A nice time yesterday to head out and make the 1.5 hour drive to the Bois Blanc Fm spot prospected on April 18. Less than a week later, it was essential to give the site more than a 45 minute once-over. The site itself is a good mix of a lot of Bois Blanc Fm material, including natural outcrops and the stuff ripped out of those that are in nice, tidy piles of about 5 metres high by 10 metres wide, and spanning about 60 metres long. There are also more than one outcrop, and more than one rock pile.
There are roughly two main types of strata.
The first is the wavy, bumpy, lumpy calcareous material that weathers blue-grey like Verulam Fm limestone. This material contains abundant rugose corals (some of them human arm-sized!), crinoids, platycerid gastropods (some of them real monsters), bryozoans, and broken bits of Burtonops. The calcareous stuff is only superficial, as it is just mudflows. In the meat of the rock sandwich is abundant, crystalline chert and quartz.
The second type has arenaceous surfaces that weather to expose a lot of massive coral colonies (tabulate, rugose, pipe, etc.), but underneath which are very fine-grained, mostly blank intervals. Bedding planes, where they exist, do not follow around fossils. IN other words, splitting will more than likely shatter through anything viable. This rock is very tough -- perhaps the toughest on par with Dundee Fm -- and Ludvigsen's statement of it being "perversely" so is accurate. There is no sense bashing into the harder material where the bugs are without having some evidence that something is inside -- a trace hairline, for example. Most of the rocks will split blank or with bits, and is a real time commitment.
What was odd about these rocks was the rarity of brachiopods That is not something I am used to in the Devonian. Also, these intervals had virtually no chert nodules.
If the shell had been complete on this one, it would have come home with me. This is an example of one of those giant platycerid gastropods. In this case, a very long lived one.
This one I did keep, despite missing some shell. All of these are more intact and larger than the ones I find in the Hungry Hollow Member at Arkona.
Plenty of examples of the arenaceous, sandy surfaces. And, not by far, the only or best examples either.
Not much comes out small in the lower Devonian! Anyhow, on to talk about the bugs
Anchiopsis are fairly typical inhabitants of Bois Blanc material, but they were not exactly numerous. In most cases, when they did appear in the calcareous material, there were broken and eroded almost to the point of non-recognition; on the arenaceous surfaces, they would take on the pitted, eroded appearance as seen here. I encountered bits of Burtonops and the impression of a Crassiproetus -- neither species examples I took home.
This one floored me. It is new to the collection: Calymene platys. Sadly, the top of the glabella was sheared off by forces long ago. Still, it is a substantially sized and robust specimen. It is very similar to the Moroccan Flexicalymene ouzregui, and just like Moroccan Devonian material, it is nigh impossible to split this rock without shattering through a bug. I will have to glue the head here, and then prep it a bit.
You can see how robust the bug is at the top of this picture. The skin is missing, but I collected the impression where the skin stuck. That will be a tough prep job.
Have a guess what this is. No, not a gastropod. I'll reveal its identity by the end of this blog post.
Some Calymene partials, and stuff I put in my pocket as the day went on. Those Pleurodictyum at the bottom are quite large!
Now what is this? It comes from the same mystery species as above. It is indeed most of the left genal spine of a Terataspis grandis.
The modified illustration above indicates where it would be placed. This fragment would have belonged to an individual of about 400 mm in length. Hardly the biggest (which would top out around 600 mm), but definitely a find to be proud of. This, and the other fragment, makes two examples in a day.
This has already been an incredible season, and it is still just shy of 50 days in. My checklist of Devonian trilobites is steadily filling out -- and I've still not visited Arkona yet this year. My 2020 goal of laser-focusing on Ontario trilobites has been paying off well. Now that much of the Devonian is "done," what remains are repeat visits to obtain more complete and better specimens, and to go a bit farther afield to prospect some Silurian and Ordovician spots.