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Silurian Fossils From Maryland, Plus a Possible Devonian Bone Bed?


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It's been a long while since I've posted on here. I haven't been able to collect much lately, but I recently went out to some new haunts and came back with some pretty intriguing stuff I'll hopefully get to follow up on later. 

 

I'll start off with an interesting discovery I've had recently. The outcrop exposes rocks stretching from the upper(?) Brallier Formation to the middle(?) Foreknobs Formation. Although I tried searching in the past for brittle star trace fossils, I was mostly unsuccessful in this regard, and over time my interest in it shifted to the much more fossiliferous beds of the Foreknobs (formerly Chemung) Formation. A couple of years ago I posted about finding a fish bone in a boulder next to the outcrop, as well as pointing out I found some potential teeth. Going over my posts, that finding intrigued me so I dug deeper into the presence (or lack thereof) of fish remains in the upper Devonian strata of the region. What I came up with was an 1887 report of the Genesee Shale from New York, an upper Devonian formation roughly analogous to the Scherr (and possibly the lower Foreknobs by the sound of it, it's all rather ambiguous) in Maryland. The authors noted multiple occurrences of fish bones and isolated teeth in sandstone and "fine pebble conglomerate"...similar in description to the rocks of my own outcrop. Coupled with the knowledge of possible fish remains I found previously I decided it'd be worth it to give the outcrop a more thorough look over, this time concentrating instead on the conglomerate facies and ignoring the shale. 

 

What I discovered has so far been fairly interesting. As I stated previously the outcrop exposes parts of the Brallier and Foreknobs Formations, including several dozen feet of shale and siltstone in the Foreknobs grading into upper siltstone and sandstone beds closer to the axis of the syncline. Towards the top of the exposed section of the Foreknobs is a bed several inches thick of hard, pebbly conglomerate. After some searching the silty shale above and below the bed is mostly unfossiliferous, although local profusions in brachiopods, crinoids, and other creatures are present. The conglomerate, however, is densely fossiliferous to the point that it forms a veritable coquina in parts running for several feet along the exposure. 

 

Because the conglomerate is so hard (made up of quartzose pebbles and sand), and the underlying and overlying beds made of much softer shale and silty rock, the conglomerate is poorly exposed outside of the exposure wall, forming something of a canopy between it and the less resistant layers. It is covered in part by a dense layer of talus from the overlying beds, likewise obscuring part of the exposure. Luckily, however, a few boulders have eroded out from the cut and are free on the ground to examine, and a few loose pieces weathered from the boulders are present around those. In these rocks I have found one chunk of blueish-white fish bone(?), and several possible tooth fragments. I recently examined the outcrop wall looking for more bone/teeth still present in the outcrop, and discovered part of a fish tooth(?) exposed slightly above one of the boulders, and similar looking black enamel(?) specks that could be fish derivatives. They are distinguished from the quartz pebbles by their shiny black appearance, whereas the quartz is mostly lighter gray and translucent. 

 

Is this a possible bone bed in the Foreknobs Formation? More scouting is of course needed, but there's a strong possibility in my opinion that, at the minimum, this conglomerate layer is a decent source of fragmentary Devonian fish remains. 

 

Note the blueish tint to the fossil. This possible bone fragment was found in a boulder of quartzose, pebbly conglomerate in the middle-upper Foreknobs Formation (Famennian). Note the associated fauna of crinoid and brachiopod fragments. Crinoid stem fragments in particular are extremely common, comprising a large part of the conglomerate "pebbles." This boulder is derived from a layer above a Cyrtospirifer disjunctus bearing shale, indicating it's Chemung age. 

chemung 29.jpg

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Another possible fish remain, this time a tooth(?) from the same boulder as the bone(?) fragment. Note the apparent presence of two "cusps," and the black, phosphatic like preservation. 

chemung 28.jpg

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This is a fairly large (compared to the other fossils), conically shaped tooth(?). The photo isn't the best as the fossil was located underneath the conglomerate overhang. I can say that it has a few vertical "grooves," for lack of a better term, down the length of the fossil. If it is a tooth it is likely missing the tip and root. 

