This earthcache will guide you to some of the best examples of
folds. Please read the instructions carefully before attempting the
cache as you will need to complete a task on the way to the
official cache coordinates. The cache is done exclusively from the
road. You will need a means of transportation in between the
different spots to complete the cache. You can stop in any points
in any order.
First, let's start with a few definitions:
Fold
The term fold is used in geology when one or a stack of originally
flat and planar surfaces, such as sedimentary strata, are bent or
curved as a result of plastic (i.e. permanent) deformation.
Fold Belt
A set of folds distributed on a regional scale constitutes a fold
belt, a common feature of orogenic zones (zones where mountains are
built) |
Folds in the Marathon area were created mostly during the Ouachita
deformation about 275 to 290 million years ago. The term "Ouachita"
comes from the Ouachita Mountains of Arkansas and Oklahoma. (These
were named by the Indians, whose words were rendered into written
language by the 16th century French explorers.). The Ouachita
Structural Belt extends all the way to the Marathon region. One of
the type of rock layer that was folded was the Novaculite.
Novaculite is very resistant and allows the structures to be
well-preserved and stand out in bold relief.
Depending on the shape of the fold, it can be classified in
different fold types:
Fold Types
- Anticline: linear, strata dip away from axial center, oldest
strata in center.
- Syncline: linear, strata dip toward axial center, youngest
strata in center.
- Dome: nonlinear, strata dip away from center in all directions,
oldest strata in center.
- Basin: nonlinear, strata dip toward center in all directions,
youngest strata in center.
- Monocline: linear, strata dip in one direction between
horizontal layers on each side.
- Recumbent: linear, fold axis oriented at low angle resulting in
overturned strata below the fold axis.
- Slump: typically monoclinal, result of differential compaction
or dissolution during sedimentation and lithification.
- Ptygmatic: Folds are chaotic, random and disconnected. Typical
of sedimentary slump folding, migmatites and decollement detachment
zones.
|
Tasks:
Coming From Marathon
- Drive South on 385, around 10 miles south around N30 05.300
W103 15.910, admire on the west side of the road, the first
examples of folds. No need to stop there, although you can take a
picture for bonus points :-)
- Go Little picnic area with marker - N 30 03.995 W 0103 16.470.
Read about the geology of the area.
a) Answer by email: What is the spanish nickname of the white rock
folds
b) Answer by email: What is the name of the high, flat-topped
mountain to the southwest.
- Park on the parking area on the side of the road at N30 02.521
W103 16.986
You can see to the North West of this point a beautiful example of
Novaculite Fold.
a) Take a picture of yourself in front of the folds. Please attach
to the online log.
b) Answer by email: What types of folds to do you see there
(Anticline, Syncline, etc...)?
c) Answer by email: How many folds are visible from this
point.
Coming from Big Bend NP, you should probably do it in reverse
order.
Have fun!, don't forget your camera. A pair of binoculars is
also useful!
Reference
- Marathon Fold Belt - University of Texas of the Permian Bassin
http://ceed.utpb.edu/geology-resources/west-texas-geology/marathon-fold-belt/
- Fold - Wikipedia -
http://en.wikipedia.org/wiki/Fold_(geology)
- Geology of the Marathon Uplift, Earle F. McBride, Department of
Geological Sciences, University of Texas at Austin ,
http://rockfractureandstress.com/Burnett%20Ranch/Geology%20of%20the%20Marathon%20Uplift,%20west%20Texas.pdf
- Continent-Continent Collision along the Southern North American
Margin: The Ouachita-Marathon Orogeny - Colorado University -
http://www.colorado.edu/GeolSci/Resources/WUSTectonics/AncestralRockies/ouachita.html
- Ouachita Mountains - James S. Aber
http://academic.emporia.edu/aberjame/struc_geo/ouachita/ouachita.htm