Carboniferous nonmarine invertebrate ichnocoenoses from southern New Brunswick, eastern Canada

Nonmarine strata of the Lower Carboniferous Albert Formation of southern New Brunswick, eastern Canada, contain relatively diverse and abundant invertebrate trace fossils comprising twelve ichnogenera, fourteen ichnospecies, and one vernacular ichnotaxon. These traces occur in two mutually exclusive, spatially and temporally recurrent ichnocoenoses, each related to specific paleoenvironments. The Rusophycus ichnocoenosis characterizes upper portions of upward-fining fluvial channels and comprises ichnotaxa reflecting different behavioral activities of arthropods. The Palaeophycus ichnocoenosis characterizes shallow lacustrine sequence and comprises ichnotaxa produced essentially by deposit-feeding invertebrates, possibly annelids (?oligochaetes). Exclusion of ichnofaunas from strata of additional and similarly intergradationa paleoenvironmenta regimes within the sequence (alluvial fan, alluvial plain, algal swamp, deep lacustrine, evaporitic lacustrine) is suggested to reflect several physical environmental constraints, notably parameters such as grain size, availability of nutrients, and oxygen and salinity levels. In combination, composition of the entire trace fossil spectrum precludes assignment to the traditional nonmarine Scoyenia ichnofacies. Comparison to previous investigations of nonmarine invertebrate ichnotaxa is hampered by variable taxonomic approaches, the lack of detailed paleoenvironmental analyses, and the limited investigations that have been used to formulate ichnocoenoses per se. Although there are some similarities to previously described examples, the formulation of alternative universally applicable continental ichnofacies clearly remains premature.