Karst in Southern Ontario and the Niagara Escarpment

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Reviewing Literature Concerning Karst in Southern Ontario with a Specific Focus on the Niagara Escarpment Skyler MacGowan, 250634552 Geo 3000Y Term Paper due Nov 16, 2015

Transcript of Karst in Southern Ontario and the Niagara Escarpment

Page 1: Karst in Southern Ontario and the Niagara Escarpment

Reviewing Literature Concerning Karst in Southern Ontario with a Specific Focus on the Niagara Escarpment

Skyler MacGowan, 250634552 Geo 3000Y Term Paper due Nov 16, 2015

Page 2: Karst in Southern Ontario and the Niagara Escarpment

Geological History of the Niagara Escarpment The Niagara Escarpment is a 725km long escarpment running from New York through

Ontario, Michigan and Wisconsin1 (figure 1). It formed 400-500 million years ago (mya)

during the Ordovician and Silurian Periodsi at a time when a warm, shallow sea covered

southern Ontario, Michigan, and parts of Wisconsin and New York1. The base layer of

the Escarpment is made up of shale deposited about 450mya and is the remnant of a

large, muddy delta that formed in the sea2. It has a distinctly red colour due to the

presence of iron in the mud that was carried to the area by rivers flowing from the

uplifting Appalachian Mountains to the east whose rocks are rich in iron2 (figure 2).

Overlying the base layer of shale are mixed beds of sandstone, dolostone, limestone and

shale2. Like the shale layer, the sediments in the sandstone layer came from rivers

flowing off the Appalachian Mountains2. The limestone/dolostone layers were created

from marine coral and as we move north there are fewer mixed beds, reflecting a more

stable marine environment2.

The top layer of the Escarpment was created approximately 420mya2. It roughly indicates

the shoreline of the ancient sea, as along the especially shallow and warm waters of the

sea where it approached land there was constant deposition of marine organisms and

these deposited organisms mixed with sediment to form a limestone layer2. During the

Silurian period some magnesium from the seawater mixed in with the limestone layer

causing the formation of the harder dolostone we see today2. The shallow continental sea

eventually dried up about 250mya2, opening up the layers deposited to erosional forces.

i Ordovician Period: 485mya-445mya. Silurian Period: 445mya-420mya.

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The layer of Queenston Shale is quite soft and has eroded faster than the dolostone

caprock, causing the steep face of the Escarpment we see today2 (figure 3).

Karst and The Niagara Escarpment Although the dolostone caprock of the Escarpment is susceptible to the development of

karst features, landforms characteristic of a “typical” karst landscape (i.e. large cave

passages, sinkholes, sinking streams) are generally not well represented along the

Escarpment and those found are almost entirely postglacialii and thus are generally under-

developed3. However, although the Escarpment’s karst features are much less poignant

than in mature karst landscapes, that does not mean karst features along the Escarpment

are absent altogether. Furthermore, as will be discussed, even though karst features along

the Escarpment are relatively immature they can still profoundly impact the drainage

patterns of surrounding areas.

The most numerous and profound karst features in southern Ontario occur along the

section of the Niagara Escarpment running from Manitoulin Island through the Bruce

Peninsula down into Grey County4. The increased prominence of this section results in

greater precipitation and steeper hydraulic gradients, important factors contributing to the

development of karst features3. Additionally, there is minimal overburden along this

section of the Escarpment whereas 22-30 metres of overburden covers much of the rest of

the Escarpment3. Water loses its acidity and hence its ability to form karst features when

it has to first percolate through sediment and thus the fact that there is minimal

overburden on this section of the Escarpment contributes to the proportionally high

number of karst features present there3.

ii The most recent ice sheet retreated roughly 12,000 years ago.

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Why is the Karst on the Niagara Escarpment not More Developed?

As explained, there certainly are karst features on the Niagara Escarpment but as a whole

they are relatively underdeveloped. This is despite the fact that in many ways the

Escarpment and the section from Manitoulin Island down through Grey County in

particular is a prime site for the development of karst featuresiii.

The primary reason for this has to do with the fact that the Wisconsin Ice Sheet only

retreated from southern Ontario about 12,000 years ago3. The movement of this ice sheet

would have removed almost all of the Escarpment’s existing karst features, setting a

maximum timeframe of about 12,000 years for the current karst development to have

occurred3. Mature karst features such as the caves found in south-central Kentucky

(which started forming 280mya5) develop over millions of years and so the biggest single

reason why karst features on the Escarpment are not well developed is simply because

they have not had anywhere near the amount of time required for these features to

properly form. Furthermore, although the dolostone caprock of the Escarpment is prone

to karst development, dolostone is less soluble than limestone and thus karst features

typically take longer to form in dolostone than limestone3.

