LATE NEOPROTEROZOIC (EDIACARAN) STRATIGRAPHY OF AVALON ZONE SEDIMENTARY ROCKS, BONAVISTA PENINSULA, NEWFOUNDLAND

New mapping has resulted in a detailed and revised stratigraphic subdivision of the late Neoproterozoic (Ediacaran Period) marine sedimentary succession in the eastern Bonavista Peninsula. The oldest exposed unit, assigned to the Drook Formation of the Conception Group, is the Shepherd Point member, characterized by mainly parallel-laminated, siliceous siltstones, mudstones and fine-grained sandstones. The overlying, fossiliferous Mistaken Point Formation (upper Conception Group) is divided into a lower, siliceous and variegated tuffaceous, silt- to fine-sand-rich Goodland Point member and an upper, grey to red, argillaceous Murphy’s Cove member. The conformably overlying Trepassey Formation (lower St. John’s Group) is divided into a lower, grey-green argillaceous Catalina member and an upper, sand-rich Port Union member. The upper Trepassey Formation rocks are overlain conformably by thin- to medium-bedded, dark grey shales and disrupted or slumped units of sandstone and shales of the lower Fermeuse Formation, designated Back Cove member. Laminae and thin beds of ash tuffs are a prolific and diagnostic part of the rock record of the eastern Bonavista Peninsula. The tuffaceous volcanicity is recorded at multiple stratigraphic levels throughout the marine section; fossiliferous beds are everywhere associated with thin tuff units. The known lateral and vertical extent of Ediacaran biota in the eastern Bonavista Peninsula has been extended significantly. More than twenty separate fossil localities from multiple stratigraphic levels throughout the late Neoproterozoic marine succession have been identified. The vertical range of Charnia-related discs and associated frond-like forms, spindleshaped fossils, bush-like fossils and radial forms in the Bonavista Peninsula succession is now known to extend throughout the Mistaken Point Formation, upward through the Trepassey Formation and into the Fermeuse Formation. Morphological variants of Aspidella occur throughout the same stratigraphic range, but extend higher into the upper St. John’s Group than the other Ediacaran forms. New mapping of the upper Rocky Harbour and overlying Crown Hill formations of the Musgravetown Group in the western Bonavista Peninsula has established locally developed to regionally extensive facies subdivisions of potential member status within the thick, shallow-marine to terrestrial succession. Some units may correlate with significant parts of the Signal Hill Group, 150 km farther east, thus highlighting the large dimensions of the late Neoproterozoic basin. The basin fill is characterized by pronounced east-to-west facies variations related in part to syn-sedimentary faulting. The development of laterally consistent, reduced, sulphide-bearing (and variably cupriferous) grey beds within the thick redbed succession was an important aspect of basin evolution.