Fossils? Associated with the Murphy Marble Fm, WNC

[klattrocks]

I'm working with Dr David Campbell on possible fossils found associated with the Murphy Marble Fm in Western North Carolina. In 1973. Don Hathaway was logging cores at the Nantahala Limestone Quarry when he found what looked to be organic remains in a couple of cores cut into the Murphy Marble Fm. The age of the Murphy Marble is enigmatic, because of the lack of fossils in it, and it doesn't have the minerals that could be used to determine radiometric ages. The metamorphic grade of the marble and associated formations are garnet to staurolite grade. It's believed that these units were metamorposed during the middle or late Paleozoic. Unfortunately we couldn't handle the cores, and we were only allowed to photograph them. Since neither of us hasn't done research on brachipods before we are looking for opinions on the of these apparent organic remains. I almost forgot to mention that these fossils were apparently in an unit above the Murphy Marble Fm in the base of the overlying Mineral Bluff Group. I didn't take the photos so I don't have a scale for them. I finally did dig up a old picture from a talk given back in 2019 at a NCFC meeting in Raleigh and got a screenshot of part of the article to give you an idea of the scale on these pics.

Edited December 24, 2021 by klattrocks
I forgot I needed to say something about the scale of these photos and added a picture that would help with the scale.

[Ludwigia]

I've no idea if they are of organic origin, but what does Dr. David Campbell think about them?

[klattrocks]

Dr Campbell hasn't expressed an opinion on what these features are to me personally. His specialty is more in the line of Tertiary gastropoda in the coastal plain. We have been hampered by Covid19 and we haven't really researched it much yet. The problem is the cores are restricted to photography only and they can't be handled or taken elsewhere for further study. Dr Campbell used the Paleontology Portal, but he really didn't get much of a response. We want to lean towards an organic origin, because neither of us know how this structure would of been formed otherwise. We haven't seen anything like this before that could of been produced structurally or by mineralization.

[DPS Ammonite]

The structures look more like an alignment of mineral grains than brachiopod fragments. The alignment of holes might represent layers of less resistant mineral to weathering. Thin sections might reveal alignment of grains. Also, garnet and staurolite rich metamorphic rocks probably don’t have preserved fossils in them due to too much pressure and heat.

[FossilDAWG]

Are these cut sections through the core, or surfaces where the core was broken?  The first image suggests a colonial coral in section to me.  I recall some publications about fossils associated with metamorphosed "marble" form somewhere in the Blue Ridge mountain area, I believe they were Ordovician although I'm not 100% sure of that.

 

Don

[klattrocks]

I'll talk to Dr Campbell about the cores and see if these are core cut surfaces or were they on breakage faces. I think these structures are in breaks in the cores. Yes many locations in the Eastern US fossils have been found in various metamorphic grades up to lower amphibolite facies. These structures being fossils can't be dismissed purely on the fact these rocks have been metamorphosed. In 1993 Dr James Tull found a Crinoid fragment in a core from the Mission Mountain fm which is the basal formation of the Mineral Bluff Group near Murphy, NC. The Mission Mountain fm lies unconformably above the Murphy Marble fm. The metamorphic grade there is also just under staurolite facies. The fossil was found in a calcerous part of the formation so the rock wasn't schistose, but in an impure marble layer within the schist. I talked to Don Hathaway and he believes his fossil? bearing cores were taken from the Andrews Schist, which is now called the Mission Mountain. His fossils? are in an impure marble layer. The paper that Dr Tull wrote on the Crinoid fragment is in GEOLOGY volume 21 March 1993 pages 215-218. The article's title is Appalachian Blue Ridge cover sequence ranges at least into the Ordovician. 

[Plax]

Interesting topic! Am reminded of the Ordovician fossils found in marble at Paoli Pennsylvania. Very poorly preserved but can't remember the reference. May have been in the periodical "Pennsylvania Geology".

