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7 Souvenirs of August


Dolostone Fossil Formation Earthcache

A cache by PathfinderMark
Hidden : 9/11/2009
In Wisconsin, United States
1 out of 5
1.5 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

This easy earthcache is at a pulloff in a roadside at a corner.
There is a good shoulder, use it. The cliff itself is a roadcut set
back only about 10' from the road, and thus is easily accessible by
most cachers.

Dolostone is one of the greatest mysteries to geologists. It is a rock that is very similar to Limestone, yet has an extremely high level of magnesium. The question is, how did the magnesium infiltrate into the limestone? Magnesium is found is salty sea water, but as you look around you, you may realize that you are at least 1,000 miles from the nearest ocean. Partial answer is found of course thatin ancient times, this whole part of what is now the North American Continent is believed to have been associated with a warm salty Silurian sea. In nearby Petosky MI, coral fossils (Petosky Stones) give yet another evidence of salt-living organisms. Whether that was part of the Pangea plate movement, a diluvian-era global flood catastrophe, or a meteoric splash-down (and several other possibilites) remain options in the geologic debate.

We look at the Dolostone, complete with its layers (sedimentary structure) and its differing levels of eroding in the cliff beside us and we must wonder: “How did this happen?”

There are at least three explanations:
1) The hypersaline model -- In this model, evaporation rates exceed evaporation rates in the coastal area. This leads to the precipitation of gypsum and aragonite, which both contain calcium. The calcium is being removed from the water, and as a result raising magnesium to calcium ratio from 5:1 to 10:1. The waters that are left behind are magnesium rich, and they flow through the coastal sediments to form the dolostone.
2) The mixing zone model -- focuses on the mixing of ocean and meteoric waters near the coast. Within this zone, waters are brackish and are potentially rich in magnesium from the ocean water mixing with the magnesium rich meteoric waters. This increase in magnesium within the sediments form the Dolostone.
3) The Seawater model -- new seawater is constantly being cycled in and out of the sediments as sea level fluctuates. After the water enters the sediment, the magnesium replaces the calcium in the sediment. This would mathematically the whole content of the modern oceans to have washed through the upper levels of the “Knox formation” of which the Dolostone formation is the most evident layer. This would thus suggest a much larger ocean or potentially even a global catastrophe that increased salinity and/or magnesium in the waters that engulfed this continent.

Dolostone is part of a moderately hard, yet sedimentary rock layering that crosses this part of Wisconsin, Illionis, and parts of Michigan and New York State. It is used in gravel driveways, as a part of asphalt and pavement, and railroads use it as track ballast.

Dolostone is primarily composed of the skeletons of pre-historic coral reefs (corals, sponges, other small cephalopods). Instead of forming limestone however, as normally happens, they formed Dolostone because of the magnesium-rich rock replacement process described above.
Hardness testing tools:
Fingernail – 2.5
Penny – 3.0
Butter knife / pocket knife blade – 5.5
Penny nail – 6.3-6.5
Use these tools to determine the harness of a piece of Dolostone (see logging requirement #3).

Congrads to
Team Hemisphere Dancer for FTF 9/20/09.

Logging Requirements: Send the answers to #1-#4 to me through my geocaching profile.
1. List the name "GC1YH3Y Dolostone Fossil Formation Earthcache" in the first line of your email. Also, list the number of people in your group.
2. Count the number of layers of FOSSILS that you can see in
this formation. Describe what the different fossil structures LOOK like (ex. Honeycomb or piderweb-like or monovalve gastropods, etc.)
3. Scratch the Dolostone using the tools listed above to determine the relative hardness of Dolostone. List that approximate hardness here.
4. (Per current guidelines, photos are no longer allowed to be required. HOWEVER they are encouraged, since they can help clarify that you have visited the location if your other logging requirement answers are vague). Take a picture of yourself and your GPSr with the rockface
visible behind you. Post the picture with your log.

I will only respond if you have incomplete
logging requirements. Go ahead and log your cache

Salt the Sandbox -- (visit link)
Journal of Sedimentary Research -- (visit link) -- (visit link)

Additional Hints (No hints available.)

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104 Logged Visits

Found it 100     Didn't find it 1     Write note 2     Publish Listing 1     

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Current Time:
Last Updated: on 8/19/2014 11:17:41 AM Pacific Daylight Time (6:17 PM GMT)
Rendered From:Unknown
Coordinates are in the WGS84 datum