Tyndall Stone: Manitoba Rocks! EarthCache
Tyndall Stone: Manitoba Rocks!
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One of the most architecturally distinctive buildings in Canada's National Capital Region, the Canadian Museum of Civilization consists of a collection of curves elegantly executed in strikingly sinuous stone. Even more remarkable, I think, is the fact that the stone used in this edifice constructed to showcase human lifestyles is itself teaming with evidence of life.
This is Tyndall Stone, quarried from a site approximately 40 km northeast of Winnipeg and deriving its name from nearby Tyndall, Manitoba. It was first used in construction at Lower Fort Garry in 1832 and can be seen in numerous buildings around the city of Winnipeg, from the Provincial Legislature to the train station and the airport. It has also been used in the construction of buildings throughout Canada and the United States, including the Empress Hotel in Victoria and the Parliament Buildings in Ottawa (look at the background next time you see a television news report from inside the House of Commons!) among many others.
Tyndall Stone is a type of limestone prized for its strength and durability as well as for its striking colour pattern. It is generally light tan or cream in colour, but heavily mottled with a reticulated network of darker stone that contributes structural reinforcement as well as an attractive appearance. It also contains numerous fossils of marine organisms. Four hundred and fifty million years ago (in what geologists call the Ordovician Period), what is now southern Manitoba was at the bottom of a shallow tropical sea. Abundant marine organisms lived in this tropical sea, mostly on or near the seabed. When these organisms died, they became incorporated into the mud, and the calcium carbonate in their skeletons provided lime that contributed to the transformation of the mud into limestone.
Tyndall Stone contains two different types of fossils. Most numerous are the networks of darker stone found throughout. These are actually “trace fossils” – traces of the passage of organisms, in this case burrowing through the mud of the seabed (fossilized dinosaur tracks are another example of trace fossils). The burrows are similar to those made in more recent times by mole shrimp, but the fossil record for such crustaceans does not extend as far back as the Ordovician Period, so what organisms created the burrows is currently unknown. Whatever created the burrows, their existence led to the formation of a different type of stone as magnesium-rich waters penetrated the burrows (but not the surrounding sediment) and formed dolomite, which is more durable than limestone and thus adds structural strength as well as an interesting colour pattern to Tyndall Stone.
The other type of fossil in Tyndall Stone is what most people more commonly think of as fossils – “body fossils” that are casts of organisms themselves, most commonly gastropods, cephalopods, and stony corals in this case – scattered through the stone and exposed in various cross-sections on the cut surfaces. Some of the more common types of body fossils are as follows (I have not described all of the types of body fossils in this stone and I have not included all of the described types in the photographs below; please feel free to explore and discover more!):
Gastropods: These include your typical snails, as well as other forms such as slugs. Fossils of both tall spiral shells and more broadly rounded ones may be found in Tyndall Stone.
Horn Coral: Most commonly seen in cross section, this type of solitary coral appears circular with ridges extending radially from the centre towards the perimeter. They are also sometimes exposed in longitudinal section (lengthwise), in which case it becomes obvious how they got their name.
Chain Coral: This colonial coral, seen in cross section, appears to form chains that wind about, joining and splitting in an irregular way. Sometimes rough (as opposed to smoothly cut) stone provides a more three-dimensional view of these corals, in which it can be seen that the “chains” are actually cross sections of structures more like walls or palisades.
Sunflower Coral: Aptly but inappropriately named, this is actually a calcareous alga rather than a true coral. Like a true coral, however, it secretes a calcium carbonate skeleton that, in a cross-sectional fossil, forms a regular grid pattern in a broad circular band around a large central “hollow”.
Cephalopods: These are relatives of today’s octopods, squids, and the “living fossil” nautilus. Like the existing nautilus they have a shell composed of a series of separate chambers. The shell may be curved (like the nautilus) or straight, but straight ones are much more commonly seen in Tyndall Stone.
To log this earthcache, visit each of the six waypoints (including the posted coordinates) and find each of the fossils illustrated in the photographs below. All of the illustrated fossils are on vertical surfaces approximately 0.5 to 1.5 m above ground level on the outside of the building, so this earthcache should be accessible by wheelchair, winter-friendly, and available 24/7. The coordinates may not be very precise due to the proximity (and sometimes overhang!) of the building, so it may take a little bit of searching to find each fossil (you may wish to step away from the building and let your GPSr point you towards the approximate location). Send me an email indicating for each waypoint which illustrated fossil is there, what type of fossil it is (all are body fossils, as described above), and the size of that particular fossil (preferably in centimetres, MAPSIT!). Please don’t post any spoiler pictures of the fossils selected for this earthcache, but feel free to post pictures of other fossils you find and of yourself and/or the general area.
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Additional References (thanks to New2GeoCache for bringing the last one to my attention):
Past Lives: Chronicles of Canadian Paleontology: Tyndall Stone (Geological Survey of Canada). http://www.collectionscanada.gc.ca/webarchives/20071122213207/gsc.nrcan.gc.ca/paleochron/17_e.php
Manitoba’s Tyndall Stone (Mario Coniglio, Department of Earth Sciences, University of Waterloo). http://www.whaton.uwaterloo.ca//waton/s9911.html
Fossils of the Tyndall Stone (Douglas Paterson, former Research Geologist for the Government of Saskatchewan). http://dfp.mediacooks.com/fossils/
Special thanks to junglehair for the earthcache that inspired this one.
This earthcache has been placed with the approval of the Canadian Museum of Civilization.
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