At this spot once stood the Winkler Hospital. Several years ago the build was demolished , a park created and this historical memorial was erected.
The stone cover on the memorial wall are Tyndall stones salvaged from the Hospital. These mottled slabs reveal a slice of life 450 million years ago.
Origin of Limestone in Manitoba
In the Paleozoic Era, during the Ordovician period, approximately 425 - 500 million years ago, a tropical sea called Lake Agassiz covered Manitoba. Limestone was formed under water by the action of organic or chemical agencies, or a combination of the two, on dissolved matter, primarily composed of calcium carbonate (calcite) and magnesium (dolomite) that was deposited in layers or beds separated by a layer of shaly material. Remains of corals, snails, cephalopods, trilobites, and brachiopods that lived in this early sea became part of the sedimentary layers.
Consolidation into solid rock may have been brought about by a number of factors. Chief among them is the growth of cement crystals of calcite, or dolomite, throughout the mass. It may also have been brought about by the weight of the material itself or of beds of other material deposited on top. Pressure due to earth movements played an important part of consolidating the deposits, and the heat of igneous intrusions was also effective.
Due to the earth’s movements, glaciation, and the receding of Lake Agassiz, the deposits were raised to dry land creating a limestone belt, about 100 miles wide, extending diagonally across the province. The limestones lie in even beds having a slight prevailing dip to the southwest at a very low angle. Manitoba’s limestones include practically all types from pure high calcium limestone through magnesian limestone to pure dolomite. It is used for a variety of purposes, including the manufacture of cement, lime, and building stone.
Tyndall Stone
Tyndall Stone is defined as a medium density dolomitic limestone. Geologically, it is referred to as the Upper Mottled Limestone of the Red River Formation of the Ordovician System. Tyndall Stone is found on the Red River Plain, one of the flattest regions in all of North America, thirty kilometers northeast of Winnipeg, in Garson, Manitoba.
The ground mass or matrix of the stone is fine grained high calcium limestone, containing many fossil fragments composed of calcite. Weaving through the matrix is a high magnesium material consisting of dolomite in tiny rhombic crystals cemented with calcium carbonate. The dolomite is what gives Tyndall Stone its’ unique mottling or “tapestry” appearance. No satisfactory explanation can be given for the formation of the mottling, but go back to the Introduction and view the animation. It is one possibility.
Textures of limestones vary considerably. Some limestones are compact, others are porous and full of cavities, still other are composed of shells and fossil remains knit together with varying degrees of firmness. All limestones are crystalline, composed of crystals of calcite and dolomite. In the groundmass of calcium limestones the crystals are rarely present in their true symmetrical forms but usually shapeless grains tightly interlocked. Dolomite crystals, on the other hand, are usually well shaped. Common sizes of individual crystals range from microscopic dimensions up to ¼ inch in diameter. It is the size of the glistening facets of freshly broken crystals that gives limestone the appearance of being either fine or coarse in grain, which is how limestone is classified.
Tyndall Stone was first used in 1832 for building Lower Fort Garry, and has since become popular for building purposes throughout Canada .
Tyndall Stone is highly fossiliferous and the fossils contribute to its aesthetic appeal. It contains numerous fossil gastropods, brachiopods, cephalopods, trilobites, corals, stromatoporoids, and others. The mottling results from burrowing by marine creatures that occurred during and shortly after limestone deposition. The identity of the burrowing organisms is not known, but fossil burrows of this type have been given the name Thalassinoides
Most fortunate for us is these slabs here do contain very well preserved selection of fossils easily seen.
To qualfy for this cache please provide the answers to these questions .
1) What do you believe the darkening of the stone is more due to ? ( normal weathering or chemical)
2) What are the dark lines mainly from ? ( reference description )
3) What are the majority of fossil types ?
4) Take a photo of a finger pointing to a fossil . Bonus points if photo is of the well preserved Trilobite.