Thursday, January 10, 2013

Minnesota Geology Pictures - Sudbury Impact Breccia

At the beginning of 2012, I started what I thought would be a weekly series called Minnesota Monday Geology, with posts regarding different geological topics around the state.  For nine months the series went by well, until the beginning of the school year where my time was taken up with work associated with school, like planning lessons, grading jail, and taking care of my three children at home.  Although I have numerous posts to finish the series somewhere in my mind, as well as several including geology from neighboring states like South Dakota and Wisconsin (including a recent trip to Van Hise rock) and several with gigapans that I've begun taking, I'm starting another series today.




Nearly 1,850 million years ago, the region that is now Sudbury, Ontario was struck by an asteroid at least six miles in diameter.  A record of this catastrophic moment in time is preserved in the rock record along the Gunflint Trail, near the Canadian border in Minnesota.  The impact breccia at this location has been interpreted as a submarine debris flow 450 miles from the impact site.  At the time of the impact, this area of Minnesota was located near the shoreline of an ancient sea.  Found directly beneath the breccia layer is the 1,878 million year old Gunflint Iron Formation, directly above the breccia layer is the 1,850 million year old mudstones and shales of the iron-free Rove Formation.  The breccia layer is almost 7 meters thick, with the lower levels containing angular pieces of Iron Formation several meters across.  The iron formation found in the upper levels of breccia are much smaller.

A more complete post on the Sudbury Impact Breccia can by found here.




Both of my sons went on a hike to the breccia outcrops last June (2012).  It can be a challenging hike through some dense underbrush for 6 year old legs.



My 4 year old was more interested in the leaf that he 'captured' than what was around him, oh well.