Pocono Group Fossils

[EMP]

I'm sorry if this is the wrong sub for this, but I wanted to show some of my finds.

 

I went out to go collecting at an exposure I had passed many times while driving to other fossil sites but never visited before. When I went to the road cut back in September and November it wasn't too badly overgrown, but was separated into two parts by trees and talus cover. The southernmost part was mostly sandstone and siltstone from the layers lying above the coal-shale beds that were exposed further north on the road. For the most part the fossils from these layers were poorly preserved plants, though I did find a rare trigonotarbid from closer to the contact between this layer and the coal-shale one.

 

 

Further north on the road from this part of the cut was the more interesting coal-shale layers, which housed many more floras, amounting to about six different species. These layers were characterized by a diverse array of plant life.

 

 

Specimens from top to bottom:

 

Hash of assorted fragments from Triphyllopteris lescuriana (?) from the sandstone beds above the coal. For the most part these rocks were not fossiliferous,  but they do occasionally have large hash slabs such as these two specimens.

 

Abdomen of the as yet unidentified trigonotarbid, possibly the first one recorded from this formation from the state of Maryland and the first one since the original found in 1930. It was interesting to find the ancient relative of the animals that infested some parts of the exposure (luckily I had a hammer to swipe all the wolf spiders away!)

 

Rhodea vespertina.

 

 

 

 

[jpc]

not sure what has happened but almost all your photos show up as broken links.  The last three are visible.  

 

edit... looks like you fixed it.  

[EMP]

 

Continued from first are Triphyllopteris lescuriana. All of the specimens I found were fragmentary, but in most I could make out the stem with at least one leaf branching out. This is the most abundant species, and makes up the majority of the leaf hash found in the deposit and is the likely culprit for the root silts as well. Likewise, T. lescuriana is the indicator fossil of the upper Pocono Group and is not found below in the Rockwell Formation or above the Purslane in the Mau Chunk Formation. Some of these specimens are beautifully preserved in black, coal rich shale which is rare for plants of such an early age.

 

 

 

 

[EMP]

From top to bottom:

Triphyllopteris biloba. A close relative to the T. lescuriana from above, however T. biloba is different in size and shape to T. lescuriana. The fossil below still displays the branching pattern of the other Triphyllopteris specimens, however, as well as showing the well preserved central vein of the leaf.

 

Lepidondedropsis vandergrachti. This is an interesting find because before this I never knew that lepidondedropsids existed back in the Mississippian, let alone the early part of the period, but apparently this genus is fairly common in upper Pocono sediments, and is often found with another species of Lepidondedropsis:

 

Lepidondedropsis sigillariodes. Close up you can see the faint imprints like in the first specimen, though they are less clearly visible in this species. I found these in the same layer of the shale, so in life they must have preferred the same or similar habitats at the water's edge.

 

 

[EMP]

 

Hash of various leafs, probably a species of Triphyllopteris (most likely T. lescuriana). These kinds of fossils are very common, and I soon had to restrain myself to just collecting the largest or best looking specimens. These two in particular are larger than one hand.

 

Root silt/hash. The plant remains in this piece are practically unidentifiable, though likely a species of Triphyllopteris. These kinds of specimens are extremely common in the coal-shale layers, and sometimes I could see entire sides of the road cut made up of the crumbly chips of this material preserved, seemingly, in situ.

 

 

 

 

[EMP]

I don't really know what species this guy is () but it is still interesting because it appears to be a twig with branches diverging off of it.

 

[EMP]

Whew, that took a lot longer than expected. Sorry for the broken up pictures, my computer wouldn't let me upload them all in one go.

 

Now, on to the geology.  

 

All of these finds come from the upper layers of the Purslane Formation, a member of the Pocono Group (classified as formation in neighboring states), which is the next lowest stratigraphic Mississippian unit in Maryland and the central Appalachians above the basal Mississippian Rockwell Formation (which is part of the Pocono Group). All of these finds date back to around 350-345 million years ago, when this part of the state was covered in a deltaic, riverine environment much closer to the equator and bordering the low laying Acadian Mountain range to the east. Around the river deltas were primordial forests of tree-like plants and ferns. When these plants died they were quickly covered by the mud of the river waters and compressed, eventually turning into the coal and fossils exposed today at Sideling and Town Hill.

 

The conditions of the terrain at the time varied, but it is believed that the seasonal wet and dry periods characteristic of the earlier Devonian continued into the Mississippian. Generally, however, conditions during deposition would have been tropical to sub tropical and wetter than they had been in the Devonian as the Acadian range eroded into the sea, which lay further to the west in Ohio and West Virginia during this time. Since this area remained further from the sea, it was exposed more directly to the eroding sediments, which lead to the formation of the coarser sandstone beds above the finer coal and shale, which formed at times when the sea level stood higher.

 

The rocks of the Pocono lay below the middle Mississippian Mau Chunk Formation, which was deposited in more arid conditions less suitable to plant life. Above the Mau Chunk are the non-clastics of the Greenbrier Group limestones, which contain abundant and well preserved marine fossils. The Pocono is a particularly interesting unit because most rocks deposited at this time (early Mississippian) were marine in origin, and flora and land fauna of this time has been poorly studied (the youngest report I can find dates to the 1980s).

