Stratigraphy and petrology of the Pouch Cove - Cape St. Francis area

Detailed mapping of the Late Precambrian volcanic and sedimentary rocks of the northeasternmost tip of the Avalon Peninsula indicates that these two rock types are largely penecontemporaneous. This fact will require change or addition to the established stratigraphic column as previously determined by regional mapping. However, the studied area can be adequately described within the framework of the established Harbour Main and Conception Groups, and additional areas should be mapped in detail before new stratigraphic names are introduced. -- The total thickness of sequence mapped in the Pouch Cove - Cape St. Francis area is approximately 2800 meters; its base is not exposed and its top is eroded away or removed by faulting. With the exception of minor folds, the sequence dips to the northwest and represents the northwest limb of an anticlinal zone which passes through Shoe Cove (southeast of the map area). -- For descriptive purposes the sequence is divided into lower middle and upper units of volcanic and sedimentary rocks. These unit divisions have only local descriptive significance and are not proposed as formal entities of stratigraphic nomenclature. Typically the sedimentary units consist of turbidite sandstones with subordinate cherts, shales and conglomerates. Numerous acidic and basic flows and tuffs interlayered with the sediments form the volcanic units. Glacio-marine and tillite deposits within the middle sedimentary unit provide an important stratigraphic marker which is tentatively correlated with glacial deposits known within the Conception Group at several other Avalon localities. Facies differences between correlated localities are related to the volcanic eruptions centered around the Cape St. Francis area. -- Intrusions of quartz diorite, rhyolite and diabase are common in the western part of the area. The quartz diorite which occurs only in the southwestern part of the map area possibly is related to the marginal zone of the Holyrood granite batholith. The rhyolite plugs and dikes postdate the quartz diorite and thus may represent the final stage of activity of a relatively degassed granitic magma. Near Cape St. Francis one such rhyolite flow appears to unconformably overlie inclined strata of the upper sedimentary and volcanic units. If verified by further work such an unconformity would imply late Precambrian deformation, uplift and erosion, possibly related to emplacement of the Holyrood granite. This concept provides an interesting basis for further stratigraphic work in this region.