Stops Of Interest: Central Newfoundland,Gander - Gander Bay Area
- Unconformity on ultramafic rocks, Little Harbour
- Tilted sedimentary rocks, west of Gander
- Gander Lake near Benton
- Weir's Brook conglomerate
- Ultramafic rocks, Ragged Harbour Brook
- Lumsden granite
- Indian Bay granite
- Dover Fault at Hare Bay
- Gambo lookout
1. Unconformity on ultramafic rocks, Little Harbour
Turn south off the TCH at the sign to
Little Harbour, just west of Gander, and drive down the gravel road to Gander Lake, parking
on the east side of the harbour. Walk east across the rocky beach and take the trail 200 m to
the next small cove.
Both the beach and the trail cross ultramafic rocks which were brought to the surface
from the mantle by faulting in Ordovician time. They were then covered by conglomerate,
derived by erosion of the underlying rock and other parts of the ophiolite suite (see Plate
Tectonics panel). Both the ultramafic rock and the conglomerate that covers it are exposed
on the beach and on the small hill to the right above the cove. The contact between them is
an unconformity that dips to the west, but is difficult to pick out. The ultramafic rock that
you walked over on the path is separated from that in the cove by a fault.
2. Tilted sedimentary rocks, west of Gander
The first outcrop west of Gander (4.3 km) on the
north side of the TCH consists of very fine-grained sandstone and shale that were deposited
on the sea floor during the Ordovician. The originally horizontal sedimentary beds were tilted
and folded during Silurian mountain building; compression of the rock has aligned very fine
mica flakes across the bedding to form a cleavage, so that the rock breaks evenly across the
bedding planes, as well as splitting along them.
3. Gander Lake near Benton
Gander Lake was probably a fiord
before it was cut off from the
sea, but not quite on the spectacular scale of the fiords in Gros Morne National Park. It is
at least 274 m deep at its deepest part, and is surrounded by hills reaching as high as 200 m
above lake level. To have a good view westward along the lake, stop on the long hill situated
on the TCH, 2.6 km east of the Benton turnoff and 10.3 km west of the restaurant at Square
Pond.
Before the last glaciation, the lake basin may have been an inlet of the sea, a part of
Freshwater Bay. When the glacier ice began to melt, a lake formed in the basin, which was
separated from the bay by an ice dam. The rising lake found a new exit northward from its
west end, where the modern Gander River flows out to Gander Bay. When the ice dam
finally melted, it left behind a barrier of sand and gravel, which we see today at the east end
of Gander Lake.
4. Weir's Brook conglomerate
The conglomerate contains a variety of pebbles derived from rocks
that once formed oceanic crust (see Plate Tectonics panel). It can be seen in a roadcut on the
west side of Route 330, 11.1 km north of the entrance to Jonathan's Pond Provincial Park
(13.4 km south of George's Point Brook). The conglomerate was deposited on the sea floor
during Ordovician time. Most of the pebbles are a light grey, coarse-grained, granite-like
rock that often intrudes ophiolite, and is exposed in a nearby quarry. Other pebbles are black
ultramafic rock, dark green, coarse-grained gabbro, white calcite and quartz, red jasper, and
grey siltstone.
5. Ultramafic rocks, Ragged Harbour Brook
These ultramafic rocks were originally a part of the
mantle that underlay the oceanic crust of the Iapetus Ocean (see Plate Tectonics panel). They
were brought to the surface during Ordovician time, when rocks from the ocean floor were
pushed eastward over the top of sedimentary rocks at the edge of the Gondwana continent.
The ultramafic rocks are exposed in a hilltop roadcut on both sides of Route 330, just west
of Ragged Harbour River (14.9 km east of the junction between Routes 330 and 332). They
have been broken along faults, and one part of the exposure has moved relative to the other.
The rocks have a cleavage and some of the original minerals have been replaced by flakes of
talc, a mineral that gives the rock a soapy feel and is used in making talcum powder.
6. Lumsden granite
Newfoundland has many rock types that are attractive in appearance and have
good potential in the building stone industry. One of these rock types is the Lumsden granite,
which occurs over a large area.
To see an example of this handsome and durable stone, go into the community of
Lumsden, and toward the east end turn north on Marine Drive, heading for the south
breakwater. Continue on pavement and gravel to the town wharves, which are protected by
sturdy breakwaters of granite blocks, as well as by an island made of the granite. You can
also walk over large outcrops on the shore. The granite consists of quartz, very large crystals
of pink feldspar (up to 15 cm long), and flakes of black mica.
Polished slabs of Lumsden granite face the walls of the lobby in Memorial University's
Alexander Murray Building in St. John's.
7. Indian Bay granite
An interesting intrusive sequence occurs in a hilltop roadcut on Route 320,
3.4 km north of the turnoff to Indian Bay (10.5 km south of the turnoff for Greenspond). The
main granite here is quite dark in appearance, and consists of quartz, large pale pink crystals
of feldspar, and flakes of black mica. It contains a large block of metamorphosed sedimentary
rock, which was enveloped by the intruding magma and is therefore older. Both are cut by
veins of younger granite pegmatite that contain white mica, light green masses of beryl, tiny
black needles of tourmaline, and small red crystals of garnet, as well as quartz and feldspar.
The minerals forming these rocks have been stretched and aligned during Silurian mountain
building.
8. Dover Fault at Hare Bay
The Dover Fault is a major break in the Earth's crust. To the east of
it, rocks of the Gondwana continent are exposed at the surface (Eastern Zone). To the west,
they are hidden beneath rocks formed in the Iapetus Ocean (Central Zone; see Plate Tectonics
panel). To see the trace of the fault in the town of Hare Bay, turn east off Route 320 at the
Salvation Army Cemetery toward Hare Bay Municipal Park, and stop where the houses end
and the road turns sharply right (1.1 km from the junction)
Look northeast across the bay to the town of Dover, which is built on the Dover
Fault. The expression of the fault is a low area or notch between higher, more resistant rocks
on either side. Gondwanan Late Proterozoic volcanic rocks lie east of the fault, and
metamorphosed Cambrian and Ordovician sedimentary rocks occur west of it. The latter
have been intruded by Silurian and Devonian granite, on which you are standing. Walk up
onto the small hill of granite closer to shore, and notice how its minerals have been stretched
and pulverized by movement in the fault zone, which passes through just east of this hill.
The steep face with fishing stages across the small bay to the east is probably made
of Gondwanan volcanic rocks, but these have been crushed almost beyond recognition by the
fault movements. Along the shore to the west of you are the younger metamorphosed
sedimentary rocks. You can see the latter along the road as you return to the highway.
9. Gambo lookout
Pull off at the signposted lookout on the hill high above Gambo on the west
side, and observe the valley. The U-shaped valley was carved by a glacier (see Glacier
panel). The sand and gravel along the highway on the way up the hill accumulated between
the ice of the glacier and the rocky wall of the valley. As the climate warmed and the glacier
melted, a much larger river than the present one flowed through Gambo Pond to the sea,
carrying meltwater from glaciers farther inland.
The large number of boulders in the riverbed, seen especially at low tide, are called
a boulder lag. They have been left behind after all the finer particles were carried out to sea
by the river.
This series of web pages provides an introduction to the publication
below, which can be ordered from the
Geological Association of
Canada 
Newfoundland and Labrador Traveller's Guide to the Geology
Edited by: S. Colman-Sadd and S.A. Scott, 91 pp. + map, 1994
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