Wisconsin Cretaceous

[John K]

30-some years ago, a friend and I spent a week or so exploring a gravel pit on his grandfathers land. The pit was a typical one for the area (so we thought at the time...): glacial gravels and sand overlying Ordovician limestones and sandstone. We were fortunate, though, in that this site had some (what we thought until recently...) Decorah shale mixed in with it. We had great fun finding crinoid stems, bryazoan pieces and brachiopods (no gem-quality ones, unfortunately... )

We also found some dark, iron stained pieces of hard sandstone, and one of them contained one of these:


(some of you have seen this before - thanks for the ID help!)

Since this part of Wisconsin has been heavily glaciated in the past (I'm on the northern tip of the driftless area of the state) I've always figured that this tooth was transported here from somewhere else. And after several really cool finds that have come to light in recent years, area scientists are wondering, too, and are starting to re-think what was previously "known" about the geology of this area:

"Rare sample(s) from dinosaur age found in Wisconsin"


UW-River Falls


Crocodile photo - Mark Hoffman

(it just so happens that Wendell Borgerson, pictured above with the croc tooth, is a good friend of mine, yet I never knew about the tooth! I'm going to have to ask to see it the next time I see him... OK - the photo is'nt showing up - it's named funny. Take a look at the article!)

Mike Middleton, the paleontologist mentioned in the above article, is a friend of mine, and after years of talking up the tooth I found as a kid, I finally talked him into going out to the old gravel pit last week. I made some phone calls, got permission to do whatever we wanted to do, and headed out. Mike brought with him two other prof's from the U, sed/strat soil folks, who were very interested in what I had been describing.

The pit had over grown a bit (!!!) since I had last been there:


there's actually a bear den behind Heidi, on the other end of the pit...


Prof. Kerry Keen digging a fresh exposure of the Cretaceous sandstones near the top of the pit. We found lots of sandstone wedges, but no teeth...



my daughter picking through the sorted gravels at the bottom of the slope.
While the academics ooohed and awwwed over the samples they found, my daughter and I picked a bunch of Ordivician fossils, weathered out of limestone "lenses" mixed in with the other gravels in the site. Nothing spectacular, but fun never the less:



This caught my eye. I though that it might be a trilobite piece or even a conularid, but is actually the inside of a bryazoan stem:



So, we left without finding any shark teeth, and the three scientists left with more questions than answers, but it was cool coming back to the site after so many years, especially after learning so much in the mean time. And, now I've got permission, and more importantly, IMHO, actual purpose to go back and do some serious digging. I'd like to get in there and take a closer look at some of those dark brown sandstone layers again...

Edited August 11, 2014 by John K

[Shamalama]

Cool trip report and congrats for helping SCIENCE! :cool:

[Auspex]

A very engaging story; "Wisconsin Cretaceous" is not a phrase I've given much thought to...

Also, I still wonder about the shark's tooth; no one is suggesting that the seaway reached that far, are they? If reworked by glaciers, where was it picked up?

[John K]

A very engaging story; "Wisconsin Cretaceous" is not a phrase I've given much thought to...

You and me both!

Also, I still wonder about the shark's tooth; no one is suggesting that the seaway reached that far, are they? If reworked by glaciers, where was it picked up?

no, I think everyone agrees that it was picked up someplace: trying to figure out where from is the challenge. Plus, it's mixed in with stuff of the same age that hasn't been transported. I'd like to get in to the site and find a couple more shark teeth, and then compare them to some known samples from further west (Minnesota/Dakotas)

[Auspex]

I wonder whether water transport could be considered; for example, when the impounded Missouri River let go, it really changed the landscape!

[Logan connaire]

Wisconsin, Eastern Iowa, and Minnesota Have a non-marine Cretaceous unit known as the Windrow formation which ranges from conglomerates to sandstones. Fossils of things such as leaves and shark teeth are not unheard of but the unit is usually not very thick and is rarely exposed but glacial till in some areas is derived from this unit. Geologic maps almost never have this unit though it does exist. 

https://conservancy.umn.edu/bitstream/handle/11299/60189/mgs-225.pdf?sequence=3 This talks about it here and there. 

[FossilDAWG]

Welcome to the Forum.

 

Don