An Early Devonian fossil assemblage in the Clam Bank Formation (western Newfoundland): implications for Lochkovian paleogeography, paleoceanography, and biogeography in the Canadian Appalachian orogen

The Clam Bank Formation records renewed middle Paleozoic, post-Salinic, foreland-basin sedimentation in the northern Canadian Appalachian orogen, but its age has been poorly constrained. The echinoderm lobolith Camarocrinus formed the basis of a long-standing late Silurian (Přídolí) age even though the macrofossil assemblage has received little attention. Previous age assessments, including an early Lochkovian interpretation based on palynomorphs, suffered from contemporary uncertainty of, or subsequent changes to, biostratigraphic zonation. Updated taxonomy and regional stratigraphy, along with addition of new fossil material, demonstrate early Lochkovian macro- and microfossil assemblages, including the species of Camarocrinus. This enables revision of middle Paleozoic paleoenvironmental frameworks within the Canadian Appalachian orogen. In the latest Přídolí, the lowermost Clam Bank Formation was part of a platform-interior coastal plain behind a rimmed shelf (now in the Gaspé Belt) in the northern Quebec Embayment. Early Lochkovian transgression established a mixed siliciclastic–carbonate seaway in the platform interior coeval with shelf-margin drowning. This history coincides with Gedinnian transgression in northern Europe but regression within the nearby Arisaig basin (Nova Scotia), the contrast illustrating local tectonic control on base level. A diverse but poorly preserved Clam Bank macrofaunal assemblage occupied a high-energy, temperate, terrigenous-dominated nearshore setting. Faunal constituents reflect mixing of Eastern Americas and Old World fauna, Silurian holdovers, and appearance of taxa earlier than elsewhere in North America. Megaplant fossils, palynomorphs, and arthropod trackways identify a wet and dry coastal terrestrial habitat. Middle Lochkovian regression appears to have terminated the marine basin.