Interesting Sedimentary Structure-Seismites

[Guest solius symbiosus]

I'll get to the seismites momentarily.

I decided to stop by the outcrop that has been producing the Reteocrinus sp. this morning. I saw a lot of the usual stuff, so I didn't bother to photograph anything(since you guys have already seen it) except this nice example of beekitization on a strophemenid brachiopod, for those that haven't seen this type of structure.

fossil about 4cm

I Have visited this outcrop about 20 times in the last couple of years, and on every visit, I have found, at least, one crinoid... many times, it was multiples. I thought that this was to be the first visit without finding anything of note.

On my first visit, I found the pinnate arms of some kind of crinoid; obviously very different from the usual Reteocrinus sp. that I have found at the outcrop. As I was preparing to leave, I noticed a small area of pinnate structure on a stone.

Usually, I would pass on something so irrelevant, but as I had only seen it, at this outcrop, once before, I decided to bring it home to further document the various echinoderm fauna at this locality.

Boy, was I surprised! When I put it under a microscope, I noticed that most of the crown was there; it only needed a little prep work... and to think, I almost left it. Anyway, I did a little prep on one side(the other side looks very promising, too). this is what I found:

Not sure of the genus, but I have an ideal.

length about 5cm

Since this trip seemed to be producing nothing, I decided to drive a few miles to another outcrop that I have been wanting to visit.

The most obvious thing that one sees at this outcrop is stunning examples seismites. Research into the origin, and interpretation of seismites is a relatively new field of study in geology. Previously, these structures were thought to form as a result density difference during diagenesis, but now they have been interpreted as seismic induced structures that occured before the sediment lithified.

They are significant because they can help locate paleo-epicenter of long past earthquakes.

These seismites are the result of the Taconic Orogeny; a time when, what is now, the East Coast was on the edge of an convergent plate boundary. There was an island arc(similar to what Japan is today) that was being "shoved" onto the continent by the collision of, what is now, Europe.

That led to a lot of earthquakin' (I don't know if that is a word, but...), which in turn disturbed the, still wet, sediments producing these curious structures.

Notice how the beds resume a normal horizontal plane in this pic. I would think that that is when the earthquake occurred that produced the seismites.

I figured that while I was there, I might as well get in some collecting.

Mid Ord

tongue of the Clays Ferry Fm.

Gastropods could be picked up by the dozens.

4 on a slab

Cyclonema varicosum

A big one (about 7cm)

One that had broken revealing calcite xls

Ambonychiid bivalves are also prominent, but they are internal molds.

Trepostomate bryozoans probably dominate the fauna here. They are everywhere.

Escharopora sp (?) and a tabulate(Favostella sp. ?)

Heterotrypa sp.(?)

Hallopora sp. (?)

But, by far, the best find of the day(and the only thing that I brought home(other than the crinoid)) was this double crinoid holdfast.

I found one other holdfast, but apparently, I didn't photograph the thing.

All in all, it was a good day; a few holdfasts, a new crinoid, and some great structure.

[Hawkeye]

I must have never been looking in the right place when I lived in KY. Your stuff is always great Solius!

[Auspex]

Is the seismite structure itself fossiliferous, and if so, are the fossils distorted?

[Guest solius symbiosus]

The bed at this location is not fossiliferous, but if it was, no, the fossils wouldn't be distorted. Deformation(strain) results from external stresses on the rock from tectonic forces(usually from afar). These structures result from seismic waves disturbing the soft sediment.

[Shamalama]

GREAT POST! I love when you explain your finds and the geology around them. Since I drove past a similar roadcut while in your area in May I know exactly what you are showing me and it all starts to fall in place.

[MikeD]

I decided to stop by the outcrop that has been producing the Reteocrinus sp. this morning. I saw a lot of the usual stuff, so I didn't bother to photograph anything(since you guys have already seen it) except this nice example of beekitization on a strophemenid brachiopod, for those that haven't seen this type of structure.

That is really interesting and cool looking. I have never seen that before. I could not find much info on it. I assume you took that one home.

[Guest solius symbiosus]

I assume you took that one home.

I left it. I have a couple of nice examples collected years ago. The only thing that I brought home were the crinoid, and the holdfasts. I rarely pick stuff up, unless it is... well, rare.

