On a warm Sunday, I made it up north to the Formosa reef road cut. It was likely my last major trip of the season, and it certainly did not disappoint. I had read and re-read the research papers on this site, which is the type locality for this massive biohermal feature situated in the Amherstburg Formation. The two main sources would be these:
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
The road cut itself is quite sizeable, and represents a massive knoll. My focus was on the windward side of the reef where skeletal debris would have been swept in by currents. The wackestones and stromatoporoidal boundstones contain a staggering amount of faunal diversity. There were certainly corals, both tabulate and rugose, but just about everything else including gastropods, brachiopods, bivalves, crinoids, and a profusion of different kinds of nautiloid. Of course, there are trilobites as well, but none have been reported complete.
The cut runs along both sides of the road, with additional access from behind the reef as well.
And it is fairly tall, too. There really is an abundance of material, much of it more fossil than matrix. What we collected in 2.5 hours is hardly representative of what this material has to offer.
This was the main focus of the visit: the windward side of the reef. Every single rock was full of fossils -- and not just coral. The weathering and oxidation made for some interesting steinkerns.
Although the material looks quite dense as it weathers a dark grey (inside is a creamy off-white with orange oxidation), it breaks apart easily. Unlike a shale that will split in sheets, this material breaks apart in angular chunks, a little like the material at Hungry Hollow (but much clearer to see what's inside). Pictured above are some usual surface features including a nautiloid cast and a chunk of tabulate coral. The material was quite easy to work with.
It took just a matter of minutes to start piling up stuff to bring home. Every rock and every split had something new and interesting. Of course, I wasn't too picky about what I was collecting as this was my first visit. It is a little like someone's first visit to Arkona when the tendency is to fill buckets with horn coral!
Nautiloids were abundant.
Weathering made for some very neat looking cross-sections, as pictured here with the exposed siphuncle.
This would be my first cyrticonic nautiloid. Quite neat!
I found a number of these small rostroconchs, too. Of course, I'm pretty full up on rostroconchs from my local imported fill site.
Plenty of gastropod steinkerns, some flat and others high-spired. Some also contained large crystals inside. There were also plenty of brachiopods of varying types, but I didn't manage to collect them this round.
Deb found this large, double-valved bivalve that popped free of the matrix. I had found a smaller more beat up one, so this example was the clear winner to be taken home.
Corals, corals, everywhere. Some had very nice crystallized cross-sections among the rugose variety, but we left those in the field. Despite this being a reef, the corals were less "in the way" compared to the Hungry Hollow Member at Arkona; many more types of fossils were given equal billing. Also not pictured were the crinoidal hash.
So what about the mud bugs? Ludvigsen reported that trilobites were rare in this material, and that is not something I could confirm from experience; just about every rock had some kind of trilobite fragment, be it a pygidium, cranidium, or librigena. By far the most abundant species would be Crassiproetus crassimarginatus (subspecies brevispinosus). Pictured above is just one (exfoliated) example of about ten or more I brought home, leaving about as many or more in the field! Ludvigsen's text reports 222 fragments found over a matter of a few years; I could probably acquire that many in a full day there. Of course, no complete example has ever been reported, and it is unlikely due to the nature of the depositional environment. One has to be content with partials.
If Crassiproetus is the most abundant trilobite represented there, the second most would be Mannopyge halli. Pictured here is a rather beat up version, and it was odd I only found the one -- but then I may have missed a few in the haste to make the most of our short time at the site. You can see the pygidial nodes like a necklace along the right edge.
In third place for relative abundance would be Mystrocephala stummi. I was pleased to find this fairly nice example which looks a bit more well articulated and robust than the more flattened examples I've found at my local spot (yes, I found a second fragment a day before this trip!). No traces of the other two most rare trilobites in this material (Acanthopyge contusa, and Harpidella sp. of which the literature reports a single cranidia).
Overall, this was an incredible trip filled with new surprises. Although I had to miss out on Bowmanville this autumn, this certainly was a significant event of the season. I do plan on returning there again, either later this year or more likely in the spring. I hardly did this site justice as there is still so much to explore.
