ELEMENTAL AND MINERALOGICAL ANALYSIS OF THE ENGADINE GROUP IN THE UPPER PENINSULA, MI

Many Silurian-aged carbonate sequences are dominant along the northern edge of the Michigan Basin, the modern day Upper Peninsula, and the northernmost portion of the Niagara Escarpment. The group of interest in this study was the middle Silurian dolostones of the Engadine group. Previous field work within the Engadine group has shown the dominant petrology to be dolostones. Previous investigations have examined the major elements in samples of the Engadine Group, but little work focuses on trace elemental analysis. Preliminary fieldwork was completed during the summer 2015 field season and included measuring stratigraphic sections and collecting samples for analysis.

Samples were brought back to Sam Houston State University to determine the mineral assemblages and elemental compositions of the samples. Two methods were used; X-Ray Diffraction (XRD) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The XRD results indicate the dominant mineralogy is dolomite and a small, less than one percent, composition of calcite. Additionally, relatively high percentages of quartz (1 – 6%) were present. Preliminary ICP data has suggested a trend of silica and aluminum content within the dolostones varying stratigraphically between members of the Engadine Group, matching major elemental data from other studies. Previous descriptions of the Engadine Group found minor detrital quartz and garnet grains in certain member. Similar detrital grains were found by petrographic analysis. In addition, these samples contained a relatively high amount of silicified fossils (corals and stromatoporoids) within several of the units measured. Stratigraphic columns were correlated between sites using field description. These correlations will further be investigated to determine the geochemical and mineralogical variation between units of the Engadine Group within the Hiawatha National Forest. These correlations will help reinforce field observations, building a more complete stratigraphic framework for the northern Michigan basin.