PETROGRAPHIC CORRELATION BETWEEN OUTCROPPINGS OF THE SILURIAN CARBONATES IN THE HIAWATHA NATIONAL FOREST OF THE UPPER PENINSULA OF MICHIGAN

Petrographic techniques were used to correlate sections of Silurian carbonates, specifically the Engadine group, in the Hiawatha National Forest (HNF) of the Upper Peninsula of Michigan in order to determine the diagenetic history of these carbonates. Overall, there currently exists a lack of knowledge in the nature and characteristics of the outcroppings of specific members within the Engadine Group. Previous investigations conducted on the Engadine group focused on quarries and core outside of the HNF with little work on the petrographic nature of these carbonates. Sections of the Silurian carbonates were visited during the summer 2015 field season, and samples were collected using a chainsaw drill coring device or as bulk hand samples. A total of eight sites were examined, with detail given to outcroppings and quarries along the Niagara Escarpment within the HNF. The samples collected (~50 total) were made into petrographic thin sections at Sam Houston State University. Standard polarized light petrographic analysis identified several lithofacies that appear to correlate across several outcrops. Fossils, especially Rugose coral, stromatoporoids, and brachiopods were observed in thin sections, in some instances not being identifiable at the outcrop scale due to weathering. All of the carbonates are dolostones varying between dolomudstones, doloboundstones, and dolowackestones, with significant sections showing silicification of fossils and quartz cementation in vugs. Cathodoluminescence assisted in viewing relic structures not visible under plain or cross-polarized light and also helped determine the relative order of diagenetic processes of dolomitization and silicification. Overall, petrology assisted in correlating sections of the Siluran carbonates, while providing additional insight into the petrographic nature of specific members of the Engadine Group within the HNF.