[EMP]

On 12/23/2021 at 9:55 PM, klattrocks said:

I'm working with Dr David Campbell on possible fossils found associated with the Murphy Marble Fm in Western North Carolina. In 1973. Don Hathaway was logging cores at the Nantahala Limestone Quarry when he found what looked to be organic remains in a couple of cores cut into the Murphy Marble Fm. The age of the Murphy Marble is enigmatic, because of the lack of fossils in it, and it doesn't have the minerals that could be used to determine radiometric ages. The metamorphic grade of the marble and associated formations are garnet to staurolite grade. It's believed that these units were metamorposed during the middle or late Paleozoic. Unfortunately we couldn't handle the cores, and we were only allowed to photograph them. Since neither of us hasn't done research on brachipods before we are looking for opinions on the of these apparent organic remains. I almost forgot to mention that these fossils were apparently in an unit above the Murphy Marble Fm in the base of the overlying Mineral Bluff Group. I didn't take the photos so I don't have a scale for them. I finally did dig up a old picture from a talk given back in 2019 at a NCFC meeting in Raleigh and got a screenshot of part of the article to give you an idea of the scale on these pics.

 

The Walden Creek Group in Tennessee just across the border produced a middle-late Paleozoic fauna, including brachiopods, trilobites, gastropods, and some other things. It is at least possible that these are organic in nature. It might be worth it to check that out. 

 

IMO I'm seeing a few brachiopod fragments. The top one looks like some kind orthid, if you put a gun to my head and made me make a guess. I'm basing that off the thickness of the ribs, and specimens I've collected in Tennessee and elsewhere. The second one looks like an orthid as well, vaguely similar to Hebertella sp. but that's just something I'd say if I absolutely had to. The ribbing appears to be too coarse for Rafinesquina sp. but too fine for any of the larger orthids. 

 

Of course, they could be something else, it's really impossible to narrow it down beyond an order. I am pretty confident these are brachiopod fragments, however, and they look to be like you'd expect from middle Ordovician - Mississippian deposits.  Definitely not Precambrian. 

Edited January 31, 2022 by EMP

[klattrocks]

Yes I'm quite familiar with the discovery of Paleozoic fossils in the Walden Creek Group, which previously was thought to be preCambrian by the Unrug's. I learned about this when Dr Shuhai Xiao and Dr. Ryan Thigpen were investigating a possible algal fossil? I had collected from the Sandsuck formation on Starr Mountain in Tennessee. Dr. James Tull found a Crinoid in a core taken from the Mission Mountain formation west of our study area in Nantahala Gorge. William Ausich who identified it as a Crinoid thought it is probably Ordovician, but he had no way to know for sure. I talked to Don Hathaway and he felt the core was actually taken in the Andrews Schist and not in the Murphy Marble. We now call the Andrews Schist the Mission Mountain fm! If this verifies this will collaborate the Paleozoic age indicated by the Crinoid in the Mission Mountain fm near Murphy. Since there is a considerable unconformity between the Mission Mountain fm and the underlying Murphy Marble fm it's still a good possibility that the Murphy Marble is Cambrian or preCambrian as previous workers have suggested. Thanks for this input. It gives something to run with now. I will pass on your observations to Dr Campbell. This is very much appreciated!!!

[Plax]

This is an interesting topic Al. Please keep us in the loop.

[EMP]

On 2/21/2022 at 9:05 PM, klattrocks said:

Yes I'm quite familiar with the discovery of Paleozoic fossils in the Walden Creek Group, which previously was thought to be preCambrian by the Unrug's. I learned about this when Dr Shuhai Xiao and Dr. Ryan Thigpen were investigating a possible algal fossil? I had collected from the Sandsuck formation on Starr Mountain in Tennessee. Dr. James Tull found a Crinoid in a core taken from the Mission Mountain formation west of our study area in Nantahala Gorge. William Ausich who identified it as a Crinoid thought it is probably Ordovician, but he had no way to know for sure. I talked to Don Hathaway and he felt the core was actually taken in the Andrews Schist and not in the Murphy Marble. We now call the Andrews Schist the Mission Mountain fm! If this verifies this will collaborate the Paleozoic age indicated by the Crinoid in the Mission Mountain fm near Murphy. Since there is a considerable unconformity between the Mission Mountain fm and the underlying Murphy Marble fm it's still a good possibility that the Murphy Marble is Cambrian or preCambrian as previous workers have suggested. Thanks for this input. It gives something to run with now. I will pass on your observations to Dr Campbell. This is very much appreciated!!!

