Geoheritage and geoconservation in the American Midwest: Silurian reefs of the Milwaukee–Chicago region

Abstract

Abstract Paleozoic reefs were first identified by James Hall (1862) in the Silurian rocks of the American Midwest. Scientifically, they were crucial in defining ancient reefs, documenting the early history of this marine ecosystem, and interpreting regional stratigraphy, palaeogeography and palaeoecology. Schoonmaker Reef in Wauwatosa, Wisconsin, is historically the most significant of these structures, as the first to be correctly identified as a ‘coral’ reef by exhibiting the transition between a reef mound and the surrounding seafloor. After nearly two hundred years of quarrying, Thornton Reef in Thornton, Illinois, is next in importance as it displays an unequalled three-dimensional exposure, demonstrating the impact of Silurian climate change on reef development. Silurian reefs were discovered and studied only through stone industry quarrying. Extensive nineteenth-century fossil collecting by local naturalists was also a key component in reef studies. These reefs are also an important part of the region's geoheritage, comprising elements of its economy, history, education and scenic landscape. Recognizing their scientific and historical importance, some reefs were part of geoconservation projects and are protected sites. However, other reefs and irreplaceable reef fossil collections need further initiatives to preserve the scientific value and historical legacy of these relatively small geological features.