Fox Hills Formation Excursion

[Thomas.Dodson]

A few weeks ago we had unseasonably warm weather and I decided to make a trip to central North Dakota and collect from some exposures of the Fox Hills Formation (Cretaceous). I've spent a lot of time in this formation but had some new areas I wanted to try.

 

Views looking up and down on the main cut of a Timber Lake Member exposure. This was the most significant new exposure of the day.

Most of the Fox Hills Formation in North Dakota is sandstone of various grain size. The characteristic concretions with fantastic preservation that occur in the type locality also occur in North Dakota, although the concretions at this site were not of that type. Some examples of the concretions of this particular exposure. Some Scaphitidae body chambers are present that were separated from the rest of the ammonite. Not exactly the quality I expect from the Fox Hills Formation.

 

 

 

[Thomas.Dodson]

Wood makes up a large portion of the concretions at this site. It reminds me of working concretions from other Fox Hills sites where my scribe will be slowly working very hard sandstone then hit a pocket of poorly preserved wood and cut it up like sawdust. The wood here was better preserved.

A Mactra warrenana with a gastropod boring. These are among the largest Fox Hills Bivalves and are common at certain sites.

A decently preserved Scaphitid Aptychi.

The best fossil of the day goes to this Serrifusus dakotensis, a new species of the Fox Hills for me. It may not be in fantastic preservation but these are very rare in the Fox Hills of North Dakota.

 

 

 

[Thomas.Dodson]

A Euspira obliquata closeup. The high spire on individuals such as this one are supposed to be a sexually dimorphic characteristic.

Scales from multiple fish species make up a large component of matrix from this site as well. I have only very rarely found non-scale vertebrate remains in Fox Hills fossils of North Dakota but the presence of scales is an encouraging sign.

There's still a lot of matrix to go through but it's always good having some matrix for winter. I'll have to post some examples of the well preserved specimens from other Fox Hills sites another time.

[PaleoNoel]

Cool finds and interesting report! Thanks for posting. 

[Tidgy's Dad]

Nice finds.

Very interesting report, thanks for sharing 

[Ludwigia]

Congrats on the S.dakotensis !

[minnbuckeye]

Great finds!! I love the contrast of the wood and the Fox Hills matrix. 

 

Mike

[RJB]

Very interesting.   Im not used to seeing this kind of preservation in Timber Lake material. 

 

RB

[Johannes]

I really like the little stem of wood! Thanks for sharing (the pictures... )

[Thomas.Dodson]

It really is unusual preservation at this site. I've been to a lot of Timber Lake outcrops and this is the strangest one. Crystallization is incredibly variable at this site and I've found some very weird diagenic alterations...

 

The most unusual thing is how the outer shell layers are eaten up in some of the concretion centers. Some retain bits of external shell. Note the Protocardia subquadrata near the bottom of image 1 that retained the outer shell layer. These were positioned in the outer layer of the concretion. I'm used to excellent outer shell preservation in Timber Lake material. In some images you can see the gap where the outer shell actually dissolved in the concretion.

 

I've prepared several bases of large Graphidula sp. (presumably culbertsoni) from these so far. The ones without outer shell are always a tougher material, the same dark type as the fossils pictured. 

 

The cavity is from a piece of wood that completely dissolved in the concretion. Some of these cavities have remains in them that are basically sawdust.

[Thomas.Dodson]

some of the mentioned Graphidula. These were all missing the spires in the concretions.

This large probably Graphidula has outer shell but was already split when I found it so I don't have the spire. I'll prepare it sometime in the coming days.

Nucula cancellata are the most common Nucula species in the Fox Hills of North Dakota but the outer shell has a tendency to stick the matrix no matter how carefully you prep. These ones are different in that regard but also lack the splendid nacreous layer that is so typical of Nucula. It's still there just rather dull in these.

 

The wood in these concretions reminds me of another Timber Lake site I've been to. The wood bits were found throughout the concretions and I was experimenting with different acids when I discovered the wood stood up to muriatic acid while it quickly ate the matrix. I couldn't resist trying to put a small piece of concretion in the acid and wound up with a concretion piece showing the 3d orientation of the wood in the rock.

 

 

[Thomas.Dodson]

A little update.

 

Nuculana scitula are the most common bivalves from this site after Protocardia subquadrata. Nothing unusual there but I like them.

Some of the mactra warrenana I've been preparing have decent shell preservation. It's a real mixed bag with the concretions from this site.

A Piestochilus scarboroughi with the spire is a nice addition. Some of the calcite obscures the spire but it's nice overall.

With some of the really hard concretions I cut around and undercut the specimen so I can scribe the gastropod from a 3 dimensional perspective. It's easier on the spire.

 

 

[Thomas.Dodson]

More scales.

 

Pretty scales.

I mentioned so many scales always being a good sign and I wasn't wrong.

Fishy stuff.

 

 

 

[Thomas.Dodson]

Isolated centrums, vertebrae, and vertebral elements. Nothing fantastic compared among fish fossils elsewhere but they're sufficiently rare in the Fox Hills to be interesting.

[Phevo]

Nice to see the different fossils found from there thanks for sharing

 

[Tunis]

Great write up and photos!!

[Jeffrey P]

Interesting mollusk fauna with some fish scales thrown in. Congratulations on these finds and thanks for sharing them. 

[Thomas.Dodson]

I've finished preparing all the matrix so this will be the last update on this trip.

 

The only "complete" ammonite to come out the matrix from this site is this rather distorted ammonite. Still pretty in its own way.

I did find a more complete Piestochilus scarboroughi with the columnella intact. A random void in the shell was stabilized before preparation which is the shiny part. I was sweating preparing the fragile columnella on this one.

A couple worn Modiolus galpinianus are worth mentioning despite the preservation because I don't come across that many of these.

Syncyclonema halli are also pretty rare, probably in part due to the small size and thinness of the shell.

 

[Thomas.Dodson]

This unknown specimen is interesting. The left outline is a flattened wing-like extension but poor preservation makes it difficult to nail down. It doesn't appear to be anything reported from the Fox Hills in North Dakota but resembles some specimens found in the Fox Hills of South Dakota. 

One last scale since it is my favorite from the site.

Keeper specimens sorted and in their trays.

Extras I need to give away. I have a lot of second cousins who enjoy this stuff and since most aren't in great preservation they'll make decent stocking stuffers.

It was an atypical mix of good and bad preservation at the same site but some rare specimens were found and I always enjoy good scales. The Serrifusus alone makes it a worthwhile trip.

[cmwilson101]

Great job on the iestochilus scarboroughi!  The scales are stunning, as is the wonky nautilus.  

[Monica]

I love the iridescence on the fish scale and the "complete" ammonite - stunning! 

[lcordova]

I love the Euspira obliquata .... if you willing to part with some I can trade you some texas cretaceous Ammonites or echinoids