Structural and stratigraphic relationships in Silurian rocks of the Port Albert - Horwood area, Twillingate - Fogo districts, Newfoundland

McCann, Alan Mervyn (1973) Structural and stratigraphic relationships in Silurian rocks of the Port Albert - Horwood area, Twillingate - Fogo districts, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Port Albert - Horwood area is situated in northeast Notre Dame Bay, Newfoundland. It is underlain by five stratigraphic units of probable Early Silurian age. In the southeast of the area the lower part of the stratigraphic succession differs from that of the northwest. -- The lowermost unit in the southeast, the Lower Formation, comprises medium bedded slates and siltstones with some limestone beds. The over-lying Stoneville Formation consists of a Lower, thin - medium bedded, sandy siltstone and slate Member, a Diamict Member mainly composed of thinly laminated beds containing outsize clasts, and an Upper, dominantly sandy siltstone Member. -- In the northwest the Beaver Cove Formation comprises a Lower, thin bedded silt and mudstone Member, a Conglomerate Member containing graded polymict conglomerate and greywacke units, and an Upper, interbedded siltstone and greywacke Member. -- Commonly andesitic, interbedded agglomerates, flows and tuffs of the Port Albert Formation conformably overlie the lower part of the succession in the northwest and southeast of the area. The overlying and uppermost unit, the Dog Bay Formation, comprises a Lower, thin bedded, siltstone Member, a Tuffaceous, massive bedded, sandy siltstone Member and an Upper, medium to fine sandstone Member which disconformably overlies the Port Albert Formation in the northwest. -- Rhyolite and diabase dykes are sometimes composite and intrude rocks of the central part of the area. Rhyolite fragments in the Dog Bay Formation suggest that intrusion was in part contemporaneous with sandstone deposition, and except for a lamprophyre dyke, these intrusions predate the regional deformation. -- Three periods of deformation, of probable Mid-Devonian (Acadian) age, are recognised. The regional, first deformation produced a zonally developed, sub-vertical, penetrative cleavage in association with folding of differing styles. This zonal development may be controlled by a rigid, probably intrusive body close to the surface beneath the central parts of the area. The second and third deformations produced flat-lying and steep kink-bands and crenulations respectively, of the penetrative cleavage and bedding. The Reach Fault is a major, probable strike-slip displacement which parallels, the regional structural trend. West trending tear faults have sinistral and dextral offsets. -- The Diamict Member of the Stoneville Formation is of probable glacio-marine origin and may have been deposited in part by ice-rafting. The Member is compared to similar deposits of Late Ordovician - Early Silurian age which occur in Nova Scotia, Western Europe and Northwest Africa, and to which it may be indirectly related.

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