The Lewisporte/Loon Bay area is located within the Central Volcanic belt of Newfoundland. It contains rocks of (?)upper Cambrian to Ordovician in age. The most important group of rocks within this area is the three part Campbellton sequence. The oldest unit of the Campbellton sequence is the Loon Harbour Formation (500-1,000 m thick) composed of mafic volcaniclastics that is conformably overlain by manganiferous cherts of the Luscombe Formation. The Luscombe Formation (370 m thick) is composed of manganiferous cherts that grade upward into highly argillaceous chert. Conformably overlying the Luscombe Formation is the Riding Island greywacke that represents the uppermost unit of the Campbellton sequence. Other units found within the map area include the New Bay Formation, Dunnage melange, Burnt Bay chert - (new), Caradocian age black slate, Goldson Formation and the Botwood Group. The Campbellton sequence is interpreted to underlie the Dunnage melange with the Riding Island greywacke representing a member of the New Bay Formation. The Burnt Bay chert (new) is inferred to directly underlie the Caradocian age black slate and overlie both the New Bay Formation and Dunnage melange. Greywackes correlative with the Sansom/Point Leamington greywackes are not found within the map area.
The dominant structure of the Lewisporte/Loon Bay area consists of a series; of moderate to steeply southeast -plunging inclined to reclined, close to tight, overturned macroscopic folds. Axial surface cleavage of these folds forms a regional penetrative cleavage that affects all rocks within the map area. These folds are interpreted to represent the first major phase of deformation that affected this area (Dl). Various local complications exist such as minor differences in style and orientations of the folds and associated lineations and cleavage. Some of the minor changes in fold orientations may be a result of a series of north-northeast trending sinistral faults that kink and offset cleavage. Important non-penetrative soft sediment structures pre-dating the major regional folding episode are found in several units.
The Carmanville melange may represent the accretionary prism of a west dipping subduction zone of the central volcanic belt of Newfoundland during the late Cambrian to medial Ordovician. Deposition of the Luscombe Formation most likely occurred in the forearc basin of this arc system during its incipient development as nearby arc-related subsea volcanism pumped large quantities of Mn, Fe and Si into the sea water to be precipitated as manganiferous chert. Development of this arc system through time lead to the deposition of the New Bay Formation and Lawrence Head volcanics adjacent to the forearc trough resulting in gravitational slope instabilities and the olistotromic deposition of the Dunnage melange in this forearc trough.
Livaccari, R.F., 1980. Geology of the Lewisporte/Loon Bay Area,
Canada. Unpublished MSc. thesis, State University of New York at
135pp., +xi; 4 folded plates (maps).
University at Albany Science Library call number: SCIENCE Oversize (*) QE 199 L37X
MS thesis (scanned
pdf - 14 MB)
Plate 1 - Geologic map of the Lewisporte-Loon Bay area, Newfoundland, Canada
(coloured geological outcrop map; scale 1:17,100, with pencil modifications) 14.8MB pdf file
(uncoloured geological outcrop map; scale 1:17,100, as in original thesis) 3MB pdf file
Plate 3 - Stratigraphic section of the Luscombe Chert in the Loon Bay area
(uncoloured stratigraphic column; scale 1:120) 0.9MB pdf file
Plate 4 - Stratigraphic section of the Luscombe Formation in the Campbellton area (Old Mill section)
(uncoloured stratigraphic column; scale 1:120) 0.8MB pdf file
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