ANALYZING PROVENANCE OF JACOBSVILLE SANDSTONE OF THE EASTERN UPPER PENINSULA OF MICHIGAN USING URANIUM-BEARING MINERALS

The Jacobsville Sandstone (JSS) is a geologic unit deposited approximately 1.1 billion years ago in the basin created by the Mid-Continent Rift and is found extensively in the Upper Peninsula of Michigan around Lake Superior and further inland with an average thickness of ~1000m. Prior studies regarding the JSS’s provenance have looked primarily at the Western Upper Peninsula (WUP) and have identified the primary source rocks to the JSS to be igneous rocks originating from the Marquette Supergroup and Gogebic Iron Range. Since studies about JJS in the Eastern Upper Peninsula (EUP) are lacking, the scientific community is left assuming that the findings in the WUP are true for the EUP as well. The JSS has been dated several times in an attempt to pin down its specific origins but these ages are poorly constrained due to the wide range of dates identified using uranium-bearing zircons for radiometric dating. These trace minerals are also valuable for determining provenance as the zircon ages will typically coincide with the source rock’s age. Determining provenance and depositional environment is important as it helps us understand geological processes and geochemical environment that the JJS deposited in and helps us to address concerns related to uranium geochemistry in groundwater wells and the radioactive decay products of uranium. In this project the provenance of the JSS in the EUP was analyzed by collecting samples from known source regions in the WUP. These samples were analyzed microscopically and petrographically to determine if they were possibly primary contributors to the uranium content found in the JSS of the EUP. This project sought to address the relative lack of research on the JSS in the eastern regions of the upper peninsula compared to the much more well studied western examples by comparing the commonly accepted source of the JSS to samples of the rock collected in Chippewa County. The mineral and trace mineral compositions of the samples indicate that the JSS of the EUP was almost certainly contributed more significantly to by other sources to the east rather than the commonly understood source rocks for the JSS found in Gogebic County. Recognizing this fact can help us gain greater understanding of Jacobsville Sandstone.