Seminar Details

Seminar Lab Date: February 2, 2026

Seminar Lab Subject: *The Role of Snowball Earth Events in Bedrock Weathering (V)

Seminar Lab Presenter: Mark Jirsa, M.Sc., Minnesota Geological Survey (retired)

Seminar Lab Location:

*** NOTE: THIS LECTURE HAS BEEN RESCHEDULED FROM JAN 26 AND CHANGED FROM IN-PERSON TO ONLINE ***

Virtual lecture 7:00 PM CT.

Participation instructions have been e-mailed to GSM members. If you are not a member of GSM and wish to attend this free seminar online, register as follows by 8 AM CT Monday, Feb 2: Go to the Contact menu above and select “Ask GSM”. In the form that appears, enter your name and e-mail address. Enter “Feb 2 lecture” in the subject line. In the message body, please enter the city and state or country from which you will view the seminar. You will receive instructions by e-mail prior to the lecture. Check your spam folder if the instructions do not appear in your in-box at least one hour prior to the lecture.

Seminar Lab Detail:

Summary: The landscapes we enjoy today are the product of two opposing forces:

1. Continental plate collisions that raise land surfaces (to mountains in some cases)

2. Chemical weathering and erosion that removes literally miles of uplifted bedrock

Thus, we stand on bedrock outcrops that were once deeply buried, metamorphosed, deformed, weathered, and eroded.

Biography: I grew up in the “wilds” of northern Wisconsin: an area of lakes, rivers, and woods. This uniquely prepared me for a 45-year long career of geologic mapping, primarily of Precambrian bedrock in the wilds of Minnesota and parts of Canada. I attended Graduate School at UMD (1976-1979).  In 1976 I worked with John Green mapping along Lake Superior shorelines and inland for the Coastal Zone Management Program to address impacts of shoreline erosion due to then rising water levels. Having fallen in love with the North Shore, I created a thesis using interflow sedimentary rocks to develop a tectonic model of western Lake Superior. After graduating UMD, I worked briefly for Exxon Minerals in NW Mn and Wisconsin. Thanks to G. B. Morey and Dave Southwick, I was hired by the Minnesota Geologic Survey in 1979. I authored or coauthored many of the bedrock geologic maps and publications produced by the MGS. I retired during covid in 2021. I continue to work with the Institute on Lake Superior Geology, and give lectures to small groups.