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S.B.Misra, Department of
Geology, Memorial University of Newfoundland, St. John’s, Newfoundland,
Canada
M.S.Thesis, Memorial University., Newfoundland. Canada, p.139., 1969
Geology of Biscay Bay-Cape Race area, Avalon Peninsula,
South Eastern Newfoundland
MISRA, S.B, (1969a)
The Biscay Bay - Cape Race area lies on the extreme southeastern part of the Avalon Peninsula of Newfoundland (Fig. 1-1). The northern and southern boundaries of the area are marked by Lat. 46º 45' and 46º 38', the eastern and western boundaries by Long 53º 2' and 53º 17'.
The area is accessible by road from St. John's which is 100 miles north of Biscay Bay. The northern half of the road (160km) is paved and there is a daily taxi service from Trepassey, the major community of the southern Avalon, to St. John's. One can also reach the area from the Trans-Canada Highway entering from the west via highways 6 and 7. Within the area, there is a secondary gravel road running from Trepassey via Portugal Cove South to the light house at Cape Race.
Most of the coast-line is accessible by foot and can be easily traversed, except at a few places between Drook and Freshwater Point where the cliffs are almost vertical. A boat is helpful for studying these cliff sections. Inland the map-area is barren and easy to traverse in all directions. The most useful traverses are those along the course of rivers where bedrock is locally exposed.
There are three settlements in the area namely Portugal Cove South, Biscay Bay, and Cape Race. The population of Portugal Cove South is 350 and that of Biscay Bay is 76 (1962 census); fishing is the main industry. Only three families live at Cape Race and it is important for telecommunications, transmitting weather signals and for its light house that directs shipping.
Most geological studies on the Avalon Peninsula have been confined to Torbay (Rose, 1952), and Whitbourne (McCartney, 1967) map areas. The area south of Lat 47 has not been mapped. The present study represents the first attempt at separation of the Conception Group from the overlying St.John's Formation in the southernmost part of the unmapped area.
Field work for the present dissertation was completed during a four month period in the summer of 1967. Topographic maps no. I K/II Trepassey East and I K/Trepassey West, prepared by Surveys and Mapping Branch of the Department of Energy, Mines and Resources were enlarged and used for field mapping. Mapping was done on a scale of 1: 10,000 and the coastal geology is shown on four separate sheets (Plates 2-1, 2-2, 2-3 and 2-4). A geological map on a scale of 1: 50, 000is also provided to give a general
picture of the area.
An early reconnaissance study by the author showed that the distribution of rock types in the area was fairly clear. Rocks belonging to the St. John's Formation are exposed east and west of the Conception Group, indicating a regional anticlinal structure. Subsequent mapping confirmed this structural interpretation.
Variations in rock types within the Conception Group were noticed even during reconnaissance studies. Later, it was found that the group is divisible into three lithological units each of formational status; the uppermost unit is fossiliferous and this represents the first discovery of definite Precambrian fossils in Newfoundland, except perhaps Aspidella terranovica Billings, a questionably organic form found in shales of the St. John's Formation.
This dissertation is a general geological study highlighted by the following:
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Discovery of Precambrian fossils
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Three-fold classification of the Conception Group
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Recognition of the St. John's Formation for the first time in this area.
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Evidence of volcanism in the basal part of the St. John's Formation
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Description of well developed turbidity features
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Regional anticlinal structure
Most of the area, a gently undulating plain with a few hills rising to 500
ft. is covered by bog, drift, and marsh with almost no trees. A general idea of
the variation in thickness of drift, which varies from one or two feet to about
thirty feet, may be had by traversing river courses. Outcrops are sparse except
in the coastal regions. Ponds up to half a mile in length, generally irregular and in some cases
oval, are found throughout the area. Many of them were produced by glacial
action and at least two ponds near Cape Race appear to be kettle holes. Boulders
of irregular shape and size, occurring on the marginal parts of the ponds, are
probably washed from till and pushed ashore by local ice due to expansion in the
volume of water after freezing.
Small streams flow from one pond to another over a gently sloping surface.
