North Dakota Pierre Shale Trip

[Thomas.Dodson]

I have an ambivalent relationship with the Pierre Shale. I try and try to find good sites that produce fossils but the end result is usually a fossil-less site. For a long time I quit trying exposures of Pierre Shale even though it's the closest fossil bearing exposure to where I live. About a year ago I decided to try the Pierre Shale again because it was close and I was too tired to go elsewhere, like the Fox Hills Formation in Central ND. Mostly I found worn Inoceramus fragments but to my surprise I found a nicely preserved caudal vertebrae from a mosasaur among float material. Following that I began to try the Pierre a little more and today, after finally getting landowner permission, I spent the day at a site with extensive exposures.

 

Most of the Pierre Shale exposures in East-central North Dakota are of the DeGrey Member. The most obvious feature of this member is a large amount of iron manganese carbonate concretions. The few fossils I find in the Pierre here are usually in these worn concretions.

 

The first fossils I found didn't come from the Pierre at all but came from glacial erratic limestone. I occasionally find older material like this among the tons of glacial material that blankets most of this part of the state but rarely do I find such well preserved/unworn specimens. Some nice brachiopods to start. I was happy to collect some of these among a split limestone boulder despite the lack of specific age/locality data.

 

Moving towards the actual Pierre Shale deposits there is distinct worn shale with bands of worn concretions.

The large tract of land I had permission to collect on was covered in these exposures.

 

 

 

 

[Thomas.Dodson]

The first find among the worn concretions was, naturally, an Inoceramus fragment. You may note the non-sedimentary glacial till mixed in these exposures. You couldn't carry all the fragmentary Inoceramus and other bivalves even if you wanted them all.

There are some more complete Inoceramus to be found as well.

Lots of nooks and crannies to explore.

This frozen seep is the only indicator that it is winter. In my entire life I've never seen a lack of snow this late. Normally there would be lasting snow on the ground by December 1st and by now there would tons of it everywhere.

A little snow in the shaded valleys. The concretions stood out among the snow too.

 

[Thomas.Dodson]

If you followed the manganese you'd find fossils. Occasionally some pockets of less worn shale and concretions showed up.

 

A view looking down the river valley. I still need to explore the exposures on the South (direction of picture) end.

Some fragments I kept with a few complete ones at the bottom. There are a couple of different species of Inoceramus reported here but I haven't gone over them yet.

Some other smaller bivalves were found among the concretions but most need prep work to start.

 

[Thomas.Dodson]

Another nice brach. Need to clean these up and prep them, there are lots in the limestone.

A bone is the most unique piece. I'm looking into it but it is probably mosasaur just based on the scarcity of the other options. I'm still learning with vertebrate stuff like this.

The texture is quite interesting.

[PaleoNoel]

Nice report! Thanks for sharing!

[Monica]

It looks like you have a lot of land to cover - hopefully there are many more fossils out there, just waiting for you to find them! 

 

That's a cool-looking chunk of bone - congrats!

 

Re: the brachiopods - perhaps @Tidgy's Dad can help with identifications (at the very least, I'm sure he'd love to see these goodies )

[Tidgy's Dad]

1 hour ago, Monica said:

It looks like you have a lot of land to cover - hopefully there are many more fossils out there, just waiting for you to find them! 

 

That's a cool-looking chunk of bone - congrats!

 

Re: the brachiopods - perhaps @Tidgy's Dad can help with identifications (at the very least, I'm sure he'd love to see these goodies )

Thanks, Monica, but I'd already had a look at these lovelies. 

As for the brachs, it's pretty much impossible without knowing the formation which is dead difficult with erratics.

First one's a productid and the next an orthid, or possibly a strophomenid, with the last, rather gorgeous one, being another productid, but I'd not risk any guesses other than that.  

[Thomas.Dodson]

3 hours ago, Tidgy's Dad said:

Thanks, Monica, but I'd already had a look at these lovelies. 

As for the brachs, it's pretty much impossible without knowing the formation which is dead difficult with erratics.

