> I have on my desk a chunk of a Pennsylvanian 'rythmite' from a classical
> locality in Michigan. Only problem is there is a vertical Neuropteran
> frond that crosses two complete sets of so-called tidal cycles. Either
> there is some other explanation for the accumulation of tidal rhythmites or
> the delicate lace-like frond remained intact and extended vertically from
> the sedimentary surface (perpendicular to bedding) while the tidal cycle
> sediments accumulated around it and eventually buried it after two months.
On Thursday, October 8, Arthur V. Chadwick wrote:
> I have scanned an image of the rock so that you can see what I am trying to
> describe visually. It is not as good as a photo, but is not bad. Next
> time we have dinner I will bring it along. The photo of the frond is at
> http://chadwicka.swau.edu/leaf.jpg the plane of the fossil is
> perpendicular to the laminae in this fine grained sandstone, which can be
> seen faintly in the lower right hand corner. A second fossil, similar to
> the first, is located mutually perpendicular to the first, and the bedding,
> on the left hand side of the specimen. I obtained some beautiful
> Stigmarian roots in a specimen of the same laminated sediment, but the
> specimen is too large to fit on my scanner! THe Stigmaria root stocks have
> been found lying parallel to the laminae and running perpendicular to them
> as well! But they are in blocks of rock weighing 100 lbs or so. The
> fossils and tidal cycles come from the Mansfield Fm. (L. Penn) in S-Central
> Indiana. see article on this deposit in Kvale et. al. Geology Apr 1989 p.365.
I agree with Art that the image at http://chadwicka.swau.edu/leaf.jpg does
indeed appear to be a Pennsylvanian plant fossil in a fine-grained sandstone/
siltstone. Check out http://www.clearlight.com/~mhieb/WVFossils/TreeFerns.html
if you'd like to see some typical Pennsylvanian plant fossils.
I also have to add that I can't make out any laminations perpendicular to this
fossil although that is most likely due to the resolution of the scanned image
and not necessarily due to the fact that they may or may not exist. I would give
Art the benefit of a doubt on this since he has the fossil sitting in front of him.
Art, may I assume your first statement that the fossil was from a "classical
locality in Michigan" was in error? That's what perked up my ears since I'm
currently in Michigan and would have checked out such a locality. You said in
your second post that it's from the Mansfield Formation in south-central Indiana.
A couple of questions. Was it collected from one of the three quarries Kvale, et
al. studied in their "Geology" paper? Have you spoken with the authors of the paper
to see what their reply would be?
I've taken the liberty of forwarding a copy of Art's comments to the three authors
of the "Geology" paper in hopes that one or more of them will join the discussion or
at least respond with an e-mail that I will post to the list. I think we need to get
a little more rigorous in our discussions (after all, Glenn and I are both geologists
but neither of us has studied these tidal rhythmites) and it would be interesting to
hear from the authors of the paper which Art's fossil supposedly casts doubt upon.
A copy of this letter will be posted separately.
- Steve.
-- Steven H. Schimmrich, Assistant Professor of Geology Department of Geology, Geography, and Environmental Studies Calvin College, 3201 Burton Street SE, Grand Rapids, Michigan 49546 sschimmr@calvin.edu (office), schimmri@earthlink.net (home) 616-957-7053 (voice mail), 616-957-6501 (fax) http://home.earthlink.net/~schimmrich/
