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Calgary Building Stone Tour: Tyndall Limestone

A cache by Shearzone Send Message to Owner Message this owner
Hidden : 02/20/2008
Difficulty:
2 out of 5
Terrain:
1 out of 5

Size: Size:   not chosen (not chosen)

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Geocache Description:

This EarthCache is the first in the Calgary Building Stone Tour aimed at highlighting the remarkable decorative building stones used to ornament many of Calgary’s buildings. Note: The cache is not limited to the posted coordinates. This cache may be logged at any building in Calgary decorated with this building stone.

Limestone is commonly used as building stone in North America, but Tyndall Limestone is unique. The colour, beauty, strength and durability of Tyndall Limestone has allowed for it to be used in a variety of ways and architectural styles. Tyndall Limestone is used extensively as an ornamental building stone across Canada.

Look at the walls next time you see a news report from the halls of the Parliament in Ottawa. The backdrop of elaborately carved walls, columns, and ceilings are made of Tyndall Limestone. Other notable buildings adorned with Tyndall Limestone include the Canadian Museum of Civilization in Gatineau, the Manitoba Provincial Legislature in Winnipeg, the Rimrock Hotel in Banff, the Empress Hotel in Victoria, the Provincial Museum of Alberta, and the University of Alberta’s Tory Building. Several buildings of downtown Calgary are also decorated with the ornamental building stone. The first building to be adorned with Tyndall Limestone was Fort Garry in Manitoba in 1832.

Occurrence and History of the Tyndall Limestone
Tyndall Limestone is an informal term applied to building stone from the Selkirk Member of the (Ordivician) Red River Formation. The best exposures of the Tyndall Limestone are found in the Garson-Tyndall area, approximately 30 km northeast of Winnipeg, Manitoba. The small village of Garson Manitoba bills itself as The Limestone Capital of North America. This is no empty boast, the limestone quarried here is probably the most frequently used building stone in Canada. The name of the stone comes from Tyndall, the closest railway point to the quarries; the railway station was itself named after the noted British physicist Professor John Tyndall.

Description of the Tyndall Limestone
Tyndall Limestone is a fine grained light coloured, fossil-bearing limestone (wackestone) with comparatively darker brown coloured fine to medium grained medium tubular-shaped (vermiform) branching network of dolomitic limestone, which give the rock a ‘mottled’ appearance.

Two major types of fossils occur in Tyndall Stone. The first are body fossils. These are the calcite shells of a variety of marine animals and plants that lie dispersed throughout the rock -- like raisins suspended in a pudding. The second are trace fossils that occur as a pervasive network of burrows.

Body Fossils of the Tyndall Limestone
Body fossils are the hard, shelly remains of organisms preserved within a rock. Tyndall Limestone is notable for its rich variety of large, excellently preserved, easily-identifiable body fossils. A close look at Tyndall Limestone will reveal many interesting fossils embedded within it. The following is a non-inclusive list of the most abundant fossils of the Tyndall Limestone that you may find:

Cephalopods are like modern squids or nautili. Cephalopods with straight shells are called Orthocone, whereas those with a curved shell are known as Winnipegoceras.

Gastropods (Maclurites) are more commonly known as snails and slugs. On a cut surface, the fossil may have a coiled appearamce.

Chain Coral (Favosites) are colonial coral that have an irregular grid pattern that sometimes resembles a distorted chain-link fence.

Horn Coral (Grewingka) is a solitary coral. In the rock the fossil has a pattern of line radiating out to an oval or a horn-like pattern.

Sunflower Coral (Receptaculites), are the largest and most enigmatic of the Tyndall fossils. Don’t let the name fool you, they are not a corals, but actually calcareous algae. The fossil occurs as a circular colony, characterized by a uniform grid pattern and a distinguishable deep hollow in the centre.

Brachiopods and trilobites may also be present but are more difficult to identify. When examining the rock for fossils, keep in mind that the shape of the fossil displayed may vary considerably depending of the random cross-section on the exposed surface of the building stone.

Trace Fossils
The shelly fossils of Tyndall Stone are certainly intriguing, but it is the trace fossils that make this limestone an attractive building stone. Unlike body fossils, trace fossils are fossilized tracks, trails, or burrows left during the day-to-day life activities of an organism. You may have unknowingly created trace fossils with your own footprints, if they were subsequently filled with sediment, buried and preserved in the geological record.