First one's a productid and the next an orthid, or possibly a strophomenid, with the last, rather gorgeous one, being another productid, but I'd not risk any guesses other than that.  

That's the problem with these poor "lost" glacial erratic fossils. I have some other nice brachiopods I collected here 15 years or so ago that I had long resigned to the unidentified. I had a look at them recently and some are Atrypa but I'm lucky to even get those to Genus. I might have to start a display section of these lost fossils.

[Thomas.Dodson]

I needed to explore the south Section and went back for round 2.

 

A Pierre Shale mound in the distance. I've heard these incorrectly called Indian Mounds here before.

Still traces of concretions but these outcrops were more worn and had less fossils.

A very worn Inoceramus with peculiar boring/damage that makes it look like something else.

This Steinkern had both valves but but was only one of two pieces I collected in the South Section. It was rather barren.

A little color among the drab landscape.

 

 

 

 

[Thomas.Dodson]

I returned to the limestone boulder pieces that contained the brachiopods from yesterday and poked around a little more. I also had the energy this time to remove a matrix piece frozen to the ground (the second pic in the first post).

 

This worn gastropod was among some other brachiopods I collected.

I went back to the area where I found the bone to comb over again. I crawled across the ground this time hoping to find small stuff I missed.

This concretion contained multiple valves. The largest valve should be identifiable.

An imprint of some different bivalve. It started snowing at this point hence the snow in the imprint.

A partial scaphopod, presumably Dentalium sp.

 

Aside from the brachiopods and the bone the preservation isn't great among these but the site numbers among the best Pierre Shale sites I've visited. Even poorly preserved fossils beats no fossil hunting and I can't ignore the good weather. I hear the Pierre Shale exposures in the Northeast portion of the state are better and I'll get around to it sometime.

 

Even poorly preserved fossils beats no fossil hunting and I can't ignore the good weather.

 

 

 

[GPayton]

Since the formation you're working in is marine Cretaceous, it's possible that the first bone fragment you posted a picture of is turtle. At least down here in Texas at the North Sulphur River, the turtle bones are easily identifiable by that same kind of glossy striated texture. I could be way off on this one though. 

[Thomas.Dodson]

4 hours ago, GPayton said:

Since the formation you're working in is marine Cretaceous, it's possible that the first bone fragment you posted a picture of is turtle. At least down here in Texas at the North Sulphur River, the turtle bones are easily identifiable by that same kind of glossy striated texture. I could be way off on this one though. 

It's certainly a possibility. Turtles, plesiosaurs, and mosasaurs are basically the only possibility for North Dakota Pierre Shale fossils like this. I assumed mosasaur by probability because they are by far the most common with only sparse remains of the others found throughout the Pierre here. Turtle would be very interesting since I don't think anything has really been reported aside from the one Archelon from the Cooperstown site.

[FossilDAWG]

If you want to go ahead and post (here, or in their own thread) your better specimens from glacial erratics I might be able to take a stab at them.  I have a bit of experience collecting from the Ordovician, Silurian, and Devonian in Manitoba, which would be the likely source area for your erratics.

 

Also, is it possible that the unusual texture on the bone might have been produced by passing through someone's digestive tract?

 

Don

[LabRatKing]

8 minutes ago, FossilDAWG said:

Also, is it possible that the unusual texture on the bone might have been produced by passing through someone's digestive tract?

 

I would agree to that.

 

I am particularly interested in the golden-orange dendritic formations on the bone sample.

 

It still blows my mind how different the specimens and geology of these are from the same formation/members closer to me are.

[Thomas.Dodson]

43 minutes ago, FossilDAWG said:

If you want to go ahead and post (here, or in their own thread) your better specimens from glacial erratics I might be able to take a stab at them.  I have a bit of experience collecting from the Ordovician, Silurian, and Devonian in Manitoba, which would be the likely source area for your erratics.

 

Also, is it possible that the unusual texture on the bone might have been produced by passing through someone's digestive tract?

 

Don

I'll probably do that once I clean and prep some of the more recent ones, thanks.

 

It's an interesting bone for sure. There's some polished texture on the ends that could also be related to digestion.

