Botanical Beach Field Trip – Nov 2, 2013 Camosun College Geos 100 & 110 Classes.
Guide by Dr. Tark Hamilton
Instructions: Bring Raingear, jacket, hat, sturdy boots, water, lunch and hand
lenses, acid bottles hammers as available. The provincial park does not allow
sampling but roadside sampling is fine. Ensure you have handed in a signed wavier
for this term. Drivers need a valid license and passengers should split gas costs.
Meet at Camosun to depart from Wilna Thomas parking lot for 7:30 AM Nov 2, return
~2:30 PM
Secondary meeting place Sooke Mall near A&W at 8:15 to consolidate cars and proceed
directly along West Coast Road to Port Renfrew and Botanical Beach. Meet in the NE
(exit end) of the parking lot and take the trail to the East end of the Beach too examine
outcrops before going up to the wave cut platform and tide pools.
On the way back we will stop near Minute Creek, Loss Creek Bridge, Jordan River and
other roadside outcrops to see different facies of the Leech River Schist, Metchosin
Volcanics and Sooke Formation.
En route to Jordan River note the geological shrine at Point-No-Point (also known as
Glacier Point). There used to be a sign here recording the little-known fact that Agassiz
worked out the glacial theory here.
I Background on bedrock Geology and the main formations we will see today.
The Sooke Formation (Late Eocene to Oligocene)
Along the West Coast of North America, and a short distance eastwards onto the
continent are a series of small Tertiary Basins. There are two dominant ages: Middle to
Late Eocene like the volcanic rocks of the Metchosin Igneous Complex, and Oligocene to
Early Miocene. Along the edge of Vancouver Island sediments of this latter episode are
called the Tertiary Carmanah Group comprising the Hesquiat Formation north of Port
Renfrew and the Sooke Formation to the south and East. There are also vast thicknesses
of equivalent aged strata in the Olympic Mountains of Washington and west of the
Cascades in western Oregon. You may have already seen the Sooke Formation in East
Sooke Park and at Muir Creek. It occurs sporadically along the coast of the Juan de Fuca
Strait and forms many of the intertidal exposures of sandstones and conglomerates from
East Sooke Park all the way to Botanical Beach. We will see coastal and shallow marine
facies. These coarse clastic rocks are porous, permeable and partially cemented by calcite
and iron oxy-hydroxides and appears as buff to grey beds up to several meters in
thickness. The Sooke Formation rests upon either the Metchosin Igneous Complex (MIC)
or the Leech River Complex (LRC) with an angular unconformity. As such it is an
overlap or successor basin that postdates the accretion of the seafloor rocks of the
Farallon plate (the Siletzia Terrane) from southern Vancouver Island to Mendocino
Califormia.
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Marine fossils of gastropods, pelecypods, oysters are common as is coalified and teredo
bored wood. The oldest known ancestor to all of the toothed whales and dolphins
(Conecetus sookensis) was found in correlated coastal exposures, as originally reported
by Russell, 1968. In a more recent article, (Barnes et al, 1994) described this as the most
primitive North American aetiocetid. A more derived, Late Oligocene species,
Chonecetus goedertorum Barnes and Furusawa, new species, from the Late Oligocene
Pysht Formation, Olympic Peninsula, Washington, has the primitive placental
mammalian tooth count of 11/11. While baleen whales were quite diverse at this time, the
Oligocene still shrouds the mysterious origin of the toothed whales.
The largest expanse of these rocks underlies the length of the Juan de Fuca Strait as an
East-West trending synclinorium holding up to 1.4 kilometre thickness of sedimentary
section, as imaged by seismic reflection profiles. An offshore exploration program by
Shell in the 1960’s determined these formations to be too thin and thermally undermature
to have generated commercial conventional hydrocarbons. On Southern Vancouver
Island, the Sooke Formation occurs generally in small basins which are now tectonically
and erosionally isolated. The largest basin is around Muir Creek and is drained by
Tugwell, Muir, and Kirby Creeks. At these sites the contact with the underlying MIC is
not exposed. The best exposures occur along the coast and up the short coastal streams.