 

What's probably the coolest part is the presence of coal in the formation. Coal is atypical of deposits of such age (early Mississippian), but it is common in the upper parts of the Purslane and was even mined (often to little avail) by locals for use in local homes and businesses until the deposits further west in the Georges Creek Basin were developed. The presence of coal in this formation is rare for Mississippian units, and it has lead to the beautiful preservation of some of the finds that is more typical of later Pennsylvanian finds.

[Fossildude19]

Very interesting site, EMP.  

Thanks for posting about it.  Good information.

Looking forward to seeing more of your finds from there in the coming year.

Regards,

[EMP]

Trace fossil of a footprint of a tetrapod. I found this specimen in the same rocks as the trigonotarbid while going over some of my finds looking for insect track ways. The print shows three of the toes of the animal as well as part of the limb and a second print next to it to the upper right. These rocks were probably deposited closer to the water's edge due to their "muddier" character.

 

A zoomed out photo of the same specimen. This one shows other tetrapod footprints circled in red.

[Jeffrey P]

Congratulations on finding some excellent material. I haven't seen too much terrestrial Mississippian fossils (plants and tetrapods) on the Forum or anywhere for that matter. I do recall an incredible exhibit of Mississippian age amphibians from West Virginia on display at the Cleveland Natural History Museum.

[EMP]

Thanks, yeah one of the reasons I posted these was to have a place to show these kinds of fossils since I have never seen land fossils from this period before. It's pretty much untouched territory, which is cool because the lack of research is how I've been finding "rare" specimens like the tetrapods. Hopefully with a little more looking I'll be able to flesh out a more complete list of the flora/fauna,since there are plenty of road cuts to look at.

[EMP]

I'm pretty sure this is another tetrapod footprint. It's not as well preserved as the other slab, but you can make out some of the toes on this one. I found this one in the same layer as the other footprints, so maybe they're more common than I thought before. These rocks were deposited closer to the water's edge, likely near a pond or slow moving body of water, indicated by the presence of both tetrapod (amphibian) footprints and insect/arthropod tracks and burrows.

[Fossildude19]

Looks like one to me.

Another cool find!

Thanks for showing us here. 

Regards,

[EMP]

Thanks

 

Hopefully I'll find more once the weather improves!

[EMP]

Maybe I should start a whole new topic on all my footprints?

 

First is"little foot", with clear toe impressions.

 

Second is another, rather poorly preserved, partial footprint similar to the post above.

[Fossildude19]

Not sure about the first one.  

 

      

 

The second one looks promising: 

 

[EMP]

Thanks for brightening up the pictures! I was wondering what happened to them

 

The first one I think is a different track like in the below link on page 63 (it's also likely been messed around with after it was made. Furthermore, it could be from a smaller animal, where there's adults there should be juveniles right?)

 

https://books.google.com/books?id=GOsoCgAAQBAJ&pg=PA25&lpg=PA25&dq=mauch+chunk+tetrapod+trace+fossils&source=bl&ots=UInQH5_XNM&sig=tqDPiJmr6IxWF226rtCK83n-DRg&hl=en&sa=X&ved=0ahUKEwikofPvyvnRAhVX-2MKHTsYDeQQ6AEIKzAE#v=onepage&q=mauch chunk tetrapod trace fossils&f=false

 

 

[EMP]

This may seem like a stretch, but I think this is a partial arthropod fossil. Before you make a call, allow me to explain why I think so.

 

First off, the fossil is split into two imprints. The rear imprint is divided into tergite like structures (segments, like on a trilobite) that may or may not show up on the photos. Above this imprint, which is well rounded and has a clear border region characteristic of Paleozoic arthropod fossils, is a second imprint that appears to be the cephalothorax region of the arthropod. Part of the right area of the head region appears to be covered by shale/missing. This one is less well preserved as the other, but a clear impression is there that shows the triangular rounded nature of the cephalothorax (head) as well as the segmented part of the lower section of the head. To the side of this are a few, very faint, impressions that appear to be legs.  

 

Here's a link showing the structures I'm referring to, but in a much better preserved specimen. Bare in mind this specimen is Pennsylvanian in age, and thus has more developed features than my Mississippian arthropod would have:

 

 

 

[Fossildude19]

Sorry, but I'm not seeing it. 

Maybe the gentleman you contacted last time could say. 
Regards,

[EMP]

Here's to nothing, again

[EMP]

How about this?

 

 

 

[Fossildude19]

Sorry, doesn't look that way to me.  

 

[EMP]

No it's definitely an impression

[Fossildude19]

Well, I was wrong before.  

I just cannot make out any kind of identifiable (to me) imprints. 

Maybe the Spider expert will chime in again.

Regards,

 

[EMP]

He replied back. It is an arthropod, but he said that it is too poorly preserved to give anything more accurate. His best guess was the arachnid order Phalangiotarbi, due to the oval body shape.