CULTURAL GEOLOGY OF THE LOWER MISSISSIPPIAN NORTHVIEW FORMATION "WORM ROCK", SOUTHWESTERN MISSOURI, USA

Burrows and other trace fossils are abundant in fine sandstones of the lower Mississippian (Kinderhookian Series) Northview Formation of southwestern Missouri. Blocks of this material especially are common in vernacular architectural applications in and around Springfield. Locally, this material is referred to as "worm rock" or "worm-eaten rock." A class project was undertaken to examine the ichnofauna of blocks used in construction of Phelps Grove Park amphitheater. Ichnospecies include Scalarituba missouriensis Weller 1899, Nereites sp., and Zoophycos sp.; previous investigators have shown that other fauna include bivalves and foraminifera. Over its depositional area, the Northview Formation ranges from approximately 1.5–25 m thick. In the area of thickest deposition, the Northview is composed of a cyclic succession of a lower light gray-green shale, and the upper part consists of interbedded very fine sandstone, siltstone, and shale. Two stratigraphic sections were measured and described north of Springfield at Noble Hill and Dunnegan to compare with the allochthonous blocks, and short cores were drilled for µCT scans to examine burrows in three dimensions. An attempt was made to estimate burrow density, but µCT scans indicate the rock was much more thoroughly bioturbated than what the surface texture would indicate.

We collected hundreds of images of top and side views of blocks used as facing stone in the amphitheater. The structure was built in 1936 by the Works Progress Administration of the New Deal. Ed Elkins, stonemason and foreman on the project, oversaw a crew of more than 40 men in building the amphitheater and several public vernacular construction projects around the city. Four columns of the amphitheater are composed of middle Mississippian (Osagean series) Burlington-Keokuk limestones; these were moved from the old Colonial Hotel. The Northview Formation is an important stratigraphic unit regionally because it separates the lower Ozark aquifer from the upper Springfield aquifer over the northern part of the Springfield plateau. While the burrowed sandstone is aesthetically pleasing material for facing stone, it remains undetermined if burrow porosity poses a risk for water infiltration in buildings or as conduits for groundwater in the subsurface.