Elsewhere the rocks are covered with glacial and deglacial deposits of both late
Wisconsinan and undatably old, pre-Wisconsinan age.
The sandstone contains angular to subrounded grains composed mainly of quartz,
plagioclase feldspar and magnetite and lithic clasts of MIC south of the Leech River
fault. Conglomerates are considerably more variable in their composition. North of the
Leech River Fault large clasts are mainly of Leech River metamorphic origin but are of
more diverse provenance than to the south of the fault, including many lithologies of the
Wrangellian terrane to the north of the San Juan Fault. Accessory minerals are biotite,
muscovite, hornblende and limonite around Muir Creek. The cement is mainly calcite.
Bored drift logs occur at the Muir Creek fossil site. The Kirby Creek exposed section is
about 160 m thick and the Muir Creek section about 130 m. Clapp reports that a bore
hole at the mouth of Muir Creek was still in Sooke Formation 450 m below present sea
level.
The formation was deposited in a marine environment of a steep shoreline of resistant
crystalline rocks. The Tertiary coastline comprised promontories of MIC, which supplied
large clasts to form the conglomerate. Between the promontories were coves and bays in
some of which accumulated sands. The coastline was probably similar to that of today.
Driftwood buried by the sands has been converted to lignite. Offshore facies are also
recognized by sedimentary structures and fossil content. In the Olympic Mountains,
equivalent age strata range from shallow neritic sands and conglomerates to bathyal
turbidite and mélange facies. There they contain clasts derived from the north on
Vancouver Island and from the East in the ancestral Cascades. This makes for a very
complex tectono-sedimentary environment at this time.
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Catface Intrusions (Oligocene)
Aphanitic felsic sills, dykes and plugs outcrop on southern Vancouver Island, cutting
both the Metchosin Igneous Complex near Sooke and to the north as well as in isolated
locations further west cutting the Leech River Complex. Here they are tronjheimites
(plagiogranites) and resemble rhyolites and dacites but are extremely low in potassium so
there is no K-feldspar, only albite, quartz and paragonite (Na-mica). These types of rocks
typically cut up through cold fore-arc regions and seem to be derived by the
differentiation of basalt. Coeval rocks also cut a swath across central Vancouver Island
from Tofino to Mt. Washington where they host Cu-Au in skarns.
Metchosin Igneous Complex (Eocene)
On Southern Vancouver Island up to a about 2 kilometers of oceanic crust including
pillow basalts, pillow breccias, overlying sheet flows and underlying sheeted dykes and
coeval gabbro intrusions. According to Massey, this represents an ophiolite sequence
(cross section of the oceanic crust). It is one of the fragments left of the Farallon Plate,
former eastern half of the Pacific basin. It is preserved here because it was subducted
until about 45 Ma, then uplifted and eroded by the younger Cascadia subduction zone. It
is also exposed to the south of the Juan de Fuca Strait in the Olympic Mountains where it
is called the Crescent formation by Tabor, in the Coast Range Basalts of Washington and
western Oregon and in SE Alaska where it forms part of the Yakutat block. Here it is
represented by transitional tholeiites and metaluminous 2 pyroxene gabbros with minor
hornblende gabbros and anorthosite. Canil has studied the low grade metamorphism of
the MIC and from Fe-Mg Chlorite geothermometry shows that it was buried to about 4-5
kilometers and about 360°C. Presumably this represents the amount of burial and
exhumation with more uplift and metamorphism to the west near Loss Creek than to the
East near Metchosin and Triangle Mountain. Since the age of the volcanics is about 56
Ma as exposed here in the subduction zone, and that subduction ceased at about 45 Ma,
the subducted basalts were 11 million years old as they were being subducted. This is not
too different from the current position of the Gorda Ridge west of Southern Oregon,
except that the ridge was offshore to the SE and subduction here at the bend in the North
American margin was down to the North.
The Leech River Complex (Jurassic? & Cretaceous)
The Leech River Complex is part of the Pacific Rim Terrane and is mapped as being
bounded in the north by the San Juan - Survey Mountain fault and in the south by the
Leech River fault. It consists of metamorphosed pelitic rocks, sandstone and minor
volcanics, chert and conglomerate of probably late Jurassic to Cretaceous age.
