Today was a gorgeous day, and it is somewhat fitting that the last day of the collecting season be sunny and warm. Yes, this was the last day... I mean it this time! As there are only 11 days left until vacation, a mountain of essays to read and grade, and the fact that winter weather is going to return and stay in earnest, today was it. The rocks were heavy and hard as always. I didn't come away with as much material as some of them were absolute duds. Like last time, most of the gains were made from a single rock. Let's lead off with the usual suspects: Left: I think I found this one on a previous trip, but it was in my bag when I was emptying it. Likely a Mystrocephala stummi with mineralized goop on the posterior border of the shell. Right: the ever-present and readily available Crassiproetus crassimarginatus. I am impressed with just how large these ones can get in this material. There were plenty of Pseudodechenella pygidia (and free cheeks galore), but all of them were on the small side and situated in the middle of larger rocks, so not really worth the effort to reduce and bring home. When tubercles are showing, that means lichids are in the house. I'll need to clean this one up. I also found (not pictured) the thorax of a Pseudodechenella that needs to be glued, and a very well defined cranidial fragment (median lobe) with exquisitely detailed tubercles. This one is pretty tricky to photograph as it seems that my devices try to overly blend the specimen and its matrix. The left is the positive, which still has some parts concealed under matrix. On the right is the negative. Yes, another candidate for Echinolichas eriopis. A few more attempts to photograph the positive from different lighting angles. What are the chances of finding a new lichid twice in as many days? This one is as large as the one I found Sunday. Whereas the former one has a bit better detail on the pygidial ribs, this one has evident pygidial spines (with tubercles!). There is still an opportunity to reveal more on the right side. It was nice to end the season on a high note. Although I never quite seemed to find an absolute complete trilobite in this material, these last three months have been filled with surprises. Trilobites in the Amherstburg are very much a faunal minority compared to the thickets of coral and bryozoans, but I made out okay for the effort. The site will now be waiting for me in spring. Down tools. For real this time! ___ At this point, I'm just about ready to summarize some key findings, pulled from my field notes, about this imported material. As stated in previous posts, it is reasonable to assume judging by the lithology and presented fauna that this is material from the Amherstburg/Lucas Fms. The nearest and cheapest source of this material for the purposes of a drainage area riprap would likely trace this material to a quarry or quarries in Ingersoll. As it is unsuitable material for cement, this material is generally stripped off. The fauna is suggestive of a minor reef community. Apart from the thickets of toppled rugose coral (likely due to wave action) and some colonial rugose as well as tabulate (Favosites) communities that have considerable in-fill suggestive of rapid sedimentation burial, the common presence of bryozoans as binders does point to reef development. Bafflers such as crinoids are more scarce in these sediments, possibly suggesting a lack of cohesion and maturity of these minor reef complexes. In some of the materials, thin black layers may suggest a shallowing sequence and possible subaerial exposure in shallow, possibly peritidal conditions. Deeper waters are reflected by the appearance of some packstone pulses with larger grain-size limestones. The upper portion of the material with black stained shale partings or a higher appearance of chert nodules (indicative of siliceous sponges) may contain stromatoporoids, branching bryozoans, and rostroconchs (?Conocardium cuneus). Likely presence of algal mats. What is known is that this environment would have been situated in the Appalachian basin, southeast of the Findlay arch (by current orientation). It is not unreasonable to expect shared faunal elements with equivalent strata found in New York, such as the Onandaga Fm, and more particularly with the Edgecliff, Nedrow, and possibly Moorehouse Members. Trilobite fauna are generally represented as a minority fauna in these relatively small coral bioherms. When present, disarticulated moults are suggestive of higher energy conditions, likely swept into gaps and pockets in the biohermal mass. Of note is the complete absence of phacopids, suggesting the environment was not well suited for their spread into this particular biohermal region. Instead, burrowing proetids are relatively abundant, including the illaenimorph Crassiproetus crassimarginatus that appears most commonly in these sediments, followed by Pseudodechenella sp.. Here is a comparative table of trilobites of equivalent geologic age appearing in three locations. A-SITE = the area under study; A-ON-FR = Formosa Reef, Ontario (Michigan basin); O-NY = Onandaga of New York.
As is evident from the table above, only two species of trilobite are shared between the three locations. My location shares three trilobite species from the Formosa Reef, and five with equivalent strata of New York. Two species (in bold) are shared across all three strata.
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Kane Faucher
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February 2024
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