With the warmer weather, I've managed to get out four days over a number of spots, mostly in the Dundee Formation. Most of these trips were checking in on mostly tapped out locations near me, but a few new prospects were thrown in. With the exception of the last site in sequence, I didn't take home much. What I did take home was fairly paltry and fragmentary. The Dundee Formation is highly variable. An enormous formation, it may have six main lithofacies listed, but this does not account for lateral variation where some spots may be more chert-dominant or sandier pulses intermixed. It would actually make some sense to split the formation up into distinct members. Much of the work in the Dundee (Uyeno et al., Birchard) focuses on conodont zones, which can be particularly useful when it comes to gradational facies, but not enough is said about the macrofauna. There is very good reason why fossil collectors do not flock to Devonian rocks earlier than Arkona: they are miserably hard, sometimes erosion-resistant, other times crumbly, or have very poor preservation. At other times, it is nothing but coral and fragments. The only tool I ended up using in the field was my hand sledge. All that being said, there is a need to explore the formation in much more detail and to persist (in my case) in creating a reliable trilobite faunal list of these units. Some of these units are more cooperative and trilobite-dense than others. SITE 1 The material is very ugly. Pitted, occasionally dominated by a vermiculating chalky chert, or even crystalline chert that breaks conchoidally in blocs. There can be fossils (and even trilobites) in this material, but it takes patience and a keen eye. Any trilobites tend to blend with the pattern and colouring of the matrix if it is this mottled, making them much harder to see. Occasionally, substantially large coral colonies can be found as in the photo on the left. On the right, an infrequent sandy pulse containing some small rostroconch and ramose bryozoan fragments. The chances of finding more fossils occurs in this lithology, and generally the presence of bryozoans increases the odds of finding trilobites as they seemed to like to party together. The biggest rostroconchs at this location. They were not rare, but hardly common -- again, appearing mostly in the sandier pulses. Other notable bedding varieties included similar material to that of Amherstburg with the dark brown on brown tangles of horizontal burrow traces appearing as stains. The only evidence of trilobite after a few hours of busting this material. I reason this is an Odontocephalus on account of the pygidial ribbing, size, and morphology of the pygidial axis. A quick exploratory prep to reveal more of the features was a bit problematic due to the crystalline nature of the matrix and its relationship with the shell. I would return to this site a few days later for a more proper examination. Site 2/3 A small one-day break from the Dundee saw me out exploring the early Devonian. The focus here would be the Bois Blanc Formation -- itself another immense geologic unit with a lot of variation both vertically and laterally. Unfortunately for me, I was in the wrong spot. A visit to the Silurian-Devonian contact was absolutely devoid of fossils save for one very abraded coral, all of it set in finely bedded, large-bloc sandstone possibly indicative of shoreline or even sabkha. The Bois Blanc Formation finds were fairly underwhelming. In terms of trilobite genera, a few Anchiopsis pygidia, a Crassiproetus pygidium, and on the reverse side of this rock a fairly disarticulated Burtonops. Judging by the grainy matrix, it just isn't a suitable facies for finding well preserved trilobites. Site 1 Again Returning to the first site for a more systematic analysis, a few more trilobite genera were found. On the left is Mystrocephala, and on the right a plump Crassiproetus. Pseudodechenella are generally like cockroaches in this formation, but only a few fragments of them were found at this location. On the right, another plump but crushed Crassiproetus. Calcite crystal clusters occasionally appeared, either in the rhombohedral form as seen in this photo, or as pyramidal points as vugs in the rock. On the right is perhaps what we can call my "prize" find of the day: an Odontocephalus entirely composed of chert. Sadly, the posterior pygidial process is gone, but this differs from the same genus at another location on account of its width. Site 4 This site is by far the most productive, and a known one to me as I had collected there numerous times last year. It is composed of a sandier facies with beds supported by giant brachiopods to the extent that it seems more brach than matrix. This material also boasts an impressive abundance of rostroconchs, as well as a virtual buffet of Devonian fossils: bryozoans, gastropod steinkerns (high and low spired), occasional coral, rare stromatoporoids, and of course trilobites -- always fragmentary. The paucity of coral and absence of crinoidal debris is suggestive of possibly an upper shelf and near-shore tidal environment. The material is well sorted and certainly not in life position. Many of the fossils are silicified, apparent by the white chalky film on the trilobites and rostroconchs, but the brachiopods seem to maintain their natural shiny nacre. Splits along what amounts to busy bedding planes will commonly separate between the trilobite's delicate chalky shell and the steinkern. Only about 10% at most of these rocks are viable for splitting if they have developed cracks due to water-erosive forces and the presence of profuse brachiopods that make for a natural weakness in the rock. Still, the only tool required again is a hand sledge. The rest of the rocks are poorly fossiliferous crystalline chert horizons or a poorly fossiliferous orange sandy facies where a few broken fossils appear sporadically. By volume, Pseudodechenella are the most conspicuously present in this material, sometimes appearing between 3-12 times on a single plane as pygidia and free cheeks. On the right is a partially covered and small Coronura that I will be doing some light prep to reveal more of to determine if the pygidium is complete. And, by volume, Coronura takes second prize, albeit usually as fragments -- usually just a fragment of a single pleura! This should not be surprising given their customary large size (up to 50 cm) and the tidal churn that has a higher probability of disarticulating larger examples. They simply cannot survive the tides. On the left was my first of the day's encounters with the Odontocephalus n. sp., in this case just a tiny fragment of the anterior cephalic denticles. On the right, a rare sight: a solitary brachiopod. The size and wings are not what make it rare, but that it appears largely alone in these profuse layers. My first encounter of the day with the pygidium of Odontocephalus. This one is in rough shape and not diagnostic enough for me to keep. The rest of the day would not yield the greatest pygidia of this undescribed species. On the right is how the Coronura usually appear: fragment of a pleura. Another Odontocephalus with skin on one side and steinkern on the other. This was by far the best preserved example of this species for the day. An oddball, and possibly plant material as opposed to an in-filled burrow. On the right, positive and negative of a smaller Coronura. Almost! One of the important diagnostic features to describe this species is to have a very crisp and complete pygidial posterior process. This one is achingly close. On the right is another oddball that looks like an almost complete trilobite. I will be putting this under the scope and scribe soon. I brought this home for archiving purposes to show the general fauna in this facies. The red numbers indicate a convenient index of the most common trilobites in this material, neatly lined up: 1. Odontocephalus 2. Pseudodechenella. 3. Coronura. The bottom line? I'm doing my due diligence in frustrating, commonly parsimonious, brutally hard, and unforgiving formations to complete the trilobite faunal list, but also to secure scientifically significant specimens. This year so far has been a bit of a disappointment, so I'm hoping my fortunes change soon as the season progresses. I may need a break from the local haunts to collect outside of southwestern Ontario if I hope to find complete trilobites. UPDATE: I performed some preliminary scribing on the oddball piece and confirmed that it is indeed a trilobite, albeit broken and missing some parts from what nature took away from it. Still a lot more to uncover on its left side, this is indisputably a Pseudodechenella sp. Although ridiculously common in the Dundee from cheeks, pygidia, and isolated pleural bits, it is a rare treat when they come out nearly complete like this. One of the tell-tale signs apart from the morphology of the pygidium is the pair of nodes positioned at the posterior lateral sides of the glabella. It will take some care and time to make this one more presentable, but I'll go ahead and declare this first blood on a (near) complete trilobite for 2021.
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Kane Faucher
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February 2024
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