29 August 2015
Mystery structure: please help identify / interpret
Posted by Callan Bentley
I have a mystery for you today:
These are samples of Tonoloway Formation carbonate (not sure if it’s limestone or dolostone in retrospect), with bedding more or less horizontal in these images, and a few petite stylolites running orthogonal to that. The top sample has a gentle fold 2/5ths of the way across. All of the samples are from the same site in West Virginia, along Corridor H.
I’m wondering about the closely-spaced vertical (bedding-perpendicular) lines. Have any of my readers observed these before? What are they? How do they form?
Thanks in advance for any insight you can share.
Well, what pops into my head are refilled tension gashes. But they don’t necessarily have a relationship to structure. Then again they might have been soft-sediment forms.
I am starting a senior thesis project with a UMD student on the Tonoloway, and was there last Wednesday. Having seen clear evidence for evaporation in the halite hoppers, I wonder whether the parallel structure you show in the Mountain Beltway blog might be seafloor aragonite precipitate structures indicative of high alkalinity? I have seen similar examples in Neoproterozoic cap carbonates and in other strata where there was apparently high alkalinity. I note that the structures seem to end abruptly, so they might have been drowned by the next sedimentary event. I would make a thin section of these both across and with the bedding to see if these palisade structures persist and to note whether they have square terminations (indicative of aragonite).