Tyndall Limestone, Manitoba

 On a cold winter day, standing in farmer’s field, in the blowing snow, shivering, you might not believe that Manitoba once lay just south of the equator, a long long time ago! You read that correctly. Manitoba once lay close to the equator!

 About 450 million years ago, during a time geologists call the Ordovician Period, the area we call Manitoba (Canada) enjoyed a warm, subtropical climate. The land was covered by a shallow, warm, inland sea. The equator was located just to the north (image of Ordovician equator) (Photo 1). The shallow, warm waters of the modern day Bahamas Banks are considered to be modern-day analogue for the ancient inland sea (Photo 2).

 A calcareous sediment accumulated on the floor of the Ordovician inland sea. Over millions of years, the sediment was transformed into a dolomitic limestone that geologists call the Tyndall Stone (Photo 3).

Recognition:

On January 24, 2023, it was announced that the Tyndall Stone will be formally recognized on the world stage by the Subcommission on Heritage Stones. The Subcommission on Heritage Stones is part of the International Commission on Geoheritage, which is under the auspices of the International Union of the Geological Sciences. The role of the Subcommission on Heritage Stones is to increase knowledge and encourage conservation and protection of extraction sites for culturally significant building stones.

Distinctive Stone:

The Tyndall Stone is distinctive because of its colour, abundance of fossils and its durability, which makes it valuable as a building stone (Photo 4).

Two fossil types occur in the rock. One type, called body fossil, is preserved in the rock. Body fossils are the skeletal remains of an ancient organism. In the Tyndall Stone, body fossils include the remains of nautiloids (Photo 3: relatives of squids and octopus), corals, stromatoporoids, bryozoans, crinoids, trilobites (relatives of crabs and spiders), brachiopods, gastropods, bivalves and calcareous algae (Receptaculites; Photo 5).

The second fossil type is called a trace fossil and is the most distinctive feature of the Tyndall Stone.  The trace fossil gives the rock its distinctive colour difference mottled appearance between the sediment representing the burrow system and the sediment that was burrowed (Photo 4). A really interesting description of the mottle types is provided by Mario Coniglio. The mottles represent burrows made by worms and crustaceans, like ancient shrimp, while the sediment was still soft on the floor of the ancient inland sea. The organisms created the burrows when they searched for food, attempted to hide from predators, created living shelters, and just rested on the sea floor. The traces preserved in the Tyndall Stone are considered to have been created by crustaceans, such as ancient relatives to modern-day lobsters, shrimp, and crabs. The dark-coloured mottles are mostly composed of small crystals of the mineral dolomite (CaMg(CO3)2). The surrounding lighter coloured rock is composed of the mineral calcite (CaCO3). Natural weathering of the mottled rock where the darker, dolomitic mottles are slightly more resistant than the surrounding, calcite-rich, lighter-coloured rock.

Together, the body fossils and trace fossils record the types and behaviours of marine organisms that lived in the warm inland Ordovician sea 450 million years ago.

Use of Tyndall Stone As Dimension Stone:

First, let’s define dimension stone. Dimension stone is a natural rock that is quarried for use as ornamental interior or exterior facing on buildings. The quarried rock is cut into blocks or slabs that meet specifications as to size and shape. Important physical characteristics of dimension stone include colour, grain texture, durability, strength, ability of the stone to take a polish, and resistance to weathering. Equally important are the textural patterns in the rock and surface finish because aesthetic characteristics can determine the popularity of a stone.

Because of its fossiliferous nature, the Tyndall Stone has been used in as a building stone since 1832, when it was used to build the fort warehouse and walls of Lower Fort Garry in Manitoba. In the beginning, Winnipeg and nearby areas were the principal market for Tyndall Stone. That market expanded and Tyndall Stone has been used to face the interior of Canada’s Parliament Buildings, the legislative buildings in Regina and Winnipeg, as well as the exteriors, interiors, steps, walkways, columns, fireplaces and floors of countless other buildings throughout Canada and the United States.

Quarrying:

Tyndall Stone is quarried at Garson, located 37 km northeast of Winnipeg, Manitoba. The Garson deposit opened in 1895. The name Tyndall Stone comes from the closest railway point to Garson. Gillis Quarries Limited started working the stone in 1910 and continues to this day.

Epilogue:

The distinctive physical and cultural history and use of Tyndall Stone was recognized on January 24, 2023 as being worthy of formal recognition on the world stage by the Subcommission on Heritage Stones. It remains an important and unusual building stone from Manitoba, Canada. So, the next time you see it, remember it all started 450 million years ago when this part of Manitoba, Canada, was located close to the equator! Yes, the continents do move around in the world of Canada beneath your feet.

Jan 27/23