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From
Professor Donaldson's course
in the Learning in Retirement Seminars at Carleton.
A note
on conservation
Help protect classic features in outcrops for others to appreciate
— especially fossils — by observing and photographing
only. Please restrict collecting to loose slabs, leaving in-place
fossils and structures for others to enjoy... many fossil localities
around Ottawa have already been stripped of the best fossils. Some
jurisdictions apply severe penalties for collecting without a scientific
permit. Check out construction sites: excavations in the local Billings
Shale, for instance, commonly provide fantastic pyritized trilobites
and
orthocones.
Trip 1: Nepean
Sandstone (Cambro-Ordovician): Stony Swamp Conservation Area
Drive south on Richmond Road less than 1 km past the T-junction with
West Hunt Club Road. Pull into the gravel parking lot on the right
marked with a blue P6 sign, just below the transmission line cross-over.
Walk west along the footpath, which leads to a boardwalk over a marshy
area. The path then swings north among cedar trees to an open expanse
of flat-lying white bedrock.
Stop1 This large outcrop displays crossbedding and ripple marks
on a single bedding surface. Loose blocky slabs provide a view of
composition, texture and parallel laminations (bedding) in the third
dimension.
This locality illustrates preservation of:
- original
horizontal bedding: same attitude as when deposited as loose sand
- primary
structures: bedding, lamination, parting, crossbedding, ripple
marks
- prominent
secondary structure: joints, which here display consistent patterns
(they occur in "sets")
- numerous
parallel linear groups of glacially formed chatter marks, near
the north side of the outcrop
The
rock is an extremely mature siliciclastic sandstone, composed almost
entirely of quartz grains held together by intergranular quartz
cement — in most sections it breaks through the framework grains
(i.e. it is well-indurated).
The texture is medium to coarse grained, well-sorted, and the framework
grains are very well rounded and highly spherical. Bedding is marked
by slight grain-size and colour differences.
Directional data
- symmetric
ripple marks seen on bedding may be shore-parallel
-
asymmetric ripple marks and the arcuate traces of crossbedding
indicate that paleocurrents were moving the unconsolidated sand
southward, probably in a shallow braided stream system at the
time of deposition (about 500 million years ago)
- several
sets of chatter marks record the movement of ice, also southward,
but much later during the Pleistocene Ice age, which ended as
recently as 8000 years ago.
Stop
2. Nepean-March Formation Contact Kanata Drive, behind Wal-Mart,
Centrum Centre
Drive north on Richmond Road, which arcs slightly to the left where
it merges with Moodie Drive. Cross Robertson Road, under the railway
overpass; stay right to get on the ramp for Hwy 417 West (Queensway).
West on Hwy 417 past March Road; exit at Terry Fox Drive North.
Turn right at the stoplight to enter Centrum Shopping Centre. At
Chapters, turn right past the "Tire & Lube Express"
of Wal-Mart; turn left at the stop sign (Earl Grey Drive). At the
intersection with Kanata Avenue, park in the wide paved rectangular
area on the left.
Although the lowermost sandstone beds here are part of the same
formation seen at the first stop (Nepean), we gain a new perspective.
Whereas the first locality presented a record at a particular instant
in geologic time, these outcrops provide stratigraphic sections,
recording successive events through time.
The few metres of section, seen here in vertical cuts, record thousands
of years of sand deposition, followed by burial, lithification and
uplift. In the section behind Wal-Mart, joints provide 3-D views
of crossbeds, so paleocurrent directions can be established. Several
joint faces are covered with oxidized crystals of marcasite, a polymorph
of pyrite. At the top of the section, look for ripple marks and
glacial striae. Pseudorainprints are abundant here (how do we know
that they are not real rainprints?
On the east side of Kanata Avenue, look for trace fossils in the
topmost, carbonate-rich (and hence differentially weathered) beds.
The flanking blocks of Nepean and March Formation show excellent
ripple marks, crossbedding, dewatering structures and biofilm structures;
some limestone blocks contain fossils and show extensive bioturbation.
The beds are tilted westward on the east side of the road, but are
nearly horizontal on the west side (behind the Wal-Mart store).
This relationship appears to be due in part to draping of the sandstone
beds against an "island" of Precambrian basement rock
to the east (the paved path above the staircase is bordered by numerous
outcrops of Grenville gneiss and granite).
