Posts Tagged ‘kentucky’

Sea Monsters

July 9, 2010

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

Hebertella sp.

anterior

Posterior

Dorsal

Apparently, I didn’t photograph the ventral… oh, well.

I have one that is even larger! Somewhere???

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Trilobite Molts-Up Is Down, And Down Is Up

July 1, 2010

A while back, Chris over at Ediacaran put up a post in his “Paleoporn” series describing the environment and sedimentology of two sites, in the same formation, where the same Cambrian trilobite is found. His post is a description of the orientation of the molts in the two different environments. In the comments, we discussed the curious habit of finding inverted cephalons, ie, ventral up cephalons while the rest of the critter is found in its normal position(dorsal up).

In a thin bed of the Clays Ferry Formation in Anderson Co. Kentucky, I find numerous partial molts from the trilobite Isotelus gigas. Some of the bedding planes are almost entirely composed thoracic segments, cephalons and cranidiums, and pygidiums from this large asasphid. Occasionally, one comes across the curious preservation described above.

During ecdysis, the cephalic sutures of the trilobites rupture allowing the critter to escape from the front of its carapace. Sometimes during the egress, the critter will push the cephalon upside down. Hence, what we have here.

When I found this one, it didn’t appear that much was there.

But, I brought home anyway. While hitting it with a scribe, I noticed the ventral, but I thought that it was trash and nearly blew through it… as more became apparent, I slowed up a bit(word to the wise).

I have found several more from the same locality, but those are all that I have photographed. However, here is a nice juvenile that appears to have had a bite taken out it.

More on that later.

Sponge Encrusting Worm Tube Encrusting Bryzoa

June 10, 2010

At a crinoid garden that I have been working for a couple of years, I found this curious example of an epibiont on an epibiont.

First, a trepostomate bryozoan found its home, then some cornulites worm tubes found the bryozoan inviting.

Finally, the sponge.

When it was alive, it had to have been pretty cool looking with the worms sticking out of the sponge.

Width of photo about 3cm

Mag x10

You know the scale

Since, it was found at one of my crinoid “gardens”, here is a double from the same locality. I have pulled about 50 crinoids from this site(too lazy to check my notebook), and the Archaeocrinus sp. out number Pychnocrinus sp. by a substantial majority(again, too lazy to check my notebook), So these are probably Archaeocrinus sp.

Many of the crinoids at this site appear to be weathered, but they are from fresh exposures??? They are found in a thin lens of mudstone within a calcarenite/calcirudite. They are early Late Ordovician. Some researchers postulate that the abrupt changes in facies in the Central Kentucky region is due to weird structural crap associated with tensional forces at the close of the Taconic Orogeny to the east.

So, that leaves me wondering… were these critters left high and dry in their shallow lagoon/inlet by a regression, and then covered by a transgression??? It seems plausible. They could have laid there for months, or longer, since there were no land critters to pick at the carapaces.

Do you have another scenario??? Let me know.

Anyway, here is the double.

Width of photo about 10cm

Here is one that I have shown before. It is from a fresh exposure, so it can’t be weathered.
Width of photo about 6cm

Structural Inversion and the Origin of a Late Ordovician Carbonate Buildup:

The Ordovician Earth System

Correlations Across A Facies Mosaic…

Correlating the Ordovician of Laurentia

May 12, 2010

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?

The abstract:

    The Ordovician (Chatfieldian) Millbrig K-bentonite Bed is a key stratigraphic marker horizon that is regionally synchronous over much of eastern and central North America. This prominent marker is an independent source of correlation among the major chronostratigraphic and sequence stratigraphic units in this region. The general stratigraphic position of the Millbrig Kbentonite has suggested to some authors that it is identical with the Hounsfield K-bentonite at Dexter, New York (the traditional type area of the Middle Ordovician, or Mohawkian Series in North America), but previously available geochemical and biostratigraphical evidence has been insufficient to confirm this correlation. Analyses of apatites and melt inclusions in quartz phenocrysts from the Millbrig K-bentonite at eight localities in Kentucky, Missouri, Virginia, and Pennsylvania and the Hounsfield K-bentonite at its type locality at Dexter, New York, using high-precision electron microprobe analysis techniques shows that the Millbrig and the Hounsfield have identical apatite and melt inclusion chemistry indicating a geochemical correlation. This correlation is supported by conodont biostratigraphy, and d13C isotope chemostratigraphy. The new data demonstrate that the Millbrig K-bentonite, and therefore the base of the Chatfieldian Stage of the North American Mohawkian Series (by definition), lies very close to the base of the traditional Rocklandian Stage of New York. Furthermore, the Millbrig Kbentonite Bed lies in close proximity to the base of the Taconic supersequence over much of the Midcontinent region and in particular lies just below the M5 sequence boundary recognized in Kentucky and Tennessee. Our results permit extension of the Chatfieldian sequences into New York State and southern Ontario, and contributes to the resolution of the long-standing uncertainty about the position of the base of the Trenton Group in Ontario. Furthermore, viewed in a broad context of regional stratigraphic relations, we conclude that our results suggest that the persistent correlation difficulties reflect diachronous effects of widespread changes in oceanographic circulation patterns that emerged during Taconic Orogeny. Finally, regional differences in the timing and character of sequence bounding surfaces and facies similarities summarized here suggest that the causes of relative sea level change during the Chatfieldian may have been primarily tectonoeustatic mechanisms.

