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The biostratigraphic and depth-related ecostratigraphic significance of a newly discovered graptolite–phyllocarid faunule containing diminutive Rhabdinopora enigma and Anisograptus compactus of early to middle Tremadoc age from the Cooks Brook Formation (Humber Arm Supergroup) is described and discussed. The faunule is identical with the La1 (Lancefieldian) graptolite–phyllocarid-bearing black shale "band" of Victoria, Australia, which was until now only known from two or three outcrops in Victoria and a single bed in northern Norway. This graptolite faunule probably represents a very distal shelf-marginal or open-ocean correlative of the Cap des Rosiers (Quebec) and Green Point (Cow Head Group, Newfoundland) late early Tremadoc anisograptid graptolite biofacies realm.
The biostratigraphic and depth-related ecostratigraphic significance of a newly discovered graptolite–phyllocarid faunule containing diminutive Rhabdinopora enigma and Anisograptus compactus of early to middle Tremadoc age from the Cooks Brook Formation (Humber Arm Supergroup) is described and discussed. The faunule is identical with the La1 (Lancefieldian) graptolite–phyllocarid-bearing black shale "band" of Victoria, Australia, which was until now only known from two or three outcrops in Victoria and a single bed in northern Norway. This graptolite faunule probably represents a very distal shelf-marginal or open-ocean correlative of the Cap des Rosiers (Quebec) and Green Point (Cow Head Group, Newfoundland) late early Tremadoc anisograptid graptolite biofacies realm.
Structural relationships at Cold Spring Pond and the recognition of ophiolitic melange bear on the important questions of timing and style of structural superpositioning of Dunnage Zone rocks above Gander Zone rocks in central Newfoundland. The latest models emphasize ductile shear boundaries and orogen-parallel movements. Previous models proposed west-to-east or head-on obduction of Dunnage ophiolitic rocks across the Gander Zone.At the Dunnage (Exploits Subzone) – Gander (Meelpaeg Subzone) boundary at Cold Spring Pond, discrete, outcrop-size ultramafic blocks and smaller quartzite blocks are randomly distributed, and they are surrounded by, or are embedded in, homogeneous black graphitic shale or phyllite. The ultramafic blocks are typical of nearby Early Ordovician Dunnage ophiolite suites, the quartzite blocks are typical of adjacent Early Ordovician or earlier Gander clastic rocks, and the matrix black shales are similar to those of Middle or Early Ordovician age that occur throughout central Newfoundland. This chaotic mixture of almost coeval lithologies at Cold Spring Pond is interpreted as an olistostromal melange; the Cold Spring Melange. It resembles melanges that are dated as Ordovician elsewhere in Newfoundland.The Cold Spring Melange is overprinted by the full range of structures and metamorphic effects evident in adjacent rocks of the Exploits (Dunnage) and Meelpaeg (Gander) subzones. These include the development of lineations, cleavages, schistosities, zones of ductile shearing, regional metamorphism, and contact metamorphism. The oldest of these effects are interpreted as Silurian, based on isotopic dating in southern Newfoundland.The formation of olistostromal, ophiolitic melange implies disruption of the oceanic tract (Exploits Subzone of the Dunnage Zone), and in the case of the Cold Spring example, juxtapositioning or transport of Exploits Subzone ophiolite suites against or across the supracrustal rocks of the Meelpaeg Subzone (Gander Zone). The age and provenance of Cold Spring components, lack of post-Ordovician components, overprinting structural relationships, and comparison with other Newfoundland melanges all support an Ordovician age of formation. Overprinting relationships indicate that major ductile shears at other Dunnage–Gander zone boundaries postdate initial Dunnage–Gander superpositioning.
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