Superior Craton EarthCache
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In order to count this Earthcache as a find, you must complete the following tasks and email the answers to me.
1. What is the elevation at ground zero?
2. Estimate the height of the outcrop of rock at ground zero.
3. What type of rock makes up this ridge?
4. Can the other two types of rock be seen from this overlook? If so, where?
This Earthcache, located in Ramsey Park, will take you to the Seime Overlook, where you can enjoy a view of the Redwood River as well as the basement rock of the Superior Craton. Not only is Ramsey Park host to picturesque views, but it also provides four miles of hiking trails, picnic shelters, campgrounds, and a zoo. Don’t forget the camera!
The extreme outer layer of the Earth is called the lithosphere. Consisting of the crust and upper mantle, the lithosphere is generally cool and rigid. The lithosphere is broken up into what are called tectonic plates. On Earth, there are currently eight major plates and many minor plates. Tectonic plates move in relation to one another at one of three types of plate boundaries and are responsible for earthquakes, volcanic activity, mountain-building, and the formation of oceanic trenches.
Within these tectonic plates are cratons. A craton is an old and stable part of the continental lithosphere that has survived several cycles of merging and rifting (breaking apart) of continents. The term “craton” is used to distinguish the stable portion of the continental crust from regions that are more geologically active and unstable. Cratons are composed of ancient basement rock (rocks found below a sedimentary platform). Basement rock is comprised of metamorphic or igneous rock. Igneous rock is formed by magma or lava cooling and hardening. This can happen either above or below the earth’s surface. In this area, the igneous rock that makes up the basement rock was formed deep below the surface of the earth. Metamorphic rock is the result of the transformation of an existing rock type by heat or pressure. Very little of the basement rock can actually be seen for it the majority of it lies below the surface of the earth--extending deep into the lithosphere and even into the Earth’s mantle in some places. The basement rock that has surfaced is usually covered by other sedimentary rock. There are a few exceptions, however, such as Ramsey Park, where there are large outcroppings of the basement rock.
Geologists have described cratons as shields and platforms. In geological terms, a shield is a large area of exposed basement rock that creates tectonically stable areas. In all cases, the exposed rocks are more than 570 million years old and sometimes date back to 2 to 3.5 billion years old. A platform is were sediments and sedimentary rock piles on top of the exposed basement rock, covering it.
Cratons are classified based on location and formation. The Superior Craton is what underlies this area. This craton forms the core of both the North American continent and the Canadian Shield. It underlies Manitoba, Ontario, Quebec, and Minnesota. The bedrock of the Superior craton was exposed in this area during the end of the Late Pleistocene Era (Ice Age). As the Minnesota River Valley was being excavated by the Glacial River Warren, the river scoured the earth down to Precambrian bedrock (rock formed before the appearance of hard-shelled animals). Because of the Glacial River Warren eroding the earth, a section of igneous and metamorphic rocks were exposed. These rocks have been the subject of intense geological study for the last 60+ years. The rocks exposed here represent the southern part of the Superior Craton and make up the Minnesota River Valley subdivision of the craton. The basement rocks found in this region--specifically in Ramsey Park--are some of the oldest rocks on Earth.
Three main types of rock can be found scattered throughout Ramsey Park: morton gneiss, sacred heart granite, and kaolinite. Morton Gneiss, a darker-colored rock, is considered to be the oldest rock in North America at 3.6 billion years old. This type of rock makes up the large part of the basement rock in this area and is especially exposed throughout the park. Sacred Heart Granite, which is about a billion years younger, can be found here in large amounts. In fact, Ramsey Creek runs over Sacred Heart granite at the falls. The third major type of rock in this park is kaolinite, a yellowish-rock, and is the youngest rock in Minnesota. This rock was created by the chemical weathering of both the Morton Gneiss and the Sacred Heart Granite. Kaolinite is formed from rocks found in hot, moist climates, such as tropical rainforests about 100 million years ago. This means that Minnesota had a tropical climate when this rock was created. Acids from the rotting vegetation in the area moved into the cracks and fractures in the Morton Gneiss and Sacred Heart Granite and broke down their mineral components. This process caused these two rocks to metamorphose into kaolinite. Kaolinite is the main ingredient in porcelain.
NOT A LOGGING REQUIREMENT: Feel free to post pictures of your group at the area or the area itself - I love looking at the pictures.
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