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December 3, 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.
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