Unexpected Culpeper Basin Find

[Andúril Flame of the West]

Hello everyone,

 

Recently I visited a golf course in Falls Church, Virginia - Fairfax county for any who are not familiar with that particular city. I recognized that I was likely to be on Culpeper Basin strata and noticed that there were numerous decorative boulders around the course. Due to their size I suspected that they had probably been sourced locally, and I took the opportunity to see if any might contain fossils. Although many of the boulders matched the Balls Bluff Siltstone rocks that I have encountered in my local stream site, I knew it was a stretch to hope for fossils and I kept my eye out mostly for carbonized plant fragments. After a while, I came upon one boulder that did not look radically different from those I had seen before - until I took a closer look.

 

The boulder contained abundant impressions of what appear to primarily be brachiopods but which could also include some bivalves. Below are some photographs that I took of some of the larger fossils:

 

Impression #1:

 

 

Looks to be a brachiopod impression though I am not experienced enough in this area to rule out bivalve. 
 

Impression #2:

 

 

Brachiopod? at the top right of the photograph and assorted material. 
 

Impression #3:

 

 

Impression #4:

 

 

Impression #5:

 

 

Additional photograph of the boulder (apologies for lack of scale):

 

 

Since it was a boulder I could not collect the specimen. As such, I cannot take more photographs of the boulder. Considering the fauna present on the piece I highly doubt that it came from the Culpeper Basin - as far as I know Unio sp. is the only bivalve known from Culpeper strata and to my eye these more closely resemble brachiopods.

 

If they are not from the Culpeper Basin, where might the rock have been sourced from? The nearest Devonian-aged formations are the Mahantango and Foreknobs formations with the Needmore Shale being a bit farther away. Do the fossils or the rock resemble what one might expect from one of these formations? 

[bockryan]

Does not look like either Mahantango or Needmore is all I can add. Have you had much luck otherwise in the Newark? I spent all of today reading old papers and have a few spots picked out to try.

[patelinho7]

23 minutes ago, bockryan said:

Does not look like either Mahantango or Needmore is all I can add. Have you had much luck otherwise in the Newark? I spent all of today reading old papers and have a few spots picked out to try.

Our collective luck is only the plant material @Andúril Flame of the Westhas found. Unfortunately we too spent many days reading old papers and haven’t had too much success. I haven’t had much time recently but I’ve got some small leads to try in the winter when the bugs and plants die off. 

[bockryan]

38 minutes ago, patelinho7 said:

Our collective luck is only the plant material @Andúril Flame of the Westhas found. Unfortunately we too spent many days reading old papers and haven’t had too much success. I haven’t had much time recently but I’ve got some small leads to try in the winter when the bugs and plants die off. 

 

There has certainly been a lot of development, the ephemeral nature of a lot of these exposures has been very frustrating! An exciting fish locality filled in with water, another plant locality bulldozed over. More are out there I'm sure though!

[Andúril Flame of the West]

11 hours ago, bockryan said:

Does not look like either Mahantango or Needmore is all I can add. Have you had much luck otherwise in the Newark? I spent all of today reading old papers and have a few spots picked out to try.

I suspected that this piece didn’t resemble Mahantango or Needmore material which makes it ever more intriguing. 
 

As @patelinho7 has said, the only luck I’ve had thus far has been plant material recovered from a stream. The majority of the funds have consisted of carbonized plant fragments with one impression of a large horsetail or similar plant. Here’s the LINK to the original trip report I made of the spot - I inadvertently mistook them as Potomac group finds at first. 
 

10 hours ago, bockryan said:

 

There has certainly been a lot of development, the ephemeral nature of a lot of these exposures has been very frustrating! An exciting fish locality filled in with water, another plant locality bulldozed over. More are out there I'm sure though!

 

The Culpeper Basin is frustrating to search but I hope it will make success all the sweeter. I’ve had my nose in ancient to recent papers and have gathered a few localities that may still yield some material. It will take no small amount of field work, but I am certain there are some new discoveries to be made in this basin. 
 

 

[Andúril Flame of the West]

@EMP, might you be familiar with the fossils or the consistency of the matrix? 

[EMP]

1 hour ago, Andúril Flame of the West said:

@EMP, might you be familiar with the fossils or the consistency of the matrix? 

 

It's similar to bluestone which is a commercial name for Devonian-aged sandstones quarried in Pennsylvania, New York, and some other places. A lot of times you can find plant fragments in them, but sometimes you can find other things like brachiopods. It just depends on exactly what layer was quarried.

 

It looks like you have a mix of pelycopods and a couple different kinds of brachiopods. The first impression looks similar to a Grammysioidea sp. which is fairly common in middle and late Devonian rocks in the central Appalachians, but can be found in older rocks, too. I'm not 100% it is that genus, but it looks similar to it. The second impression looks like a rhynchonellida brachiopod. Impression 3 is a little harder to tell, but might be a spiriferid. 

 

All in all, it looks like a fairly typical Devonian-aged fauna for the area, but I don't think it necessarily comes from Virginia. I think the best you can do as far as locality information is the central Appalachians. As for the age, given the fossils and the lithology my best guess would be its late Devonian, similar to the Venango Formation in Pennsylvania (in Virginia the equivalent would be the Foreknobs Formation or Big Stone Gap Formation), but that's just a guess. It's very hard to confirm from the one boulder. 

 

 

 

 

[Fossildude19]

50 minutes ago, EMP said:

The first impression looks similar to a Grammysioidea sp.

 

Respectfully, I disagree.

 

This is Grammysioidea.

 

 

 

I think Anduril's find much more closely resembles a brachiopod, something like Pseudoatrypa or Athyris.

 

 

[Tidgy's Dad]

I think it might be Spinatrypa. 

[Fossildude19]

25 minutes ago, Tidgy's Dad said:

I think it might be Spinatrypa. 

 

 

Better match. Thanks, Adam.

 

[Andúril Flame of the West]

I appreciate the help @EMP, your extensive knowledge on the stratigraphy and fossils in the area has been extremely helpful. I find it interesting that such a stone would end up in a golf course, but perhaps that is not so strange after all. 
 

Also, appreciate the additional identification help. @Fossildude19, the illustrations that you attached are very informative, especially for one who is not very familiar with brachiopod identification. Is there a source where you got these images from? I have some Mahantango/Needmore/Foreknobs material that I have not yet sorted through and I suspect those could be helpful for putting labels to some of those finds.

Edited August 1, 2023 by Andúril Flame of the West

[Fossildude19]

6 hours ago, Andúril Flame of the West said:

Also, appreciate the additional identification help. @Fossildude19, the illustrations that you attached are very informative, especially for one who is not very familiar with brachiopod identification. Is there a source where you got these images from? I have some Mahantango/Needmore/Foreknobs material that I have not yet sorted through and I suspect those could be helpful for putting labels to some of those finds.

 

I use Karl A. Wilson's "Field Guide to the Devonian Fossils of New York" 2014. 

 

It is sort of an updated version of David M. Linsley's  "Devonian Paleontology of New York" 1994.

PM me if you would like a PDF copy of Linsley.