Next Seminar: Monday, March 11, 2019 7:00 PM

Geology of the Minnesota Arrowhead

Mark Jirsa, M.Sc., Minnesota Geological Survey

LOCATION: University of Minnesota East Bank campus

Kenneth Keller Hall, 200 Union St. SE, Minneapolis MN 55455 Room 3-210. MAP

Summary:

This presentation describes rationale, methods, and preliminary results of geologic mapping underway in northeastern Minnesota.  The MGS is in year 4 of a 6-year effort to create Part A County Geologic Atlases for St. Louis and Lake counties.  The two-county area includes parts of the Boundary Waters Canoe Area Wilderness, Voyageurs National Park, Superior National Forest, several state forests, and major watersheds.  It also encloses parts of the Mesabi Iron Range, the “Cu-Ni District,” and the Duluth metropolitan area–the 4th largest in Minnesota.  Because these are two of the largest counties in the state, we’ve divided them for mapping purposes into 3 subareas for bedrock, and 4 for surficial mapping (see maps). Work in each subarea involves one or more seasons of field mapping by 4 to 6 geologists; rotary-sonic drilling, trenching, and acquisition of drill hole; compositional, petrographic, geochronologic, and geophysical data. Work in the Central Arrowhead subarea is complete, including all components of a typical geologic atlas Part A—database, bedrock and surficial geology, bedrock topography and depth to bedrock, Quaternary stratigraphy, and sand distribution models.  Components of the other subareas are in various stages of completion. To make the data available in a timely manner to individuals, agencies, and companies conducting studies in the region, preliminary products for all subareas are being published as they become available.  The on-going repository for these products is MGS Open-File Report OFR2016-04. Once preliminary work in all subareas is complete, the data will be recombined into county geologic atlases, targeted for completion in 2021. 

The accompanying maps of the arrowhead region show county boundaries (black lines), Voyageurs National Park (VNP) and Boundary Waters Canoe Area Wilderness (BWCAW) boundaries (white lines), and the location of mapping subareas (red lines).  The first map shows 3 bedrock subareas; the second map shows 4 surficial subareas.

Biography:

Mark is a geologic mapper with the Minnesota Geological Survey—a research and service branch of Winchell School of Earth Sciences at the University of Minnesota.  He obtained a BS degree from the University of Wisconsin-Eau Claire, and an MSc from the University of Minnesota-Duluth (1980).  His mapping and research utilizes the combination of outcrop, petrographic, geochronologic, geophysical, and drilling information to improve and convey the understanding of Minnesota’s ancient bedrock crust.  He is author/coauthor of more than 100 maps, publications, and abstracts. He is the current project manager and mapper for geologic atlases of St. Louis and Lake Counties, is an executive board member—Institute on Lake Superior Geology, and has spoken at many past GSM seminars.