What Is Coquina?
Coquina is an organic rock composed almost entirely of marine debris. The detritus is sometimes mollusk shells and/or shell fragments. Trilobite fossils, coral, and shell debris are very common elements in many specimens of coquina. Since all three are composed of calcium carbonate, coquina rock is classified as limestone.
A Bit About Trilobite Fossils
Trilobites were organisms that existed in Earth’s oceans many millions of years ago. Currently, on all 7 continents, geologists have found fossils of their existence. It is a common occurrence to view these fossils conglomerated into coquina rock. An image of a trilobite fossils is located below.
Where Does Coquina Form?
Most coquina forms in shallow coastal marine waters where a steady and abundant supply of sand-size fossil debris is deposited by waves and currents. The waves and currents in this process must be strong enough to completely remove clay and silt-size particles from the larger particles in the debris. Most coquina-forming sediments are found in tropical marine waters. (warmer environments tend to have a more abundant supply of debris). They usually form along ocean beaches or sand bars located right offshore. A few coquina deposits are known from freshwater, lacustrine environments that include banks of rivers and lakes. In the United States, coquina can be found off of the coasts of Florida and North Carolina. The Gulf Stream Current largely accounts for the deposition of oceanic sediment on these beaches.
Image of the Rock Cycle:
Logging Tasks:
- At the GZ, you will notice several specimens of coquina. Are they predominantly made up of shells, coral, or trilobites?
- Describe the texture and color of the rock in a few sentences.
- After examining the rock cycle image provided in the description and your observations at the GZ, do you believe that the coquina rocks are considered to be metamorphic, sedimentary, or igneous? Explain a bit about your rationale.
- As of June 2019, earthcaches are now allowed to have a required photo logging task. Please provide a photo of yourself, your GPSr, or a personal item that proves that you have visited this site. Please post this in your log.
**Please do not post your answers in your log or it may be deleted at the discretion of the CO.**
Sources:
https://en.wikipedia.org/wiki/Dunham_classification
https://geology.com/rocks/coquina.shtml#:~:text=What%20Is%20Coquina%3F,is%20present%20in%20many%20coquinas
https://www.gsi.ie/en-ie/education/rocks-minerals-and-gems/Pages/The-rock-cycle.aspx
https://en.wikipedia.org/wiki/Trilobite
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