CEMENTATION HISTORY WITHIN THE SILURIAN CARBONATES OF THE HIAWATHA NATIONAL FOREST, MICHIGAN

Refinement of the Silurian stratigraphy to outcrop scale field observations has been extremely challenging within the Hiawatha National Forest (HNF) of the Upper Peninsula of Michigan. Collected samples were analyzed petrographically, geochemically (bulk analyses), and geophysically. These data were used to delineate the Cordell Formation of the Manistique Group, and the Rockview, Rapson Creek, and Bush Bay Formations of the Engadine group. More information is required to further differentiate these formations into their respective members. The dolomite cements filling in pore space is a diagnostic property which was utilized in this research in differentiating these formations.

For this study, dolomite cements were analyzed optically using cathodoluminescence microscopy (CL) from samples collected from the HNF. Three types of cements have been observed within these formations. Under CL these cements have repetitive zoning of different red and yellow-green wavelengths and intensities ranging from dull to bright. Electron Microprobe analysis is planned to identify the trace element composition of these cements. Bulk trace elemental data suggests that the Upper Engadine units differ in the amount of CL activators (e.g. Mn²⁺) and quenchers (e.g. Fe²⁺) detected, from the Lower Engadine and Manistique units. CL observations generally agree with these observations.