I'm an assistant professor of Geology at Calvin College in Grand Rapids, Michigan
and a discussion recently came up on a mailing list I frequent (evolution@calvin.edu).
Art Chadwick, a professor of Geology at Southwestern Adventist University in Keene,
Texas (http://chadwicka.swau.edu/faculty/personal.html) has mentioned that he collected
a Neuropteris-type frond from the Mansfield Formation of south-central Indiana which
is perpendicular to the tidal laminations which were described in your joint "Geology"
paper of April, 1989.
From this, Art argues against your tidal rhythmite interpretation for the Mansfield.
Here is Art's post from October 5 where he discusses this fossil and it's implications:
> These very delicate lace-like leaves would have to have stood vertically in
> the water column, unsupported, with no evidence of decay, while daily tidal
> currents swept repeatedly across them, for two months (at least). Not a
> chance. There is a problem with that interpretation. But maybe it would
> be easier to explain away the leaves than to attempt to reinvestigate the
> data on the cycles.
Here is Art's post from October 8 when challenged about the sample:
> 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.
As he mentions, the fossil may be viewed on his web page. This, and other,
posts may be read at the Evolution Mailing List archive at:
http://www.calvin.edu/archive/evolution/199810/author.html#start
Several of us on the mailing list would be very interested if either of you
gentlemen would care to comment on Art's claims that a vertical fern-like frond
which appears to be perpendicular to laminations within the Mansfield Formation
negates your idea of a tidal rhythmite interpretation for this unit.
If you like, you could post a reply directly to the evolution listserver by
first subscribing. To do this, send e-mail to:
Majordomo@lists.calvin.edu
with the command:
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in the body of the e-mail message. If you care to reply directly to me, I would
be happy to post your reply to the list.
I thank you for your time and look forward to a reply.
- 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/
