SURVEY OF TYPES AND DISTRIBUTION OF STROMATOLITES ON A SILURIAN-AGED SEAFLOOR AT HIGH CLIFF STATE PARK, SHERWOOD, WISCONSIN

High Cliff State Park located near Sherwood, Wisconsin was the site of a local quarrying and quicklime company that lasted from the mid-nineteenth to the mid-twentieth century. It became a state park in 1957 in part to preserve the Niagara Escarpment, a geomorphological feature extending from southeastern Wisconsin into southern Ontario, Canada and finally ending near Niagara Falls in New York. The uppermost unit present is the Silurian-aged Mayville dolomite, which is highly bioturbated, but still preserves several identifiable fossils, including stromatolites, corals, and Thalassinoides. The purpose of this research was to survey the distribution of stromatolites and associated organisms to determine preferential living conditions. The dolomite at this location is thinly-bedded and past quarrying activities at this site separated the dolomite along the bedding planes. Therefore, the surface of some exposed layers corresponds to an intact seafloor from a specific moment in time.

A Ranger Finder was used to survey the site to accurately determine the location of each fossil. The data was plotted on a site map along with the locations of landforms present on the ancient seafloor. By mapping the locations of the fossils compared to the gently undulating seafloor, it was possible to determine their preference for sunlight. Total relief of the seafloor was approximately 1.5 m.

Outside of bioturbation, the survey resulted in the mapping of four categories of fossils (based on type and appearance): rings, mounds, hills, and honeycombs. The ring stromatolites have visible, flat-lying growth rings whereas the mounds are raised up from the seafloor. The hill stromatolites are also raised but contain no visible rings. The fourth category, the honeycombs, are not stromatolites but the coral Favosites. The Favosites observed here are lower in the center and grow in circular colonies. Many stromatolites as well as the Favosites at the site are located on higher ground, often clustered together. Stromatolite clustering on higher ground indicates a need to be closer to the sunlight for photosynthesis. Initial surveys of the floor of a nearby quarry show less bioturbation and no other identifiable fossils, but further surveys need to be conducted for an accurate study of how fossil diversity changed at the site over time.