 

35 minutes ago, LabRatKing said:

I am particularly interested in the golden-orange dendritic formations on the bone sample.

My initial thought was traces from scrapers like most of the Inoceramus have but I don't know why some are so superficial then.

 

 

[Thomas.Dodson]

Another closeup and some scraped Inoceramus.

 

[LabRatKing]

54 minutes ago, Thomas.Dodson said:

Another closeup and some scraped Inoceramus.

 

Beautiful! Looks like the dendrites are radiating from bored ichnos like we see on extant species. I hypothesize the ones on the bone are leftovers from encrustations prior too full burial that the eroded away?

 I’m totally guessing but  that indicates pretty anoxic conditions during deposition and burial?

 

Our inos down here are highly compressed in morality plates and heavy on the Fe2 and 3 content so even the matrix is brick colored.

[mikeymig]

The bone says fish to me. A big fish.

[FossilDAWG]

I have the impression that those Inoceramus are internal molds.  I that case the "scapings" would have been something like tubes on the inside of the shell, perhaps something like tube worms.  Am I misunderstanding things?

 

I never collected much in the Pierre Shale in Manitoba, mostly because I didn't own a vehicle and had to borrow the family car so transportation was an issue, but also because the Manitoba Pierre Shale is notoriously barren of fossils.  There is one site, near Millwood I think, that has produced some nice ammonites and a crab but otherwise it's a whole lot of empty shale.

 

Don

[Thomas.Dodson]

53 minutes ago, FossilDAWG said:

I have the impression that those Inoceramus are internal molds.  I that case the "scapings" would have been something like tubes on the inside of the shell, perhaps something like tube worms.  Am I misunderstanding things?

 

I never collected much in the Pierre Shale in Manitoba, mostly because I didn't own a vehicle and had to borrow the family car so transportation was an issue, but also because the Manitoba Pierre Shale is notoriously barren of fossils.  There is one site, near Millwood I think, that has produced some nice ammonites and a crab but otherwise it's a whole lot of empty shale.

 

Don

I was under that impression at first as well but I believe most are not molds now. I can't speak for every specimen but many still show traces of the outermost shell layers and most show cross sections throughout the developed calcite prism layers of other parts of the shell so I think it's just the odd preservation.

Note that a second layer of  even with the outermost layer

 

Multiple layers of shell on this one.

 

For those curious about Inoceramus shell layers they can get quite thick and stratified. This figure comes from "The giant inoceramid Platyceramus platinus as a high-resolution paleoclimate archive for the Late Cretaceous of the Western Interior Seaway" (Wallitzer) and illustrates the multiple layers well.

 

Most of the Pierre here is a barren shale wasteland as well but it seems the Gregory and Pembina Members are much more fossiliferous. Some parts of the DeGrey yield interesting finds. This is most obvious in the Cooperstown site where vertebrate remains of multiple species, including an Archelon and several mosasaurs, were found. Even the people who don't much about fossils here know about Cooperstown. https://www.dmr.nd.gov/ndfossil/Research/Articles/Cooperstown/Cooperstown_Pierre_Shale.html

[Thomas.Dodson]

This is the mosasaur vertebrae that convinced me to try Pierre Shale sites again. I figured I'd post it here as well since it fits in. This one was found at a small and worn DeGrey exposure about 10 miles north of the site in this thread.

[Thomas.Dodson]

One of the only sizable (12 cm) concretions I brought back had some decent (for this site) Pteria sp. in it.

This might be an amorphous Pteria. The variation in Pteria linguaeformis from the Fox Hills Formation where I collect is incredible.

 

 

[Thomas.Dodson]

I prepped most of the erratic brachiopod limestone and there are some decent brachiopods. @Tidgy's Dad @FossilDAWG Want to take a stab at the better ones pictured?

#1

#2

#3

Brach #4

 

 

[Thomas.Dodson]

I'm sure some aren't diagnostic, all the more-so being erratics but I decided to post the whole variety.

Brach #5

Brach#6

Brach#7

 

 

[Thomas.Dodson]

Brach#8 is my favorite.

Some gastropods also came out of the limestone.