Metamorphic grades range from sub-greenschist to amphibolite facies and vary markedly
between domains. Fairchild and Cowan argue that the complex underwent two similar
deformational events during which regional shortening induced macroscopic linear
structures, parasitic folds and axial plane cleavage. Regional, progressive low-pressure
greenschist to amphibolite facies metamorphism began during the first deformational
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event and extended into the waning stages of the second. The P-T range is inferred as
having been 1.5 - 3.5 kbar (150 - 350 MPa) and 500° to 600° C. K-Ar age determinations
from biotite and hornblende indicate metamorphism at about 41-39 Ma. Fairchild and
Cowan suggest that the Leech River rocks were emplaced against Vancouver Island by
left lateral slip on the San Juan fault after 41-39 Ma.
Yorath argues that the muds and immature lithic sands of the Leech River Complex
accumulated near the toe of a Late Jurassic through Early Cretaceous age convergent
continental margin, essentially the fore arc accretionary wedge. According to Yorath the
rocks were transported northward and thrust beneath Wrangellia along the San Juan Survey Mountain fault around 55 Ma. While this fits reasonably well with the geology as
interpreted on southern Vancouver Island, Ned Brown and Jim Monger see different
relations for equivalent age lithologies in the San Juan Islands. There they see this panel
of rocks as being thrust over the top of Wrangellia. There is a controversy here to say the
We will go direct to Botanical Beach for the low tide, then we will make roadside and
logging road stops on the return journey to see several facies of Sooke Fm and LRC and
MIC.
As with many convergent margin and marginal basin settings, the lithologies are all
oceanic and there is no older underlying crust. The stratigraphy here either all formed in
the ocean basin, or on the margin of the ocean basin and was subducted underneath and
added to the edge of the continental margin.
II Road Log Jordan River to Botanical Beach
Set your odometers or note mileages to be able to add in the strip log km to get your
position and be able to read the road log west from there to Botanical Beach.
km 0.0 (Beyond Jordan River the road is of irregular quality)
Jordan River If you set your odometer here you can use the following brief notes to look
for features and outcrops which may be stops on the return trip.
7.0 On right is exposure of Sooke Formation conglomerate. What is the dominant grains
size? Check for any fossils in this exposure and discuss what type of environment this
conglomerate was deposited in.
We are getting closer to the Leech River fault and the fault contact/ terrane boundary
with the LRC.
18.6 MIC on the right. Tm3 Muller, Tmc Massey. Close to Leech River fault. Note the
extensive deformation, veining and secondary mineralization.
19.0 View over kame terrace (extending N.W. toward Port Renfrew) deposited against
ice in the strait. The ice tongue in the strait dammed up lakes in the valleys and also acted
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as a barrier to sediment transport. Here is a good example of kame and kettle terrain
where sand and gravel accumulated plus blocks of ice which later melted. It took time
before vegetation became established and much mass wasting occurred. Removal of the
vegetation has also encouraged mass wasting recently. There have been many gold
workings in the area.
20.9 Loss Creek. The trend of the valley follows the Leech River fault. On the north
side is the Leech River Complex. Loss Creek valley has a continuous sequence of glaciolacustrine silts 460 m thick from 150-610m ASL. The ice-dammed lake was over 10 km
long. There are equivalent facies at Kirby Creek but a flattened Thuya occidentalis log
proved too old for radiocarbon dating. How many times do you suppose this type of
environment has repeated along this coastline? The old log bridge was wiped out by a
mass wasting event from the north side. There is still evidence of the slide.
25.3 Steepish hill. These hills were much more interesting before the road was paved and
when there were lots of full logging trucks galloping around.
28.3 Minute Creek. Leech River rocks with chiastolite variety of andalusite
porphyroblasts and arsenopyrite to the north side of the road. New bridge. Both Minute
Ck and the smaller ck to the west have good exposures of recumbent folds overturned to
the east and porphyroblastic and schistose foliation textures.
33.3 Road turns inland along route of former overflow channel from ice-dammed lake
in San Juan valley.
