Age(s) of rocks in Lake Michigan?

[Fletcher]

I have a couple of crinoid pieces I've picked up from the shore of Lake Michigan in NE Illinois and I'm interested in finding out what time period(s) they're likely from - I've had no luck finding out much about rock sourced from the lake itself, and it seems like everyone has something different to say about what's underlying the shore here, so I thought I would put this out on the forum and see if anyone knows.

[Rob Russell]

Hello Fletcher, and welcome to the forum.

In my opinion anything found along the shores of the lake could be anything from Ordovician to Devonian aged rocks. The glaciers pushed all kinds of material around.

However, I believe the underlying sediment in northeast Illinois is Silurian in age.

[Fletcher]

In my opinion anything found along the shores of the lake could be anything from Ordovician to Devonian aged rocks. The glaciers pushed all kinds of material around.

However, I believe the underlying sediment in northeast Illinois is Silurian in age.

Thanks! I figured there would likely be more than one possible age, but I wasn't sure exactly what range I should be considering.

[Raggedy Man]

Thanks! I figured there would likely be more than one possible age, but I wasn't sure exactly what range I should be considering.

Hello and welcome to the forum. There is a pfd, "Geology of Michigan and the Great Lakes" I was going to post, but the file size is too large. I'm sure if you search that title you'll have no problem finding it. The information contained in it should help answer any questions you have. I hope this helps.

Best regards,

Paul