Guadalupe Mtns GeoTour: Castile Varves EarthCache
Guadalupe Mtns GeoTour: Castile Varves
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This easily accessed highway roadcut along Highway 60/180 in New
Mexico exposes spectacular evaporite and dolomite varve deposits in
the Permian-aged Delaware Basin.
Part way between Carlsbad, New Mexico and Guadalupe Mountains
National Park, this stunning outcrop offers freshly cut exposures
of the Castile Formation interbedded dolomite and gypsum.
The Castile Formation
The Castile Formation represents an evaporite filling of the
approximately 1,800 ft deep basin left at the end of Guadalupian
time. It was clearly was deposited in deep water as indicated by
the absence of shallow-water sedimentary structures and the
presence of fine-scale lamination. The laminae consist of regular
alternations of white anhydrite laminae and darker laminae
containing a mixture of organic matter and carbonate. The
anhydrite-carbonate pairs are known as a Varve. On this outcrop,
the anhydrite may be altered to gypsum due to water getting into
the rock. The laminations have very nice lateral continuity and
individual laminae have been traced for more than 70 miles!!!
What is a Varve?
Laminated bedding in the Castile Formation is interpreted as
Varves. The carbonate and organic (dark) layers represent
near-annual freshening of the salt water in the basin and as a
result plankton growth. The anhydrite (white) layers represent
restricted, more evaporitic conditions like the salt flats west of
El Capitan.
Approximately 260,000 carbonate-evaporite Varves have been counted
in this formation. This suggests rapid deposition of thousands of
feet of evaporites in the Delaware basin. The small folds you may
observe in the lamination bedding of the Castile at this outcrop is
post-depositional and believed to show chages in water content of
the rock as it was uplifted and deformed.
To Log This Earthcache Email me the
following:
1. Measure a one foot vertical section of the outcrop with a
ruler, dollar bill, or even your shoe, and count the number of
varves observed in that section. (Remember, One varve = One light
bed and One dark bed)
2. Based on what you read above, how many years did it take
to deposit this One foot section?
3. Are the laminated beds perfectly flat? If not, describe a
few features you see in the bedding.
4. Describe how you believe any deformation in the badding
occured.
Optional: Post a photo of yourself at the coordinates with
the outcrop or view of the Guadalupe Mtns behind you.
I want to stress safe parking at this outcrop. Please be
sure to pull completely off the highway onto the wide shoulders.
Even then, watch for traffic before opening your doors, and
entering and exiting the vehicle.
Additional Hints
(No hints available.)