[manta]

Very nice

[Terry Dactyll]

solius symbiosus...Thanks for the geology lesson..... I may not enjoy reading myself, I cant sit still long enough.... but Im learning from your experiences this way..... another piece of the jigsaw.... I might not know the technical terms, but I fully understand the processes.... thanks for that.....

[Guest solius symbiosus]

... I cant sit still long enough...

Haha, me neither.

[PHACOPS]

Love your posts solius.I live in cincinnati and do a alot of trips to ky.Been wanting to try the outcrops around bardstown have you hunted there?And also the outcrop near hazard ky.

[Guest solius symbiosus]

I have collected some of the Devonian of that area, but not Silurian. And no, not in that area. It has been many years since I collected anything(and I hate this term)Carboniferous.

[Guest solius symbiosus]

Surely, we should plan a trip sometime. There are a few members from this area.

[PHACOPS]

yea that sounds good im actually planning on going down there the weekend of the first of august i have permission to go to a quarry in jeffersonville indiana if your interested

[MikeD]

I left it. I have a couple of nice examples collected years ago. The only thing that I brought home were the crinoid, and the holdfasts. I rarely pick stuff up, unless it is... well, rare.

If you go back to that area, do me a BIG favor and pick it up for me please (if you can find it again) and I'll get it sometime in the future whenever my plans to visit home finally materialize. I think it is very cool.

[Harry Pristis]

I'll get to the seismites momentarily.

<snip>

Since this trip seemed to be producing nothing, I decided to drive a few miles to another outcrop that I have been wanting to visit.

The most obvious thing that one sees at this outcrop is stunning examples seismites. Research into the origin, and interpretation of seismites is a relatively new field of study in geology. Previously, these structures were thought to form as a result density difference during diagenesis, but now they have been interpreted as seismic induced structures that occured before the sediment lithified.

They are significant because they can help locate paleo-epicenter of long past earthquakes.

These seismites are the result of the Taconic Orogeny; a time when, what is now, the East Coast was on the edge of an convergent plate boundary. There was an island arc(similar to what Japan is today) that was being "shoved" onto the continent by the collision of, what is now, Europe.

That led to a lot of earthquakin' (I don't know if that is a word, but...), which in turn disturbed the, still wet, sediments producing these curious structures.

Notice how the beds resume a normal horizontal plane in this pic. I would think that that is when the earthquake occurred that produced the seismites.

<snip>

Solius . . .

I think the term is "earthquakery" or in the original French, "earthquakeury."

How does one distinguish the jumble of strata in your images from slumping of unconsolidated or not-quite-consolidated sea-bottom? That is, was the original energy from earthquakery or from gravity?

A quick search for "seismite" produced images of some waves in shale -- very mild compared to your example. I understand the possibility of variation in the degree of disruption based on a number of factors. I just don't know how to distinquish between seismite and gravitite.

[Auspex]

<Here I go "thinking" again...>

For slumping to be the cause, I would think that proximity to an elevated mass (continental shelf, offshore river canyon, etc...) would be required. Even then, a quake could have been the trigger for a "landslide".

If the paleogeology of the formation can be deduced, the likelihood of a major slump can be assessed.

[Harry Pristis]

<Here I go "thinking" again...>

For slumping to be the cause, I would think that proximity to an elevated mass (continental shelf, offshore river canyon, etc...) would be required. Even then, a quake could have been the trigger for a "landslide".

If the paleogeology of the formation can be deduced, the likelihood of a major slump can be assessed.

I believe you're "thinking" on too grand a scale. The depth of these disturbed strata appears to be be shallow. The exposures of such seismites (or gravitites) are quite limited though occurring in a number of states, if I understood what I read.

An underwater landslide is still a landslide, NOT a seismite. Doesn't it seem possible that the same earthquake could produce waves in unconsolidated sediments in Tennessee and slumps (small-scale landslides) of unconsolidated material in Kentucky. My question remains, How do you distinguish between a seismite and a slump?

"The likelihood of a major slump" is irrelevant since we're talking about local exposures which are relatively shallow in depth and may or may not be geologically-connected to other, similar exposures.

