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Today Deb and I made the two hour drive up to just outside the town of Formosa, Ontario, to have a look at the Formosa reef limestone, which is part of the Amherstburg Formation. This road cut is the type locality for this material, and it was humbling to be at the exact same location that researchers of yesteryear such as Ludvigsen and Fagerstrom derived their material that formed the basis of their published work on it. 

 

Here are some shots of the road cut. Hardly does it justice. This represents a single, massive biohermal knoll. I've wanted to visit this site for a while now, having read two key papers on it.

 

 

 

Most of the non-coral fossils are found on the south edge of the cut, as it is assumed that this was the windward side of the knoll that captured much of the debris swept in by the currents.

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The knoll is much bigger in person. The matrix is not too tough, and it tends to weather a dark grey, while the inside has a lot of oxidation and crystallization. It breaks a little like Hungry Hollow Member, and has the oxidated appearance (in parts -- this stuff is quite varied!) of the shell beds at Deep Springs Road. The cut also runs behind the road. 

 

We only had a few hours, and there is so much material. The impression of a nautiloid was neat until we came upon veritable nests of them.

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Within five minutes we were already piling up finds. 

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Some shots of one of the sections we were working. Note the big tabulate coral. These rocks are very much more fossil than matrix, and definitely a coral reef with both tabulate and rugose corals in abundance. Much of our work was within the crinoidal packstones and stromatoporoidal boundstone.  

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We had some field friends for company. :) 

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This rock gives an indication of how busy these can get, and the state of preservation. The limestone is very much dominated by nautiloids, brachiopods, gastropods of all kinds, bivalves, and crinoid ossicles. Trilobites are reported to be "rare." That was not my experience, as just about every rock had some kind of trilobite fragment.

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We collected a whole flat's worth of fossils. If the drive wasn't so long, we would have stayed much longer. 

 

On to the finds...

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Tons of nautiloids, including this slightly curved one (I'll have to check through Fagerstrom to get the IDs -- sorry). I found the weathering of some of them to show the siphuncle pretty neat.

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All manner of gastropods to be found. I only picked up a few, and may have a high-spired one somewhere in the box.

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Rostroconchs were fairly common, but also quite small.

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Deb found this large bivalve steinkern that popped free of the matrix. Both valves showing!

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And of course trilobites. 

There are five species reported in the Formosa reef, with Crassiproetus crassimarginatus as by far the most abundant, followed by (in order of abundance) Mannopyge halli, Mystrocephala stummi, Acanthopyge contusa, and Harpidella sp. For the few hours we were there, I only managed to find three of the species. 

 

Pictured here are just some of the Crassiproetus. They were plentiful.

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One example of Mannopyge halli and one of Mystrocephala stummi.

 

In all, quite a haul for a few hours. Of course, one is not as discerning on a first visit and may tend to collect everything. Still, I really do want to go back as it is a fairly productive site. Full trilobites are highly unlikely given the depositional conditions, and I have not read of any full ones being reported there. 

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Great report, photos, and finds, Kane!

Glad you got out, and that you were successful. 

Thanks for the field trip! :) 

 

The cyrticonic cephalopods with the ornamentation are extraordinary!   :wub: :drool:

You do appear to be the rostroconch whisperer.  :P 

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Glad you had an interesting and successful hunt, Kane! Nice report and I love the nature pics!

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Both diversity and abundance is a combination that is hard to beat!  I have never been there, but I'll have to remedy that!  I really like those nautiloids :wub:.

 

Don

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Cool stuff Kane! Makes me wanna go back to some of the spots I’ve read about in research papers. :D

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Manticocerasman

nice report Kane .

 

the nautiloids are great :D

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Wonderful fauna and report, I love the nautiloids and rostroconchs. I have yet to collect any rostroconchs, despite them supposedly occurring in my local Mississippian and looking every time I go.

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Great stuff, Kane!  I, too, like the nautiloids :)

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Thanks, everyone. :) 

The nautiloids were certainly a surprise. The rostroconchs were not as plentiful as my other location (once upon a time I found them to be rare!). The diversity is certainly much more than these photos suggest.

 

The research papers certainly prepared me for what to expect in some ways, as well as directed/optimized the efforts, but nothing quite compares to being there in person and reading the rocks firsthand. The two papers I drew most from would be:

 

Fagerstrom J.A. (1961) The Fauna of the Middle Devonian Formosa Reef Limestone of Southwestern Ontario. Journal of Paleontology 35.1: 1-48.

Ludvigsen, R. (1987) Reef trilobites from the Formosa Limestone (Lower Devonian) of southern Ontario. Can. J. Earth Sci 24

 

As we only explored a small yet highly productive area of a few metres, there is still a great deal to explore (the cut runs long and high on both sides of the road). In order to do it justice, next time I'm thinking of getting motel room and making it a multi-day dig -- hopefully with some field comrades to share the site with. :hammer01:

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An amazing site, Kane. Congratulations on your great finds and excellent report. I too, am a big fan of those nautiloids, but the trilobites are cool as well. Looks somewhat similar to the Schoharie Formation fauna from New York which is also Lower Devonian. Let me know the next time you plan to go. I might be interested. 

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Northern Sharks

Based on your 2nd pic, you can almost hear Kane shouting "There it is!!!! Stop the car!!!"

BTW, how is the car???

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5 minutes ago, Jeffrey P said:

An amazing site, Kane. Congratulations on your great finds and excellent report. I too, am a big fan of those nautiloids, but the trilobites are cool as well. Looks somewhat similar to the Schoharie Formation fauna from New York which is also Lower Devonian. Let me know the next time you plan to go. I might be interested. 

Thanks, and will do, Jeffrey. :) You're not far off on the age, either. It is age-equivalent to the Edgecliff Member of the Onandaga Fm (upper limit of the Lower Devo), although a good number of the species are endemic to the Formosa, while others (particularly the brachs) have a lot of overlap with the NY strata.

 

Just now, Northern Sharks said:

Based on your 2nd pic, you can almost hear Kane shouting "There it is!!!! Stop the car!!!"

:default_rofl: Too true! Those tire burnouts actually weaved something fierce. Admittedly, Deb was initially hesitant to park the car on the side of the road, but it isn't that busy. The occasional drivers would wave to us as they passed by. 

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