This geologic formation visible in the roadcut is called a
dolostone body. It is a highly altered rock with enhanced porosity
that can hold oil if oil has moved through the area after the
dolomitization has occurred. Several of this have been documented
in the area and hundreds have been mapped around the state. These
isolated dolostone bodies are spatially related to mapped faults,
and have been interpreted as products of hydrothermal fluids that
moved along fault conduits, replacing adjacent limestone. This
particular outcrop is affectionately referred to as the
“Lightbulb” by local geologists due to the outline the
feature displays at the outcrop. It is considered an excellent
example of faulted, fractured, and dolomitized Lexington Limestone.
Geologists from all over the country have come to see this
particular structure.
The Lightbulb was formed by replacing bedded limestone of the
Lexington Limestone. The complete transition from bedded limestone
to dolomite is present in the roadcut. The dolostone body is
overlain by unaltered limestone at the top of the roadcut,
indicating that the dolomite was emplaced by fluids moving upward
along the fault. A small fault is present on both sides of the
highway, but dolostone is much better developed above the fault on
the northwest side of the roadcut. Only traces of saddle dolomite
occur on the southeast side of the road. This dolomite body is
unique in that the entire transition from limestone to dolostone is
visible within a single outcrop. The Lightbulb contains
matrix-replacive dolomite and vugs (cavities inside rock) lined
with pink saddle dolomite, characterized by curved, saddle-like
crystal morphology. Filled vugs can sometimes be found in this part
of the county and on hot days petroleum can be seen to leak out of
them.
To get credit for finding this earthcache please email me (do
not post the answer when logging this cache)
1. The thickness of the unaltered limestone above the dolostone
body.
2. The title of the historic marker that is 150 feet to your
right.
You can go ahead and log your find but logs might be deleted if
the answers to the questions are not emailed to me. Posting a photo
of yourself in front of the earthcache is encouraged, but is not
required.
