AW Geology lesson

From WildWiki

Educational Goals:

At the conclusion of this lesson, students will have learned:

Return to Water Curriculum

1. A basic overview of the history and geology of the Canadian Shield

2. How major rock types were formed, and to identify them

3. To identify major rock characteristics

4. How glaciers carved out geological features of the area, and how to identify such features

History:

Wabakimi Park is located within the Canadian shield, a geological area of exposed rock that extends outward in a broad circle from Hudson Bay, covering an area of 4.82 million square kilometers in eastern Manitoba, much of Ontario and Western Quebec, and northern portions of Minnesota, Wisconsin, and Michigan. The exposed rocks are crystalline igneous and metamorphic rocks, about 80% of which are granite. This bedrock was formed during the Precambrian era, starting as long as three billion years ago. While this bedrock is the basis for the geology of this area, glaciers within the last 500,000 years have been extremely important in shaping the modern geological landscape of the Canadian Shield. Glaciers removed sedimentary rocks and carved out the millions of lakes that are characteristics of the Shield.

Wabikimi is the site of "maximal erosion". The glaciers in the Wisconsin period (the last or most recent glacial period) eroded much of the area from Hudson Bay to the upper Great Lakes and deposited it in the area, ironically enough, around Richmond, Indiana (that is why there is such good soil in the midwest). What it left behind was predominantly flat bedrock and lakes. The bedrock here is some of the oldest in the world. This contributes to the ecology of the area in the fact that soil is nonexistant or sandy, and all the plants had to adapt to minimal soil with a poor nutrient load. But life continues as lichen begin to grow in cracks and fissures in the bedrock and mosses grow in the more forested areas.

Glaciers act as "bulldozers" and as sandpaper. You can see evidence of both in Wabikimi.

As bulldozers, glaciers push debris into piles, called moraines. You can also see evidence of other types of pushing including:

• Glacial erratics- random, large boulders precariously balanced in the middle of nowhere
• Eskers- "glacial poop". As glaciers melted and receded, streams often formed in the middle of the glacier. As it receded, these streams gathered debris and dumped it off the glaciar in a relatively narrow and linear line. These are evidenced in Wabikimi by long, linear stretched of forested areas.
• Kettles- these are left over ice chunks from the glaciers. Basically, a large "ice cube" with nowhere to go. As it melts, it creates bogs with high acidity. Sphagnum moss loves this habitat as does Tamarack.

Major Rock Characteristics of Wabakimi:

Gneissic---alternating bands and layers of light and dark minerals, in coarse metamorphic rocks.

Foliated---contains distinct layers (mineral bands separated by rock).

Lineated---parallel mineral bands.

Massive---No foliation or lineation.

Migmatite---a rock containing metamorphic and igneous rocks, in alternating layers.

Glacial Features:

The glaciers that covered the Canadian Shield during the Pleistocene Ice Age, which ended only 10,000 years ago, are responsible for many of the physical geological characteristics of the landscape.

Glacial Polish---When glacial ice moved across the ground it picked up the loose soil and rocks at the grounds surface, which then attached to the bottom of the ice, making it very coarse. The movement of the coarse ice over surface rocks then eroded and smoothed these rocks. The large, unlayered, crystalline and hard rocks characteristic of much of the Canadian Shield are the most polished. This smoothness can be noted in such rocks within Wabakimi.

Glacial Striations---Glaciers often picked up large boulders, in addition to the smaller rocks on the ground surface. When a boulder caught in the bottom of an ice sheet was dragged across the polished ground surface, it would cut out a groove. These grooves or lines are common features in the Wabakimi area.

Till---When the rocks and soil on the moving ice were deposited, they were scattered across the landscape in a disorganized array of rocks, pebbles, sand, boulders, silt, and clay. This scattered material is called “till”.

Moraine---This term is used to describe the topography of accumulation of till. There are several types of moraines.