Paper No.
239-14
"ELKO CRATER FIELD" REVISITED -
RECONNAISSANCE REPORT
VERISH, Robert S., P.O. Box 237, Sunland,
CA 91041, bolidechaser@yahoo.com.
USGS Map Sheet MF-1168 by Ketner &
Roddy (1980) is entitled "Map Showing the Elko Crater Field, Elko
County,Nevada".
This poster reports on a subsequent field
survey of this "Elko Crater Field". This survey was
conducted during Spring of 2001, and was
intended to be only a reconnaissance effort for the purposes of securing
evidence of ejecta or meteoritic
material, and to examine the stratigraphy
of the craters. This survey did not result in any finds of ejecta or
meteoritic material. A close inspection of the
stratigraphy of the "crater rims"
did not reveal any evidence of disordered layering. All of the above is
considered as negative evidence for an impact
origin for the Elko Crater Field. An
exposure that is nearby a cluster of "craters" in the Susie Creek
area revealed evidence, which affords an
interpretation for a terrestrial geologic
origin for all of these depressions. A thin (~1m) veneer of colluvium overlies
a section of volcaniclastic sediment
that can be divided into an upper and lower
unit. The upper unit (~20m) is a light brown to tan-colored coarse sand that
is interbedded with thinly
layered, fine-grained tuff. The lower unit
is predominantly a greenish-gray bentonitic (expansive) clay. The base of the
lower unit is not exposed in the
Susie Creek area, but where the tributaries
come in contact with this unit, a flat-floored streambed is produced. The
"craters" only occur within
exposures of this formation. In addition,
many small landslides and soil slumps are in evidence throughout the Susie
Creek area. The Elko Craters are
interpreted by this writer as being a
subsidence feature within the "upper" volcaniclastic unit, the
result of groundwater sapping of the "lower"
bentonite-rich unit. Typically, these
depressions are rimmed by the uppermost "veneer" of cobble-rich
colluvium which (in a process that is still not clear)
armors the rim against erosion, giving the
appearance that the rim is "raised". Regardless of whether this
interpretation is valid, the Elko Crater Field is a
unique and geologically striking feature
that requires additional investigation. Should this interpretation have some
merit, and given the ease these features
can be discerned in satellite imagery,
there is the implication (if similar conditions can exist on Mars) that
features originally interpreted as being craters
may actually be depressions produced
through subsidence by groundwater sapping.
2002 Denver Annual Meeting (October 27-30,
2002)
Session No. 239--Booth# 104
Impact Stratigraphy (Posters)
Colo. Convention Center: Exhibit Hall