So today I decided to spend part of the morning at that site near my house, the infamous "riprap hill" and associated pit. I've long suspected most of the rocks I split there were trucked in, and have confirmation of that due to the three different kinds of trilobite I've pulled from it (two in the last four months - Anchiopsis anchiops and Mannopgye halli).
I had been finding examples of rock from the Hamilton Group, Dundee Formation, Bois Blanc Formation, and the Amherstberg Formation. A good and wide range of Devonian age rocks.
As can be seen above, the usual assortment of brachiopods and a gastropod. My expectations were low as I'm running out of rocks to break after four years of scouring the place.
Ok, but what about this? I get the line by Morpheus in the Matrix in my head saying "what if I told you everything you knew was a lie?" So at first I was in disbelief: this must be a shell impression, not the impression of a trilobite pleura. But I've seen this before. In the Ordovician. Yes, it is a fragment of a Pseudogygites. The nearest Ordovican outcrop is 300 km away.
If I needed further proof, I flipped over this piece of shale and saw a fossil barely bigger than the head of a pin. Putting it under the microscope, it is indeed the cranidium of a Triarthrus.
Oookay, then. Confirmed: dumped rocks that span over 100 million years. From a field perspective, this is going to make things much tougher in terms of certainty over finds, but I suppose it means a veritable potential bonanza of finds spanning a much broader range of geologic history.