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| Coiled cephalopod, Hoploscaphites sp., in concretion. This same concretion contains Baculites, gastropods, and bivalves. |
South Dakota has an amazing variety
of geological features present on the landscape and an interesting array of formations
cropping out along the roads. I have a
particular love for the state since in 1965 I left my home in central Kansas and
traveled north for additional education.
It was a long trip, 325 miles, for a small town kid sort of striking out
on his own (my undergraduate education was less than 100 miles away from home,
and in the same state). In fact, it was
downright scary!
The first thing that I noticed upon
my arrival in eastern South Dakota was the fact that most of the rock exposures
were covered by what we lovingly called “glacial crap”. The second was that in some of the stream
valleys, where a few exposures existed, there were old friends from western
Kansas—the Niobrara Formation, Carlile Formation, Dakota Formation, etc. These rocks made me feel more “at home”!
But the real excitement came from
our field trips to “West River” and the badlands and the Black Hills. I had visited these areas the previous summer
on a road trip with a couple of college buddies but at age 20 our minds were mostly
on other “things”. We poked around at
the rocks, collected a few, did some hiking but always kept our eyes out for
the other “things”. I knew that I wanted
to return to South Dakota with a knowledgeable guide. And so I did.
In the summer of 1966 I started a
thesis project West River and to break up the driving from Chamberlain (my work
station) I often stopped at the little community of Wasta. Today Wasta is located at Exit 98 on high
speed (75 mph legal but often faster) I-90.
In the “old days” Wasta was just a little store on U.S. 16 where one
could purchase a cold soda, and explore the Pierre Shale.
I had previously examined a few outcrops
of the Pierre in extreme western Kansas (Wallace County), mostly near McAllaster
Buttes, and found the formation to be rather unfossiliferous (a few nondescript
baculites) and kind of “ugly”. The
Pierre represents deposition in the deepest waters of the Western Interior Seaway
during the latest Cretaceous, and many tens/hundreds of miles from the nearest
shoreline. I sort of put the formation
in the back recesses of my mind---until I explored South Dakota!
The Missouri River Trench, as
South Dakota geologists call the feature, exposes the Pierre from near the
South Dakota—Nebraska border (Fort Randle in the south central part of the
state) all the way north into North Dakota.
In fact, there are even exposures along the Missouri River near Yankton in
the south eastern section. Geologists
from South Dakota Tech have been studying the unit for years and have described
a number of new vertebrate critters. In
addition, invertebrate fossils are numerous.
From the Missouri River Trench
west to the Black Hills (and beyond) the Pierre crops out at numerous localities but especially along the major streams. I found that special
exposures were located along the Cheyenne River near Wasta. Suddenly the Pierre lost its ugliness (my
earlier opinion) and became exciting!
Exposures of the Pierre along the
Cheyenne River yield concretions and these concretions are often
fossiliferous. Most fossils are mollusks
including the pelecypods Inoceramus sp. and Pteria sp., the
cephalopod ammonites Baculites sp. and Hoploscaphites nodus, the
gastropods Margaritella flexistriata, Amauropsis sp., Drepanochilus
sp., Anisomyon sexculcatus, the scaphopod Dentalium gracile,
as well as the coral Micrabacia americana (Sharman, 2008). But most collectors are not interested in the
snails but in the beautiful straight-shelled cephalopods (Baculites sp) and the coiled cephalopod Hoploscaphites. These
ammonites often have mother-of-pearl present and the suture patterns on the
shells are quite distinct. They are
really spectacular fossils and collectors will notice South Dakota specimens in
museums around the world.
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| Baculites sp. in concretion. |
Today, as I understand the
situation, the private land is very difficult to access and collect. Therefore, if you plan on collecting I would
suggest contacting the various rock and mineral clubs or rock stores located in
or near the Black Hills. I have found
them to be a wealth of information.
It is not always fun experiencing
the aging process but---the alternative is not very appealing either! What I do have are my memories and I often
think of those days where collectors could wander around South Dakota, visit
with the ranch owners in a friendly fashion, and bash open concretions looking
for those ammonites.
REFERENCES
CITED
Sharman, G. R., 2008, Petrology,
Geochemistry and Paleontology
of Fossiliferous Concretions from
the Cretaceous Pierre Shale, South Dakota [abs.]: Geological Society of America
Abstracts with Programs, v. 40, no. 5, p. 85.
mike