THE PALEONTOLOGY OF THE ROCK ELM DISTURBANCE: PIERCE COUNTY WISCONSIN

The Rock Elm Disturbance is a four mile diameter semicircular region, of deformed Cambrian and early Ordovician sediments. The disturbance is a meteorite impact site (Cordua et al., 1999), as shown by intensely fractured quartz grains, a rim faulted at high angles and a central basinfill grading into a gentle to steep central uplift. Prior to this study, the age of the impact was unknown. The basin fill consists of two members, the lowermost being the Rock Elm Shale. Fossils in the Rock Elm Shale include brachiopods, molluscs, trilobites, crustacea, conodonts, and annelids (in the form of Scolecodonts). Fossils identified to the genera level for both conodonts and scolecodonts, aided in narrowing the age of the basin fill to the middle Ordovician. Genera identified were Lumbriconereites, Arabellites, Staurocephalites, Protarabellites, Leodicites?, and Oenonites for scolecodonts; and Polycaudus?, Curtognathus?, and Chirognathus? for conodonts.