What are these Mud Cracks doing here? EarthCache
What are these Mud Cracks doing here?
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The Mud Cracks can be found off of TN Hwy 31 approx
5.7 miles north of US Hwy 11- W. Turn right on Mountain Valley Road
and proceed for about 2.2 miles. Please see parking
coordinates!
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Mud Cracks or Petrified Dragon Skin
First, to answer the question posed in the title of this
Earthcache and in the photo caption, the Mud Cracks are just
doing what Mud Cracks do and contrary to
what rock&crystal tried to convince their 13 year old
daughter, they are not Petrified Dragon Skin! (She didn't
buy it either!)* They, the
Mud Cracks, are just sitting here and weathering away! In a
few million years, you may not be able to see them. Look while you
can! Now how they got here, that’s another question?
Mud Cracks form when muddy sediment is exposed to
the atmosphere and dries up. They have a characteristic polygonal
shape when viewed from above. When viewed from the side, the cracks
are “V”-shaped, with the wider part of the
“V” toward the surface. Thus, mud cracks, when
preserved in the rock record, indicate that the sediment formed in
an environment that was alternately wet and dry, like a tidal flat
or the flood plain of a river. The distinct "V" shape of the crack
in cross-sectional view can indicate which way is up. It takes a
very active environment, where sedimentation is fast, to preserve
delicate features such as mud cracks. But, over several million
years, conditions changed, and the environment became more
tranquil. Very slow-moving rivers carried less sediment to the
coast, and the coastal waters began to clear. Thus the sediment was
deposited and with drying, the Mud Cracks formed and were
left for our viewing pleasure.
Yes, the nearby Clinch Mountains were formed by uprifting
that occurred during the Alleghenian orogeny. This orogeny (another
name for “mountain forming”) is one of the geological
mountain-forming events that created the Appalachian Mountains
which incudes the nearby Clinch. Approximately 350 million to 300
million years ago, in the Carboniferous period, when Gondwana
(later to become Africa) and what became North America collided,
forming the super continent, Pangaea. This collision exerted
massive stress on what is today the Eastern Seaboard of North
America, resulting in a large-scale uplift of the entire region. It
was during this time the Clinch Mountains were formed. Much, much
earlier there was a lot of inland water in the area.
Before the Clinch Mountains were formed, the inland seas
and rivers had developed. It was due to these seas and/or slow
moving rivers that mud was deposited, dryed and the cracks filled
in by other sediment to form our Mud Cracks. The cracks were
filled in by carbonate (later to become limestone) material which
soldified and created the interesting pattern and color of our Mud
Cracks. The well developed rocks that are the Mud Cracks are
Ordovician in age which proceeds the above mentioned Alleghenian
orogeny.
The Mud Cracks are not perfect polygons. The reason
for this is the cracks were flattened prior to bedding. This is
known as a ‘strain marker’, which is a feature with a
well-known original shape that has been changed due to some sort of
strain or pressure. If you look close enough, perhaps you can count
the original sides.
Close up and Personal
Please Note! In order for you to claim a find of
this Earthcache, you must complete the following: 1. Post a
photo of you and/or your GPSr pointing to the Mud Cracks.
While it would be nice, it is not necessary to show your face in
the picture. Via email only, answer the following questions:
A. What is the length of the Mud Cracks? B.
What is the width of the cracks? C. As mentioned earlier,
the cracks “have a characteristic polygonal shape”. How
many sides are in a polygon (trick question) and what made them
‘lopsided’ (squished)?We hope you have enjoyed this
little bit of geology as much as we did. We are certainly not
geologists………..far from it! We have found the
subject becoming more and more interesting so from a strictly
amateur point of view, we simply want to share these wonderful
local geological phenomena with you. We are learning as we go
along.
* Many
thanks to rock&crystal for sharing the Dragon Skin story
with us. It sounds like something I would try to pull on my
grandkids!
This Earthcache was approved by the
Geological Society of America
| We have earned GSA's highest level: |
 |
Additional Hints
(Decrypt)
"Cbyl" jnag n penpxre? Fbeel sbe n yvggyr trbybtvpny uhzbe. Lrf, V xabj, irel yvggyr uhzbe jnf vaibyirq!
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