The Mall Bay Formation (Ediacaran) and the protracted onset of the Gaskiers glaciation in Newfoundland, Canada

Abstract

The Gaskiers is the oldest Ediacaran glaciation and thus represents Earth’s first icehouse since the end of the Snowball glaciations that characterized the Cryogenian world.Age bracketing of the 300-m-thick marine tillites of the Gaskiers Formation to 581–580 Ma has previously been taken as an indication that the Gaskiers glaciation was short-lived. New studies of the underlying ∼ 1000-m-thick Mall Bay Formation on islands offshore of Newfoundland, Canada, reveal a hitherto unrecognized protracted onset to the Gaskiers glaciation that nearly triples its known stratigraphic thickness and elucidates progressive stages in the development of an Ediacaran glaciation.The Mall Bay Formation consists predominantly of mudstone and fine-grained sandstone deposited in a deep-water, SW-NE trending, turbidite-dominated axial basin with abundant input of volcanic ash.No evidence of glacial activity was observed in the lower half of the Mall Bay Formation.Cold-climate proxies first appear approximately 550 m below the top of the formation in the form of glendonites (stellate pseudomorphs of the cold-water carbonate ikaite) that attest to cold bottom waters and hypothesized downwelling, while the preservation of outsized clasts, frozen aggregates (till pellets), and coarse sandstone lags near the same stratigraphic level imply the presence of icebergs floating above the depositional environment.Evidence for cold bottom waters and an influx of sediment from floating ice persists to the top of the Mall Bay Formation. There is a progressive stratigraphic increase in the abundance and size of iceberg-rafted debris in the formation that implies increasing proximity of glaciers to the study area.Pebbles showing dropstone features first appear 120 m below the top of the formation, and the lowest bed of pebble diamictite occurs 4 m below the top of the formation.The overlying cobble to boulder diamictite of the Gaskiers Formation likely represents the Gaskiers glacial maximum when glaciers reached the local shelf edge and glacially derived debris poured down the slope into the axial, turbidite-dominated Avalon Basin.The Ediacaran Gaskiers glaciation shows little similarity to the older panglacial Snowball glaciations of the Cryogenian but exhibits paraglacial features similar in many respects to the Paleozoic glaciations of Gondwana that followed it.