33.8 Access road to Juan de Fuca trail. A 2 km side trip here shows massive
olistostromal conglomerate facies of the Sooke Formation containing car and house sized
rotated blocks of the Leech River Schist. Alternatively, these blocks were from the
overlying headwall of the Leech River Thrust and are all that remains of an erosional lag
lowered down onto the exhumed footwall and into the creek which cuts down into it.
40.2 Enter Port Renfrew
41.7 Turn left off highway onto Cerantes Road toward Botanical Beach. The road in
part follows another overflow glacio-lacustrine outwash channel route.
IV Botanical Beach Tour and Discussion Questions
43.3 Enter Provincial Park. Take away only the rocks you had with you when you
arrived. At parking lot go round the loop to the last trail entrance. Park.
Take the Juan de Fuca trail near the East end of the parking lot, not the Botanical Beach
loop trail.
Immediately at the entrance to the beach there is an unconformity of Sooke Formation
on Leech River Schist.
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Q1) What type of unconformity is this?
Q2) What does it signify?
There are exposures along the beach which are good for working out what rocks occur
within the L.R.C. and what rocks comprise the Sooke Formation just above the
unconformity.
Q3) The LRC comprises metamorphosed ______________ and________
rocks of_________ metamorphic grade.
Q4) The foliation in the schist strikes about (azimuth) ___ and dips at about __ ° in a
_______ direction.
The overlying Sooke Formation has a shallow dip to the S.
Q5) What caused this dip and when did it happen?
Inspect the Sooke Fm for grain size, clast lithology and cement (we will compare this at
other sites).
What was the depositional environment? Was it shallow water, deep water , low
energy, high energy …?
There is a photograph in Yorath’s book which is claimed to be of Sooke Fm and LRC.
See what you think.
Go along the beach about 100 m to the east of the trail head.
Q6) Are there any intrusions? If so, what is their composition and relationship to the
LRC and Sooke Fm. Can you suggest an age and correlative formation for these rocks?
At this point you may wish to revise your interpretation of the major unconformity here.
Discuss this in terms of what other kind of unconformity this might be and how much
time is likely missing here.
From here, the plan is to walk to the West, across the small creek in a loop around the
cliff and intertidal platforms to examine the tide pools and the Sooke Formation to the
west and back down through the unconformity again into the LRC and return to the
vehicles by another escape path above the beach.
Depending on recent wave action, there are sometimes exposures of trace fossils in the
upper portion of the creek which crosses the beach. See is you can find them without
slipping and falling in the water.
Q7) Are these fossils of animals or fossils of behavior? What was the environment like
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when they were formed? How much energy and oxygen did it take to form these?
Trips usually spend about 1-2 hours from here on, as there are biological and ecological
as well as geological splendours.
Low tide today March 25, 2012 is between 7:00 AM to about Noon, so pay attention to
the sea state, surge and escape routes as you go out on the wave-cut platform and see the
tide pools and the inter-relationships among the landscape, geology and biology.
Q8) How old is the wave cut platform and what evidence is there for this?
Watch out for rogue waves. A few people have waved goodbye here lately.
In the tidepools are smaller side-wall depressions made by purple sea urchins. Discuss
how sea urchins influence the shape and size of the tide pools. Also try and find,
anemones, coralline algae, chitins, barnacles, mussels and other animals. What do you
think the likelihood of preserving these kinds of animal communities in the fossil record?
What might that fossil and sedimentary record look like and how might it get preserved?
Q9) What other physical and chemical processes are involved here in making these
“botanical beach gardens”?
Note the wave-cut notches in the cliffs, differential erosion, the lips on some of the
high intertidal zone tide pools and concretions in the cliff faces.
Q10) What kinds or sequences of processes are responsible for these small scale
erosional features?
There are also joints in some of the rocks. Are they randomly oriented or is there a
consistent pattern.
Q11) What do you think controls the joint distribution? When were the joints formed,
and why are they not in all rocks? What do you think they mean? Are these rocks
structurally deformed or not and what is the evidence?
A large flat-floored amphitheatre nestled in the cliff used to be used for dances.
Orchestras have even played here. What is the location of the highest driftwood> What
does that tell you?
