Silver Bluff - Earthcache EarthCache
Silver Bluff - Earthcache
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HAPPY 10th ANNIVERSARY EARTHCACHES! (January 10, 2014).
At the posted coordinates, you will have an excellent opportunity to view the Silver Bluff Outcrop and study some of its special features discussed below.
This Earthcache is in the Alice Wainwright Park. Park hours are Sunrise to Sunset. Please observe these posted hours and rules.
Silver Bluff
Silver Bluff is part of a low coastal ridge (a portion of the Atlantic Coastal Ridge, see GC42P2M) that averages approximately 8 feet above sea level to the base of this outcrop. It is a limestone ledge made up of the Oolitic Limestone (see GC18KXJ). The Miami Limestone, previously known as the Miami Oolite, was formed during the Pamlico sea stand in the Sangamon and Early Wisconsin Glacial Periods (130,000 years ago), when the sea level was approximately 23 feet higher than today. The Silver Bluff was formed by wave action thousands of years ago during a recession in the Middle Wisconsin Glacial Period (10,000 years ago) when the sea level was only about 8 feet above the present sea level. It has been described as a wave-cut bench because it was formed by ocean wave action, and is part of a 2 mile long terrace between the Miami River and Coconut Grove.
Special Features
Fracture
At the posted coordinates you should be able to spot a vertical fracture. This was likely caused by the dissolution of the limestone carbonate by acidic rainwater. As slightly acidic rainwater (carbonic acid) moved into the small opening in the limestone, it dissolved the limestone and, over a long period, created this deep fracture.
Joint
About 50 feet east of the posted coordinates (near the coconut tree), along the limestone wall, if you look closely, you will see a steeply inclined joint between two layers of the rock. This is a natural fracture in the formation and was not caused by any mechanical stresses on the formation.
Bioturbation
Bioturbation is present in the form of fossilized burrows which are created by a crustacean called the Callianassid shrimp. At the posted coordinates, near the base of the large tree, you should be able to locate a highly visible fossilized tube in the limestone created by this burrowing shrimp. This one is damaged, so you are able see that it is hollow. There is a 2nd tube about 50 feet to the east in excellent condition, but locating it is optional.
Completing the Earthcache:
To get credit for completing this Earthcache, please send your answers to the following questions to our profile Email. Incorrect answers may lead to further questions from us, or deletion of your find log. You may log your find after you have transmitted your answers.
1. During which Glaciation Period was the Silver Bluff formed?
2. How was the Silver Bluff ridge formed?
3. Estimate how high the base of the Bluff is above the present sea-level (feet or metres).
4. Please locate and study both the Fracture and the Joint? Which one has a visible opening/gap?
5. What is the length and width (diameter) of the Callianassid shrimp’s fossilized tube near the tree? Inches or cm please.
Optional:
1. Photos are optional, but they are welcomed. You may add photos of you and your party standing in front of the wall.
2. Walk east along this section of the Bluff and study the face of the wall. Can you find the 2nd fossilized tube?
References include the following:
Goescienceworld.org
USGS.gov
Artesian water in Tertiary limestone in the southeastern States 1966, Stringfield, Victor Timothy USGS Professional Paper: 517
Wikipedia
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Treasures
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