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Addressed in this FAQ list:
| 1 |
Boxwork |
| 2 |
Sequatchie Valley |
| 3 |
Dinosaur eggs, bones, etc. |
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1. Boxwork
This is such a remarkable pattern; it must be
man made.
Is it man made?
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No. This is not man made.
"Boxwork" is a fairly common, natural occurance in
the flat-lying Pensylvanian sandstone that caps the plateaus
in the Chattanooga area. People report finding "boxwork"
on Lookout, Elder, and Mowbry Mountains, and on Walden Ridge.
It consists of square or rectangular cells separated by relatively
thin vertical walls. The cells are commonly recessed and range
from one to several centimeters across, although larger examples
of "boxwork" have been described.
"Boxwork" originates as orthogonal planar fractures,
perpendicular to bedding. Fluids, laiden with cementing agents,
pass through the fractures. The extra cement, iron oxide in this
case, is deposited in the sandstone immediately adjacent to the
fractures. Sandstone in the rectangular spaces between fractures
lacks the extra cement; it remains relatively soft and weathers
away to become recessed.
In this photo, notice the fine dark line that is medial to
each ridge. This line is in the vein that occupies the original
fracture. Also notice the red color where ridges have been broken.
The red color is due to iron oxide.
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2. Sequatchie Valley
Sequatchie Valley is exceptionally long, narrow,
and straight.
Is it a rift valley like the east African rift
valley?
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NO. ABSOLUTELY NOT!
Despite the rumors and the numerous web sties claiming
it to be such, Sequatchie Valley (white arrows on the digital
relief map) is NOT a rift valley.
In fact, Sequatchie Valley more closely relates to a compressional
geologic structure, the Sequatchie Valley anticline. (In a sense,
a rift valley is just the opposite, a tensile geologic structure.)
At the crest of the Sequatchie Valley anticline (an upward
fold), Pennsylvanian sandstone was breached by erosion. (This
sandstone serves as a resistant cap rock for the plateaus in
the Chattanooga area.) The valley was formed by extensive weathering
of the underlying Ordovician, Silurian, and Mississippian limestone,
which occupies a structurally higher than normal position at
the core of the anticline.
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| Schematic cross section, A-A', showing (1) Ordovician
(O) through Pennsylvanian (IP) strata, (2) present-day topographic
profile, below which geologic units are colored, (3) large geologic
structures including the Sequatchie Valley anticline (SVA) and
the Lookout Valley anticline (LVA), and (4) possible topographic
profiles of the geologic past (t0 = oldest, t2 = youngest). Section
is not drawn to scale and is vertically exaggerated. See digital
relief map for approximate line of section. |
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3. Dinosaur eggs, etc.
What about all the dinosaur bones and eggs that
people find along the shores of Lake Chickamauga and elsewhere
in the Chattanooga area?
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For now, let it suffice to say that these are oddly shaped
masses of chert that have weathered from Cambrian and Ordovician
carbonate rocks (limestone and dolostone). Indeed, many of these
masses are egg shaped and are concentrically layered. Others
are elongate with bulbous ends and closely resemble large bones.
But, they are neither eggs nor bones; they're just chert.
Chattanoga is blessed with abundant fossils, but not those
of dinosaurs.
Photo(s) and a more detailed explanation are coming soon.
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