LSCHNELLE Posted July 3, 2015 Share Posted July 3, 2015 Any one have ideas as to the type of fossil? This apparent fossil is in a highly crystalline limestone bed from the Middle to late Cambrian Morgan Creek Limestone Member of the Wilberns Formation western Llano Uplift in Texas. The same rock has evidence of at least one 2" to 3" size trilobite (separate from this wavy feature), several smaller trilobites, and it has glauconitic (green) and ferrous (orange) particle sections (probably from trilobite and sea life feces or other matter). The area has stromatolites that may be associated with the upper part of the Member (picture) - so it could be associated with stromatolites - but it seems just to the the single impression - not multiple as you would expect with stromatolites. And, the rock was not taken from the stromatolite bed area. The fossil rock may be from any part of the Morgan Creek Member due to faulting in the area. This 2' x 1' rock fragment was detached from the bedrock. The member is known to have three trilobite zones [Elvinia (bottom), Taenicephalus (middle), and Idahoian (top)] based on studies by J. L. Wilson (1949) and W. C. Bell (1950). I believe most of those trilobites should be very small (mm scale) not cm scale. The scale of the darkened impression is about one inch wide and it has ridges (see blue arrows). It appears to be part of a much larger fossil. There are trilobite fragments in the immediate area, but I am not aware of trilobites having wavy undersides. So, it would be more likely a large brachiopod or bivalve. Did they get this large in late Cambrian times? The side view should help you to envision where the rock separated along the wavy seam. I would like to try and carve it out, if it will hold together - although it is not apparent that it has more than one side. Thanks for the help. Lee Schnelle Link to comment Share on other sites More sharing options...
Auspex Posted July 3, 2015 Share Posted July 3, 2015 Just looking at the image, the material seems to be calcite or aragonite, judging by the crush fractures. If it is, arthropods can be ruled out. Do the ridges look like they could be an artifact of the crushing? "There has been an alarming increase in the number of things I know nothing about." - Ashleigh Ellwood Brilliant “Try to learn something about everything and everything about something.” - Thomas Henry Huxley >Paleontology is an evolving science. >May your wonders never cease! Link to comment Share on other sites More sharing options...
ZiggieCie Posted July 3, 2015 Share Posted July 3, 2015 Welcome to the forum. Great description of your find. Link to comment Share on other sites More sharing options...
LSCHNELLE Posted July 3, 2015 Author Share Posted July 3, 2015 I am not certain. The rock separates with a change in crystalline structure at the parting. You are seeing the matching halves of the wavy structure. The darker color is the outside edge. No other adjoining fossils appear to be affected by faulting stress - if that is what you are implying. The crystalline structure may just appear that way due to nature of the filling matrix. The wavy structure also appears to extend out into the adjoining rock. Could this be part of a very large trilobite or pelecypod? I may just have to carve it out to see. Link to comment Share on other sites More sharing options...
JohnJ Posted July 3, 2015 Share Posted July 3, 2015 Based on all the fracturing visible, I think you are inviting 'total devastation' of the tiny bit you're after. Still, you might try using insulin needles under a microscope to reveal a little more. The human mind has the ability to believe anything is true. - JJ Link to comment Share on other sites More sharing options...
FossilDAWG Posted July 3, 2015 Share Posted July 3, 2015 Are the crescent-like lines on the specimen just cracks, or could they be imbricating thin plates? Some Cambrian echinoderms had this structure, for example Walcottidiscus. However, that would not explain the folds. Cambrian bivalves are rare and small as far as I know, and I am not familiar with brachiopods that would have that structure either. However that certainly doesn't mean that such fossils are impossible, obviously. I, also, would be very cautious about "carving out" this fossil. It would be a shame to lose a unique or potentially important specimen, and I have certainly destroyed more than one fossil by pushing the prep just a "little bit farther". Are you doing a study of this particular formation? Your post indicates much more than the usual level of familiarity with the literature. Welcome to the Forum! Don Link to comment Share on other sites More sharing options...
LSCHNELLE Posted July 3, 2015 Author Share Posted July 3, 2015 Don: The lines are crystalline cracks not plates. I studied where to find trilobites in Texas and this formation and the Chappel limestone are two of the closest in my area without going to the Pennsylvanian age formations. This loose large 2" to 3" thick rock was broken open to look for trilos and no prep has been done. I have retained most rock fragments except a piece of trilobite steinkern that fell out. The rock separated on its own at the wavy point. It is a crystalline calcarenite. So, a lot of trilobite and other detritus is present. The crystalline structure (cracks) may be secondary replacement mineral of the outer fossil structure. I am not certain how fragile they are. Since the fossil separated at the wavy area, I suspect it would be easy to separate the remaining fossil. If the fossil has two different walls and a 3D shape,then that may be a poor approach since I may be viewing the inside wall. I am just baffled by the large size. I don't think it is an echinoid. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now