[non-remanié]

I'm sure Solius will come up with a more detailed answer, but simply, I think one picture is not enough to tell the difference. Sedimentary structures often require more thorough regional analysis and a quick googling of the Clays Ferry shows that these synsedimentary deformation structures have been previously argued to be seismic in origin. An important consideration MAY be lack of a preferred orientation throughout a widespread regional laterally traceable bed. Beds formed by slumping would be more localized and less randomly deformed, lack slide planes, and as Auspex stated would require a nearby elevated source.

I believe you're "thinking" on too grand a scale. The depth of these disturbed strata appears to be be shallow. The exposures of such seismites (or gravitites) are quite limited though occurring in a number of states, if I understood what I read.

An underwater landslide is still a landslide, NOT a seismite. Doesn't it seem possible that the same earthquake could produce waves in unconsolidated sediments in Tennessee and slumps (small-scale landslides) of unconsolidated material in Kentucky. My question remains, How do you distinguish between a seismite and a slump?

"The likelihood of a major slump" is irrelevant since we're talking about local exposures which are relatively shallow in depth and may or may not be geologically-connected to other, similar exposures.

[Auspex]

I believe you're "thinking" on too grand a scale. The depth of these disturbed strata appears to be be shallow....

Thanks, Harry! Being referred to by you (no matter how obliquely) as a deep thinker is an honor!

[Guest solius symbiosus]

Gravitites? That is one that doesn't appear in print often. As I understand, gravitites form at, or near, the slope, and is a general catch-all for various types of lithologies associated with movement down the slope. I thought that they were a melange, but I found something describing turbidites as a gravitite???

Seismites form in-situ, on the shelf(though, I would think that they could form on the abyssal plain???), and preserve some of the original bedding structure.

[Harry Pristis]

Gravitites? That is one that doesn't appear in print often. As I understand, gravitites form at, or near, the slope, and is a general catch-all for various types of lithologies associated with movement down the slope. I thought that they were a melange, but I found something describing turbidites as a gravitite???

Seismites form in-situ, on the shelf(though, I would think that they could form on the abyssal plain???), and preserve some of the original bedding structure.

I was having some fun, Solius -- I thought I was making up the word "gravitite."

I certainly did not include turbidite in my personal definition, since turbidites do not retain any stratification. The famous turbidite flow is the Burgess Shale where "faunal zones" were identified, but no stratification occurs.

I agree with 'Toothpuller' that without laterally traceable beds across a region, it's tentative to identify any local exposure as anything more than slumping. Do you have information that your local exposure is connected to other exposures of disturbed bedding?

[Guest solius symbiosus]

Yes, the work is ongoing, but they appear to have an extensive lateral extent. Perhaps, with some work, they will turn out to be good chronological indicators. The facie relationships in this area are very complex, and this could be one of the tools that better that understanding.

Perhaps, one day, they will used to illustrate temporal relationships across large regions.

[non-remanié]

hahaha I had a feeling that your use of gravitite was "Harry being Harry" but it was coherent and I was not surprised to see that it was actually a term. I had never heard it used before, but I haven't even taken a geo101. I just happen to be currently reading up on some of these basics and was glad to be able to use this thread as a little virtual geo-field trip.

I did find this which refers to the regional seismite beds

http://strata.geol.sc.edu/PDF-Files/Appala...rPopeRead97.pdf

And if you do a google image search for "slump deformation" it does seem like there are differences from Sol's pictures.

I was having some fun, Solius -- I thought I was making up the word "gravitite."

I certainly did not include turbidite in my personal definition, since turbidites do not retain any stratification. The famous turbidite flow is the Burgess Shale where "faunal zones" were identified, but no stratification occurs.

I agree with 'Toothpuller' that without laterally traceable beds across a region, it's tentative to identify any local exposure as anything more than slumping. Do you have information that your local exposure is connected to other exposures of disturbed bedding?

[Harry Pristis]

hahaha I had a feeling that your use of gravitite was "Harry being Harry" <snip>

hahaha Yes, you can rely on me being Harry.

We might as well get this on Google.

Definition of "gravitite": A geological feature, generally on a small scale, whose origin can be attributed to the force of gravity, such as slumping of unconsolidated strata, rock-falls, and turbidite flows which are preserved in the geological record. A gravitite is contrasted against a seismite, a geological feature whose origin can be traced to shock waves from earthquake or other seismic activity.

On Solius' suggestion, I've added turbidite flows to the definition. Any other suggestions, Solius?