TRIP 2 Precambrian
gneiss of the Grenville Province: Erskine Johnson Elementary School
Drive west on Queensway (417) past Moodie Drive. Take
March Road exit to Kanata. At the lights, continue straight through
on Campeau Drive, turning right on Teron Road (first intersection
to the right beyond lights), left on Beaverbrook, then right on Varley
Drive. Follow this curving under-repair road past Georges Vanier Catholic
School to Erskine Johnson Elementary School. Pull into parking lot
past the school, and park in a spot near the colourful playground
items.
Examine the cluster of glacially scoured outcrops of gneiss behind
the school temporary buildings. Radiometric dating methods show that
these rocks, which are part of the Grenville Province, are more than
1.0 billion years old. Because the Paleozoic sandstones of the Nepean
Formation, as well as all younger sedimentary strata, were deposited
above them these Precambrian rocks are commonly referred to as "basement
rocks". These
outcrops of metamorphic rock with minor igneous intrusions display
classic roche moutonnée shapes that indicate southward movement
of the Pleistocene ice sheet.
things to note:
- steeply
dipping, folded foliation in these coarse-grained gneisses
- mineral
lineation parallel to fold axes
- pegmatite
dykes cutting the gneiss; some contain very large crystals of
quartz and feldspar
- dykes
of aplite (sugary textured granite) and of diorite (dark gray,
fine
grained; rich in mafic minerals)
- mafic
inclusions, boudins, and large crystals of garnet
TRIP 3
Ordovician Limestone, Ottawa Group: Parc Brébeuf, Gatineau
Drive north on Island Park Drive, continuing over
the Champlain Bridge to reach the north side of the Ottawa River.
Turn right on Rue Brunet (first stoplights), go past Parc Moussette,
and turn right on Rue Bégin. Turn right again on Rue Maricourt,
and park where permissible (there is a parallel-parking area where
Rue Maricourt curves sharply away from the river).
The tapered base of the Brébeuf statue contains at least
500 cobble stones representative of the many rock types within the
Grenville Province. Their clean polished surfaces, reflecting derivation
from a gravel pit in Pleistocene outwash, provide an opportunity
to study the mineralogy, textures and structures (foliation, lineation,
intrusive contacts) typical of Precambrian terrane to the north.
Along the shore are bedrock platforms of gently dipping limestone
rich in a variety of fossils: corals, stromatoperoids, cephalopods,
gastropods, mollusks, brachiopods, crinoids, bryozoa, trace fossils,
and fragments of trilobites. The artistically arranged limestone
blocks in the retaining walls display a wide range in grain size,
as well as primary structures such as bedding, ripple marks and
crossbedding. Secondary structures include joints and stylolites.
Note how features are accentuated on
weathered surfaces.
To the east, a large boulder of Precambrian gneiss marking the Voyageurs
Portage shows excellent folded foliation in three-dimensions. Immediately
north, Rue Bourget has a curb along the south side consisting of
two rows of stone paving blocks. Most are Nepean sandstone (set
both on edge and parallel to bedding), but a few are granite. Some
of the sandstone blocks display an unusual secondary structure,
Liesegang banding. Walk back along
Rue Bourget to the parking area. Walk east along the bike path (look
out for speeding cyclists and rollerbladers) around the transformer
station to its northeast fenced corner. Take the last gravel footpath
to the east (just before the T- junction in the bike path) out to
the south shore of an inlet on the Ottawa River. Excellent views
of folds in limestone beds can be seen along the northeastern shore
of this inlet.
Drive north on Rue Bégin to Taché Blvd, and follow
Taché east to Chaudieres Bridge. Drive partway across this
bridge, turning left on Middle St. to access Victoria Island. Park
in the lot opposite the old generating station, and walk past the
Ottawa-Hull Navy Association building to an outcrop on both sides
of the downhill-sloping road beyond the Cul de Sac sign.
Megaripples are evident on coarse clastic flat-lying beds of Ottawa
Group limestone. Interbeds of carbonate mud show abundant trace
fossils both perpendicular & parallel to bedding. Shelly fossils
include bryozoa, brachiopods, crinoids and orthocone cephalopods.
Crossbedding and stylolites are locally prominent, as are desiccation
cracks, which indicate intermittent exposure.
TRIP
4 Hog's Back Falls
From campus, head to the locks on the west side
of the library and walk south (left) along the canal for about 10
minutes until you reach Hog's Back Road. The falls are on the left.
