FACIES AND ARCHITECTURE OF A NEOPROTEROZOIC VOLCANICLASTIC SUBMARINE DEPOSITIONAL SYSTEM: THE MISTAKEN POINT FORMATION, NEWFOUNDLAND

The Mistaken Point Formation (MPF) is a 400 M thick late Neoproterozoic siliciclastic-volcaniclastic unit that crops out in the Avalon Zone of Newfoundland, and is recognized as one of the world's leading Ediacaran fossil-bearing deep-water successions. Tectonostratigraphically, MPF sits as the uppermost part of a thick succession of the volcaniclastic submarine fan strata of the Conception Group, deposited at or near the transition of a fore-arc basin to pull-apart basin. Thus, MPF strata can provide insight into whether the basin transformation affected key elements of the local sedimentary environment during MPF sedimentation, including turbidity currents, bottom currents, or hybrid events. The lower Middle Cove Member is defined by medium-bedded, locally fossil-bearing green sandstone and siltstone with abundant volcanic ash; and the upper Hibbs Cove member is defined by medium-to-thick beds of red-green siltstone interbedded with fine-grained sandstone. Eleven facies from fourteen stratigraphic sections were recognized and reveal details of sedimentation processes and paleoenvironmental conditions. The abundance of volcanic ash layers suggests proximity to an island arc and deposition by hemipelagic fall out of volcanic ash from discrete eruptions. The lack of wave-generated structures and erosional features suggest that deposition occurred in a deep-water setting, on a generally flat submarine fan, lacking prominent distributary channels. Architectural analysis from two key outcrops shows tabular stratification, supporting mainly lobe deposition. Preliminary stratigraphic evidence suggests MPF strata were deposited by concentrated density flows and low-energy turbidity currents with an overall upward reduction in sediment concentration and flow energy. This transition of flow energy is exhibited by a gradual decrease in overall sediment grain-size, upward loss of unidirectional current sedimentary structures, and the absence of discontinuous erosional surfaces in the upper Hibbs Cove Member. Ongoing investigations of the facies, paleoflow, and provenance will be used to constrain the conditions of basin reconfiguration and provide environmental context for Ediacaran fossils.