There are also rims or raised lips on the edges of the tide pools here. Discuss how they
formed keeping in mind that the pools themselves are erosional features.
Examine the nature of the beach just at the western foot of the wave cut platform. Note its
composition, grain size and discuss what is here and where it came from. What does this
tell you about the processes of sedimentation on exposed beaches?
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Take care to scan the edge of the woods here as bears and cougars frequent the area
looking for a free lunch of deer or sea lion, or just a free lunch! Lions and tigers and
bears, oh my!
Travelling around the cliff you will see again the LRC. Where is the unconformity and
how would you draw it in if you were making a map here?
Look for evidence of different lithologies, deformation, metamorphism hydrothermal
veining and intrusions.
Q12) Once you have found some of these things, try and work out the sequence of events
here.
Return to the vehicles. Walk toward the park exit. Near the large park sign at the service
road are recent exposures of LRC with loose blocks.
IV Return Road log with stops as time allows. If you have to be back early switch to
an early car and leave the bus for those visiting the last 3 stops as this will take
about ½ hour additional compared to the straight return.
Leave Port Renfrew.
Reset odometer to O.O at Deering Road near the Community Centre but stay on
Westcoast Road.
You are now looking east along the San Juan River valley which was occupied by an
ice-dammed lake which extended about 10 km to the east. The lake formed between the
land and a glacier where the sea now sits.
(Skip the next stop today)
5.9 Turn RIGHT along access to Juan de Fuca trail
8.2 (2.3 km from highway) pull over to the left and park on logging road.
Walk toward bridge. The left hand side of the road is paved with hand specimens of the
LRC. Is the grade of metamorphism the same as at Botanical Beach or higher or lower?
Why?
Stand on the left hand side of the bridge and view the LRC.
Note the orientation of foliation. At first the orientations seem to be quite variable.
Why?
This is in fact not just LRC but large blocks of LRC in a sand and gravel matrix.
Climb down to the exposure and inspect the large and small clasts for lithology and
rounding and sorting. What is the cement? Are there any fossils?
What was the depositional environment? Similar to that at Botanical Beach? Why, or
why not?
Return to highway. Reset odometer.
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0.0 Turn RIGHT onto highway.
10.4 Exposure along strike of L.R.C.
(Skip this stop today)
11.2 Pull off road on R.H.S. and park near Minute Creek bridge.
Walk across road to the small creek . Descend on North side of road. Walk upstream.
Look out for elegant hand specimens in creek bed. There are rounded blocks plus blocks
that fell in this winter. Observe textures and structures.
Return to vehicles.
13.7 Sombrio River
14.1 Steepish hill down STOP AT BOTTOM
18.5 Descend into Loss Creek valley. Stop by the Bailey Bridge to look at the rocks.
18.7 Pull over on right hand side of road, and park just before or after the single lane
Bailey Bridge. On the Left Hand Side (north) of road is the LRC adjacent to the
Leech River fault. Here the LRC is greenish-grey chlorite schist. The trace of the
fault is the slope uphill to the south, so we are standing in the trace of the old pre-45
Ma subduction zone thrust fault.
18.8 See also notes for 20.9 km from this a.m. about mass wasting.
Return to vehicles.
Cross bridge and head toward Jordan River. Ascend past shattered Metchosin Igneous
Complex as we are now down into the footwall block of the Farallon Plate subduction
zone.
STOP
32.8 Cautiously pull right off road immediately after power pole with support.
Here we are back in the Sooke Formation. Across the road is an exposure of
conglomerate unconformably on top of the Metchosin Igneous Complex Samples of
conglomerate may also be found in the fill below road to the east (and in large blocks) on
the south side of the road. The clasts are basalt and gabbro of the MIC, with some fossils.
Note also the underlying MIC and post-depositional structures.
Q13) Is the MIC basalt, gabbro, or what? What kind of clasts and fossils are here and
what do they tell you about the environment they formed in? What geological formation
does this outcrop belong to? How high above sea level are we and what has happened to
put these rocks here?
VI After this stop you are on your own for returning to Sooke to change rides or
return to Camosun or home. Thanks for attending and drive safely.
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