First of all, I am not a rock girl. In fact, the information on this cache page is pulled from sources that do know about rocks--thank goodness for search engines and a brother who is a real life geologist! So here goes......hope you have fun finding this sciency rock stuff!
This area can be very busy! Pay attention to your surroundings.
NOTE: This EC is wheelchair accessible, but no need to get out of the car as it can be completed from your vehicle.
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The Arkoma Basin is an east to west trending structural low that is about 315 miles (507 km) long and 175 miles (283 km) wide with an area of about 33,800 square miles (87,542 sq. km) bounded by the Ozark uplift to the north and the Ouachita Mountains to the south. (See Image 1)
Before the beginning of Mississippian time, the area called the trough of the Arkoma Basin was exposed and subsequently subsided. The basin then experienced maximum subsidence during Atokan time based on the great thickness of the Atoka Formation. The Atoka Formation consists chiefly of alternating beds of sandstone and shale. This outcrop of the Atoka Formation in Fort Smith, belongs to the Pennsulvanian series of the Carboniferous system. (See Image 2)
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Sandstone is a sedimentary rock composed mostly of quartz sand, but it can also contain significant amounts of feldspar, and sometimes silt and clay. The color of sandstone varies, depending on its composition. Because it is composed of light colored minerals, sandstone is typically light tan in color. Other elements, however, create colors in sandstone. The most common sandstones have various shades of red, caused by iron oxide (rust). In some instances, there is a purple hue caused by manganese.
Sandstone has two major applications, as crushed stone and as dimension stone. Dimension stone is any rock material that is cut into specific sizes, typically as blocks and slabs. Crushed stone is used in the construction of roadways and road structures such as bridges, and in buildings, both commercial and residential. (Source 1)
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Shale is a sedimentary rock composed of very fine clay particles. Clay forms from the decomposition of the mineral feldspar. Other minerals present in shale are quartz, mica, pyrite, and organic matter. Shale forms in very deep ocean water, lagoons, lakes and swamps where the water is still enough to allow the extremely fine clay and silt particles to settle to the floor. Geologists estimate that shale represents almost ¾ of the sedimentary rock on the Earth’s crust. Geologists are specific about the definition of the rock called “shale.” Shale is composed of clay particles that are less than 0.004 mm in size. (Source 1) For reference, a dollar bill is .1092 mm thick.
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To claim a find on this Earthcache, please send your responses through the email on my profile page OR through the message center using the link found near the top of this cache page. Please do not post your responses in your log, other than your images. Found it logs that are not supported by the required information, will be deleted. (There is not a physical cache to find.)
1. Name of this Earthcache: "another brick in the wall, well not really....." along with the people in your party. (One email with answers will cover all geocachers listed in the email.)
2. What are the main colors of the sandstone and shale at GZ?
3. Can you see a tilt or is the formation somewhat flat?
4. Which directional path does this formation go: north/south or east/west?
5. How does the thickness of the sandstone change from the top to the bottom of the exposed formation?
6. Add a picture of you or your party or a navigation device or other personal item with the sandstone formation in the background to your log.
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Sources:
https://mineralseducationcoalition.org (Source 1)
https://scholarworks.uark.edu/cgi
https://pubs.usgs.gov/pp/0221e/report.pdf
https://www.bigbluesaw.com/articles-list/big-blue-saw-designing-for-waterjet/deciding-on-a-material-thickness.html
Brown, Bryan J.; Petroleum Geologist, Arkansas Oil and Gas Commission
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