In Tyndall Limestone, the trace fossils are evident as a ‘mottled’ texture. The mottled areas have a tubular, vermiform shape that branch and bifurcate, extending as deep as a metre below the seabed surface. This image is a schematic block diagram of what the network of burrows might look like in three dimensions.


These trace fossils are well-known to ichnologists (those who study trace fossils) as Thalassinoides. Since the Cretaceous, Thalassinoides tunnels have been excavated as dwelling and feeding burrows by mole shrimp. However, it is unlikely that mole shrimp or any other decapod crustacean made these deep burrows in the Ordovician because these arthropods have a well-documented fossil record that starts 250 million years later in Jurassic rocks. So what animal made these burrows? Unfortunately, no body fossils have been identified in or near the burrows to give even a suggestion. One is tempted to say "worms", but when paleontologists attribute a trace in sediment to the activity of "worms" it is generally an expression of ignorance rather than an actual identification. We simply don't know what animal is responsible for the deep burrows and the mottles in Tyndall Stone.

The difference in colour between the burrows and the surrounding rock is due to differences in grain size and chemistry. As the animals burrowed through the soft, limey mud, they lined their burrows with slime to add strength to their tunnels. Furthermore, the sediment inside their burrows is loosened and reworked, compared to the more tightly packed surrounding mud that hardened before the less dense sediments in the burrows. Later, magnesium-rich waters percolated through the rock and deposited dolomite in the burrows, but couldn't penetrate the tightly cemented limestone rock. The darker colour of the burrows may be a result of oxidation of trace amounts of iron in the dolomite, or of pyrite that was deposited along with the dolomite.

Depositional Environment
Four hundred and fifty million years ago (late Ordovician Period), the environment of present-day southern Manitoba was a warm, shallow, inland sea, just south of the equator. Many different types of animals lived in this ocean. Some, such as corals, sponges, molluscs, and algae, are still around today. Others, such as trilobites and stromatoporoids, are extinct. All of these creatures lived just below, on or above the soft, muddy sea floor. After they died, their remains became part of it. The calcium carbonate in their skeletons made the mud limey, so that when it hardened into rock it became limestone. Fossils of these animals and plants are visible today in Tyndall Stone. Other animals burrowed in the mud of the sea floor for food or protection. And it is the preserved burrows of these creatures that make the beautiful mottling which gives Tyndall Stone its unique appearance.

More information can be found at the following site:
www.epl.ca/ResourcesPDF/Fossilsofcityhall.pdf

To log this cache:
In order to log this cache, you must:
- Estimate the average thickness of the burrows and email me the answer
- Estimate the percentage of the rock that is composed of burrows and email me the answer
- Take a picture of at least one body fossil with your GPS for scale and identify it. Please post your answer as the picture caption. I will be lenient with answers, but I will not accept 'I don’t know'. Take a look at previous pictures to help you identify your fossil. If you are unsure, post your picture anyway and take a guess. If you are incorrect, I will help you identify it. All I ask is that you modify the caption to the right answer because it will help subsequent finders identify the fossils they have found.
- State the building and post your (best possible) co-ordinates of where you made your observations in your log

Logs without an accompanying email or the required photo will be deleted. Do not post a log for this EarthCache until you (a) have emailed the answers and (b) are prepared to post the photo.

Happy EarthCaching!

References:
Canadian Society of Petroleum Geologists, 1997. Lexicon of Canadian Stratigraphy, vol. 4: Western Canada. ed. D.J. Glass.

Geological Survey of Canada, 2006. Past Lives: Chronicles of Canadian Paleontology - Tyndall Limestone. http://gsc.nrcan.gc.ca/paleochron/17_e.php

Dixon Edwards, W. A., 2004. EUB/AGS Rock Walk IV - A Rock Walk Through Downtown Edmonton. C. I. M. AGM tour and guidebook, May 12, 2004; in AGS Rock Chips, Fall/Winter 2003 edition. http://www.ags.gov.ab.ca/publications/pdf_downloads/rockwalkhandout.pdf

McCracken, A.D., Macey, E., Monro Gray, J.M., and Nowlan, G.S., 2007. Tyndall Limstone in GAC’s Popular Geoscience. http://www.gac.ca/PopularGeoscience/factsheets/TyndallStone_e.pdf

Mussieux, R., and Nelson, M., 1998. Urban Geology: Building Stone of the Provincial Museum and Government House. In: A Traveller’s Guide to Geological Wonders of Alberta.

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