One of my favorite parts of geocaching is discovering and learning new about this giant world that we live on. Beaches are a common attraction for vacationers. There are others that see beaches as an attaction too. My goal is that you will use this Earthcache look closer at the beach and understand that a beach is not just sand.
Beaches are often made of sand. What is sand? Myrtle Beach sand is white sand. The sand here is white because there is a large content of quartz and calcite from shells. The texture is fine, not coarse. This makes the sand feel soft when walking on the beach. In this area, there is not a river or stream draining into the ocean, so the organisms that are common in the upland areas do not get mixed with the sand. Shells, however, come from the ocean.
Shells are a large componant of the Myrtle Beach's sand. Wind and waves wash the shells onto and off of the beach. The waves break the shells and they become smaller until you might not realize they are still pieces of shells.
Let's dive deeper into the shells. These shells were alive to begin with. Why are they here? There must have been many shells to create this big of a beach Are there still shells that are alive? Yes. One of those shells is called the Coquina Clam (Donax Variabilis).
The Coquina is a small clam about 1 inch in length (2.5 cm). The Coquina is shaped like a wedge with colored bands circling around the shell's center. The colored bands can be white, tan, brown and even some black. The species is part of the Donacidae family. The Donacidae Variablilis is more abundant in Myrtle Beach area. If you see Coquina on this beach or any other beach, then it is said that this indicates that this is a healthy sandy beach. This is important!
Coquina filters the water and feeds on the microalgae and detritus. This keeps your beaches looking clean and white. The Coquina are also food for shore birds and some fish like Pompano and "whiting". There are so many Coquina in a healthy beach. Over 1000 Coquina have been found in a 10' x 10' area.
So how do Coquina survive? Watch this video. The following video and the pictures on this page were taken right at this geocache.
Coquina 1
Coquina 2
Coquina 3
Note how the Coquina buries itself into the sand. It stretches out of the shell and pulls itself into the sand and disappears. It is constantly pulling itself into the sand after each wave.
Wait a minute. An earth cache must be about geology and living shells are not geologic. There is more to the story....
We already talked about the Coquina that live here on the beach die and are crushed and become calcite part of the beach sand, but as time goes on Coquina become a geological formation. "The geological formation of coquina involves a series of processes that lead to the consolidation of shell fragments into a solid rock." (https://geologyscience.com/rocks/sedimentary-rocks/clastic-sedimentary-rock/coquina/)
https://www.sandatlas.org/wp-content/uploads/00276-coquina.jpg
The process has already started here. There has to be a large number of Coquina shells. To have a large number, you need a healthy beach like this one. The second step is the compaction of the shells. Compaction occurs as the shells are compressed with the weight of more shells and sand. The third step is called cementation. As you might guess, there has to be a way that the shells stick together. This binding agent is most of the time from calcium carbonate. Where does calcium carbonate come from? From the coquina shells themselves. At this point the Coquina is rock. The fourth step is what makes Coquna a hard and durable sedimentary rock. The fourth step is called Lithification. Lithification is when the compaction of step two is combined with the cementation of step three.
So is there Coquina Rock here? I did not see any large rocks like the one here. But maybe below the beach sand where the weight compresses the shells you might find some Coquina Rock. Is Coquna Rock used for anything? The answer is yes. It has been used to build forts and buildings in places like St. Augustine, Florida. Other places include: Brazil, Austrailia, India, Caribbean Islands, and Spain. Another use of Coquina Rock is for beach and shoreline protection from erosion. Note that Coquina Rock is easily carved and it can break. This limits that uses of the rock.
To Log this Geocache, please message me the answers to the following questions:
1. Put your feet into the water and face the beach. Let a wave pass and as soon as the beach no longer is under water, scrape about one inch of sand away. Do you see any Coquina? Repeat this. Look especially in spots where you see dimples in the sand. Try this in a few places.
2. How many did you find?
3. What color were they?
4. What will will the Coquina eventually become?
5. If Coquina are here, then what does this indicate about this beach?
6. Do you see any Coquina Rock here?
7. Where might you find some Coquina Rock? (Think down)
8. Is there value in digging for Coquina Rock here? Why or Why not?
Please post a picture or two of you and any Coquina you can. They are quick!
https://www.myrtlebeach.com/blog/myrtle-beach-sand/#:~:text=Myrtle%20Beach%20is%20known%20for%20its%20white-sand%20beaches,deepens%20slightly%20as%20additional%20minerals%20become%20more%20prevalent.
https://www.dnr.sc.gov/swap/supplemental/marine/coquinaclam2015.pdf
https://geologyscience.com/rocks/sedimentary-rocks/clastic-sedimentary-rock/coquina/