The Mall Bay Formation (Ediacaran) and the Protracted Onset of the Gaskiers Glaciation in Newfoundland, Canada

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Fitzgerald, Danielle M.
Keyword
Mall Bay Formation , Ediacaran , Gaskiers glaciation , Gaskiers Formation , Avalonia , Ediacara biota
Abstract
The Gaskiers glaciation (580 Ma) immediately preceded the appearance of the Earth’s first large, complex, soft-bodied, fossils of the Ediacara biota. The Gaskiers glaciation is generally regarded as being short-lived and confined to the stratigraphic extent of the Gaskiers Formation in eastern Newfoundland, Canada. New research on the underlying km-thick, siliciclastic Mall Bay Formation (ca. 608–580 Ma) in the Avalon Peninsula, including the formerly unstudied Colinet Islands, challenges this interpretation by providing evidence of a protracted onset to the Gaskiers glaciation. In agreement with previous literature, the Mall Bay Formation is here interpreted as a lower slope to basinal turbidite succession. Dolomitic glendonite occurs throughout the uppermost 550 m of the formation and provides evidence for persistent near-freezing bottom waters. Interpreted iceberg-rafted debris in the form of dispersed outsized clasts, frozen aggregates, and sandy lags of ice-rafted debris reworked by contour currents also occurs through the uppermost 550 m of the formation, implying glacier expansion to sea level. Cobble-sized glaciogenic dropstones in the uppermost 150 m of the formation imply that the ice sheet reached the shelf edge by this time. Just below the top of the formation, glaciogenic diamictite debrites were introduced into the slope setting, perhaps signaling the arrival of the ice sheet margin at the shelf edge in proximity to the study area, causing a significant increase in slope instability due to loading of glaciogenic material. Stratigraphic trends suggest a gradual increase in the intensity of glacial activity, peaking with the Gaskiers Formation. This study extends evidence for Ediacaran cold periods over a longer and earlier period and has broader implications for understanding the evolution of Ediacaran glacial systems. Additionally, a prolonged paraglacial state before the appearance of the Ediacara biota implies that their predecessors may have evolved under stenothermal cold-water conditions. Rock flour from glacial activity could have acted as fertilizer, amplifying the production of photosynthetic oxygen and the export of bioavailable phosphorus to the seafloor. Overturning of cold surface water, as recorded by glendonites, may have increased the ventilation of oxygen, providing favorable conditions for the appearance of the Ediacara biota.
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