We document the occurrence of a marine bed, and its associated biota, in the Lower Pennsylvanian (Langsettian) Tynemouth Creek Formation of New Brunswick, and discuss its implications for paleogeography, stratigraphy, and paleoecology. This is only the second marine interval found in the entire Pennsylvanian fill of the Maritimes Basin of Canada, the other being recently found in the broadly same-age Joggins Formation of Nova Scotia. Evidence for the new marine transgression comprises an echinoderm-rich limestone that infills irregularities on a vertic paleosol surface within the distal facies of a syntectonic fluvial megafan formed under a seasonally dry tropical climate. Gray, platy ostracod-rich shales and wave-rippled sandstone beds that directly overlie the marine limestone contain trace fossils characteristic of the Mermia Ichnofacies, upright woody trees, and adpressed megafloras. This association represents bay-fills fringed by freshwater coastal forests dominated by pteridosperms, cordaites, and other enigmatic plants traditionally attributed to dryland/upland habitats. The fossil site demonstrates that marine transgressions extended farther into the interior of Pangea than has previously been documented, and may allow correlation of the Tynemouth Creek and Joggins Formations with broadly coeval European successions near the level of the Gastrioceras subcrenatum and G. listeri marine bands. It also helps explain the close similarity of faunas between the Maritimes Basin and other paleotropical basins, if transgressions facilitated migration of marine taxa into the continental interior.

This study provides experimental evidence confirming the significance of microbial mat presence in controlling the spatial and temporal development of chemical microenvironments which become established inside and outside decaying fish carcasses. Dissolved oxygen (DO) and pH profiles were monitored over 1,000 days with microelectrodes positioned inside and adjacent to carcasses. In the vicinity of fish, the DO varied from an oxygenated green upper layer to an anoxic bottom stratum and the pH was alkaline. Inside the fish, the DO and the pH were decoupled during the first week, in that anoxia remained constant and the pH decreased and became acidic. Once covered by the mat, the fish carcass turned oxic and pH returned to alkaline levels. This novel second phase occurred from day 90 to three years and would likely remain after this time. Based on the fish soft tissue quality at the end of the experiment, we discuss whether oxic-alkaline microenvironmental conditions could promote organic preservation and long-term mineralization.