Ediacaran proximal glaciomarine sedimentation in the Bonavista Peninsula, Avalon Zone, Newfoundland, Canada

Multiple glaciations characterize the Neoproterozoic icehouse Earth period. The Ediacaran Gaskiers Glaciation corresponds to a localized glaciation limited to > 30° paleo-latitude and relatively short duration (i.e., < 1 Myr) compared to the Cryogenian glaciations, but was significantly followed by rapid Ediacaran biota evolution. The Gaskiers Glaciation (ca. 580 Ma) is best characterized in sedimentary successions exposed on the Avalon Peninsula of southeast Newfoundland, where the Gaskiers Formation records deepwater glaciomarine sedimentation overlain and underlain by deep-marine turbidites. Here, we present a sedimentological and stratigraphic analysis of the correlative shallow glaciomarine Mercantile and Trinity diamictites in the Bonavista Peninsula and associated shallow-marine to fluviatile strata of the Rocky Harbour Group. The glacial Mercantile and Trinity diamictites consist of a clast-rich diamictite with abundant faceted, flat-iron, stoss-and-lee, or bullet-shaped clasts, and rare striated clasts (< 1–2%), overlain by a clast-poor diamictite with dropstones, dump, and grounding structures. The proximal glaciomarine Monk Bay Member underlies the Trinity Diamictite and consists of stacked 5- to 15-m-thick upward-coarsening, shallow-marine clastic parasequences with rare dropstones, each capped by a gravel layer up to 2 m thick. The overlying postglacial Kings Cove North Member comprises a distinctive pistachio silicified tuff, a mudstone succession > 50-m-thick, and an uppermost stratal unit of thick-bedded turbidites. Parasequences of the Monk Bay Member are interpreted as deposits of marine-terminating glacial advance and retreat cycles controlled by climate-driven forcing. The gravel-rich transgressive layer capping each parasequence records wave reworking of likely ice-rafted material. These cycles culminated in the deposition of the Trinity diamictite, marked initially by a continuous rainout, followed by finer-grained fallout of ice-rafted debris. Overlying this, the Kings Cove North Member records glacio-eustatic flooding of the shelf, driven by a glacial retreat that marks the end of the Gaskiers Glaciation on the Bonavista Peninsula and coincident glacio-eustatic sea-level rise, which outpaced glacial-isostatic rebound.