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.
The Precambrian sequences of the Avalon Zone in Canada (southeastern margin of the Appalachian Orogen) are interpreted as a Pan‐African orogenic belt incorporated into the Appalachian Orogen during Palaeozoic times as its southeastern margin. The Precambrian evolution of the Avalon Zone was genetically unrelated to subsequent Palaeozoic evolution. The Avalon Zone shows marked similarities in age, tectonic history, and facies development to the Pan‐African belts adjacent to the West African Craton. Precambrian evolution of the zone began with circa 800 Ma rifting of a sialic gneissic basement and deposition of a Middle Proterozoic(?) carbonate‐clastic cover sequence. Early crustal rifting was associated with localized partial melting and metamorphism. Limited crustal separation led to the restricted development of circa 760 Ma oceanic volcanics. Continued rifting and subsequent closure of these narrow ocean basins led to the eruption of widespread subaerial volcanic suites, block faulting, granite plutonism, and local, late Proterozoic sedimentary basin formation. Precambrian evolution of the zone terminated with the Avalonian Orogeny (circa 650‐600 Ma), a deformational event, the affects of which are most evident locally along the northwestern margin of the zone. The controlling features of the Proterozoic evolution of the Avalon Zone are a series of linear intracratonic troughs and small ocean basins that formed during thinning and separation of the crust by ductile spreading, rupture, and delamination (cf. Martin and Porada 1977). The variation in degree of crustal separation led to subsequent variation in orogenesis during late Proterozoic compression. The zone marks the original westward limit of Pan‐African activity and displays no apparent genetic link with the Appalachian Orogen in Canada until Devonian times.
The Aillik Bay lamprophyric dyke swarm comprises abundant sannaites, plus rarer olivine sannaites, aillikites and carbonatites. Sannaites are characterized by phenocrysts of Ti–Al titansalite plus rarer olivine and phiogopite in a groundmass dominated by pyroxene, biotite, titanomagnetite, and K-feldspar. Minor mineral phases may include apatite, nepheline, analcime, carbonate, rutile, and pyrite. Most sannaites contain well-developed leucocratic ocelli, which are commonly zoned. Olivine sannaites are similar, but olivine (Fo77–85) is more abundant, and ocelli are rarer. Both types occur together as banded dykes, and calculations support the suggestion of a common parental melt.Aillikites have zoned phenocrysts of olivine (Fo71–87) and mica in a groundmass of carbonate, apatite, mica, titanomagnetite, and perovskite. Carbonatite dykes usually exhibit textures with features akin to those of the aillikites. The mineraiogical and geochemical characteristics of the aillikites are distinct from those of kimberlites.It is the intent of this paper to provide new data on these rocks. These data are used to support one of several viable models for the generation of all dyke-rock types by partial melting of LREE-enriched mantle at depths of 90–110 km. Carbonatite dykes are believed to represent the smallest melt fraction but are the latest emplaced dykes. These small melt fractions may have followed structural weaknesses created by earlier lamprophyre magmatism.
A unique occurrence of Mesozoic breccia cut by lamprophyric-carbonatite dikelets, near Makkovik, Labrador is interpreted to relate to the opening of the Labrador Sea. The breccia has been dated by nannofossils; vitrinite reflectance studies show that some time during or after deposition the rock was heated to at least 170 °C. It is suggested that shallow seas extended westward beyond the present Labrador Marginal Trough during early Jurassic time and that the period of late alkaline igneous activity is related to the rifting between Greenland and Labrador that commenced about the middle of the Mesozoic Era.
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