Red Rocks Unconformity Earthcache
In Colorado, United States
Size:  (not chosen)
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In this earthcache you will learn about geologic unconformities.
The earthcache is located in the Red Rocks Park, which is easily accessed from Highway 470 to Highway 74 through Morrison. There are numerous signs to direct you to the park. Proceed to the Visitor Center. The earthcache is located very near the Top Circle Lot parking area, close to the Visitor Center.
At the coordinates you will find a geologic unconformity.
An unconformity is a gap in the sequencing of the layers of rock. Layers of sedimentary rock are laid down flat, parallel to the earth's surface. This is the law of original horizontality. Younger or new layers always overlie the older layers. This is the law of superposition. An unconformity exists when this orderly stacking of layers of rock is interrupted or broken.
There are four kinds of unconformities:
1. Angular unconformity
An angular unconformity occurs when the rocks on the top are level and the rocks below are tilted. This was the type of unconformity that was originally discovered in the 1780's by James Hutton in Scotland. He noticed the unconformity and recognized that significance of the amount of time that must have passed for the formation of the unconformity. An angular unconformity occurs when the oldest rocks are laid down, and then these rocks are tilted and eroded flat, and the next set of newer rocks are laid down on top of the flatened, but tilted rocks. See the drawing.
A nonconformity occurs when sedimentary rocks are laid down on top of a non-sedimentary rock, like a lava flow or other type of igneous rock, e.g. granite or gneiss.
A disconformity occurs when there is a gap in the succession of the rock layers. The older rocks are laid down, but because of erosion, some of the normally-expected subsequent layers of rock are missing. Then newer layers of rock are formed on top of the older rocks. The result is a sequencing of parallel rock layers that do not contain all of the expected layers.
A paraconformity is a discontinuity that is not visible. These may be difficult to observe and may discernable only from other investigations. An example of a paraconformity would be a unexpected gap in the normal layer of fossils contained in the rocks.
At the coordinates you will see the unconformity. You can walk right up to the plaque and examine the two types of rock. How does the gneiss feel? It is rough or smooth? How does the sandstone differ?
To log this earth cache you must do the following:
1. Determine the length of the gap in TIME between the formation of the two types of rock of the unconformity.
2. Determine what type of unconformity this is.
3. Describe difference in the physical characteristics of the two types of rock -- the gneiss and the sandstone.
4. What do you think caused the erosion that resulted in the large gap in time?
Please send me an email with the answers. Please do NOT post the answers in the log.
(No hints available.)
Last Updated: on 3/18/2015 3:07:52 PM Pacific Daylight Time (10:07 PM GMT)
Coordinates are in the WGS84 datum