NE Iowa Paleozoic

[ClearLake]

I read a lot of fossil hunting reports on here, but I don’t post many.  I think it’s primarily because it is usually many, many months after I have gone when I finally get everything cleaned up, ID’d and take photos, etc.  It just seems too after the fact to me at that point, haha.  But this time, due to a wonderful “tour guide” we had, I wanted to get something posted in a relatively timely fashion.  Because of that, I haven’t had time to do a lot of research I need to do on specific ID’s but luckily I’m somewhat familiar with most of what we found to make at least an educated guess.

 

I have seen numerous folks on here show some of their finds from the Ordovician and Devonian of Iowa and nearby states and it always looked intriguing to me as I have collected the Ordovician in the (relatively) nearby Cincinnati area and the Devonian in the Great Lakes area and Oklahoma.  I wanted to see how the Iowa stuff compares.  So my wife and I opted to take the long way home from Indiana to Texas and swing through Iowa (and on to South Dakota, but that was more for sight-seeing).  I had done some research on sites to check out and contacted Mike @minnbuckeye to see if he could help me high grade my list.  Being the absolute gentleman that he is, he did one better and offered to act as our tour guide for a day of collecting through the Ordovician!  What a guy!!  I can’t thank him enough for taking the time to do this.  We had a great day and hit a bunch of nice spots, most of which I had not found on my own and certainly didn’t know some of the very important details of the sites.  Many folks have said it in other trip reports and I can only add to the chorus of how valuable it is to go with someone that knows the area and how nice it is of TFF members such as @minnbuckeye to offer their time and energy to do it.

 

Based on Mike’s recommendation, we spent our first day doing some collecting in the Devonian rocks of the Coralville, Iowa area.  The first spot we could not access due to some current road construction but we made our way to the next one and spent several hours along the Iowa River/Coralville Lake collecting from the Coralville Formation of the Cedar Valley Group.  You quickly learn how Coralville got its name as the rocks are a coral/bryozoan limestone.  There are brachiopods and other fauna, but corals make up the bulk of the fossils at this site.  And there were some very nice ones as you can see in the pictures below.  Beautiful Hexagonaria, huge horn corals and others.  We also went to the Devonian Fossil Gorge and a nearby state park, both of which have nice exposures of Devonian rocks with fossils, but no collecting.

 

Here is a shot of the area, fossils litter the ground.

 

This represents our total haul from this site

 

The horn coral in here were abundant and quite large.

 

Corals

 

What I believe are Hexagoanaria corals.  I think with a little cleaning, these will look really nice and I like the juxtaposition with the horn coral.

 

Brachiopods and bryozoans

 

 

A nice piece that was a little too big to take.

[connorp]

[ClearLake]

The other collecting spot we hit that day was the well-known Graf nautiloid location (Ordovician Maquoketa Fm.).  Unfortunately it was late in the day by the time we got there (we had other sights to see such as the World’s Largest Strawberry and the Field of Dreams movie location!) so it was getting dark and I had limited time, but I did manage to gather a few pieces, none of which are all that spectacular, but with a little prep work, should look fine.

Isorthoceras sociale

 

What the site look like.  The famous nautiloid "death assemblage" is in a relatively thin bed near where I am standing.

 

Bright and early the next day we were to meet Mike (@minnbuckeye) at a roadcut near the town of Elgin and started our quest with the Upper Ordovician Maquoketa Formation.  At this spot we were in search of Isotelus trilobites and with Mike’s knowledge (and hard work) we found plenty.  It is an interesting zone that I must read more about.  Other than some graptolites, there are virtually no other fossils in the beds other than trilobites.  They are plentiful but mostly molts (we were not fortunate enough to find a whole one) and while there are lots of cephalons and pygidia, I saw very few body segments.  It was very interesting.  I’m not saying this is representative of the whole Maquoketa, it was just this one zone at this location.

 

Our haul from this site, nearly every piece has multiple trilobite partials.

 

An Isotelus pygidium and cephalon (free cheek missing)

 

You can see here, they came in all sizes!

 

Hypostomes are not uncommon.

 

I thought this was a neat association of two trilobites.

 

Heads, tails, cheeks, just missing a body.

 

If you look to the left, you will see a face and to the right a tail of what I assume is a Flexicalymene (at least that's what I would call it if I were in the Cincinattian).  More research needed.

