Genesis and Evolution of the I-170 Pennsylvanian Project

A personal account by Norm King

I became familiar with the I-170 exposure in St. Louis through amateur paleontologist Barry
Sutton, to whom I was introduced by Carl Cook. Mr. Cook was a curator for the exhibit of
Russian dinosaurs and other vertebrate specimens in St. Louis at the City Museum during
October of 1997, and had invited me to view that material. I learned that Barry had been
collecting fossils at the I-170 site for several years, and was struggling to understand the
stratigraphy and sedimentology of the site. We agreed that I would return at a later time to
look at the I-170 exposure to see if I could provide some insight about the origin of the
fossiliferous rock units there. Carl, Barry, and I visited the outcrop in July of 1998 on the
hottest, most humid day I have ever worked in the field.

Initially I thought the sequence of rocks was typical for any Midcontinent Pennsylvanian
depositional cycle, with a deep-water phosphatic shale (Lake Neosho Shale) underlain by
transgressive deposits (apparently including the Amoret Limestone) and overlain by a major
regressive limestone (the Worland Limestone, that forms the cap rock at the I-170 exposure).
Due to the demands of working on other projects at the time, I took only hurried notes during
just a few hours on the coutcrop. Months went by, and after exhausting Barry's patience, I
finally (in early 1999) supplied a brief summary of the stratigraphy and depositional history
of the beds exposed at I-170 that he could add to his website. I attempted
to use standard concepts for Pennsylvanian stratigraphy as the framework for my
interpretations. Although I had found some unexpected features that aren’t completely
consistent with the “model,” I did not attempt to explain the discrepancies. I was satisfied to
simply present the concepts of Pennsylvanian cyclic depositional patterns, and I claimed
that they were appropriate for understanding the I-170 section.

My bluff didn’t work. Almost immediately, questions came in about the rock descriptions and
interpretations. Some writers expressed concern that I had portrayed a sequence of strata and
depositional conditions somewhat “out of sync” with their understanding of Pennsylvanian
stratigraphy. While I provided answers for Barry to post on his website assuring the
questioners about my observations, I had to admit that I could not readily explain why the
interval at this outcrop is different from what people expected.

After a little cajoling from Barry, who had to defend my story since it was on his website, I
conceded that perhaps the locality deserved another visit. I returned for additional study of the
outcrop in the spring of 2002. During my first additional visit, I measured and described the
section at a location where the exposure is unusually good and complete, and a lot different
from the interval I had used earlier for my understanding of the stratigraphy. Then Barry
pointed out another spot where the succession of beds is a little different yet, so we studied
that location as well. Then we went to one more location where the strata are really different
from any of the sites we had already examined. It then became clear that I could write up any
of the four sections I had measured and described so far, and each one would result in a
somewhat different history, perhaps none of which would be quite what people were expecting
based on general knowledge of Midcontinent Pennsylvanian stratigraphy.

Indeed, the stratigraphy varies continuously along the outcrop. No single place has a “typical”
section because there is no typical section there. Moreover, I certainly had not expected to find
a boulder conglomerate in the interval. I was (and still am) unaware of such a lithology
described in previous literature on the Midcontinent Pennsylvanian. It also didn’t help that all of
the units, except for the varicolored claystone at the base of the section and the Worland
Limestone at the top, are absent at one place or another along the outcrop.

We began taking photographs of the rocks to show their major features and to document the
stratigraphic succession, with the objective of displaying these on a website. I sliced and
polished several slabs of rock, and scanned them to be able to show their details.

All the while, in the more in-depth technical discussion “paper” I was writing, I was trying to
explain the rocks in terms of the well-known model of Pennsylvanian cyclic deposition,
interpreting each unit in terms of its place in one or more transgressive-regressive depositional
cycles that had been recognized (and named) previously. In fact, this model embodies the very
pattern that some of the visitors to Barry Sutton’s website had expected to see in my
description of the strata exposed at I-170, but didn’t. In the next year I made a few more visits
to the outcrop, and spent much time revising, expanding, and fine-tuning the write-up. Before
long I could see that, after taking pains to explain the cyclic depositional model, much of the
ensuing discussion revolved around making excuses for why the succession at I-170 doesn’t
seem to match what the model says should be there. My experience as a teacher told me this
would not be a good way to try to bring this story and the associated illustrations to readers
who are not familiar with the history of concepts relating to Midcontinent Pennsylvanian

That’s when I discarded the existing text and started all over again at the beginning. This was
almost exactly on the date (June 1, 2003) we had once set as the deadline for going public
with the Altamont website, and I was becoming concerned about the amount of time I had
already spent on it and how many other projects I had delayed in order to finish it. I began to
think of this as “The geology project that ate me.”

In the mean time we presented a poster talk at the Geological Society of America’s North-
Central Section meeting in March of 2003 in Kansas City, Missouri (view GSA abstract) that
incorporated my initial ideas and concentrated on placing the sequence into the regional cyclic
depositional framework. Although the presentation went well, I have since modified some of
my ideas. Another objective for the poster, however, was to exhibit many of the photographs
and captions that were to be in the web publication, to gage the public reception and to receive
feedback from our professional colleagues (view scenes at the GSA meeting).

Although I accept that Midcontinent Pennsylvanian strata incorporate a record of repetitive
transgressive-regressive depositional cycles, and recognize that much of the I-170 section
may readily “fit” into such a framework, I have not tried to force any particular unit at I-170 into
any specific role in the framework. That framework was established in the “western outcrop
belt” that stretches from northeastern Oklahoma to central Iowa, but the I-170 exposure in St.
Louis is closer to the Illinois basin and is more than 150 miles away from the nearest
exposures of correlative strata in western outcrop belt. Any differences here may be
significant, so they shouldn’t be either overlooked or downplayed. Nearly all of the summer of
2003 was devoted to rewriting the technical discussion in light of these considerations.

One of our objectives was to release a web document that is comparable in quality to those
published through traditional media. A properly constructed website document requires as
much editorial attention and quality control as traditional publications. There should be no
grammatical or typographical errors, it should be free from sloppy and imprecise language, and
the conclusions should follow from the evidence presented. Links should work smoothly, and
navigating around the website should be easy. Just taking care of these issues took nearly a
month of fairly concerted effort by both Barry and me. We also solicited critiques about the
quality of the scientific discussions and interpretations from outside reviewers, and waited to
hear back from them to incorporate their suggestions (which were many). As comments come
in after release, we anticipate continuing to “fine tune” the mechanical aspects of the document
as well as the science reported in it.

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