Also, as described, between the caprock dolostone and the base layer of shale the

Escarpment contains mixed beds of shale, sandstone, limestone, and dolostone. These

mixed beds thin out as one moves northwards and are mostly absent on the portion of the

Escarpment north of Grey County2. Shale is an aquitard meaning that development of

karst features can only occur within those materials that overlie the shale. Its presence

iii I.E. it’s one of the largest dolostone plains in North America, local water acidity and erosive ability is comparable to that of more southerly locations, it has high precipitation and hydraulic gradients, and in this section of the Escarpment there’s little overlying sediment3.

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south of Grey County is therefore a big part of the reason why karst features along the

Escarpment become less common south of Grey County. Finally, as explained, south of

Grey County the Escarpment is overlain by up to 30 metres of glacial till which

substantially reduces the water’s ability to dissolve the dolostone layer3.

Moving Forward The karst features on the Niagara Escarpment are almost all very young and with time

they will become more profound and influence drainage patterns to a greater degree,

especially along the section of the Escarpment running from Manitoulin Island down

through the Bruce Peninsula and into Grey County. In a 1976 study by Cowell on karst in

the Bruce Peninsula, Cowell hypothesized that eventually almost all drainage into

Georgian Bay from the Bruce Peninsula will take place underground3. However, it will

be a very long time before a situation like this occurs because as mentioned mature karst

features and landscapes develop over a very long time.

Having said this, just because the Niagara Escarpment and southern Ontario do not have

many well-developed karst features that does not mean these areas cannot exhibit

drainage patterns similar to what one would expect to see in a mature karst landscape.

Once conduits are 1mm or greater in diameter they can become significant in the

karstification process4 and southern Ontario, including the Niagara Escarpment has quite

a few features like this that have developed in the past 12,000 years since the last ice

age6. This has important implications for groundwater protection strategies in southern

Ontario and along the section of the Escarpment running from Manitoulin Island down to

Grey County in particular7.

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A tragic example of what can happen when karst features and their impact on local

drainage patterns are not well understood and appreciated is the Walkerton tragedy of

2000 in which E.coli contaminated Walkerton’s water supply, causing seven fatalities.

Subsequent tracer tests found that water moves very quickly (200-500m daily) through

the thin overburden and karst features in the carbonate bedrock underlying Walkerton8.

These karst features allowed runoff from nearby farms to rapidly enter the community’s

wells without having undergone the normal filtration process that would typically take

place in an area void of any karstic features.

So, even though the Niagara Escarpment and southern Ontario more generally may not be

a mature karst landscape, karst features certainly are present in these areas and

consequently at times they can exhibit drainage patterns characteristic of mature karst

environments. In conducting my research for this paper I found a general paucity in

research of karst in southern Ontario as there have only been a few researchers who have

looked into this topic and most of their literature has focused exclusively on the Bruce

Peninsula. Therefore, going forward, more research on karst in southern Ontario is

required as karst areas are highly susceptible to groundwater contamination and as we

saw with the Walkerton tragedy, a failure to understand such drainage systems can have

dire consequences for human health.

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Figure1:MapoftheNiagaraEscarpment

Figure2:StrippedPor0onofQueenstonShaleatCheltenhamBadlands

Note: red colour of the shale is due to presence of iron which was transported here by rivers flowing from the Appalachian Mountains whose rocks are high in iron.

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Figure3:CliffFaceoftheEscarpmentClosetoRa9lesnakePoint(Milton)

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References 1) The Niagara Escarpment | Bruce Trail. Retrieved November 6, 2015, from http://brucetrail.org/pages/about-us/the-niagara-escarpment 2) Gilhespy, B. (2015, April 15). Escarpment Geology: Another part of our Living Landscape. Bruce Trail Magazine, 22-29. 3) Cowell, D. (1976). Karst Geomorphology of the Bruce Peninsula, Ontario. Hamilton, Ont., Ontario: McMaster University. 4) Brunton, F., & Dodge, J. (2008). Karst of Southern Ontario and Manitoulin Island. Sudbury, Ontario: Queen's Printer for Ontario. 5) Wagoner, J., & Cutliff, L. (1985). Mammoth Cave. Arlington, Va., Virginia: Interpretive Publications. 6) Brunton, F. (2013). Karst and Hazards Lands Mitigation: Some Guidelines for Geological and Geotechnical Investigations in Ontario Karst Terrains. Sudbury, Ontario: Queen's Printer for Ontario. 7) Harvey, D. (2003). Grey and Bruce Counties Groundwater Study. Waterloo, Ontario. 8) Worthington, S., Smart, C., & Ruland, W. (2001). Karst hydrogeological investigations at Walkerton. Dundas, Ontario.