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Date of Award

1-1979

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Geology

Supervisor

Professor Gerard V. Middleton

Abstract

Central western Newfoundland is mainly underlain by marine deposits ranging in age from Early Cambrian to Middle Ordovician. These deposits can be geographically separated into two parallel belts: on the east a platform sequence, and on the west a basin sequence. The latter constitutes the Curling Group.

The Curling Group comprises two distinct units: a shale unit below (Middle Cambrian-Lower Llanvirnian), consisting a shale, micritic limestone, limestone breccia, chert, and dolomitic siltstone; and a sandstone unit above (Upper Llanvirnian), consisting of medium- and coarse- grained sandstones plus scarce conglomerates.

In the shale unit shales predominate. Black, green, red, and gray shales are present, which may form units by themselves or appear interlaminated. Contrasted with modern deep-sea shales, the shales in the Curling Group are rich in silica and in magnesium; the black shales show a much higher content in organic carbon than the other varieties; many samples are calcareous or dolomitic.

Thinly-bedded micritic limestones are interbedded with shale. The limestone beds are massive or show parallel lamination; bases and tops are flat and sharp. The limestone is rich in organic carbon. Limestone breccias are abundant locally but overall they are a minor lithologic component. Bedded and nodular chert forms two well developed units in the northern half of the region, but only a few beds in the southern half. Yellow-weathering dolomitic silstones are resistriced to the northern half of the region, where they are abundant; they form thin beds or cyclic, coarsening-upwards, units.

The sandstone unit consists of medium-grained to conglomeratic sandstones, interbedded with scarce shale; conglomerates are scares and contain pebbles and cobbles of limestone and chert. According to bedding characteristics, grain-size, and sedimentary structures, the sandstones have been divided into several types. The main mechanism of deposition of the sandstones appears to have been turbidity currents, but with the concurrence of other mass flow mechanisms in the late stages of depostition, or immediately after deposition. The distribution of sandstone types and the geometry of the deposits, suggest the development of several small submarine fans. Nonetheless, it is not clear whether the fans developed wholly at the base of slope, in the manner envisaged by the submarine fan model, or rather as prodelta fans on a platform and shallow basin.

The sandstones are quartzose wackes with less than 10% feldspar and about 40% rock fragments. Paleocurrent measurements show that provenance was from the east, with the possible exception of the sandstones on Woods Island which may have been derived from the west. Petrography and paleocurrents suggest derivation from the metamorphic Fleur de Lys Supergroup, presently exposed east of the Long Range Mountains, with the possible exception of the sandstones on Woods Island.

The Curling Group is currently interpreted as a nappe with roots to the east of the Long Range Mountains, and now lying on the platform sequence. New graptolite ages, petrography, and lithological correlations, presented in this thesis, suggest instead, that the Curling Group is approximately in place relative to the platform sequence, and that is passes laterally (eastwards) to the platform sequence.

An appendix is included giving details about the graptolite collections from the Curling Group secured during work for the present thesis. The collections were studied by Dr. D Skevington, Memorial University of Newfoundland.

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