As you walk along the sidewalk here, look at the stone cladding on this building (15 Sir Winston Churchill Square). You will see dozens of fossils of historic sea creatures.
Like several other office and government buildings in Downtown Edmonton, 15 Sir Winston Churchill Square is clad in Tyndall Stone. However, due to the smooth cut of the stone blocks here, and the fact that you can walk right alongside this building on the sidewalk, these are some of the most accessible fossils in the City.
Tyndall limestone is a dolomitic limestone that is quarried from the Red River Formation near Tyndall, Manitoba. Tyndall Stone is used in some of Canada's most important buildings- the Parliament Buildings in Ottawa, the Legislatures of Manitoba and Saskatcehwan, the Empress Hotel in Victoria. In Edmonton, the Federal Building and City Hall are other examples of buildings finished in Tyndall Stone.
Limestone is formed when ocean-dwelling organisms such as oysters, clams, mussels and coral use calcium carbonate (CaCO3) found in seawater to create their shells and bones. As these organisms die, their shells and bones are broken down by waves and settle on the ocean floor where they are compacted over millions of years, creating limestone from the sediments and the pressure of the ocean water.
Most fossils are formed when a plant or animal dies in a watery environment and is buried in mud and silt. Soft tissues quickly decompose leaving the hard bones or shells behind. Over time sediment builds over the top and hardens into rock. As the encased bones decay, minerals seep in replacing the organic material cell by cell in a process called "petrification."
The Tyndall Stone on this building has two types of fossils. Most distinctive are the various fossilized sea creatures. Tyndall Stone will often contain gastropods, brachiopods, cephalopods, trilobites, corals, and stromatoporoids. Most visible in this location are the brachiopod fossils. Brachiopods are shellfish that somewhat resemble clams (although not directly related). Brachiopods still exist today, and are found usually in cold water in marine ocean environments.
The second type of fossilization that is present here are "thalassinoides". Thalassinoides are fossilized burrows of sea creatures in the sediment. Tyndall Stone is notable for its thalassinoides, which in smooth cut stone shows up as mottling: in scientfic terms: dichotomously or T-branched boxworks, mazes and shafts, unlined and unornamented". In ordinary person terms: "the darker coloured lines and squiggles you can see in the limestone".
Interestingly, City Hall across the street (and the bases of the sidewalk lights on the east side of 100 St!) is also clad in Tyndall Stone. However, most of the Tyndall Stone at City Hall is very rough cut- making it much more difficult to make out the fossils in the rock.
To log this earthcache, you must complete three tasks:
1. Based on the above, provide a brief description on why Tyndall Stone often contains fossils.
2. Describe, in your own words, the thalassinoides that you see at this location. Describe the colour, lengths, and general characteristics.
3. Take a photograph of you, your GPS or a trackable with one of the brachiopod fossils or other sea creature fossils on this building clearly visible in your photograph. In light of the changes to Earthcaching Guidelines in June 2019, this task is mandatory, and logs not including a photo will be deleted.
References:
Manitoba's Tyndall Stone: http://www.whaton.uwaterloo.ca/waton/s9911.html
Tyndall Stone (Wikipedia): https://en.wikipedia.org/wiki/Tyndall_stone
Introduction to Brachiopoda: https://ucmp.berkeley.edu/brachiopoda/brachiopoda.html
What is Limestone?: https://www.irvmat.com/kids/whatIsLimestone.htm
The Formation of Fossils: http://scienceviews.com/dinosaurs/fossilformation.html
