Fossils are everywhere! Even in the Bahamas!
At the end of December I went to San Salvador for close to two weeks as a Carbonate Research Assistant at the Gerace Research Center (College of the Bahamas). This place is amazing and the people are super friendly. The weather was in the 80’s!
Well, while doing scientific expeditions in search for the perfect carbonate sand samples to bring back to the USA. I was able to get in a little bit of fossil hunting.
This particular fossil site is in Cockburn Town and is said to be one of the best preserved fossil reefs in the world. San Salvador is best known for its well preserved trace fossils and carbonate fossils. I did some shell collecting and picked up a few cool pieces to take home. I was told by my professor that you are not allowed to dig into the actual reef formation for fossils, but picking up loose pieces that were away from the main formation exposure is okay.
My professor is equivalent to the Michael Jordan of geology on this island. He has spent over 30 years mapping the geology on this island and at this particular site in Cockburn he was the first to figure out how to determine sea level by using fossil reefs in situ and endless amounts of other discoveries involving carbonates. There are also a ton of carbonate research papers published by him if you want to learn more about his research (look up Dr. Carew).
These fossil reefs are Pleistocene in age (Cockburn Town Member/Grotto Beach Formation) and I tried my best to search for shark teeth, but for some reason vertebrate fossils do not fossilize in this formation. I hypothesis that this could be due to the fact that the sand here is extremely porous (means a lot of open spaces within the sediment) and made primarily of calcium carbonate, which is known to dissolve easily over time and can form karst features such as caves (some known as blue holes on this island, which are underwater caves and extremely dangerous to scuba dive in). The lack of anoxic conditions in this type of environment would make it difficult for organisms to fossilize.
However, in order to obtain a well preserved fossil specimen in this kind of environment you would need rapid burial (could be possible during storm events), on-going deposition, and a low energy environment. This may be only part of the reason why the reefs are so well preserved here. Furthermore, there must have been a large abundance of shells and corals in order to make it into the fossil record!
Another cool fact that I learned about the island from another professor in our group is that the caves (may be variable by scale) on the island are formed due to bacteria eating away the limestone and are not forming by acid rain infiltration. She discovered this phenomenon by scuba diving in the blue holes and studying the bacteria within it. New experiments are showing that acid rain causes very little dissolution over time. The bacteria being discovered in these caves show pH levels that are so acidic that they are off the scales (look up papers published by Dr. Schwabe for more info).
I had a small talk about fossils with another professor who is the trace fossil expert of the island from Emory University. He told me that fossil crocodiles have been found in caves on other islands around the Caribbean. That would be very cool to find! However, I was unable to find any records of vertebrate fossils found from the Cockburn Town Member. I would definitely come back here again and maybe next time I will find that undiscovered vertebrate fossil.