Sunday, March 9, 2014

Fossils in the St. Peter Sandstone

The St. Peter Sandstone, a Middle–Late Ordovician unit that deserves the appellation "sandstone" like few other formations, has proven itself a very useful formation. Its extremely pure quartz sand is prized for various industrial applications, like glassmaking. It is readily excavated, so digging sewers and burying utilities is simplified. It has a tendency to form caves, which coupled with the ease of excavating makes it an ideal substrate for underground storage, cheese aging, mushroom growing, some types of brewing, and so on. More frivolously, it has provided a vast natural canvas for people who like to carve their names in things, and it has rewarded generations of graduate students looking for thesis and dissertation topics. At 100+ feet (30 m+) of uniform sand with few apparent bedding structures, and an off-white color that weathers to a kind of sickly gray, it is also an excellent natural soporific if you are not interested in any of these things. This most useful of formations is very much a bust paleontologically, which seems like some kind of a metaphor, but I'm not going to push things.

It's...beautiful. Yeah. That's what I was thinking.

Well, almost a bust. There is a site near Decorah, Iowa, where many finely-preserved fossils have been found, but it's a bit of a cheat, because the fossils are in a shale bed within the sandstone. (Update: it turns out that the fossiliferous bed, the Winneshiek Shale, is a distinct unit separated from the overlying St. Peter Sandstone by a disconformity. Therefore, we don't have to worry at all about the fossils being part of the SPS. Also, removed a dead link.) A few fossils have been found in Minnesota. Witzke (1980) had some conodont jaw elements from the subsurface near the St. Paul Hotel. Mazzullo and Ehrlich (1987) reported a few burrows at Battle Creek and Dayton's Bluff. The best stuff, though, was found back in the 1890s by Frederick W. Sarderson.

Frederick W. Sardeson is a fascinating personality. He was a brilliant geologist who came up with a biostratigraphic scheme that has long been used in the Paleozoic rocks of Minnesota, and a noted fossil collector whose specimens are a major part of the University of Minnesota's paleontological collections, and were sent as far as London (the type of the edrioasteroid Pyrgocystis sardesoni Bather 1915; in hindsight possibly the first fossil described from the Brickyard if a slip of "west bluff" for "east bluff" is assumed). He also had some unfortunate personality traits that led to him being fired from the University: he was arrogant, sarcastic, and off-putting to his colleagues in the department. He didn't want to go along with the new department head's plan to emphasize technical and economic aspects of geology over Sardeson's preferred pure science, and ended up dismissed (Weiss 2000). It's glib to say he was fired because he was disliked, but it certainly didn't help. In hindsight, it's hardly surprising that he had trouble with his colleagues: as a student, he was caught in animosity between factions at the state survey and the University, which led to his stratigraphic scheme being adopted with minimal credit and a bizarre series of events that culminated in a false preprint being sent out to poach the naming of several brachiopods he was describing (Weiss 1997, 2000). Coincidentally, Sardeson was replaced by none other than...Clinton R. Stauffer. I feel like I'm a postmorten press agent.

Part of Sardeson's work as a student involved the paleontology of the St. Peter Sandstone. In a testament to his skill as a fossil collector, he located and successfully collected fossils from three St. Paul-area localities in the sandstone. "Successfully collected" is a major part of the achievement: the fossils were natural molds and casts of great fragility. The sites can all be attributed to the modern area of Mississippi National River and Recreation Area; in the interest of security, I will not divulge the exact locations (although I doubt that anyone could find fossils at the sites today, because of erosion and construction, and also because it's the bloody St. Peter Sandstone), but they were in Dayton's Bluff, Highwood, and South St. Paul (Sardeson 1892, 1896).

Sardeson described the fossil assemblage from the three sites as including nearly two dozen species of bryozoans, brachiopods, monoplacophorans (described as snails), bivalves, nautiloids, and snails (Sardeson 1896; reevaluated in Sloan 1987; note that the 1896 paper also includes a few fossils from the top of the formation at Fountain, Minnesota, which I overlooked before and have now corrected [2014/08/06]). He named 16 new species, which is probably a bit much given the preservation of the material involved. On the other hand, the names are still more or less technically valid because of the lack of comparable material. Later in life he became very leery of naming new fossils and wrote sarcastic asides about paleontologists whom he considered creators of specious names (Weiss 2000). I have seen some of his St. Peter Sandstone fossils, and they are about as advertised: humble natural casts of mostly snails. I include below a plate from Sardeson (1896) to give you an idea, on the off chance you see one. (Update: see post "Fossils in the St. Peter Sandstone 2: actual fossils" for some museum specimens.)

1 and 2: bivalve Tellinomya absimilis; 3: bivalve Tellinomya novicia; 4: snail Murchisonia gracilis; 5: snail Holopea obliqua; 6 and 7: brachiopod Crania? reversa; 8 and 9: snail Ophileta fausta; 10: nautiloid Orthoceras (?) sp. undet.; 11 and 12: nautiloid Orthoceras minnesotense; 13 and 14: nautiloid Orthoceras; 15: bryozoan (Ptilodictya?); 16 and 17: snail Pleurotomaria aiens. From Sardeson (1896).


Bather, F. A. 1915. Studies in Edrioasteroidea. VI. Pyrgocystis N. G. Geological Magazine 6(1):5–12.

Mazzullo, J. M., and R. Ehrlich. 1987. The St. Peter Sandstone of southeastern Minnesota: mode of deposition. Pages 44–50 in R. E. Sloan, editor. Middle and Late Ordovician lithostratigraphy and biostratigraphy of the Upper Mississippi Valley. Minnesota Geological Survey, St. Paul, Minnesota. Report of Investigations 35.

Sardeson, F. W. 1892. Fossils in the St. Peter Sandstone. Bulletin of the Minnesota Academy of Natural Sciences 3(3):318–319.

Sardeson, F. W. 1896. The Saint Peter Sandstone. Bulletin of the Minnesota Academy of Natural Sciences 4(1):64–88.

Sloan, R. E. 1987. The St. Peter Sandstone of southeastern Minnesota: fauna. Pages 50–51 in R. E. Sloan, editor. Middle and Late Ordovician lithostratigraphy and biostratigraphy of the Upper Mississippi Valley. Minnesota Geological Survey, St. Paul, Minnesota. Report of Investigations 35.

Weiss, M. P. 1997. Falsifying priority of species names: a fraud of 1892. Earth Sciences History 16:21–32.

Weiss, M. P. 2000. Frederick William Sardeson, geologist 1866–1958. Minnesota Geological Survey, St. Paul, Minnesota. Bulletin 48.

Witzke, B. J. 1980. Middle and Upper Ordovician paleogeography of the region bordering the Transcontinental Arch. Pages 1–18 in T. D. Fouch and E. R. Magathan, editors. Paleozoic paleogeography of the west-central United States. West-central United States paleogeography symposium. Society of Economic Paleontologists and Mineralogists, Rocky Mountain Section, Denver, Colorado.

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