Hog's Back Falls;
view to the north-northwest (JAD)
Examine
the map below and find the symbol placed on the large island near
the bridge. Visualize how the symbol portrays strike, which is the
intersection of inclined layers (e.g., bedding) with horizontal
surfaces (here conveniently provided by the pools of water). The
direction of dip is indicated by a short tick on the side of the
long strike line symbol. Look at other parts of the exposed bedrock
and add strike and dip symbols of your own. The rocks are folded,
so you should see systematic pattern emerge.
On
your copy of the map, circle where the exposed part of a fault surface
displays parallel linear marks. These marks parallel the direction
along which the blocks moved relative to each other when the fault
was active. Was the movement mainly horizontal or vertical?
Look for fossils in the stone blocks used to construct the walls
of the NCC gazebo. Can you recognize any fossils that you saw during
our walk along the Rideau River last week?
Walk along the river course pathway to view erosion, clusters of
boulders that have been concentrated by removal of the finer-grained
components of glacial till, and upstream imbrication. Position them
on the sketch map.
TRIP 5 Building
Stones and Monuments of the National Capital region
A variety of rocks have been used as building stone
in downtown Ottawa. Next time you're downtown or in the Market area,
look at the following buildings from a geological perspective.
Parliament
Buildings
Nepean Sandstone, Potsdam sandstone,
Wallace Sandstone, Ohio Sandstone, Tyndall Limestone, Ottawa Limestone,
Missisquoi Black Marble (actually limestone), Stanstead Granite,
Grenville Marble, Tennessee Marble
Paving
stones around Centennial Flame
Tadoussac Granite Gneiss
Entrance
to stairs descending to locks
Deschambeault Limestone
Chateau
Laurier and Old Union Station
Stanstead Granite, Indiana Limestone
British
High Commission
Baltic RapakiviGranite (ovoid feldspars with halos),
black Norwegian Anorthosite
Lord Elgin Hotel
Deschambeault
Limestone
CS CO-OP building, Hope building, Sparks Street
Italian Marble
E.R. Fisher, Sparks Street
Serpentine Marble
TD Bank
Sparks Street
Grenville Marble (sand blasted)
Scotia Bank
Sparks Street
Adair Marble, Eramosa Marble (both actually dolostone)
Bank of Montreal
Sparks Street
Queenston Limestone, Stanstead Granite, Cararra
Marble. Mexican Onyx (Travertine)
The Shoe Box, Le Papillon
Sparks Street
Lac St. Jean Anorthosite
Hallmark
Sparks Street
Black Italian Marble
Wellington Building, National Press Club
Stanstead Granite,
Indiana Limestone
Langevin Block
Wallace Sandstone
Dimension
stones commonly used in the Ottawa-Gatineau Region include
Nepean
Sandstone (Cambro-Ordovician, Kanata)
Potsdam Sandstone (Cambro-Ordovician, Kingston, New York
State)
Wallace Sandstone (Carboniferous, Nova Scotia)
Old Red Sandstone (Devonian, Scotland)
Ohio Sandstone (Berea Formation, Mississippian, Wakeman,
Ohio)
Tyndall Dolomitic Limestone (Ordovician, Garson, Manitoba:
contains Receptaculites, Maclurites, other gastropods, burrows,
orthocones, and corals)
Ottawa Limestone (Ordovician, local)
Cobourg Limestone (Ordovician, local)
"Adair Marble" (actually dolostone: Amabel Formation
- Silurian, Wiarton, Ontario)
Eramosa Dolostone (Silurian, Wiarton, Ontario; stromatolitic;
used mainly as "Waterfall Rock" in landscaping)
Queenston Limestone (Niagara)
Deschambault Limestone (Lowville, Quebec)
Missisquoi Black Marble (actually limestone, Philipsburg,
Quebec)
Indiana or Salem Limestone (Mississippian, Bedford, Indiana:
main source of dimension stone in USA)
Tennessee Marble (Knoxville, Tennessee)
Italian Marble, Carrara Marble
Mexican Onyx (travertine)
Tadoussac granite gneiss (Precambrian, Saguenay, Quebec)
Stanstead Granite (Beebe, Quebec)
Vermillion Bay Granite
Lac St. Jean Granite
Standstead Granite
Peribonka Granite (actually gabbro, Lac St. Jean)
Tadoussac Granite Gneiss
Rapakivi Granite ("Baltic Brown", Finland)
Labradorite Anorthosite ("Norwegian Blue Pearl"),
Larvakite (Labradorite Syenite)
Serpentinite
Vermont Slate
Verde Antique (Roxbury, Vermont)
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