Wednesday, November 23, 2011
Florida Key's Narrative
Kyra Claxton
October 7-9, 2011
GLY 3552C (Sed Rec 1)
Friday, October 7—Venice Beach, FL 10:00am
Venice beach was a beautiful place. After parking the vehicles and a short walk through the dunes, reveals a picturesque view of crashing waves, sandy shoreline, and annoying seagulls. It was low tide, so the water would crash over the Low Tide Terrace. It is in this area that the wave’s energy is concentrated the most. With this energy; carbonate materials, quartz, and other organic material is broken down into grain size proportions. The swells were roughly a foot tall and strong enough to push a person over. I know because I almost fell several times. The beach face did make it a little difficult to avoid the sudden waves. In some areas the beach face was a meter in height.
Venice Beach can be considered a kind of barrier beach (figure 1). This is mainly due to the multiple sand dunes that lined the beach. A barrier beach acts as a natural defense for the mainland and disperses a storms immediate energy.
 |
| Figure 1 |
Saturday, October 8 ---Windley Key Fossil Reef Geological State Park 9:00am
Windley Key quarry was a beautiful little park. The visitor center holds tons of information about the creation of the quarry, the surrounding geological area, and interesting facts about coral reefs. Windley Key quarry was formed in the early 1900’s and was opened until 1960’s. The quarry was first used for building the railroads in the keys. It was later used to create decorative rocks called “Keystones” (Windley).
Let’s take a slice of the earth. Starting at Windley Key and going five miles offshore (figure2)
 |
| Figure 2 The Key Largo Limestone makes for the base structure at Windley Key. Indicated in orange, is the new growth of coral. Yellow represents sediment and broken, dying coral. Blue is to designate the areas of sediment that has begun to lithify and become limestone. Although Key Largo limestone is mainly fossilized coral; many things can determine from a core sample. For example, we can determine when the sea level dropped, how long the area remained dry, temperature, water quality, and other extreme events.  In the visitor center, an approximate three meter core sample was taken from a well known dive/snorkel site called Hens& Chickens. This core sample was named the “Bicentennial Core” (Figure 3). The sample was almost entirely composed of fossilized coral that built upon itself. Coral has banding similar to that of a tree’s growth rings. This is called Sclerochronology. This method is used to determine the growth of lime-producing marine organisms. With careful calculation of the growth rate of different types of corals and the length of the core sample, it has been determined that the core sample held at the visitor center, dates back over 360 years. The banding in the coral also shows signs of stress from freezes, low water quality, and climate changes (Windley). Figure 3  In other core samples taken from the Key Largo limestone, a laminated band would break up the fossilized coral structure. This laminated limestone, also called calichee, formed through the leaching and reprecipitation of calcium carbonate, CaCO3. This process only occurs on dry land. Therefore, by taking various core samples throughout the Key Largo Limestone, we can see where and when dry land once existed in the keys (Figure 4) (Windley).Figure 4  Throughout the limestone, streaks of red were visible. These streaks were actually accumulation of red Sahara desert sand (figure 5). At first, it is confusing to think that sand from an African desert can be in limestone from the Florida Keys. In Africa, desert sand storms occur regularly. If the storm is large enough, the dust can get caught up in trade winds (figure 6). These trade winds carry the red dust and deposit it throughout the Florida Keys. Most of this sand settles in the coral reef and eventually becomes a part of the limestone. This process still goes on today (Windley). Here is a cool side note. In America; when we see a beautiful deep red sunset, it’s actually the sun reflecting off of the sand during a sandstorm in the Sahara desert. figure 5, Red Dust in Key Largo LimestoneFigure 6, Wind Currents  After exploring the visitor center, our class went outside to investigate the quarry (figure 7).   Figure 7 The area was fairly open, with scattered limestone blocks that were left behind. The quarry wall ranged from around 1.5 to 2.5 meters in height. The challenge was to try and identify the different types of coral in a section of the quarry wall. My section was roughly 1.6 meters in height and one meter in width (figure 8). Windley Key quarry. Figure 8 Quarry wall    Figure 9 Brain coral Figure 10, Star Coral Figure 11, Sea Urchin Spines & fragments Saturday, October 8 ---Blue Hole Quarry, Big Pine Key 11:00am  In essence, Blue Hole Quarry is more of a large pond now. However the geology of Blue Hole is different from that of Windley Key Quarry. Instead of being made of Key Largo limestone, it is made of Miami Limestone. Miami Limestone is layered underneath the Key Largo limestone. Blue Hole Quarry shows some of the first exposures of the Miami limestone in the southern keys. Like Windley Key Quarry, Blue Hole was used to make roads and railways. It was easier to use local limestone instead of hauling in limestone from another site that was farther away (Blue Hole). You will however, see some Key Largo limestone that was hauled into to Blue Hole for roads.  