Geoscience 240 – Lab 5: Introduction to Facies Pleistocene Sea Level Changes in Hecate Strait
and Modern and Ancient Hexactinellid Sponge Reefs
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LAB 5: INTRODUCTION TO FACIES: PLEISTOCENE SEA LEVEL
CHANGES IN HECATE STRAIT AND MODERN AND ANCIENT
TETHYAN HEXACTINELLID SPONGE REEFS
PART 1: WISCONSINAN HOLOCENE FACIES IN HECATE STRAIT
Read and examine the coastal evolution posters by Hetherington et al and the Barrie et al paper on
Hecate Strait and the Queen Charlotte Region. Note the maps on the posters and other figures
containing sedimentological information (seismic sections and facies strip logs of cores containing
grain size, sedimentary structure, fossil and 14C age information. Pay particular attention to the sea
level changes. Some of this is eustatic (ice versus water on the planet) and some of it is glacialisostatic (loading, unloading & flexing the local crust). Answer each question and discuss this with
maps or other illustrations.
1. What was the temporal duration of Wisconsinan ice cover in Hecate Strait?
2. Note the location and depth of Goose, Mitchell and Moresby Troughs. Speculate on their
origin. Examine the reflection seismic profile and core END92A21 off Hotsprings Island.
Note the erosional profile. What type of sediments and depositional environment made the
deeper strongly reflective layers? How does this contrast with the modern water depth and
environment? What does this indicate for the original depositional environment at 10.5 Ka
(this location currently at -116 m sub sea level)?
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Geoscience 240 – Lab 5: Introduction to Facies Pleistocene Sea Level Changes in Hecate Strait
and Modern and Ancient Hexactinellid Sponge Reefs
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3. Examine core END87A23 on Cook Bank. What is the significance of the 14C date at 90 cm
sub seafloor? What kind of organism was responsible for this material and would it be
found there in living position today?
4. Note the Paleo Delta including its bed-forms, geomorphology from reflection seismic and
maximum grain size from the coring information What was the approximate water depth of
the top-set beds at the time of deposition between 11.4 and 11.0 Ka? Examine the position
of this delta and speculate on the source of the river which likely fed into it. Has the sea level
changed or has the land level changed and what might cause either to happen?
5. Examine the Eastern and Northern shorelines of Rose Spit in Naikoon Provincial Park on
Graham Island in air photo and beach exposures. What are the active coastal processes
occurring there today? Describe or sketch a cartoon map and cross section of what you
think the coastline of Naikoon Provincial Park might look like in 50 years?
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Geoscience 240 – Lab 5: Introduction to Facies Pleistocene Sea Level Changes in Hecate Strait
and Modern and Ancient Hexactinellid Sponge Reefs
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6. Sketch a simple cartoon map with an outline of the modern Gwaii Haanas (Queen Charlotte
Islands). Show the approximate location of the shoreline circa 10 Ka in a. different colour.
Discuss any uncertainties based upon what you know about glacial isostatic (gravitational
equilibrium) loading and global sea level changes. Where were the fishing grounds for the
Haida at that time? How did the coastline change between 17 Ka and now?
7. The oldest Salish cultural sites date to about 6 Ka. Examine the Sea level curve and
speculate on where one might seek older archeological evidence to confirm oral tradition
that the coastal First Nation people have been here longer. According to oral tradition, the
Haida have always lived in Gwaii Haanas. Have they always lived at the modern locations
for Kung, Masset, Skidegate, Cumshewa, Tian, Tanu, Ninstints and Skedans? Where do you
think there might have been village sites prior to 6 Ka presuming they were still shorebased communities?
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Geoscience 240 – Lab 5: Introduction to Facies Pleistocene Sea Level Changes in Hecate Strait
and Modern and Ancient Hexactinellid Sponge Reefs
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PART 2: MODERN HEXATINELLID SPONGE REEFS AND ANCIENT ANALOGUES
Hexactinellid sponge reefs are know from the Triassic and Jurassic margins of the Tethys and from
modern refugia on sediment-starved, high-latitude continental shelves in cold waters like Canada’s
West Coast, and more recently off Antarctica. Hexactinellid sponges are primitive sponges which
filter feed on dissolved organics and small bacteria, in contrast to most modern sponges which have
well developed cilia and feed on phytoplankton. The two dominant (abundant) species are
Aphrocallistes vastus (Cloud sponges, thin, fragile, transparent) and Heterochone calyx (Finger
goblet, thicker, more opaque). Both species are present in Georgia Strait, Haro Strait and the
Saanich Inlet but only Aphrocallistes is present in the bioherms (organic reef of mound-like form
built by a variety of marine invertebrates, including corals, echinoderms, gastropods, mollusks, and
others) in Hecate Strait. Other species like Ferrea occa while not so abundant are important as 1st
colonizers and often provide a better substrate for other species to nucleate upon. Sponges like the
rosellid “boot sponges”, e.g. Rhabdocarpus dawsoni are solitary, do not form reefs and just collapse
to a mat of spicules when they die. Examine the two sponge reef posters by Conway et. al. and the
extant (modern) and fossil organisms provided and perform the following tasks:
1. Draw and label Heterochone calyx labeling the filter feeding inlet pores and the osculum
(exit current port). Explain how this colonial organism maximizes its surface area to feed.
