The “headless” trilobite:
An I. gigas that was found in the Clays Ferry Fm. in Anderson Co. Kentucky. When I found it, it was posterior-dorsal up. Wow, I was excited! Oh well…
Neat-none the less.
Usually, brachiopods don’t get me very excited(sorry lophophorate nerds), but occasionally I come across something in the field that causes me to do a double take.
Have a look at this monster. It is an orthid brachiopod that was collected from the Millersburg Mb. of the Lexington Limestone in Fayette Co. Kentucky
Apparently, I didn’t photograph the ventral… oh, well.
I have one that is even larger! Somewhere???
Recently, in an email exchange with another Paleozoic geek, we discussed the relationship of the stratigraphy of Ontario with that of Kentucky. The discussion centered around the Veralum Formation up north(Canada), and which units of the Lexington Limestone(Kentucky) share a temporal equivalence, i.e., which beds of the Lexington were deposited at the same time as the Veralum.
It has been know for some time that the Bobcaygeon Fm. of Ontario was deposited at about the same time as the Curdsville mb. of the Lexington Lm. Further, the ecology and the environment was very similar; many of the same rare echinoderm/trilobite assemblages are found in both beds.
Outside of the carbonate build-ups of Central Kentucky, that time in the Ordovician represented a transgressive sequence, so one would assume that the relationship could be established by looking at the stratigraphic record for both areas.
Mitchell, et. al. in 2004 did just that. Proceeding from the works of previous authors, they studied a prominent meta-bentonite(the Millbrig K). Since, ash falls are distributed over a large region, could they be correlated?
One of the real gems of this paper is the correlation chart. Using the ash falls, they correlated the rocks from Illinois through Kentucky, and then up through the foreland basin of New York.
So, pertinent to the email exchanges, it appears that the Veralum’s equivalent in Central Kentucky is the Tanglewood and Millersburg members, and some basal units of the Clays Ferry and Kope Formations in the Outer Bluegrass region.
Further reading and references:
Discovery of the Ordovician Millbrig K-bentonite Bed in the Trenton Group of New York State: implications for regional correlation and sequence stratigraphy in eastern North America
Charles E. Mitchell, et. al.(2004)PDF
USING GIS TO ASSESS THE BIOGEOGRAPHIC IMPACT OF SPECIES INVASIONS
ON NATIVE BRACHIOPODS DURING THE RICHMONDIAN INVASION IN THE
TYPE-CINCINNATIAN (LATE ORDOVICIAN, CINCINNATI REGION)
Alycia L. Stigall(2010), et. al.
Ordovician K-bentonites of eastern North America
Dennis R. Kolata, et. al.(1996)
Nestled in the rolling hills of Central Kentucky, the quaint little town of Versailles is a welcome respite from the rigors of city life. It is better known for its picturesque scenery of Thoroughbred horse farms and the fine bourbon whiskey produced in the region, but there is evidence of a violent catastrophe that struck the region long ago, in the Paleozoic.
The Versailles “cryptoexplosive” is an enigmatic 1.5 km circular structural feature located a few kilometers north of the town. The structure was originally referred to as ‘crypto'(ie, hidden) because an explanation for this, and a couple of other similar structures in the region, was lacking.
At the time, it was thought that a plume of water enriched magma approached the surface; out gassed, and then the structure collapsed-resulting in the features now observed at the surface(I’m not a tectonic guy, so could someone explain how a water rich magma can be found this far from a convergent boundary; are there examples??? Or, was this before the mechanisms of Plate Tectonics were understood?).
By the ’60s, geologists began to recognized the similarities of the structural features of the Versailles abnormality to other structures that were better explained as extra-terrestrial, in nature. In the ’70s, geophysical surveys were conducted in the area in an effort to determine whether, or not, the abnormality was an at-depth structure associated with mantle plumes, or whether the structure was a shallow feature that was not associated with the basement tectonic features observed in the region.
While lacking primary structures such as shatter cones or shocked quartz, the consensus among geologists, due to structural features, is that the Versailles cryptoexplosive is the eroded remains of an impact of a meteoroid.
Further reading and references:
Addendum-the stratigraphic nomenclature of the area has changed; now, the Cynthiana is recognized as part of the Lexington Limestone. The Million Shale of Nichols is now known as the basal part of the Clays Ferry Fm.
As an aside, here is Tony Rice doing Nine Pound Hammer.
In my younger years, as I do still, I loved his playing with JD Crow down at JDI where the beer/whiskey flowed freely.