Dakota Sandstone 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?
2. Describe the color of the Dakota Sandstone.
3. Estimate the height of the exposed sandstone at this location.
4. Look closely for cross bedding (mostly horizontal lines of sediment) in the sandstone. Based on this, what direction do you think the water was flowing when it deposited the sandstone?
This Earthcache is located along a stretch of the bike trail that follows Antelope Creek. If you are without a bike, you can access the earthcache by parking at the Lincoln Zoo parking lot. Enjoy!
The rocks lining the banks of Antelope Creek belong to a special group of sediments called Dakota Age Sandstone. Geologists estimate that this sandstone is more than 130 million years old and can be found underlying most of Nebraska. This particular formation can extend as far as 100 feet below the place where you are now standing.
Dakota sandstones are major producers of oil and water. Salt water can be found in some parts of the sandstone--especially throughout the Lincoln area. The saline water is thought to have originated from an ancient sea that once covered the area.
During the age of the dinosaurs, much of central North America was under water--under a great, 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 North American 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 Cretaceous Era.
It was during this time of the Western Interior Seaway that deposition of the sediments that would eventually become Dakota sandstone began. The deposition of the Dakota sandstone also marked a reversal of millions of years of erosion. As the inland sea formed, the base level of the rivers in the area rose. The base level or a river, often referred to as the mouth of the river, is the lowest point at which it can fall. For the majority of large rivers, the base level is seal level; however, smaller rivers and streams use the level of a larger, nearby river or lake to determine its base level. All rivers and streams erode toward sea level--the ultimate base level. When the ocean levels rose and as the middle of North America became flooded, a new, higher base level was created. The raising of the base level during this time period reduced the velocity (speed) of the area rivers and caused the rivers to deposit Dakota sandstone; the rise of the base level did not allow the rivers to sustain high volumes of sediment because of the decrease of velocity.
The deposition of the Dakota sandstone occurred along the coast of the Western Interior Seaway--a coast that moved further and further eastward as the inland sea grew in size. This created a ridge of Dakota sandstone under much of present-day Nebraska. Other traces of Dakota sandstone can be seen in Iowa and Kansas and as far east as portions of Minnesota and Wisconsin.
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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