 

I have several other small, black fragments from pieces of the conglomerate that have weathered off of the exposure face, but they are too small to get a good picture of, unfortunately (their small size would limit any identification anyways). 

 

 

chemung 26.JPG

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This fossil is interesting as it appears to be part of an armored fish(?), and by the apparent lithology of the rock it is situated in appears to be derived from one of the shale layers adjacent to the conglomerate. Because I found it in the scree at the foot of the outcrop, it's impossible to really identify which layer it comes from with the means I have available. 

chemung 27.jpg

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Fossildude19

@Paul1719  

 

The blue/white first item definitely looks Like some sort of bone or armor plating. 

Congratulations on a great find. :) 

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That's pretty impressive. I'd like to see some of these bones fully prepared out of the matrix. That first bone, for instance, might be osteichthyan rather than placoderm; I'd want to see it isolated from the rock there. The Fammenian age is especially interesting, as well.

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Devonian bone beds are certainly very intriguing, but I visited other sites after having difficulties collecting in the hard conglomerate. After stopping by the Devonian site I continued to a site known for it's Silurian eurypterids, to little avail. I then proceeded to a third outcrop I had been wanting to visit for a while, but always put off for one reason or another. Finally I decided to go out on a limb and explore an outcrop of Silurian aged Rose Hill Formation. 

 

The Rose Hill Formation is the basal member of what in Maryland is called the Clinton Group, a Llandoverian to Wenlockian aged unit that includes the Rose Hill and overlying Keefer Sandstone and (in Maryland) Rochester Shale. The Rose Hill itself is an assembly of mostly middle Silurian aged shales, siltstones, sandstones, and minor limestones. It is well known as a source of iron ore, the Cresaptown Ironstone (a ferruginous sandstone) having been mined near Cumberland for decades, helping make the city an early industrial center given it's close proximity to Pennsylvanian aged coal, Mississippian/Siluro-Devonian limestones (for flux), and shales for fire clay. The Rose Hill itself is divided into three "zones"; a lower zone, a middle zone noted for it's Calymene cresapensis fauna, and an upper zone noted for it's Liocalymene clintoni fauna. The Cresaptown Ironstone occurs within the middle zone, and each zone is separated from the other by a sequence of mostly barren, drab colored shale. 

 

The Rose Hill Formation is sporadically fossiliferous, some layers literally being made of dense assemblages of shells and others being large devoid of life. Even within units there is local variation between their fossil contents, a shale bed in one spot being fossiliferous while that same layer in another locale is largely barren. As such collecting in the Rose Hill can be rather difficult compared to the much more fossiliferous Rochester Shale and McKenzie Formation, especially given it's stratigraphic position; the underlying Tuscarora Sandstone often forms ridges while the Rose Hill occupies the slopes, nestled between the Tuscarora topped ridge and a smaller, adjacent hill capped by the more resistant Keefer Sandstone. Likewise, it can be frequently covered by talus from other formations, or just poorly exposed in the intervening valleys. 

 

Still, I have always wanted to collect some in the Silurian strata, as I've built up a large collection of Devonian specimens and had only visited one or two Silurian sites previously. Thankfully I came across an outcrop of Rose Hill tucked away in a corner, and I went out on a limb and decided to go there instead of my usual haunts. I was glad I did! 

 

The outcrop exposes what I believe is the upper zone of the Rose Hill Formation, possibly with some of the basal Keefer Sandstone exposed at the top (a white colored sandstone). The 1923 MGS report states that the upper Rose Hill is marked by gray, argillaceous limestone, which I found several pieces of in the rock scree, as well as gray siltstone. Below that is some gray shale, which is all that is exposed at this site but the Rose Hill is several hundred feet thicker elsewhere, and includes several alternating beds of shales, siltstones, and sandstones. 

