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The Controversy Over Utah's Upheaval
Dome
written in 1996 by Matt Morgan
October 2006 - Updates are in progress...
For many years Upheaval Dome, located in the heart of Utah's Canyonlands
National Park, was thought to have been just an ordinary salt dome. The "salt dome
theory" was well accepted in the scientific community, primarily because the
Canyonlands area contains numerous salt domes. However, recent stratigraphic and
geophysical evidence suggests a more exciting and controversial origin: meteorite impact!
Upheaval Dome is 1.5-miles wide from rim to rim and is over 1/4-mile deep. The rocks
contained within the depression form concentric rings and are the only tilted strata for
miles, thus the name "Upheaval". So what could cause such an unusual structure?
Let's look at the two most common theories:
Salt Dome Theory
This theory stems from the possibility that a body of salt lies beneath Upheaval Dome.
300 million years ago, a vast inland sea covered the Canyonlands region (Figure 1,
Illustration A).
Over millions of years the sea evaporated, leaving a large deposit of salt (Illustration
B). Sediments were deposited over the salt, forming thick layers of rock (Illustration C).
The overburden weight from the rocks pushed down on the salt. Since the salt is less dense
than the rocks above, it becomes buoyant. Pushing up the overlying layers of rock, the
salt forms a dome (Illustration D). Erosional processes remove the overlying layers of
rock, exposing the tilted strata below. A "crater" is formed (Illustration E)
Meteorite Impact Theory
Only until recently has the idea that a meteorite impact created Upheaval Dome been
taken seriously. Approximately 60 million years ago, a large body 1/3-mile in diameter,
smashed into this area and created a large meteorite crater (Figure 2, Illustration A , B,
and C).
The upturned beds found rimming the crater were produced when the rocks rebounded and
extended from the tremendous force of the impact (Illustration D). Over millions of years,
erosional processes removed much of the overlying layers of rock. Upheaval Dome is the
remnant of the lower portions of the crater, with fragments of the impacting body
completely gone (Illustration E).
The Evidence
There are several key pieces of evidence that point to a meteorite impact for the
origin of Upheaval Dome. In 1993, Eugene Shoemaker and Ken Herkenhoff found shatter cones
within the sandstone of Upheaval Dome. Shattercones, as their name implies, are
conical-shaped pieces of rock that have small grooves radiating from a central point
(Figure 3).
It is believed that shatter cones form when shockwaves from a meteorite impact move
through the surrounding rock, leaving the grooves behind. Shoemaker and Herkenhoff also
found shocked quartz, which is ordinary quartz that has been highly fractured from an
impact, within the sandstone. Even more evidence for the impact theory was presented in
1995 by John Louie, a seismologist at the University of Nevada-Reno. Louie set out to
determine if there is a rising salt plume beneath the surface of Upheaval Dome. Louie and
his colleagues used a technique called seismic refraction, where a seismic wave is sent
nearly parallel to a series of high velocity rocks and the travel time of the seismic wave
is recorded. From the return time, the thickness of the underlying rocks can be
determined. If Upheaval Dome was created by a rising salt plume, the rocks should show
more deformation with increasing depth. However, if Upheaval Dome was created by a
meteorite impact, the rocks will be deformed only near the surface. Louie found that the
velocity of the seismic waves do not slow down (as they would through salt) as they pass
through the rocks beneath the structure. This suggests, almost conclusively, that no salt
dome exists beneath Upheaval Dome. "Upheaval Dome is the remnant of a meteorite
impact because everything underneath it looks like it was punched out by a force from
above", Louie said in the Salt Lake Tribune. Add the seismic evidence to the
shocked-quartz and shatter-cones found at Upheaval Dome and you have a "classic"
meteorite crater.
Further Study
Continuing their NASA-funded project, Shoemaker and Herkenhoff are mapping the rocks
that make-up Upheaval Dome. They found that some of the strata beneath the dome are
thicker than others. Both believe this is central uplift of the crater, formed by the
rebound of the rocks after impact. Shoemaker also believes the original crater was 3 miles
wide and was formed by a comet or asteroid 1000-feet in diameter. It is possible that
further mapping may reveal the actual size of this catastrophic event. Upheaval Dome, is a
really exciting place located in Utah's Canyonlands National Park. Definitely, a site that
should not be missed!
Matt Morgan
Mile High Meteorites
http://www.mhmeteorites.com
References
Louie, John. 1995. "Upheaval Dome Seismic Refraction Analysis". On-line
document at:
http://www.seismo.unr.edu/ftp/pub/louie/dome/refraction.html
Siegel, Lee. 1995. "NASA: Big Meteorite Whacked Utah". The Salt Lake Tribune.
I would also like to thank the National Park Service and the Canadian Department of
Natural Resources.
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