Miami Oolite EarthCache

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Hidden : 1/14/2008
Difficulty:
2 out of 5
Terrain:
1 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

A highly accessible urban location gives an excellent view of the Miami Oolite, a limestone which comprises most of the surface geology for Miami-Dade County.

A Short Primer of the Geology of South Florida
(Source material: (visit link) and (visit link) also: Land from the Sea by John Edward Hoffmeister)

The landscapes we see today in South Florida are a direct result of geologic events of the past. For example, the rocks beneath the Big Cypress Swamp are among the oldest in South Florida. Six million years ago, a shallow sea covered this area. Sediments of silt and sand and particles of calcium deposited on the bottom of this sea gradually cemented into limestone. Today this rock is called the Tamiami Formation.

Other rocks beneath South Florida were formed during the time of the Great Ice Age. Although no glaciers developed in Florida, their effects were felt here. As glaciers in other areas of the world expanded, much of the earth's water supply was trapped in the ice. Sea levels in South Florida lowered as much as 300 feet below present levels.

The Great Ice Age was actually four shorter ice ages with periods of warming in between. During these warmer "interglacial" stages, the ice melted and returned to the sea. The last interglacial stage occurred about 100,000 years ago (The Pleistocene). At its peak, the sea level in South Florida rose 100 feet above present levels.

The rocks beneath Southeastern Florida were formed in this sea. Calcium carbonate settling out of the water coated tiny bits of shell or sand in layer upon layer. The resulting spherical grains of limestone are called ooids (named for their fish egg appearance). The Atlantic Coastal Ridge which runs from Mahogany Hammock northeast to Miami was formed as long shore currents pushed the ooids up into a long ridge. The ooids later cemented into rock known as Miami Oolite. Miami Oolite also covers most of the area east of Everglades National Park and most of Florida Bay.

As in most areas of South Florida, subtle changes in elevation result in dramatic changes in vegetation communities. Pine forests are found on the high ground of the Atlantic Coastal Ridge. Where fire has been excluded, pines give way to hardwood hammocks. In wetter areas near the end of the ridge, dwarf pond cypress grow. South of the ridge sawgrass prairies take over again. A narrow band of mangroves fringe the southeast coast, and the shallow waters of Florida Bay today provide an abundant food supply for great numbers of wading birds.

The Miami Limestone or Miami Oolite occurs at or near the surface in southeastern peninsular Florida from Palm Beach County to Dade and Monroe Counties and in the keys from Big Pine Key to the Marquesas Keys. The Miami Limestone consists of two facies: an oolitic facies and a bryozoan facies. The oolitic facies consists of white to orangish gray, oolitic limestone with scattered concentrations of fossils. The bryozoan facies consists of white to orangish gray, sandy, fossiliferous limestone. Beds of quartz sand and limey sandstones may also be present. Fossils present include mollusks, bryozoans, and corals.

This Earthcache Site:
At this earth-cache location, we see an oolitic facies exposed by the mechanical cutting of the rock to make room for road right-of-way through this natural “high spot”. This site, which is in the Village of Pinecrest, occurs in the midst of the Atlantic Coastal Ridge. The natural habitat here was pine rockland (see GCMJJP or GCM8DB). The Village took its name from the native slash pines (Pinus elliotti var. densa) that still persist among homesites despite the clearing of the habitat. The trees you see on top of the exposed face are not the native conifer, but an invasive-exotic angiosperm called Australian pine (Casuarina equisetifolia) (see GCX86X). Another excellent exposure of the oolitic facies of the Miami oolite is observable at GCJWE8.

Note that much of the striations in the rock occur at an angle. This is due to a phenomenon called Cross-bedding. Wave action during the formation of this rock was from the south. The constant movement of water layed these sediments at this angle. If you study the rock more closely, you will also notice the occurrence of tubes. These are typically the casts left by tree roots or marine organisms.

To claim credit for this earth-cache, take a picture of yourself at the site and answer the following questions:
1) Is this “coral rock”?
2) Is the origin of this rock organic or inorganic? (Organic = was the rock or parent material formed by living organisms?)
3) Describe the colors you see in the rock.
4) Measure several of the tubular casts and provide a length range.

Once your answers have been verified, please post your picture as you log the cache.

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