 

In terms of fossil content, the limestone was the most fossiliferous, no surprise given the description of the unit by the MGS. It's fauna includes abundant brachiopod, ostracode, and...trilobites! I couldn't believe it! I found more trilobite remains in probably twenty minutes here than in my past decade of collecting elsewhere (ok maybe a slight exaggeration, but I definitely had to be selective of what pieces I kept and what I brought home after a while). The trilobite bed is located in a silty covered, argillaceous limestone (to be differentiated from the other, less silt-covered limestone with the shelly coquina), associated with ostracodes and minor brachiopods. Going back to the literature such trilobite rich beds are reported from the Rose Hill, and are comprised in the upper beds mostly by Liocalymene clintoni. Because the trilobite remains are mostly fragmentary, I haven't been able to get a good ID on any of them, and am tentatively identifying them as L.(?) clintoni(?) due to them being located in the upper, Liocalymene clintoni zone. I found one mostly whole specimen which had been inverted before fossilization, possibly because of turbulence in the sea or a storm. Given the fragmentary nature of the fossils, how many of them are overturned or on their side, and crossbedding in some of the sandstone, this was likely a high energy environment, possibly a shallower sea or a storm rocked area. It's possible the localized profusion of fossils could be the result of waves/underwater currents depositing the remains in shallow depressions on the sea floor, similar to the surf zone on modern beaches (albeit this would have been in deeper water than such a near shore environment). At any rate, the large size of the trilobite (I estimate around three inches long if complete) would seem to indicate it as a different species from Liocalymene clintoni, possibly Calymene cresapensis or C. niagarensis. 

 

The gray shale below the limestones was mostly filled with a crinoid, tentaculitid, and brachiopod fauna. A few trilobite fragments were present in grayer, shaly type rock below the limestone, though whether this was float or from the underlying shale I am unsure. Given the lack of trilobites in the gray shale blocks, it's likely to be just float (and most literature seems to indicate the trilobites occur in the limestone layers anyways). 

 

But perhaps the most interesting fossil of the day came from the gray, argillaceous limestone near the top of the exposure. Here the limestone is a virtual coquina of shell fragments, comprised mostly of ostracodes and brachiopod pieces. Going through some of the fossils I recognized a distinctive, shiny black feature in one of the rocks. Upon closer examination it appeared similar to the possible fish teeth(?) from the Devonian outcrop discussed above, and so I was immediately intrigued. Thinking at first it was a tooth, I have since learned about acanthodian spines from searches online, and they at least bear a superficial resemblance. My fossil is made of a shiny, black material, not unlike sharks teeth from Calvert Cliffs further east. It bears a few "grooves" (for lack of a better word) down the length of the feature. It's mode of preservation is completely unlike any of the other fossils in the limestone bed, which are preserved mainly in a white calcite like mineral. This one is almost phosphatic. I have since found a few other fragments after going over some of the other pieces of limestone. Could this be the remains of a Silurian fish, possibly acanthodian? Maybe. I have also found what could be a large coprolite(?), with one of the possible fish remains(?) located near it. This was found in the underlying, silty covered limestone, however, and not in the layer of the possible spine(?). If they are fish remains I'd imagine they'd be fairly important, as I have not heard of any such remains from the formation or from the state, and as such I am fairly hesitant to give it any positive ID one way or the other. 

 

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Possible fish remain

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

 

Note the "lines" down the length of the specimen. I've seen similar features in Miocene sharks teeth, but I'm unsure what they're called, exactly. 

rose hill 2.jpg

rose hill 3.jpg

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35 minutes ago, Fossildude19 said:

@Paul1719  

 

The blue/white first item definitely looks Like some sort of bone or armor plating. 

Congratulations on a great find. :) 

 

Thanks @Fossildude19!

 

Any ideas on the "teeth"? 

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Possible fish remain

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

Note the similar mode of preservation to the above fossil, and the seeming "groove" down it's size. It's pretty small, however, making any positive identification likely very difficult. 

rose hill 16.jpeg

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Trilobite molt fragment

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

Trilobite molt fragments (thoracic segments), ostracodes, and other fauna

Upper Rose Hill Formation, middle Silurian (Wenlockian)

rose hill 22.jpg

rose hill 19.jpg

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Trilobite cephalon, possibly L. clintoni

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

A molt fragment from an argillaceous limestone. The given identity is based on the MGS reporting only that species from this horizon of the Rose Hill in this area. It's possible it is one of any other calymenid species reported from the Rose Hill elsewhere. 

rose hill 5.jpg

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23 minutes ago, EMP said:

Possible fish remain

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

 

Note the "lines" down the length of the specimen. I've seen similar features in Miocene sharks teeth, but I'm unsure what they're called, exactly. 

rose hill 2.jpg  rose hill 3.jpg

I think this is acanthodian. There's a lot of bone in there, though, for sure. Would you be interested in me putting you in touch with an expert who might be interested in studying these fossils?