 

[ClearLake]

Next we headed north towards Decorah, Iowa and hit a couple of sites, the first one was in a great exposure of the somewhat older (Middle Ordovician) Decorah Formation where we found brachiopods, gastropods and abundant Prasopora bryozoans (as well as other bryozoans). 

 

The bryozoa Prasapora  (some show the underside)

 

The brachiopods (at least five different types) and some bryozoans on the hash plate

 

A couple of planispiral gastropods and some ramose bryozoa.

 

The other site near Decorah was a roadcut which exposed the slightly younger Dubuque Formation of the Ordovician Galena Group.  I’m new to Iowa stratigraphy, so hopefully I have interpreted and identified these correctly.  This exposure produced very nice and large gastropods as well as less numerous brachiopods and trilobite pieces.

The gastropod Hormotoma which get quite large and seem to be the most common fossil here.

 

Another very nice gastropod

 

A nice little trilobite pygidium, maybe more is under there??  We'll do some prepping and see.

 

 

I believe this is the face of another trilobite.  Mike may have told me the name, but I have forgotten.  Research to do!

 

 

Two cephalopods.  I'm not familiar with this type with the slight curve to it, I'll look it up.

 

Another piece I thought was very nice with the flattish gastropod and other stuff.

[ClearLake]

Lastly, we hit a roadcut and quarry spoil pile up in north Winneshiek County that I believe are also Dubuque Formation.  Here we found a very nice large gastropod, numerous brachiopods and a couple of very large cephalopods.  I’ve found plenty of straight nautiloids in the Ordovician of the Cincinnatian strata, but nothing ever as large as these monsters!

 

My wife found this gastropod (Hormotoma), it was the biggest one of the day!  Cant wait to clean it up a bit more.

 

There were a fair number of brachiopods at this site, most were some sort of Strophomena, but you can also see there was a Cincinnetina and some others.

 

These two nautiloid were quite large, they would have been quite the sight if complete.

 

The next day, I was hoping to make a quick stop at the Prairie Fossil Park near Rockford, but we just ran out of time, so I will save that for the next trip when I get back to visit some other Ordovician spots and hit the Pennsylvanian strata of Iowa.  Thanks again to @minnbuckeye for being such a great host!

 

That wraps up this trip, hope you enjoyed, we had a great time. 

[connorp]

42 minutes ago, ClearLake said:

I believe this is the face of another trilobite.  Mike may have told me the name, but I have forgotten.  Research to do!

Thaleops I believe. Really great finds!

[ClearLake]

8 minutes ago, connorp said:

Thaleops I believe. Really great finds!

Oh, great info, I'll look that one up.  Thanks

 

I found a great paper from 2004 that discusses all the species of Thaleops, Ill go through it more when I have a moment.

Edited October 1, 2020 by ClearLake

[Fossildude19]

Excellent report and finds! 

Thanks for the field trip!  

[connorp]

2 hours ago, ClearLake said:

If you look at some of these in the right light you can probably make out nacre ('mother-of-pearl'). It can be quite pretty. This is one of the earliest occurrences of nacre in the fossil record I believe.

[Nimravis]

Great trip report and finds.

[ClearLake]

12 hours ago, Fossildude19 said:

Excellent report and finds! 

Thanks for the field trip!  

 

10 hours ago, Nimravis said:

Great trip report and finds.

Thanks!!

[sharkdoctor]

Great report and photos!

[LabRatKing]

Excellent report. I’m not too far away, may head up there and try my luck soon. Likewise if your headed this way, I’ll be more than happy to show you around this side.

[Ludwigia]

Great report and great finds too! Thanks for sharing.

[ClearLake]

8 hours ago, sharkdoctor said:

Great report and photos!

Thanks!

1 hour ago, LabRatKing said:

Excellent report. I’m not too far away, may head up there and try my luck soon. Likewise if your headed this way, I’ll be more than happy to show you around this side.

Thanks, Nebraska is a state I haven't tried yet.  On our way home we came through the western side but did not do any fossil hunting.

1 hour ago, Ludwigia said:

Great report and great finds too! Thanks for sharing.

Thanks!  On our way home through Kansas, we made a 15 minute stop at one Cretaceous roadcut and I did pick up a decent little ammonite, but nothing like those beauties you are finding and preparing!

[LabRatKing]

Took me years to get those. I’ll post some Iowa/Nebraska ammonites tomorrow. Only one of them is worthy!

[LabRatKing]

@ClearLake Nebraska is fairly lousy for collecting. Most everything is thankfully protected, but there are more common sites that are open house and tons of fun!