Paleoenvironmental analysis of the late Neoproterozoic Mistaken Point and Trepassey formations, southeastern Newfoundland

Abstract

The Mistaken Point and Trepassey formations (Conception and St. John's groups, respectively) comprise a terminal Neoproterozoic, deep-marine succession of fine-grained turbidites and volcanogenic deposits that are part of the Avalonian Terrane. Debris-flow beds, slumped units, the low dispersion of turbidity-current paleoflow directions, and the absence of wave-generated structures together indicate that the sediment was deposited on a deep-water, southeast- facing slope. Channels were not present in the study area. The upward increase in the abundance of slump structures suggests that these units represent toe-of-slope and mid-slope environments, respectively. These units prograded over basin-floor deposits of the Drook and Briscal formations, which have (axial) paleocurrent directions that are orthogonal to the inferred downslope flow that characterized the overlying deposits. Within the Mistaken Point and Trepassey formations, a diverse assemblage of soft-bodied, non-phototrophic Ediacaran organisms is preserved beneath volcanic ash layers on more than one hundred surfaces. Individual fossiliferous surfaces can be correlated up to several kilometres. The felling orientations of frondose fossils indicate that contour currents, as well as up- and downslope currents of tidal and (or) wind-forced origin, influenced the sea floor in the intervals between event beds when the organisms lived. The contour currents may have been responsible for sustaining the organisms in this deep-water setting. The current-produced inclination of the frondose organisms at the time of ash deposition allowed their preservation by preventing the accumulation of ash beneath them.