I found these marks on the S-plane of a marble layer. The area has been affected by upper-greenschist (at least) facies metamorphism. Is it possible to be some kind of fossil? The width of view is apprx. 13 cm.
Jozef Michalik: The objects are similar to mollusk shells. Their inner structure would be probably recrystallized, but trying to find at least rests of it would be useful. Also try to check the rock structure in a wider vicinity.
hi, it could be. in the Alps wi found fossils even at higher grades and in highly deformed rocks. The best surfaces are on eroded boulders, where the differential erosion could act (see the monumental Ellemberger 1958 at this proposal). do you have a wider image? just to see if these kind of features are the simple expression of heterogeneities in the deformed marble or if really are two anomalous bodies. Is the marble rich in shales (now micaceous impurities) or sands?
Dear Jozef,
these structures might be anything and there is nothing to see (?) what is exclusive to molluscs. I will suggest by these pictures nobody is able to say anything about the possibly fossil origin of the structures.
Dear Alexandrides,
you need to provide cuts (in different layers) throug these objects, like Adam recommended. Also informations about age and sedimentological setting of these metasediments (?) could be useful.
Best regards
Johannes
Dear Adam, Jozef, Harry, Federico, Johannes and Joachim, thank you very much for your suggestions.
The area apart from the grade of metamorphism, is very hightly strained, perfectly isoclinal folds occured, even sheath folds and also very high rates of extention observed. Sheath folds have been observed inside the same layer but in a distance. So, it is difficult for me to imagine, how all that deformation have left these hypothetical fossils unaffected, but on the other hand is a little bit difficult to be random structures, especially the left one.
Also, there is indeed a great presence of quartzitic veins inside the the marble layer. I can' t answer for sure about the age of the sediments or the metamorphism, because the area is located in the (supposed footwall) rocks of the Nestos Thrust in northern Greece. It's an area with great uncertainties in the section of rocks origin and metamorphism timing due to many controversial interpretations.
Once again, thank you all
Ioannis Alexandrides
Hi Alexandrides, I agree with the others; it could be a mollusk, but also a metamorphic structure. Other views of the object could useful to understand. Good luck with your work!
lorenzo
Without doubts, two findings could be accidental "toys of the nature", especially in this case. On the other hand, sometimes metamorphic "shadows" occur even in clearly metamorphic complexes. The only one thing you need is to repeat your findings. Otherwise, uncertainty degree is too high...
You need thin sections to provide more informations. It could be organic or inorganic impossible to decide only with this view.
Dear Alexandrides.
You have a good review of possible origin of those mysterious structures. I can add one more yet: burrows; they are often infill with sediment different from surrounding lime mud, so their preservation in both diagenesis and metamorphism can also be different. Anyway, as it has also been stated by other Responders, thin sections analysis is the first step to solve the problem.
Best regards,
Adam Bodzioch.
Hi Alexandrides
Do you have any more close-up photos ? With this low magnification it remains very difficult tell anything.
Best,
Joachim
Adam, at the first impression i had the same idea, especially because the marks on the left has a hint of bifurcation (up to the right), but i'm not really convinced…in this my note you can find some examples of burrows in highly deformed triassic marble which suffered a first blue schist event followed by a upper green schist/lower amphibolite barrovian event in the central Alps…again the best surfaces to recognize them are the eroded one. in the case of alexandrines i'm quite skeptical...
Article The Soja and Luzzone-Terri nappes: discovery of a Briançonna...
Once again, thank all of you for your kind suggestions
This outcrop was found during a geological mapping in a very steep mountainous area.
The picture shows the S plane of a marble boulder, which was laid inside the riverbed of a seasonal stream.
Due to lack of time and heavy equipment for sample collecting, and due to the fact that I didn't expect to find fossils in multi-deformed rocks, I don't have any specimen to proceed in thin-sections making.
Kind regards to all of you who gave some of your precious time to help me.
Ioannis Alexandrides
Hi.I think it is a mysterious structure during metamorphism.but I believe that for get answer You need thin sections.
I agree. If feasible, a thin section might help unravel the nature of such mysterious marks
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