Their ability to perform geological work is largely dependent on the volume of
the water provided to them by the ponds of their initiation. Such streams start
meandering just after their initiation because of the gentle gradient of the
land and low erosive power of the streams. The main rivers of the area for a
southward radiating pattern and have uncovered the drift to expose bedrock,
especially near the sea. Some of the rivers that constitute the drainage system
are Back river, Portugal Cove brook, Drook River, Briscal Cove River, and
Freshwater River.
The coast-line shows a continuous exposure of bedrock except for local
beaches of boulder, gravel, and sand especially at Biscay Bay, Portugal Cove
South, and Long Beach. Its outline and shape vary in accordance with lithology
and structure. A flat indented coast has developed on the well cleaved friable
shales of the St. John's Formation while a steep indented coast has developed on
the hard, siliceous massive cherts of the lower part of the Conception Group.
The coastal areas where greywackes and argillites are exposed are gently sloping
except where controlled by structures.
Most of the coves and embayments run either along fault planes or fold axes
though glacial action has modified their form in many instances. Examples of
fault controlled valleys may be seen at Drook, near Mistaken Point, and at Cape
Race. A weak zone is locally produced in the crushed axial plane of a tight
folded structure (Fig. 1-2). Erosion of rocks by sea action has resulted in a
small natural bridge on the coast-line between Freshwater Point and Briscal Cove
River.
Some parts of the coast-line have indentations parallel to the strike of the
beds and they have been formed by wave action along bedding planes e.g. the
coast-line on the western bank of Cape Cove near Cape Race. Wave erosion has
also resulted in development of deep vertical gorges along joint planes in cherts of the lower unit of the Conception Group. The material loosened as a
result of compression along the joint planes is carried out to the sea by
retreating waves.
Considering the relative influence of lithology and structure, it is the
latter that plays a decisive role. This is the reason why the coast near Cape
Race is steep even though developed on the St. John's shales and it is gentle
near Pigeon Cove Point even though formed on cherty argillites and cherts. In
the coast-line development, the significance of lithology in the Torbay map-area
(Rose, 1952) and of structures in the Harbour Grace area (Hutchinson, 1953) was
reported, their relative role has not been described in the other parts of the
Avalon Peninsula.
In the map-area, there are three well developed beaches and associated beach
bars, at Biscay Bay, Portugal Cove South, and Long Beach, aligned approximately
in the east west direction. The orientation of the beach bars indicates they are
the result of the waves produced by strong northerly prevailing wind. The beach
bars consist mostly of shingle (Fig. 1-3) which is bounded by pebbles and boulders.
Although most of the material for the development of the beaches is derived from
the drift in the off shore area, some of it is brought also by rivers that meet
at the bay-heads.
All three beaches are bay-head beaches separating a small lagoonal area in
each case from the main body of water. The lagoonal areas in the case of Biscay
Bay and Portugal Cove South are filled with water but at Long Beach it is marsh.
There is no evidence of raised beaches in the map-area.
Glacial drift, chatter marks and other erosional and depositional features
all indicate that the area was glaciated. During the period of glaciations the
hills were flattened and the valleys widened into U-shaped forms that have not
been altered by subsequent drainage.
Plaination of the area is generally complete and flat boulder surfaces have
resulted where the finer material has been washed out, although Brueckner (1967,
Personal communication) is of the view that a boulder surface between Capaheden
and Portugal Cove South is the result of solifluxion. The boulders in the drift
consist of chert, siliceous argillites, siltstone, greywackes and rarely shales, mostly of local origin. Glacial boulders of igneous or volcanic rocks are almost absent but a diorite erratic of approximately 20 ft diameter was seen inland about six miles north of Portugal Cove South.
| Fig. 1-1 |
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Location map of the area showing index of previously mapped areas in the Avalon Peninsula. The area marked by dots is the Biscay Bay - Cape Race area. |
| Fig. 1 - 2 |
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A tightly folded anticline in the Cape Cove Formation between Mistaken Point
and Briscal Cove River. Sea waves formed a cave along the anticlinal axis by
taking the rock material away. This is how an embayment starts along a fold
axis.
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| Fig. 1 - 3 |
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Typical boulder beach of southern Avalon viewed looking east toward Trepassey. The beach material is derived from glacial drift. |
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