Newly found fossils in the Conception and St. John's groups of the Bonavista Peninsula considerably extend the known geographic distribution of the Ediacaran fossils in Newfoundland. They occur in deepwater sediments and are preserved as epireliefs, forming census populations underneath volcanic ash layers throughout a more than 1 km thick turbiditic sequence. the exposed fossiliferous units comprise the Mistaken Point, Trepassey, Fermeuse, and Renews Head formations. the remains are tectonically deformed, with long axes of elliptical discs aligned parallel to cleavage strike; shortening of originally circular bedding surface features is on the order of 30-50% (averaging ~35%).The assemblage includesAspidella, Blackbrookia, Bradgatia, Charnia, Charniodiscus, Fractofusus, Hiemalora, andIvesheadia.These occur throughout the succession, withAspidellabeing the most common genus, followed byCharniaandCharniodiscus.Four new taxa are described, with candelabra-like fossils with aHiemalora-like base referred toPrimocandelabrum hiemaloranumn. gen. and sp., bush-like fossils toParviscopa bonavistensisn. gen. and sp., ladder-like fossils toHadryniscala avalonican. gen. and sp., and string-like fossils with basal disc toHadrynichorde catalinensisn. gen. and sp. the remains also include dubiofossils. The stratigraphic ranges of some taxa on the Bonavista Peninsula are longer than previously reported from the Avalon Peninsula, withFractofususspindles present in the Trepassey Formation,Bradgatia, Charnia, Charniodiscus, andIvesheadiareaching as high as the Fermeuse Formation, andAspidellaextending into the middle of the Renews Head Formation. the spindles in the Trepassey Formation are comparable to those found mainly in the stratigraphically older Briscal Formation on the Avalon Peninsula.

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The following new U–Pb dates are provided for zircons from volcanic and intrusive rocks of the Avalon Terrane of Newfoundland: Burin Group ophiolite (Wandsworth pegmatitic gabbro), [Formula: see text]; Marystown Group ash-flow tuff, [Formula: see text]; Rock Harbour Group rhyolite clast in conglomerate, [Formula: see text]; Harbour Main Group ash-flow tuff, [Formula: see text]; Harbour Main Group flow-banded rhyolite, [Formula: see text]; porphyritic rhyolite plug intruding Harbour Main Group, 632 ± 2 Ma; Holyrood Granite, [Formula: see text]; rhyolite dyke, Harbour Main Group, [Formula: see text]; and welded ash-flow tuff, "Grand Beach porphyry," [Formula: see text]. All of the dated zircons are simple, single-age populations with no trace of inheritance. These dates confirm that the ophiolitic Burin Group represents an older and separate event that correlates precisely with the Bou Azzer ophiolite of Morocco and that the Rock Harbour Group does not represent continental volcanism that preceded that event. The Rock Harbour, Marystown, and Harbour Main groups and the Holyrood Granite (632–608 Ma) are all part of the younger 650–550 Ma pulse of Pan-African orogenesis that affected a broad area extending through Africa, Asia, western Europe, southern England and Wales, and eastern North America. However, a shortage of high-precision dates throughout these terranes precludes very exact correlations and thus very exact interpretations in terms of specific tectonic or magmatic events. Although these dates require some revisions in the stratigraphy of the Newfoundland Avalon Terrane, they do not support suggestions that the Avalon Terrane comprises a "collage of suspect terranes." The age of the Grand Beach porphyry (394 Ma) places it squarely with the Acadian granites of the Appalachians and removes it from consideration as part of the Marystown Group.

Distinct groupings of late Neoproterozoic tectonomagmatic and depositional events at 760 Ma, 685-670 Ma, 635-590 Ma and 590-545 Ma are recognized within the peri-Gondwanan margin of the Newfoundland Appalachians. This pre-Iapetan orogenic activity resulted in amalgamation of distinctive tectonic packages prior to deposition of a shale-rich platformal cover of terminal Neoproterozoic to Early Ordovician age, east of the Appalachian central mobile belt. The late Neoproterozoic successions chronicle, in part, the development of segments of a larger peri-Gondwanan orogenic system that was dispersed prior to, and variously reworked during, the protracted evolution of the southern Iapetus Ocean.The oldest orogenic events yet identified in the Newfoundland Avalonian belt occurred at and prior to 760 Ma and are manifest by the accumulation of submarine mafic volcanic rocks, the emplacement of oceanic gabbros, and the associated deposition of unique clastic and carbonate olistostromes. As early as 685 Ma, arc-related volcanic and associated arc-root plutonic complexes of felsic to intermediate composition developed along the orogenic belt in an overall contractional environment. These complexes, which are preserved together with amphibolite gneisses and associated intrusive rocks, were inhomogeneously deformed and then uplifted prior to the onset of widespread (635-590 Ma) volcanism, marine sedimentation, and coeval calc-alkaline plutonism, the products of which were deposited upon or emplaced into the 685-670 Ma basement. Locally, pre-600 Ma rocks have been inhomogeneously deformed prior to a complex volcanic, plutonic, and structural event (590-545 Ma), partly extensional and partly contractional in nature, during which the classical Ediacaranbearing and younger sedimentary successions of the Avalonian belt accumulated.Diverse tectonic elements that evolved prior to the Cambrian were variably dispersed at several times, perhaps most significantly during late Neoproterozoic orogenesis. Pronounced terminal Neoproterozoic and early Paleozoic tectonothermal events were recorded on the inboard Iapetan margin of the belt, while elsewhere, terminal Neoproterozoic through Cambro-Ordovician platformal sediments were deposited, in most cases without apparent hiatus. These contrasting peri-Gondwanan terranes were reamalgamated and again dispersed during complex transpressional orogenesis of Silurian age related to closure of the Iapetus Ocean, and ensuing collision of Gondwanan and Laurentian elements of the Appalachian orogen.

In 1986, 1181 km of marine seismic reflection data was collected to 18–20 s of two-way traveltime in the Gulf of St. Lawrence area. The seismic profiles sample all major surface tectono-stratigraphic zones of the Canadian Appalachians. They complement the 1984 deep reflection survey northeast of Newfoundland. Together, the seismic profiles reveal the regional three-dimensional geometry of the orogen.Three lower crustal blocks are distinguished on the seismic data. They are referred to as the Grenville, Central, and Avalon blocks, from west to east. The Grenville block is wedge shaped in section, and its subsurface edge follows the form of the Appalachian structural front. The Grenville block abuts the Central block at mid-crustal to mantle depths. The Avalon block meets the Central block at a steep junction that penetrates the entire crust.Consistent differences in the seismic character of the Moho help identify boundaries of the deep crustal blocks. The Moho signature varies from uniform over extended distances to irregular with abrupt depth changes. In places the Moho is offset by steep reflections that cut the lower crust and upper mantle. In other places, the change in Moho elevation is gradual, with lower crustal reflections following its form. In all three blocks the crust is generally highly reflective, with no distinction between a transparent upper crust and reflective lower crust.In general, Carboniferous and Mesozoic basins crossed by the seismic profiles overlie thinner crust. However, a deep Moho is found at some places beneath the Carboniferous Magdalen Basin.The Grenville block belongs to the Grenville Craton; the Humber Zone is thrust over its dipping southwestern edge. The Dunnage Zone is allochthonous above the opposing Grenville and Central blocks. The Gander Zone may be the surface expression of the Central block or may be allochthonous itself. There is a spatial analogy between the Avalon block and the Avalon Zone. Our profile across the Meguma Zone is too short to seismically distinguish this zone from the Avalon Zone.