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

Blackriveran carbonates from the subsurface of the Lake Simcoe area, southern Ontario: stratigraphy and sedimentology of a low-energy carbonate ramp
Jonathan L. Grimwood, et. al.(1999)

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)

In the “Garden”

May 8, 2010

Upon returning to the Bluegrass region of Central Kentucky a couple of years ago, the first outcrop that I planned to visit was the type section for the Millersburg mb. of the Lexington Lm.

Generally, though out the Late Ordovician, most of the Laurentian margins were experiencing transgressive sequences, but here, regressive shoal complexes associated with deep-seated tectonics produced the carbonate clastics common to the area.

The Lexington Lm. is a complex assemblage of limestone and shale facies where the changes can be abrupt-both laterally and vertical. The formation is generally a transgressive sequence that grades upwards into the deeper water limestone and shales. However, in the inner-bluegrass region, the Tanglewood and Millersburg members are an exception to the transgressing sea sequences.

The Tanglewood is a thick sequence of coarse-grained calcarenites with local unconformities and tidal influenced structures; many of the beds are cross stratified(The header for the blog is one of those sequences).

The Millersburg is typical of the complex facie relationships of the region. It inter-tongues with the other members of the Lexington above and below, and in some places, it is absent; it isn’t even consistent within its own framework. Drive a few kilometers down the road, or climb/ descend a few meters in the column, and the fauna/lithology changes. The Millersburg is nodular limestone and shale that was deposited above the wave base.

But, I love it! The Millersburg is one of my favorite members of the Lexington Limestone. It is the unit in which I found my first trilobite, and one of my first crinoids. While, it is more known among local invert geeks for the common fossils found in its beds, there are some beds that produce spectacular finds(if you read this blog, you will notice that most of the stuff contained in it is from the Millersburg).

So, back to the start of the post. Driving out Main Street, I noticed that those nefarious engineers had widened the road. It used to be a nice drive in the country; now it is a four lane highway with a median and shoulders to park your vehicle if it decides to quit working. That sent shudders up my spine! Then, as I approached the type section, my heart fell out. It was gone!

The type section gone? How could it be? Perhaps it was ignorance; maybe the reason was economic? Who knows? But, It was gone!

Unfortunately, the destruction of significant geologic treasures is common. I have to assume that the reason is ignorance… how many engineers could know the significance of what they are destroying when they plan their construction projects?

My favorite outcrop was no more. Oh well! One has to move on, and so, I did. About a kilometer down the road, and a 10 or so meters down in the column, there was a tongue of Millersburg sandwiched between some shallower stuff of the Tanglewood mb.

On one of my first visits to the site, I found a nice Pychnocrinus sp., but I didn’t find the bed that it came from. It was located in the float at the base of the outcrop.

width of photo about 10cm

With this clue, my latter visits to the site were spent in the area where I found that little cutie. At first, I wasn’t having a lot of luck locating the bed in which the crinoid was from, but then I climbed a little up in the column, and perched at the edge of a ledge, I found this large pinnate structure.

width of photo about 12cm

Just above the ledge was a bed of clay that pinched out a couple of meters in both directions. That small bed has produced over 40 crinoids in just the face of the bed.

Curiously, a lot of the crinoids appear to be severely weathered… even when pulled fresh from the rock. The rapid changes in lithology-vertically- is thought to be a result of changes in sea level due to tectonic forces related to the Taconic Orogeny. The bed might represent a paraconformity where a small uplift drained the area resulting in the bed’s exposure.

Pychnocrinus (?)

This is one that I found recently. microscope stage for scale

Calyx encrusted by a bryozoan(I’ve never seen this before)
width of photo about 20 cm

Lots of partials(you know the scale by now)

Some are hard to recognize, at first

I have prepped a lot of the crinoids, and some have turned out, nicely. I’ll put some of those up in the future.

Further reading and references:

Contributions To The Geology of Kentucky: Ordovician System

From the Cincinnati Arch to the Illinois Basin: geological field excursions

LITHOSTRATIGRAPHIC FRAMEWORK OF THE TANGLEWOOD BUILDUP, LEXINGTON LIMESTONE (UPPER ORDOVICIAN) OF THE BLUE GRASS REGION, CENTRAL KENTUCKY

Sequence stratigraphy and long-term paleoceanographic change in the Middle and Upper Ordovician of the eastern United States

Extinction, invasion, and sequence stratigraphy: Patterns of faunal change in the Middle and Upper Ordovician of the eastern United States

Unknown Critter/Flora

May 3, 2010

I have encountered this strange structure a few times in my quest to understanding the Ordovician of Kentucky. It is rarely seen, and I always ignored the thing since it didn’t seem relevant to what I was studying. Though recently, I found a few of these, intimately associated, in what might be a lagoonal environment???*

That grabbed my attention, and I submitted photos of this thing to several well known paleo-researchers. Most had no ideal, but Dr. Young clued me in! Probably, algal balls. He suggested a thin section would be determinate, but I still haven’t cut the thing.

