Camp Nelson National MonumentSince we were introduced to Club Late Ordovician two years ago, two more parks have joined this exclusive organization for National Park Service units that include fossiliferous Upper Ordovician rocks. One is Saint Croix National Scenic Riverway, thanks to some isolated occurrences of the Platteville and Decorah that were protected from erosion by ancient faulting along the St. Croix Valley. These outliers represent the most northerly and landward outcrops of these formations, and are worth a post of their own at some point. The other new member is the newest NPS unit, Camp Nelson National Monument in Kentucky.
Camp Nelson is rather more famous for its Civil War history, but the Camp Nelson area is also notable for its geology. In fact, per Andrews (2005), "Because of the quality of exposures, accessibility, and the importance of the site in research and geologic education, the Kentucky Society of Professional Geologists has named the Camp Nelson area as Distinguished Geologic Site 2."
The park overlays four Ordovician formations, in ascending order the Camp Nelson Limestone, Oregon Limestone, Tyrone Limestone, and Lexington Limestone (Wolcott 1969). They are all examples of your classic marine Ordovician limestones; no points for guessing that brachiopods and nautiloids are implicated in Camp Nelson NM joining Club Late Ordovician. (Not surprisingly, these limestone formations are also karst-formers, and caves and sinkholes are common in the area.) The Tyrone Limestone is known to include the Deicke K-bentonite (Kolata et al. 1996), making it partially correlative in time to the Decorah Shale. Redating of the Middle/Late Ordovician boundary may in fact put all four of these limestones into the Late Ordovician.
As the name indicates, the Camp Nelson Limestone was described from the area of Camp Nelson (Miller 1905); the type locality is a little to the south of the monument, around the area of the Kentucky River crossing. You can also find some nice faulting on the south side of the river (Andrews 2005). The Camp Nelson Limestone appears to be the oldest formation exposed in Kentucky. This was a bit surprising to me, and leads to the reflection that, thanks to accidents of geography and erosion, the bedrock at the surface in the entire state of Kentucky is younger than most of the bedrock exposed in Minnesota.
Hiding conulariidsI really hope to have a more complete update later, but suffice it to say that while tracking down references to a conulariid species from the Grand Canyon, I stumbled across George Winston Sinclair's 1948 thesis on conulariids. In this thesis there is a great deal of information about Minnesota's Ordovician conulariids that Sinclair did not publish in his lifetime, including several unpublished species. There is also the implication that at one time the University of Minnesota collections contained two-to-three-dozen conulariid specimens from the Glenwood Formation on up. This came as a surprise, because I did not recall having seen more than a half-dozen or so on my trips. Several possibilities presented themselves:
- The conulariids were being kept separately from the other fossils when I visited, or were just somewhere I hadn't known to look;
- The conulariids have been lost or stolen: if so, not much more can be added;
- The conulariids passed into Sinclair's hands: this seemed worth following, because Sinclair built up a collection of conulariids and I knew that certain elements of the University of Minnesota collections had gone to others. For example, material from Berkey's Taylors Falls work was donated to the Smithsonian in recent years (Yochelson and Webers 2006).
|UMPC 6608, holotype of the conulariid Ctenoconularia obex, from the "Sprechs Ferry" (=lower Decorah) of Minneapolis.|
One other conulariid note:
It turned out that one of the other conulariids Sinclair named came from the St. Peter Sandstone of Minnesota: Climacoconus humilis, described in Sinclair (1942) and promptly forgotten by virtually the entire universe (it's based on Carnegie Museum 4753 from Faribault, by the way). Maybe it's just my myopia showing, but it doesn't seem right that it's made almost no impression in the literature, even to be refuted. We are, after all, dealing not only with the St. Peter Sandstone, famous for having practically no body fossils, but also an uncommon and distinctive type of fossil!
Dystactophycus revisitedBack in July 2016, I showed a photo of a strange rock with concentric rings, which provided an excuse to riff on Dystactophycus, a possible trace fossil of a swirling crinoid. At the time, I thought it was unlikely that the photographed rock was Dystactophycus, or indeed of organic origin at all. A few months ago, the collector confirmed my general suspicions: he told me that mutual acquaintances have identified it as a modern fracture pattern, consistent with his later observations of features produced by air hammers punching into the Platteville.
ReferencesAndrews, W. M., Jr. 2005. Geology and the Civil War in central Kentucky: Camp Nelson. Field Trip Guidebook, American Institute of Professional Geologists 42nd Annual Meeting.
Kolata, D. R., W. D. Huff, and S. M. Bergström. 1996. Ordovician K-bentonites of eastern North America. Geological Society of America, Boulder, Colorado. Special Paper 313.
Miller, A. M. 1905. The lead and zinc bearing rocks of central Kentucky, with notes on the mineral veins. Kentucky Geological Survey, Lexington, Kentucky. Bulletin 2.
Sinclair, G. W. 1942. The Chazy Conularia and their congeners. Annals of the Carnegie Museum 29(10):219–240.
Sinclair, G. W. 1948. The biology of the Conularida. PhD Thesis. McGill University, Montreal.
Wolcott, D. E. 1969. Geologic map of the Little Hickman Quadrangle, central Kentucky. U.S. Geological Survey, Washington, D.C. Geologic Quadrangle Map 792. Scale 1:24,000.
Yochelson, E. L., and G. F. Webers. 2006. A restudy of the Late Cambrian molluscan fauna of Berkey (1898) from Taylors Falls, Minnesota. Minnesota Geological Survey, St. Paul, Minnesota. Report of Investigations 64.