The Miami limestone here also shows the same redness as that of the Key Largo limestone (Figure 12), that had the Sahara dust. The Miami limestone also shows some of the erosion that is occurring to the exposed surfaces. Weaker sections of the limestone are easily eroded away, while the stronger sections are smoother and withstand erosion a little better. Figure 12 Chemically, both the Miami limestone and the Key Largo limestone are essentially the same thing. However it’s their physical appearances that help to determine the differences between the two. The Miami limestone is primarily all ooids; whereas the Key Largo limestone is a collection of fossilized shells, coral, and other marine calcium carbonated material. Even in thin sections, these two stand out. When I was cutting billets to make thin sections, I noted that the Miami limestone is softer, as it was cut fairly quickly. The Key Largo Limestone was much harder in comparison, as it took more time to cut through the tough limestone. Under the microscope, the Key Largo limestone appears as though everything was very fluid before hardening (figures 13 & 14). Miami limestone is all ooids that are cemented together (figures 15 &16).   Figure 13 Figure 14 Key Largo Limestone Plain Light 40x   |
Figure 15, 40x Figure 16, 100x
Miami Limestone Plain Light
Saturday, October 8 ---Veteran’s Memorial Park, Little Duck Key 2:00pm
Racing to beat another oncoming rain shower, our class ventured out into the water of Little Duck Key. Here, we would have to scavenger hunt for green algae plants. It was easiest for those with their swim masks to float above the waist deep water in search for the hidden plants. Unfortunately, mine broke in my bag. So I had to joined ranks with a handful of others who were walking in a line searching for the elusive plants. Every step we would take would stir up lime mud and create a cloud that would float past us. Walking single file became essential to limit the lime cloud that formed. Eventually we did find what we were looking for. Small patches of Penicillus, Helimeda, and Udoteas were found. I looked up to see how far our class had ventured out in the waist deep water. I was shocked to see that we were already about ninety meters out from shore!
Helimeda Penicillus Udotea
Penicillus, Helimeda, and Udoteas are crucial in creating a limestone factory. Helimeda and Udotea both have calcium carbonate structures. So when they die, it breaks down and deteriorates. The calcium carbonate then adds to the limestone that is forming in that area. Penicillus creates a lime mud with tiny aragonite and calcite crystals.
The sand sample that I collected there appeared to be medium-sorted, angular grains. It did have some trace amounts of lime mud in the sample. When I got back to the lab, I reviewed the sample under a stereoscopic microscope. I found that I was fairly correct on the samples sorting and roundness. While looking at the sample, I found a shell fragment, a porous fragment of a plant, and an intriguing red worm! That was a real surprise when I found the little critter on a grain of sand. I tried to look at it without the aid of the microscope, but all I could see was a tiny red line.
I must say that it was pretty amazing to look at sand under a microscope, because you will never know what you will find till you take a look.
Saturday, October 8 --- Anne’s Beach, Long Key 4:00pm
(figure17)
Anne’s beach was truly a picturesque place. The only challenge was getting to those spots. The main part of the beach composed of lime mud and carbonated materials. Walking along the shoreline, I found an area where the lime mud accumulated and began to turn into a more solid formation. Because of the short rain fall that occurred just before our class arrived, it was like walking on slick clay. So after a ton of slipping and sliding, I was able to get a quick picture of eight inch tall lime mud buildup (figure 17). The holes in the mud are from crabs that built their homes in it. Farther down the beach, the lime mud formation had begun to erode away. It almost looked as though the waves had sculpted the mud into some amazing shapes. 
I brought back a sample of the lime mud and viewed it under the microscope. The grains were still too small to make out, although it looked like fluffy white clouds.
Sunday, October 9 ---Molasses Reef and Eagle Ray Pass 9:30am
After about an hour of snorkeling in molasses reef, we climbed back onto the boat and drove to another site called Eagle Ray Pass. It was named this because eagle rays are often seen traveling along the undersea highways in that area.
The Florida reef is an amazing structure. For a while it was even considered a barrier reef, and the third largest at that. However, in all reality, the Florida reef is actually considered a “reef tract” as it discontinues in multiple places (Bryan pg 294).
The reef is broken up into three major zones; the fore reef, the reef crest, and the back reef. The fore reef is on the outermost part of the reef and is mainly composed of star coral and brain coral. The reef crest is the tallest part of the reef. It takes the energy given from waves and disperses it. This part of the reef is made from stronger coral, like the elkhorn coral, that can withstand such brutal beatings (Bryan pg 295-296).
The back reef is closer to land and also the largest zone. The water here is calmer and allows more life to thrive. Filled with small patch reefs, sea grass meadows, and wave marked sand shoals; the back reef thrives in these protected waters. Here soft corals, such as the fan coral, are more abundant. Even though brain coral and finger coral are the dominate species in these waters (Bryan pg 296).
(Bryan, pg 295)
Like I said, the Florida Reef is an amazing structure. Although it can take a long time to form. Hopefully, these reefs will still be thriving for future generations to enjoy.
Work cited
Bryan, J.R., Means, G.H., Scott, T.M. 2008, Roadside Geology of Florida. Roadside Geology series, 1st Ed, Mountain Press Publishing Company, 368 p.
Windley Key Visitor Center information
Blue Hole Visitor information flyer
# posted by kyraclaxton : 2:36 PM
Subscribe to Posts [Atom]
Post a Comment