Western Extent of Lake Superior Agate Distribution

I am having a hard time finding any good answers as to where the Western boundary of Lake Superior agate distribution resides. The glacial geology of the Midwest makes this a tough question and I can't find a whole lot of easily interpreted information about the relative direction of advancement for the different glacial periods. I guess the meat of my inquiry would be: is it possible that Lake Superior agates may have been deposited in Eastern South Dakota and far Western Minnesota (even if they are covered by hundreds of feet of more recent glacial overburden,) and, if so, what was the approximate timeframe of their deposition?

Any help would be greatly appreciated.

Thanks,

Ryan

I can tell you that I have found them in Woodbury and Ida counties in NW Iowa......Mike

They have been occasionally found in eastern Nebraska (Cass county) and northeastern Kansas.
[www.kgs.ku.edu]

Ryan,
The easy answer to your question is: as far as the glaciers advanced west and south; however, I know it's not that simple. There is no reason to believe that agates couldn't have been distributed to far west Minnesota and S. Dakota during the Wisconsinan or earlier glacial advances. As David pointed out, they have been found in Iowa and Kansas. I have heard of agates being found in Nebraska and even some reports of Lake Superior agates being found as far south as Arkansas and Louisiana, having been carried by the Mississippi River. I doubt that you will find a definitive answer to the western extent of agates anywhere. The best guess would be where is the furthest extent west the glaciers proceeded after leaving the Lake Superior region?

As far as the timing of the glaciers, remember that there were four separate major glacials in N. America; the Nebraskan, Kansan, Illinoian, and Wisconsinan. The first glacial in the Pleistocene (Nebraskan) began about 1.8 million years ago and the last glacial maximum (Wisconsinan) was about 16,000 years ago, with many advances and retreats in between. It is possible that Lake Superior agates could have been moved at any time during this period and deposited elsewhere in the midwest and great plains. For the different relative directions of glacial movements, you might be well advised to find a glacial geology textbook or some of the better physical geology textbooks used in first year college courses.

Hope this helps.....



Edited 2 time(s). Last edit at 07/15/2012 02:13PM by Paul Brandes.

Hi Ryan,

There's nothing finer than a good ol Laker! Spent many a time looking for them in WI, but the furthest one I ever found was in Hannibal MO area while walking the creeks for geodes.

I can tell you that the eastern boundary is approximately a line that runs from Platteville WI to about the Ashland WI area.

If you really want details about the extent, all you would have to do is study the glacial drift patterns. I think the WI glacial episode was one of the largest episodes that pushed material down to the KS and NE area. You'll have to do some interpolation being that the source was a smallish area and the glacier had sort of a broadcast pattern in a SW direction. I think the source was in northern MN or under Lake Superior. Then you'll have to figure out which way the rivers are running (usually a SE direction) which would show you the agate drift that occurred after glacial deposition. That's why most of WI is not productive, even though it was covered with all of the glacial episodes.

There are also some nice books out there about the agates, and Scott Wolter's book here is a great read. [lakesuperioragate.com]

Good Luck,

Dave