THE BEST LAID PLANS OF MICROBES AND MATS: VARIATION IN LAGERSTÄTTE PRESERVATION IN THE SILURIAN ERAMOSA FORMATION OF ONTARIO

The middle Silurian (Wenlock Epoch; Sheinwoodian Age) Eramosa Formation of southern Ontario, Canada preserves a diverse assemblage of biomineralized and soft-bodied taxa. Deposited in near-shore environments on the rim of the intra-cratonic Michigan Basin, the Lagerstätte contains chordates (heterostracan fish, articulated conodonts), arthropods (trilobites, eurypterids, scorpions, phyllocarids, ostracods), echinoderms (ophiuroids, crinoids, lepidocentrid echinoids), lobopodians, brachiopods, cephalopods, polychaetes, and dasyclad algae. Lagerstätten, while sites of exceptional preservation, are not free from biases (paleo-environmental, taphonomic, anthropological, etc.). The Eramosa Lagerstätte is found across multiple localities, with varying faunal compositions and depositional environments. Because of these potential biases, understanding the taphonomy within each locality is important for accurately interpreting the biodiversity and ecology of the Lagerstätte. Using scanning electron microscopy (SEM) and integrated energy dispersive X-ray spectrometry (EDS) the preservation of soft-bodied taxa from the three main localities (Wiarton, Hepworth, and Park Head) are compared. The main forms of preservation are phosphatization, carbonaceous compressions, and molds/casts. Preservation is controlled geographically, with authigenic phosphatization being more common in the Wiarton locality than in Hepworth or Park Head. The presence of microbially induced sedimentary structures (MISS) at Wiarton support a microbially-mediated preservation pathway inducing phosphatization. These results are compared to the similar preservation pathway from the Waukesha Biota of Wisconsin, USA. However, the presence of several localities, shelly marine fauna, and additional preservation modes within the Eramosa provide a wider lens to view Silurian carbonate Lagerstätten.