The New World Island Complex and its relationships to nearby formations, north-central Newfoundland

Reusch, Douglas N. (1983) The New World Island Complex and its relationships to nearby formations, north-central Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The New World Island Complex consists of chaotically mixed volcanic and sedimentary rocks in a 1 km wide belt that extends 30 km southwestward from Cobbs Arm, on eastern New World Island, centrally located in the Dunnage Zone of the Newfoundland Appalachians. The complex comprises four lithic units, locally preserved in partial stratigraphic sections: Squid Cove Volcanics - basalts (non-orogenic tholeiites), autoclastic breccias, red shale, limestone, pyroclastic breccias and tuffs (Arenigian to Llandeilian); Cobbs Arm Limestone (Llandeilian); Rodgers Cove Shale - interbedded black shale and chert (Caradocian); and Muddy Cove Clastics - quartzitic greywackes, shales, polymictic conglomerates, and shaly conglomeratic breccias (Ashgillian to Llandoverian). -- Imbricated slices of competent volcanic rocks over 3 km long are separated by mylonitic and clastic shear zones. Intervening sedimentary slices contain boudinaged interbeds (1 cm to 100 m across) and tight fold hinges. These pass laterally into melange with discrete blocks of volcanic rocks, sandstones, and locally black shale in a sedimentary matrix. The blocks have sheared margins in places, and one large slab of Ordovician limestone is deeply penetrated by Silurian shale. Angular fragments in shaly conglomeratic breccias include black shale and limestone derived from the local stratigraphic section in adjacent fault blocks; one limestone clast is inhomogeneously deformed. -- The New World Island Complex is followed to the northwest by sandstones and conglomerates (Crow Head Formation) of Upper Ordovician to Silurian age. These are locally continuous with Caradocian black shale and older rocks in the complex. Farther northwest, pre-Caradocian volcanic rocks like those in the New World Island Complex (Clarkes Cove Volcanics) are unconformably overlain by coarse Silurian conglomerates (Indian Cove Formation) in another structural slice. The New World Island Complex structurally overlies Silurian conglomerates (Milliners Arm Formation) to the southeast. Compared to sediments of the same age in the third slice to the northwest (Indian Cove Formation), these were deposited farthest from a source area that lay to the northwest. -- Steeply dipping faults in the New World Island Complex are locally folded by folds related to cleavage, and elsewhere truncate folds of the same generation. -- The New World Island Complex is viewed as having formed by syn-sedimentary thrusting which juxtaposed Ordovician rocks with unlithified Silurian sediments, incorporated them as blocks within sedimentary matrix, and telescoped a southeast-facing basin.

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