Chalkstone Along the Missouri EarthCache
Chalkstone Along the Missouri
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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. Describe the color of the chalkstone.
2. How many layers of chalkstone can be seen? How can you tell these are separate layers?
3. Describe the effect the Missouri River and other erosion has had on the chalkstone.
4. Estimate the height of the chalkstone.
This Earthcache is located at the Myron Grove Public Water Access along the Missouri River. Although this area only provides boat launch services, vistas of the Missouri River and the chalkstone bluffs can be seen here. There is also an informational sign explaining more about the Missouri River. Enjoy!
The ridges that border the Missouri River on its southern edge at this location is made up of Niobrara Chalk that was created during the dinosaur age. When the dinosaurs roamed the earth, the world was warm and the oceans were at a high level. Present-day North America was divided by a large, shallow, inland sea known as the Western Interior Seaway. This seaway was created as two tectonic plates collided, causing the Rocky Mountains to form and creating a depression in the middle of the continent. This large depression and the high sea levels at the time allowed waters from the Arctic Ocean and the Gulf of Mexico to flood the central lowlands, creating a sea that grew and receded.
During the time of its existence, the inland sea was filled with shell fish. When these organisms died, their skeletons drifted slowly downward--along with their calcium shells. This resulted in a slow, soft, invisible rain of tiny flecks of calcium carbonate that very, very slowly built up at the bottom of this sea. These fossilized shell fish built up for tens of millions of years and eventually created the chalkstone ridges that now dot the Missouri River today.
The chalkstone formation was exposed with the sea retreated and was covered again with debris by the latest glacial episode. Following the glacial period, erosion worked to expose much of the chalkstone. In southeastern South Dakota, weathering and glacial erosion have completely removed the Niobrara Formation except for a few areas along the Missouri River.
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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