When informed of Dr. Young’s opinion, another researcher concurred, but he hadn’t seen any, this large, from the local biota; one other was skeptical.

So, have you seen anything similar?

mag x20

These were found in a mud bed, of limited lateral extent(a few meters), interbedded within the calcarenites of the Tanglewood mb. of the Lexington Limestone.

*perhaps, that is my familiarity with the barrier islands???

Too, why can't I figure out the code of wordpress?

I’m not a ‘puter geek, but I thought that the site was HTML??? Any suggestions?

Derby Day

May 1, 2010

I guess if you are not from Kentucky, you might not understand, but…

The first Saturday in May is a holiday in the state. It rivals any national holiday- at least, here! I have yet to meet a Kentuckian that doesn’t celebrate the day. It is a day that people that normally don’t drink, find themselves waking up, and pestle mint for the obligatory julep… or 10… or more!

Now, I work nights, and I usually drink when people are asleep, but it is a welcome respite that many other of my fellow Kentuckians are sippin’ corn this morning.

Will a fillie do it this year… it has been along time! The 136 running of the Run for the Roses should be an exciting race.

Cheers, Tim

A Lovely Critter

April 25, 2010

When driving to my sister’s house in Anderson Co. Ky, the road that I travel traverses the beautiful Kentucky River gorge. The Kentucky River is a meandering stream that was entrenched in its gorge by an uplift in the area during the early Pliocene.

The relatively recent uplift in the area has resulted in an immature drainage of the subsurface that is especially noticeable in periods of heavy rain. In the winter, after a low pressure system moves through the area dropping rain, and if the temps drop below freezing, stunning examples of the immaturity can be seen at many outcrops(more on that in a later post???)

Crossing the gorge on this route, one notices the Austin Nichols distillery; makers of some of the finest Bourbon that money can buy, and a progenitor of some of the greatest times that I have ever had…
Photobucket

… and probably at least one divorce!

The outcrop in the middle right of the photo is the Logana member of the Lexington Limestone. The Logana is a sequence of alternating limestones and shales that is, for the most part, poorly fossiliferous. For that reason, I never gave it much thought. However, at the base of the Logana is the Curdsville mb of the Lexington.

The Curdsville, though sparsely fossiliferous, has been known to produce, exceptionally rare and well preserved, echinoderms and trilobites in shaley partings separating some of the beds.

Finding a place to park for this outcrop is challenging; there used to be a roadside park adjacent to the outcrop in the days before the interstate system, but alas! No more(Too, It is dangerous, as the road is curvy and only about a meter distant). As luck would have it, about a kilometer up the hill is an area where a suitable place to pull over can be found.

So one day, with a little time on my hand, I checked it out.

I found a large boulder that had probably been blasted when the road was cut, and on the boulder was found this Iocrinus sp.
width of photo about 12cm

A few centimeters from the crinoid, this holdfast was found.
width of photo about 10cm

At the time, I only had a hammer and chisel, so I chopped the two pieces from the rock. Hence, the breakage.

Apparently, Iocrinus sp has not been found accompanied with a holdfast, often, and there is some debate as to its type holdfast, ie, was it sessile???

If the holdfast found intimately associated with this critter was its own, well…

addendum: I have worked the outcrop extensively. It is dangerous, and not worth your time. I have “pulled” anything of any substance… which was little, and there are many more productive outcrops in the region. DON’T GO THERE!

Not Seen, Often

April 21, 2010

Years ago, while at a friend’s farm in Anderson Co. Kentucky, I noticed a small bed of rock(calcilutite) in the Clays Ferry Formation(early Late Ordovician) that was composed of, almost entirely, “orthoceras” cephalopods and partial pieces of the trilobite Isotelus gigas. Upon further examination, I discovered that the bed contained quite a few complete, or nearly complete, trilobites.

With a little patience, and a hammer, one could pull, at least, one or two complete “bugs” with every trip.

One day while working the creek, I noticed a piece of float that contained 5 crinoid heads. I left the area shortly after, and unfortunately, was never able to locate the bed that contained the crinoids. Interestingly enough, the piece of float also contained a few conulariids(I’ll post those soon). The reason for the post is this beautiful, and somewhat rare, disparid crinoid-Columbicrinus sp. that was found that day. It is the best of the bunch. Now, that I am back in the area, I hope that the bed that contained this handsome critter will finally be located.

The grid is 1/4in(0.625cm)

Same scale

It Came From Outer Space

April 18, 2010

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.

USGS 7.5 min quad of the area(Versailles Ky)

Cross section of structure(again, from the USGS quad)

Explanation(from same)

Google relief map of the area(annotated)

Further reading and references:

A shallow seismic refraction study of the Versailles cryptoexplosion structure, central Kentucky.
Harris, 1990

The Geology of Kentucky
USGS

Earth Impact Data Base

Geophysical Investigation of the Versailles, Kentucky, Astrobleme(pdf)
SEEGER

Kentucky Academy of Science: 92 annual meeting(pdf)

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.