2. Draw and label Aphrocallistes vastus (cloud sponge) labeling infiltration ports and
osculum. How does this species maximize its surface area? Take a fragment of this and of
Heterochone calyx (Lady finger) from the jars provided and draw or describe how can
you tell these sponges apart.
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Geoscience 240 – Lab 5: Introduction to Facies Pleistocene Sea Level Changes in Hecate Strait
and Modern and Ancient Hexactinellid Sponge Reefs
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3. Examine the side-scan sonar and reflection seismic images on the poster and compare the
sidescan image to the geological map. Note the rough, dark, reflective character of the
glaciated seabed (linear iceberg furrows) compared to the sponge mounds. Speculate on
why these features are so non-reflective (acoustically transparent)? Assuming that the
speed of sound in sea water is 1500 m/sec and that the sound has to go both down and
back, how thick are the thickest bioherms surveyed here? Approximately how long did it
take these bioherms to grow this large?
4. Are these bioherms comprised entirely of Hexactinellid spongess or is the ecology more
complex? How well do you think these bioherm communities would withstand bottom
trawls or oil spills from diluted bitumen?
5. Speculate on how these animals could be responsible for trapping sediments (like
carbonate packstones, boundstones or bafflestones) or for growing high porosity reefs that
might one day make it into the geologic record. Where else might bioherms like this occur?
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Geoscience 240 – Lab 5: Introduction to Facies Pleistocene Sea Level Changes in Hecate Strait
and Modern and Ancient Hexactinellid Sponge Reefs
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6. Examine and draw the large flat fossil Hexactinosa from the Yatova Formation in Eastern
Spain and note the two species of ammonites found with it covering this Tethyan sponge
reef.
7. Examine and draw the small (palm sized), thick microbolite encrusted Hexactinellids from
the Swabian Alb (this is an area located in Southern Germany). Note the overall thickness of
the sponge reefs in the German photos and comment on how they compare to those in
Hecate Strait today.
8. Note from the map of the Tethys in Europe, that all of the primitive sponge bioherms
occurred inside sediment-starved transform margins. Compare modern thicknesses to
those in the rock record from the Oxfordian (Upper Jurassic) of Spain and Germany.
Speculate on sedimentation rates, longevity, compaction effects and preservation. What has
happened to turn the European sponges and reefs into rocks? What are the replacive
(diagenetic) minerals there compared to the primary silica skeletons? What happened to
turn these sponges into rocks?
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Geoscience 240 – Lab 5: Introduction to Facies Pleistocene Sea Level Changes in Hecate Strait
and Modern and Ancient Hexactinellid Sponge Reefs
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9. Draw and compare the Oxfordian ammonites from Spain to the Maastrichtian (Upper
Cretaceous) Baculites (orthocone) from Alberta (these may be found in the hallway directly
across from the Geoscience lab – see straight horn ammonites). What has happened to this
family of cephalopods in the intervening 100 Ma? How can you tell their relative ages from
their gross morphologies and evolutionary changes?
10. Draw and describe the Quartz-Crystal Fan (west cabinet in hall) which came from a mound
several meters high and many meters across in Namibia between the underlying Marinoan
(Late Proterozoic-Snowball Earth) glacial marine deposits and the overlying Cap
Carbonates. Alsoo examine the thin sections from this rock and from cnidaria in the
sediment thin section box. The oldest known solitary sponge fossils are 40 Ma later than
this. Do you think this is a fossil “sponge” or not from your observations and explain why?
Examine the modern boot sponge (Rhabdocalyptus dawsonii) and discuss the relative
merits of these more primitive forms for trapping sediment and building structures
compared to hexactinellids (Precambrian to Recent).
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