Laramide Posted March 31, 2021 Share Posted March 31, 2021 (edited) During an afternoon break I found a dozen or so promising concretions at an outcrop of Fayetteville shale. I'm thinking of going the freeze/thaw route as my history of hammering concretions is a but hit or miss. Curious as to the opinion of the forum on the best technique. Also, should I consider setting a couple aside and try to get whole fossils by remove the matrix? Thanks in advance. Edited March 31, 2021 by Laramide Link to comment Share on other sites More sharing options...
Thomas.Dodson Posted March 31, 2021 Share Posted March 31, 2021 Any examples or specific information on the types of concretions? It seems there are multiple types of concretions found in the Fayetteville Shale and examples of specific ones may help us to recommend methods. Freeze-thaw is pretty simple. It's the expanding ice that exerts pressure as it changes from liquid to solid. Because of this just make sure the concretions are saturated with water before freezing and make sure they freeze solid before you thaw them. Then repeat. The amount of time to soak varies by the rock and the continuing process of repeated soaking and freezing can take a while but it's easy enough. 19 minutes ago, Laramide said: Also, should I consider setting a couple aside and try to get whole fossils by remove the matrix? Maybe. How big are the concretions? Do you have air scribes to work the concretions from the outside? 1 Link to comment Share on other sites More sharing options...
Laramide Posted March 31, 2021 Author Share Posted March 31, 2021 (edited) 6 hours ago, Thomas.Dodson said: Any examples or specific information on the types of concretions? They are sideritic concretions. Numerous Emstites fayettevillea have been found at this outcrop. Quote How big are the concretions? Do you have air scribes to work the concretions from the outside? 5-15 cm spheroid shapes with an elongated axis. Yes, I have access to an air scribe. Edited April 1, 2021 by Laramide Link to comment Share on other sites More sharing options...
FossilDAWG Posted March 31, 2021 Share Posted March 31, 2021 Freeze-fracture works best if there is a specific plane where the fossil is located, and the fossil produces microfractures or a plane that water can enter preferentially. When the water freezes it expands and enlarges the microfractures until they coalesce and the nodule splits. This works well for the Mazon Creek nodules but more commonly the fractures are throughout the nodule/contretion and so it just ends up shattering in a jigsaw puzzle of pieces. I have totally blown up some Alabama crab concretions that way for example. I would think that a septarian concretion would be a great candidate for a disaster. If I had those nodules and a scribe, I would go that route. If most nodules are empty I might try to split them with a hammer (not too vigorously), and any that have an ammonoid inside I would glue back together as necessary and prep with the scribe. Don 1 1 2 Link to comment Share on other sites More sharing options...
Laramide Posted March 31, 2021 Author Share Posted March 31, 2021 Thanks for the advice. That is now my plan (although I did throw one 5cm sacrificial/experimental concretion in the freezer). Link to comment Share on other sites More sharing options...
Oxytropidoceras Posted April 1, 2021 Share Posted April 1, 2021 4 hours ago, Laramide said: They are sideritic concretions. Numerous Emstites fayettevillea have been found at this outcrop. The siderite concretions from the Fayetteville Shale that contain Emstites fayettevillea are discussed in: Stevens, J., 2020. Fayetteville and Imo Shales: Punctuated Upper Mississippian Shallowing Upward Sequence, Southern Ozark Region, Northern Arkansas (Master's thesis, University of Arkansas). University of Arkansas, Fayetteville, ScholarWorks@UARK Web page with download link PDF file of MS thesis Yours, Paul H. 1 1 Link to comment Share on other sites More sharing options...
Thomas.Dodson Posted April 1, 2021 Share Posted April 1, 2021 8 minutes ago, Oxytropidoceras said: The siderite concretions from the Fayetteville Shale that contain Emstites fayettevillea are discussed in: Stevens, J., 2020. Fayetteville and Imo Shales: Punctuated Upper Mississippian Shallowing Upward Sequence, Southern Ozark Region, Northern Arkansas (Master's thesis, University of Arkansas). University of Arkansas, Fayetteville, ScholarWorks@UARK Web page with download link PDF file of MS thesis Yours, Paul H. Interesting. It seems the author preferred to slice through the concretions and fossils inside with a rock saw. Most other specimens illustrated were from the fissile shales, naturally worn from concretions, or on the exterior of concretions. It seems like pretty tough material. Those septarian cracks throughout really aren't to be trusted with freeze thaw so I'd go the scribe route. 1 Link to comment Share on other sites More sharing options...
Laramide Posted April 1, 2021 Author Share Posted April 1, 2021 (edited) 1 hour ago, Oxytropidoceras said: The siderite concretions from the Fayetteville Shale that contain Emstites fayettevillea are discussed in: Stevens, J., 2020. Fayetteville and Imo Shales: Punctuated Upper Mississippian Shallowing Upward Sequence, Southern Ozark Region, Northern Arkansas (Master's thesis, University of Arkansas). University of Arkansas, Fayetteville, ScholarWorks@UARK Web page with download link PDF file of MS thesis Yours, Paul H. Haha... funny you should mention that. I know Josh (the author) and chose the outcrop due to advice I got from him and Walt (Dr. Manger) a couple of years ago...although I haven't read his thesis. 57 minutes ago, Thomas.Dodson said: Interesting. It seems the author preferred to slice through the concretions and fossils inside with a rock saw. Most other specimens illustrated were from the fissile shales, naturally worn from concretions, or on the exterior of concretions. It seems like pretty tough material. Those septarian cracks throughout really aren't to be trusted with freeze thaw so I'd go the scribe route. Yeah I know he made thin sections because he was looking at ruptured septal chambers. Maybe I should consider using a rock saw on a few....okay I guess I'll read the paper before moving forward....maybe even give him a call...not sure why I didn't think of that before... Edited April 1, 2021 by Laramide Link to comment Share on other sites More sharing options...
Thomas.Dodson Posted April 1, 2021 Share Posted April 1, 2021 Just now, Laramide said: Yeah I know he made thin sections because he was looking at ruptured septal chambers. Maybe I should consider using a rock saw on a few....okay I guess I'll read the paper before moving forward....maybe even give him a call... Not just thin sections. He took thin sections of the best ones but for most of them he just sliced the concretions in half. 1 Link to comment Share on other sites More sharing options...
Laramide Posted April 1, 2021 Author Share Posted April 1, 2021 (edited) 46 minutes ago, Thomas.Dodson said: Not just thin sections. He took thin sections of the best ones but for most of them he just sliced the concretions in half. Thanks...I just remember him showing me some of the thin sections and talking about the ruptured chambers...but then again that was a while ago... Now I'm feeling a bit foolish, should've just asked someone I know... Edited April 1, 2021 by Laramide Link to comment Share on other sites More sharing options...
Scylla Posted April 1, 2021 Share Posted April 1, 2021 1 hour ago, Laramide said: Thanks...I just remember him showing me some of the thin sections and talking about the ruptured chambers...but then again that was a while ago... Now I'm feeling a bit foolish, should've just asked someone I know... II f you did that only you would know what to do. Now we all know what to do if we ever get to that outcrop. 1 Link to comment Share on other sites More sharing options...
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