More Seismites, and some fossils, too

North of Frankfort Ky, some outstanding outcrops of Ordovician rocks are exposed in road cuts along U.S. 27. The outcrops represent an accumulative sequence of sedimentation spanning several millions of years, and the fauna represented in the rocks are typical of Mid.-Late Ordovician shallow tropical seas-brachiopods, partial trilobites, bivalves, gastropods,… ect. All of the usual stuff.

I want to show you a few more photos of some seismites, but first, let me regress. I was in the area to work an outcrop that has been producing large numbers of crinoids, and other interesting oddities(like this and this). But, that morning I wasn’t having much luck finding anything. Though, as I was packing up to leave, I noticed some pinnate structure in a small stone.

Normally, I would pass on something so insignificant, but as this was a second species of crinoid at the outcrop, I picked it up and threw it in the backpack to further document the fauna at the site. When I started working this outcrop, I found a couple of pinnate arms from some kind of crinoid. Until this trip, I hadn’t seen any other crinoids other than the Reteocrinus sp. that are found in abundance in a small talus pile at the base of a small outcrop.

This is the insignificant pinnate structure after a little prep! I haven’t identified the critter yet, but I have an ideal.

A few other photos from the outcrop.

A big ol’ ambonychiid bivalve.

A hypostome from the trilobite Isotelus gigas. The critter that molted this would have been a monster… probably about 25cm!

Rynchonellids litter the ground at this outcrop.

A nice Hebertella frankfortensis.
anterior view

posterior of above

Strophomenids are nearly as common(Rafinesquina sp. in the lower center left).

A trepostomate bryozoan exposing the “tubes” of the zooecia.

A change in lithology from the Millersburg to the Tanglewood members of the Lexington Lm.

Cross bedding in the Tanglewood (a few centimeters from the contact).

On to the Owenton Rd.

A photo of the outcrop along the Owenton Rd. after turning from the bypass. I pulled this photo from Graham Young’s wonderful blog-Ancient Shore. He was in the region for the North American Paleontological Convention, last summer.

As the day was getting hot and humid, I didn’t spend much time at the outcrop looking for fauna, but I did find a few crinoid holdfasts(apparently, I have deleted them from my hard drive. I will re-photograph, and put them up in the future). But, I did save photos of the thick sequence of seismites.

close up of above


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4 Responses to “More Seismites, and some fossils, too”

  1. Shamalama Says:

    I remember seeing similar features a little farther up the road and wondering what they were the last time I visited. Were the layers that are above the layers that became seismites in place when the ground movements occured? Are the seismites limited to specific lithologies, stratigraphic layers or regions?

    • Solius Symbiosus Says:

      Dave, no the layers above were not in place at the time of the quake. If the layer above is a homogeneous calcarenite, it is interpreted as a tsunami deposit.

      Apparently, they are restricted to calcisiltites, calcilutites and finer grained calcarenites, but not in calcirudites or clays. Rast and Ettensohn’s paper mentions that they form in sandstones, I don’t know if this is a reference to the Martinsburg Fm of Va, or the siliciclastics of the Garrard here in Central Ky… probably the former as the Garrard hasn’t been referred to as a sandstone in years??? And, yes they can be used as a temporal correlation device of limited extent. As the energy required to liquefy and cause plasticity of the beds is fairly large, these things form close the epifocus. Hence, their value in locating past seismic activity.

      As you know, I’m an invert geek, but I think that I have the interpretation correct. However, you might want to read the paper linked. And, there are some other great papers in the biblio in the link.

      As an aside, Dr. Rast was my structural instructor back in the day. The man was a genius structural geologist… one of the first in the field. Dr. Ettensohn was the instructor of the first class in geology that I ever took. That was a long time ago when he first came to the university. He is really more of a paleoecologist/paleontologist, and one of the only instructors left at the university from my time there. As such, I enjoy stopping by his office to show him my latest find.

      When I was at the university before, my advisor was the paleontologist(probably what sparked my interest); the lady taught me pretty much everything that I know. She gave me a job in the museum and we spent many countless hours discussing the local fauna.

      Callan Bentley over at
      Mountian Beltway
      is hosting this month’s Accretionary Wedge. The theme is heroes that influenced you. I should write something up about her.

      If you are unfamiliar with his blog, check it out. It is a good one!

  2. Crinoid Holdfasts « Swimming The Ordovician Seas Says:

    […] last two are the ones that I mentioned in this post. They were recovered from the Clays Ferry Fm. in Franklin Co […]

  3. crinoids « Swimming The Ordovician Seas Says:

    […] have mentioned the outcrop a couple of times before(like here and here). I found it on a fluke; I was trying to find another outcrop in which a friend had pulled a […]

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