The long October weekend is here, and despite it raining this morning, I was able to get out yesterday and have plans to make a few visits to my Bois Blanc Formation rubble between bouts of turkey and getting caught up with essay grading.
The number of rocks that are highly fossiliferous is dwindling, but I'll have enough to see out the rest of this year. This small haul of trilobite partials would be considered a fairly good outing: three fragments of Acanthopyge contusa and two fairly preserved pygidia of Crassiproetus crassimarginata. That brings my total Acanthopyge fragment count to about 9, and 13 lichids overall. If I could only find a complete example, I could stop collecting the fragments.
As the material is very rostroconch-dominant, I only pick up the odd one on occasion if they look nice.
I hope to get out a few more times in the next while and update this post if more neat finds are made. So, to be continued...
So another four hours out back, and I didn't do too poorly. It took me a bit longer of trial and error to find the right productive rock, and it was this one rock -- and only this rock -- that produced the days finds.
I suspect this to be another lichid genal spine (possibly Acanthopyge contusa). Left: negative and positive. Right: closeup.
Just missing its cheeks, an otherwise complete Pseudodechenella sp. None too shabby! This would be the day's best. Perhaps I'll have another go tomorrow.
Well, it was a challenge to find more productive rocks to split. Four hours, and not much to show for it. In fact, it was the first visit in some while where I didn't even find a trace of a lichid. But sometimes a small find can be just as rewarding.
This looks very much like a Mystrocephala stummi to me (compare with the image from Ludvigsen on the right). If so, that would make a new species find for me. Although the pygidium axial width is not 1/3 or more of the entire pygidial width, I can make out the little nodules along the heavily incised pygidial ribs. Of course, the fact that it is only reported in the Formosa reef (Amherstburg Fm) possibly problematizes the assigning of this rock to the Bois Blanc, but so did the appearance of Acanthopyge contusa. There's trilobites from both formations here, sometimes on the same bedding plane. Perhaps another visit tomorrow? For now, round 1 of turkey.
Five hours and I've pretty much managed to tap out a section of much of the viable rock. It wasn't until the last half hour that I was able to find anything at all, with much of the time spent splitting duds, blanks, bits, and other false leads. If the fourth of four sections has any viable rocks left, they are massive armour stone boulders that even I can't either move or do more than splinter/fracture the edges. So on I moved to section two.
As with a lot of the lichids in this material, the preservation is generally poor, but this Acanthopyge contusa positive and negative is still fairly articulated with the course tubercles and delineated goblet-like pygidium axis. That brings me to 15 lichid fragments, with eleven of those from this species. I probably have more examples of this species than any museum.
Once more into the breach before I give the site a rest for a bit. My focus tomorrow will be a return to section two. There's still some source rock to go through from where I obtained this pygidium. If time and energy permit, I might poke around section one (fairly tapped out) and section three (mostly blank or lenticular coral limestone + domes). I've put in 16 hours in 4 days.
And another five hours in the proverbial hole, and that will be all for now as I need to get back to much-neglected work. But on to the finds that close out these five days of persistence.
Yes, it's yet another Acanthopyge contusa. Although the photo doesn't do it much justice, this is a very nicely preserved cranidium despite missing a lobe on the right. The tubercles are nice and clearly defined.
The trip-maker? What appears to be a cranidium that compares favourably to Terataspis grandis. Image on the right is from Ludvigsen's text. But, sadly, it is just another Acanthopyge.
Here is the same specimen in sunlight, and the negative below.
So, the final tally:
5 days (21 hours)
12 Trilobites (7 lichids, 4 proetids) = 7 Acanthopyge contusa, 2 Pseudodechenella sp. (one almost complete), 2 Crassiproetus crassimarginatus, 1 Mystrocephala stummi
Not bad at all. Spending all this time out there has forced me to revise assumptions about this material, and it may be a blend of Bois Blanc, Amherstburg, and Lucas Fms. Not sure when I'll be going back, but my hammering arm needs a break!
