This earthcache will require you to visit two sites approximately 3 km apart. The two sites can be visited in any order, but are best enjoyed by starting at the posted coordinates. Please note: the property owner has not granted permission to walk up to the quarry; please remain on the road allowance. At the church you can observe and answer the questions while remaining on the sidewalk.
Sand and Sandstone
Sandstone is a sedimentary rock formed by the lithification (turning into stone) of sand. Sand is a relatively coarse particle (coarser than clay and silt, finer than gravel) created by the weathering (mechanical or chemical breakdown) of rocks. The term “sand” also refers to any soil that is composed mainly of sand particles (as opposed to clay or silt particles, or organic matter).
Sandstone is composed of three “ingredients”:
- Sediment – tiny fragments of rock (usually the mineral, quartz)
- Matrix – finer-grained sediments (clay and silt) that were also present in the sandy soil
- Cement – mineral matter that binds the sediment into rock (usually silica, calcium carbonate, or iron oxide)
Depending on what minerals and organic material were present when the sand lithified, the colour of sandstone may range from off-white to black, gray, brown, red, or pink.
Sandstone forms in locations where layers of sand have accumulated by sedimentation. This may have occurred as a result of being blown into beds by wind, or by being deposited by moving water, as in a river delta. When sand is buried, the pressure of the upper layers of material, coupled with slightly higher temperatures, cause the minerals in the sand to be reshaped and move. Sand grains, normally separated by tiny pockets of air (pores) due to their size, knit together more tightly as they are squeezed into a smaller space. When other minerals are introduced into this environment (for example, silica or calcium carbonate carried by moving water), the minerals cement the compacted sand grains together to create new rock. If iron oxide is the cementing material, it may give off a rusty red colour.
The Boissevain Formation
In geology, a formation is a unit used to classify different layers of rock (‘strata’) by their comparable properties. In a geologic cross section, different formations illustrate boundaries between different depositional environments, but not necessarily different geological eras. Formations are subdivided into members, or aggregated into groups, depending on the similarities or distinctions of the surrounding layers.
The Boissevain Formation dates back to the Cretaceous period (ca. 145-66 million years ago). It is the uppermost/youngest formation in this part of Manitoba, though further south it is overlain by the Turtle Mountain Formation (and itself overlies the Riding Mountain Formation). It is ~40 m thick and is composed of sandstone and shale, most of which is out of sight below ground. In this area, the formation may be overlain by deposits of glacial till or sand and gravel. Shales of the Cretaceous period bear oil, and the relative proximity of the shales to the surface in this part of Manitoba has given rise to a thriving local oil industry.
Boissevain Formation sandstone was quarried extensively when this area was settled. It was used in the construction of many local buildings, several of which remain to this day.
The Quarry (posted coordinates)
The quarry you will visit reveals an exposed portion of the Boissevain Formation. Ripple marks and evidence of crossbedding are present, suggesting the sand was deposited in this location by moving water, rather than by glaciers alone or by wind.
The quarry wall displays a profile showing beds of sand and sandstone interspersed with other features. Perhaps the most distinctive feature is a darker coloured ‘concretion’ layer starting at the topsoil and extending down and to the left as viewed from the quarry floor. This concretion has been cemented together by calcium carbonate, which was likely introduced due to rising groundwater at some time in the past.
The floor of the quarry is littered with blocks of sand and sandstone. The darker ones are much harder; the lighter ones are unconsolidated sand and will crumble easily – the result of being compressed but having no cementing agent necessary for lithification.
St. Paul’s United (Methodist) Church (waypoint 2)
A notable building constructed using Boissevain Formation sandstone is the former Boissevain Methodist Church, built in 1893. The stone, sand, and lime used in the construction were locally sourced. Some limestone was also imported from Garson, Manitoba (“Tyndall stone”) for decorative purposes. The sandstone blocks are held together with mortar. As a general principle, the harder the sandstone blocks, the less mortar is required to reinforce them.
There are other surviving buildings in town built from these materials. See if you can identify any as you drive around.
Sources
- Government of Manitoba. MB GeoTour 8 – Boissevain Methodist Church with Upper Cretaceous Boissevain Formation building stone. <https://www.youtube.com/watch?v=mv0mNMZ9-7o>
- Government of Manitoba. MB GeoTour 9 – Boissevain sand north quarry within the Upper Cretaceous Boissevain Formation. <https://www.youtube.com/watch?v=l621vtTFFsI>
- Mitchell, Brooks. All About Sandstone. 09 April 2016. <http://geology.about.com/od/more_sedrocks/a/aboutsandstone.htm>
- Turtle Mountain Conservation District. Taking Care of Our Watershed – A Watershed Plan for the East Souris River Watershed, Manitoba, Canada. http://www.tmcd.ca/wp-content/files_mf/esrplanmay302006final201215.pdf
- https://en.wikipedia.org/wiki/Geological_formation
- https://en.wikipedia.org/wiki/Sand
- https://en.wikipedia.org/wiki/Sandstone
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To log this earthcache as found, first e-mail or message me the answers to the following questions (don’t post them in your log!). You may log it as found without hearing a response from me, but e-mails with missing or poor answers to the first five questions may be deleted, and the cacher notified as to the reason(s) why. For the first three questions, please remain on the road allowance, as the property owner has not granted permission to walk up to the quarry.
Questions
1. Describe the colour and thickness of the concretion.
2. What is the approximate height of the quarry at its tallest point?
3. Though we know calcium carbonate was a cementing agent, what evidence do you see to suggest iron oxide may also have been present here?
4. Note the relative ratio of sandstone to mortar in the church walls (you don’t need to provide numbers). What does the quantity of mortar used suggest about the relative hardness of this sandstone?
5. Which features of the church are adorned with white limestone?
6. (Optional) Post a photo of yourself with either the quarry or the church (or one of each) in the background.
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