Cannonball Formation Excursions 7/14/2021 (For Gastropod lovers)

[Thomas.Dodson]

Continuing from my recent trips to outcrops of the Cannonball Formation I made my way South towards the area of the Cannonball Formation type locality. I stopped at a couple roadcuts in Morton County on the way down but spent most of the day on the Cannonball River in Grant County.

 

A burrowing owl off a country road.

I believe this is Escobaria missouriensis among Cannonball sandstone. It isn't one of the species of cacti I frequently see.

The only fossil that came from here is Nototeredo globosa bored wood(?).

Pictures don't properly show how steep the outcrop at this site is. The only material found here was shell fragments that are fragmentary even by Cannonball standards.

Most of the way up.

From the top.

Another hike in elsewhere and another Cannonball River cutbank.

Trace burrows in a sandstone ledge that fell from the outcrop.

There wasn't much here either, just some shell fragments. Pretty typical for the Cannonball in my experience.

 

[hemipristis]

Love the scenery!   I can’t wait to return to the states and start stompin’ localities like this!

[Thomas.Dodson]

At this point I had already eaten up most of the day with time and hike intensive sites but I made it to one last site I had planned. In this case the landowner didn't mind me driving right down to the river so it was significantly easier. I had some onlookers to greet me.

After a long and labor intensive day it seems it was finally paying off. Lots of free weathered gastropods and some bivalves and some in sandstone ledges.

A nice Drepanochilus perveta. The wing is intact (shown further below after preparation).

The main exposure. Most fossils seemed to occur just above or below the concretionary ledge.

Euspira obliquata.

Rhombopsis gracilis.

Indet. Bivalvia. It seems that gastropods are much more common than bivalves in the Cannonball.

What appeared to be a tooth was in fact a Drepanochilus wing. It fooled me at first.

I did attempt sieving for teeth but didn't find any. I didn't spend nearly as long here as I would have liked due to how late it was at this point but I'd love to return this summer.

 

Some pre-cleaning pictures. I had to clean everything with abrasion and then consolidate as the shell just absorbed water like paper. 

 

[Thomas.Dodson]

It's always nice to get a North Dakota site with so many free weathered fossils. A little abrasion at very low pressure (20-40 psi) was all that was necessary for most of these. Still, some of them didn't get finished or attempted at all because the shell was often softer than the matrix.

 

Euspira obliquata, one of the species that occurs in both the Fox Hills and the Cannonball.

A coral, Paracyathus lloydi.

There weren't many internal molds to be found. I found this internal bivalve mold (maybe Crasatella evansi based on the hinge line and inflation) and a single internal gastropod mold.

Caestocorbula sinistrirostella.

This is the Drepanochilus perveta from the sandstone block.

Specimens without the wing.

A wing and base. 

Mesorhytis dakotensis. I also found a single whorl that appears to be this species.

Rhombopsis gracilis.

This specimen appears to be what was described in 1920 report as Psilocochlis? occidentalis. It wasn't included in the 1990 Neogastropoda revision for the Cannonball Formation in North and South Dakota so I'm they might be rare.

The outer whorl section is covered in what is basically pyritic/concretionary sandstone so I gave up trying to remove the matrix from it.

I think these are valves of Caestocorbula.

These little gastropods appear to be Vitticoncha torelli.

Another one that was absent from the 1990 revision, the original 1920 report describes a Turritella haresi which matches this.

A bivalve section that appears to most closely match Miltha Plustomiltha) cedrensis.

I also prepped out this Arctica ovata from a large sandstone block from a previous site.

And removed another shark tooth from a concretion that I missed.

Edited July 18, 2021 by Thomas.Dodson

[Myrmica]

What a great trip!  The burrowing owl was a nice find of an extant species.  Do you think that the burrows were from ghost shrimp?

[Thomas.Dodson]

1 hour ago, Myrmica said:

Do you think that the burrows were from ghost shrimp?

Possibly. They are most likely decapodian at any rate.

 

They could be the trace genera Ophiomorpha based on the branching pattern. I've seen some smooth/indistinctly pelleted Ophiomorpha(?) burrows from the Fox Hills although I'm not aware of the exact reason behind the smoothing. Some Ophiomorpha burrows are less distinctly pelleted and preservation and wear might also be factors. They might also just not be Ophiomorpha. For what it is worth Ophiomorpha is common in the Cannonball and the other ichnofossils reported from the Cannonball don't come branch in this way.

 

 

[Jeffrey P]

Very nice gastropod fossils. Thank you for collecting and displaying them.