When it rains, it pours.
With what were to be the last big two trips of the season -- one to my prospected Cobourg Fm roadcut near Nottawasaga Bay, and the other to Bowmanville -- were bust.
The trip up near Collingwood did not yield any complete trilobites. Worse, the stuff was weathering into blank, undulating nodules with the occasional bits. Small, junky fragments of about five typical Cobourg Fm trilobites were all I came away with, and the usual giveaway gastropod steinkern and miscellanea. I spent a good deal of time (including in a misting rain on a cool morning) splitting to no avail, and surface collecting the weathered rubble to slightly better luck. Photos of my underwhelming finds:
So, Isotelus, Flexicalymene, Ceraurus, Pseudogygites... in fragmentary form + gastro and sundry bits.
The "prize" were all these Thaleops cephalons. So, fairly skunked for an eight hour round trip drive. I won't be bothering this roadcut anymore.
As for Bowmanville, funny story. Forty clicks out from London as we are making our way, our car decides to give up the ghost on the 401. That means getting a tow back into town, it means not being able to get refunded for a hotel room some three hours away, and it definitely means no coveted Bowmanville trip for me. As trips to the quarry are limited to the two times a year they let collectors in, and with a new rule about putting a hard cap on the number of collectors, my luck in not being bumped to the waiting list for next spring meant little if our wheels would not get us there.
So, what was going to be the final big trip of the season went up like a puff of smoke. That bummed me out a bit. But the season is not quite done as I continue wrestling the stone at my personal backyard spot.
It's a lot of fighting to get the rocks out and broken down, with some just too large to do much other than shatter. But here's another pygidium of Acanthopyge contusa.
Genal spines belonging to another lichid, but unsure if it belongs to Acanthopyge or Terataspis. None of my literature describes the genal spines of Acanthopyge contusa, so it remains uncertain.
A giant and fully inflated Crassiproetus pygidum.
Two poorly preserved lichid pygidia, and an uncertain fragment.
Another Acanthopyge contusa cephalon (two angles).
The mystery deepens, or am I closing in on the formation these rocks are coming from? I still need to retrieve the positive, but my trilobite comrade Scott says it seems to compare to Trypaulites erinus. Initially, I had passed it off as a Pseudodechenella until I got home and looked at more closely: too many pygidial ribs and an axis much more tightly tapered. A dalmanitid! This one sits on the exact same bedding plane as the Acanthopyge pictured above, with only about 3 cm of daylight between them. So... what are these rocks? According to the reported material, the Bois Blanc Fm has the following trilobites:
The ones in bold are those that I have found in this imported fill. But the trilobite out of place here is the Acanthopyge contusa that is only reported in the overlying Amherstburg Fm. The evidence seems more to suggest that a) I am dealing with Bois Blanc material for sure, and b) Acanthopyge specimens in the mix may mean it had a longer geological range, first appearing a bit sooner. That would not be an entirely absurd hypothesis.
The rocks at my spot are starting to thin out in terms of giving up nice finds, taking much more effort for less reward. As the days grow shorter and colder, the fossil days of the season are in their twilight. That being said, it is not officially "down tools" yet; there are still a number of weeks left where I can squeeze out the odd day or two a week between teaching duties.
In the hopper is some planning to visit the type locality of the Formosa Reef (Amherstburg Fm). Full trilobites in those reefal environments are as unlikely as my current backyard spot, but I'm hoping to find a fragmentary example of at least one species of trilobite I do not have as this year has been a bit light on collecting species I don't already own. I'm also expecting a scribe I picked up for cheap that will bridge the gap between my ME9100 and the Aro, and I have another Asaphus lepidurus coming to be prepared. Looking over my materials this year, I'm not sure I'll have enough to last me through the winter, so I may spend more time planning out the 2020 season.
But it's still the 2019 season. I will continue breaking rocks until the snow comes.