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Trilobite molt fragment, calymenid

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

Trilobite molt fragments, calymenids

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

Note the argillaceous nature of the limestone, and the associated ostracode fauna. Ostracodes are extremely abundant in the Rose Hill, and indeed the Silurian layers a whole, in stark contrast to their relative absence from the Devonian aged Mahantango and Needmore. 

rose hill 6.jpg

rose hill 8.jpg

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Trilobite molt fragments, calymenids

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

Note the possible mudcracks(?) in the specimen, possibly indicative of a nearshore environment for this specimen? It is preserved in a reddish sandstone, potentially from the Cresaptown or from one of the overlying sandstone layers, and not from the limestone or shale. As such it could represent a temporary drop in sea levels. The Silurian sea fluctuated quite a bit in water level during the period, going from the beach sands of the Tuscarora Sandstone to the shallow sea deposits of the Rose Hill, to the deeper (though still fairly shallow) Rochester and McKenzie, to the alluvial Bloomsburg Formation, back to marine deposition with the Wills Creek Formation. 

 

rose hill 9.jpg

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8 minutes ago, jdp said:

I think this is acanthodian. There's a lot of bone in there, though, for sure. Would you be interested in me putting you in touch with an expert who might be interested in studying these fossils?

 

I wouldn't mind, no. If you don't my asking, what is the bone you see? 

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Possible fish remain

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

Note the similar preservation to the other possible fish remains(?). This one is smaller, however. 

rose hill 11.jpeg

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That’s gotta be the same place I was hunting, I should have spent more time there! Guess the black streaks could be fish remains. Nice finds!

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The big element is probably an acanthodian fin spine. I don't know about the other bone fragments. If you DM me, I can put you in contact with a friend of mine who specializes in these animals and this interval.

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Possible fish remains

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

There are two possible fish remains(?) in this specimen - the two oblong features. They have a "rough" texture, similar in some aspects to the possible bone(?) from the Devonian shale I mentioned above. The one on the right has a possible fish remain(?) in it preserved in shiny, black material. Potentially a coprolite? It is also possible these are mud covered pelycopods or pentamurids, though none are reported from this area for the Rose Hill. 

rose hill 18.jpeg

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Trilobite pygidium, calymenid

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

@piranha, any ideas on these identities? 

 

There are other molt fragments around the specimen, and parts of a cephalon(?). Potentially all from the same animal, though that's not confirmable one way or the other. 

rose hill 13.jpeg

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5 minutes ago, WhodamanHD said:

That’s gotta be the same place I was hunting, I should have spent more time there! Guess the black streaks could be fish remains. Nice finds!

 

No, this was off a different road. And no bryozoans or stuff like that from what I could tell. I believe the same formation, however, given the similarity in the rock types. 

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Trilobite molt fragment, calymenid

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

Trilobites appear to be a lot more common before the middle Silurian regression in sea levels here, as I've struggled finding any trilobites in Devonian or late Silurian rocks. 

rose hill 7.jpeg

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Ostracodes

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

Ostracodes are extremely prolific in much of the Silurian strata, forming veritable coquinas with their shells. Note how many of them are inverted. 

rose hill 10.jpeg

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Leptaena sp.

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

Leptaena sp.

Upper Rose Hill Formation, middle Silurian (Wenlockian)

 

Note the different style of preservation from the possible fish remain(?) from the same layer. No species of this genus is listed from the Rose Hill in the 1923 report, but I've heard of them being found in the formation elsewhere. Definitely a very intricate brachiopod. Note the shell dense coquina. 

rose hill 21.jpg

rose hill 4.jpg

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