydrocarbon reservoirs known. These ancient hydrocarbon traps have been extensively eroded, potentially releasing the bleaching gas into the atmosphere. The magnitude of the reservoir suggests that hydrocarbon escape could be significant in global carbon fluxes and possibly influence climate.

Lee Siegel | Source: EurekAlert!
Further information: www.utah.edu/

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