Abstract

Ordovician and Silurian rocks crop out in two main fault-separated belts in eastern New World Island, Notre Dame Bay, Newfoundland. Along Cobbs Arm on the northeast coast, the Ordovician of the northern belt, with tops facing north, has hundreds of feet of lava, agglomerate, and fragmental volcanic rocks with lenses of Maclurites-bearing limestone. Overlying are about 100 feet of calcarenite, and of siliceous argillite with upper Caradocian-Trentonian graptolites, locally repeated. The basal Silurian, 100 feet of argillite with Llandoverian brachiopods and corals, lies on the limestone and siliceous argillite along and east of Rogers Cove; pebbles of the latter rocks are common in the lower part, and a few pebbly lenses have fragments of plutonic rocks as well. The Silurian has thousands of feet of north-facing graywacke, silty argillite, and polymictic conglomerate in the main belts south and north of Cobbs Arm. Sole markings on the lower graywacke beds have a dominant north trend in widely scattered localities on the island; to the north at Herring Neck, Silurian conglomerate (Goldson) has boulders to a foot in diameter, diminishing westward. In western New World Island at Intricate Harbour, Ordovician lavas and cherts are succeeded by several hundred feet of argillite, then by bedded conglomerate (“Hornet”) containing brachiopods in the base that seem to be late Ordovician Cincinnatian or Ashgillian. The main belts seem to be separated by a high-angle fault, but the northerly belt may have been thrust northward over the southerly one, and the fault subsequently tilted northward; thus the rocks in the northerly belt may have been most southerly at deposition.

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