 

I doubt the Murphy Marble is anything older than late Cambrian if your brachiopods are from it. If you all found crinoids in the Mission Mountain than it's at least Ordovician, unless it's actually an eocrinoid, which could make it Cambrian. To put it in perspective the upper Chilhowee Group (which is confirmed lower Cambrian based on nevadiid trilobites) does not have articulate brachiopods, but the Walden Creek Group does. My admittedly limited guess would be these fossils come from between the two, but that's only if I absolutely had to assign an age. I don't know a whole lot about the Murphy Marble, but based on things like Cades Cove, I assume it could be possible that it might be part of a window or something? That might also explain the unconformity you mention. In that case the Murphy might be more related to the Ordovician limestones around Sevierville-Knoxville, which do have a decent invertebrate fauna. The brachiopods at least bare a cursory similarity to orthids I've found in the Leipers Formation of eastern Tennessee. 

 

 

13 hours ago, Plax said:

This is an interesting topic Al. Please keep us in the loop.

 

I agree, it is a fascinating topic. A lot of people don't imagine the Blue Ridge having fossils, but if you dig deep enough there's actually been a fair amount found over the years. These certainly wouldn't be the first of their kind. 

[klattrocks]

I well definitely get back with any important updates on our research. Don Hathaway's cores with the brachiopods he believes were actually taken from the Andrews Schist during coring and not in the Murphy Marble. We now know the Andrews Schist as the Mission Mountain fm. The lithology of the core does look to be different from the Murphy Marble. The Murphy Marble as far as I know hasn't ever produced any fossils. Also the formation doesn't seem to have the minerals within it that can be dated by using radiometric methods. The unconformity above the Murphy Marble and below the Mission Mountain fm represents an unknown amount of time missing from the stratigraphic column so the discovery of brachiopods in the Mission Mountain doesn't shed much light on the age of the Murphy Marble. If indeed the brachiopods are Orthid brachiopods that only constrains the deposition time of the Mission Mountain fm from the Ordovician to the Mississippian time frame. I will have to check on this, but I think they now believe that the units of the Murphy Marble Belt were metamorphosed during the Acadian Orogeny in the Late Devonian so the Devonian Period would be the youngest possible age for the Mission Mountain. Hopefully these brachiopods can be classified down to the family and genus levels to further narrow down the period of time the Mission Mountain was deposited. Even if we get no further than getting more or less a consensus these are brachiopods this is still a very important discovery for our understanding of Southern Appalachian geology.

[klattrocks]

It looks like the brachiopods are indeed Orthids. The range in time for them is from the Ordovician to Mississippian. Now it looks like there are two different genus of Orthids present and those ranged from middle Ordovician to Upper Silurian! It looks like the suggestion of Hebertella for one of the brachiopods may be correct. If we could identify the brachiopods down to species it would narrow down the range of Mission Mountain fm deposition even further.

[EMP]

On 3/3/2022 at 1:18 AM, klattrocks said:

It looks like the brachiopods are indeed Orthids. The range in time for them is from the Ordovician to Mississippian. Now it looks like there are two different genus of Orthids present and those ranged from middle Ordovician to Upper Silurian! It looks like the suggestion of Hebertella for one of the brachiopods may be correct. If we could identify the brachiopods down to species it would narrow down the range of Mission Mountain fm deposition even further.

 

Sounds interesting. My suggestion would be to read about the Chickamauga Group/Cannon Formation/Leipers Formation in the Tennessee/Georgia area. Again, don't know much about the Mission Marble, but my first thought would be these are part of some kind of window/related to the thrusting during the formation of the Blue Ridge. It's also possible they're autochthonous, but from what I've read it seems like a lot of these carbonates are allochthonous units. 

 

There aren't any upper Silurian rocks in the area, so I'd say you could probably safely confine it to between the middle Ordovician and lower Silurian. That's assuming they're not autochthonous, however. 

[Dr. Jeff Greenberg]

I do have a comment about the Murphy Marble age. Back in about 1977, there was a well-attended field trip to the main quarry. One of the leaders had published in the guide we used, that the Marble was certainly Ordovician. This was based on his identification of a Maclurites gastropod in the rock there. The photo he used for evidence was not impressive. Two grad student colleagues and I found a loose piece of the marble with what appeared to be solution cavities. In one cavity, there was a small, .5cm or so, flat-coiled gastropod. It had pretty obviously been a recent critter that was sort of "glued" in the hole, maybe by re-precipitated calcite. We three took the find to the leader and he acknowledged, without bothering to really test it, that yes, we had found another one! Obviously the credibility of discoverer and the age were far from respected. We took a pen and broke the snail out of the cavity. It certainly was not a preserved fossil and did not have the asymmetry of Maclurities.