I'm a H.S. Biology/Gen. Science teacher, but I have a BS in Geology from KU. Being from Kansas, marine sedimentary rocks are something we are rather used to studying, as the Bahamas look a lot like what Kansas looked like during the Pennsylvanian and Cretaceous periods (shallow marine ecosystem). Shallow marine ecosystems are characterized by sandstones/limestones. Deeper marine rocks are typically your mudstones/siltstones/shales.
To start, the ocean floor is made of is an igneous extrusive rock known as basalt, that forms in midocean ridges where ocean plates are pulling themselves apart. As that rock migrates away from the MOR due to convection currents below the crust, it accumulates sediment that is a mixture of very finely grained minerals and biotic content, which forms the sedimentary rock shale. This occurs in a deep ocean environment. As the ocean floor approaches continents, we see shallowing/sedimentation from continental material due to erosion/deposition of our fluvial systems (rivers) and wave action on the continent itself. If you look at a relief map of the southern US and the Bahamas, you can see that long shore drift (unidirectional erosion caused by waves) has carried sediment from the continent to the SE, forming the underwater peninsula that Florida and the Bahamas are a part of. This would likely mostly be sandstone, and would provide a shallow marine ecosystem to form those limestones/cross bedded sandstones. Keep in mind that 12kya, sea level was several hundred feet lower, and much of this area would've been above water, and before the last million years or so, it would've been about where it is today. Oscillating sea level will have different areas either exposed to the elements to form paleosol or karst, in shallow water to form limestones/sandstones, or in deep water forming shales/siltstones, depending on the time period whichever rock layer in question was being deposited.
My assumption based on what I'm able to read in the abstract/figures is that each island is probably somewhat unique depending on it's location within this marine setting, so each island will likely have a different sequence of rock, even if the general pattern remains for the region.
So, that all said, discussion on the rock types described in the paper you shared (again, I'm only able to see the abstract and figures).
Bioclastic/Oolitic limestones. Bio clastic just means life rock...essentially. It's just saying that the limestone formed from bits of dead sea creatures. Oolitic limestone is formed when concentrations of CaCO3 and the environmental conditions are primed for oolites to form. Oolites are precipitates that form little tiny spherical balls of CaCO3 that look like everlasting gobstoppers or hail stones. Typically a piece of sand works as the starting point, and then concentric layers of CaCO3 forms around that grain. This occurs in very warm, very shallow marine areas, like, well, the Bahamas. As life accumulates over time, so too does it's CaCO3, and you get a build up of that material on the ocean floor enough to form layers of rock.
Eolian cross bedded sandstones form above ground. Typically, eolian sandstones are formed in deserts and arid conditions, but in this case, likely the dunes beachside. Paleosols are ancient soils, calcite and karst surfaces form from erosion. Karst topography is a very special type of erosionary surface that occurs to limestone/dolomite. It's how caves and sinkholes form, as the rock dissolves in solution. These are all types of rock indicative of being exposed to the elements for long periods of time.
So, from what I can gather, due to continental erosion, this region is a shallow marine area. This set the stage for the buildup of organic material in the form of CaCO3 and limestone. As sea levels lowered, it would expose the the shallower areas and you would get paleosol/karst form. As sea level rose, limestones/sandstones would once again build. This was likely an oscillating buildup of erosion/deposition over 10s of millions of years.
Not being an expert in the region, I can't give you too many more specifics than that, but that's the more general explanation.
I too have had the opportunity to snorkel in the Caribbean - such a wide array of spectacular sights! But your story has me laughing at my own experience birding just yesterday. We have white-throated sparrows on our property and I noticed a color variation which I presumed to be gender-related (think cardinals, mallards, heck nearly every duck where the male has much more attractive plumage). So I googled it 🤦 and was pleasantly surprised to find out that the color variations occur in both sexes and is more indicative of an aggressive/territorial behavior (hey, I'll make sure our nest is secure) versus a more nurturing behavior (hey, I'll make sure the kids get fed). Typically they form mating pairs with opposite color patterns which works well, but sometimes they are left with only a similar colored mate and their family raising efforts are less than ideal. So not what I was expecting ... in fact, it was such the opposite of what I was expecting that I shall never forget it. Or maybe, I was just intrigued to learn about something other than Covid?
But I whole-heartedly agree with your recommendation to spend time outside just observing and asking questions (such a completely worth-while endeavor which sadly is overlooked in our modern concrete world). I truly do enjoy marveling at what is known while still being cognizant of the much greater unknown.
You are right, there is a huge literature on the geology of the Bahama Islands. Much of the work was done by (or sponsored by) petroleum companies from the 60’s onward. Petroleum geologists saw the Bahamas as a modern analog for limestone reservoirs around the world. One unique aspect of the Bahamas in the presence of large oolite shoals. Oolites are almost perfectly spherical carbonate sand grains that are precipitated in agitated seawater. They are not common in the modern coastal environments, but are major oil reservoirs around the world.
I am a retired petroleum geologist. Early in my career, I had the option to take a company training class to the Bahamas, to learn about these carbonate sands and reefs. At the time, I opted out since I had babies, and I thought I could go later. Alas, these trips didn’t survive the low oil prices in the 80’s. I am currently working on a PhD in geology. A few years ago, I had the opportunity to take a class in the Bahamas. We saw many of the classic localities on Andros Island (the big island), with Paul Harris as our guide (he did his Ph.D. in 1979 on the oolite banks at the north end of the island). It was like a pilgrimage. Even though I came back covered with many insect bites, it was so fantastic to see the carbonate rocks forming under my feet. I recommend looking at the Bahamas with Google Earth. You can see the oolite shoals forming in many areas around the Bahamas where you have strong waves or tidal action.
Thoroughly enjoyed vicariously experiencing your trip to the islands – a much needed respite from this corporate drudge. About the ability to think through a novel unknown... it's heart-rending how so many colleagues do exactly what you seek to avoid, which is only expressing what you think you know by regurgitating what has been fed to you in an advanced learning institution, or doing a quick internet search, then regurgitating that surface level pablum as having achieved some sort of SME status. Diving in, metaphorically or not, to the unknown yields emotionally / intellectually resistant, dead-eyed fear, and / or future retribution from the purported SME’s. Does it shore-up their internally felt incompetence? Nope - but the cycle invariably continues. It’s difficult being inquisitive and having fun hypothesizing to reach a better understanding when presented with novel unknowns and getting it wrong until further research can be undertaken, when the knee-jerk impulse of those around you is to seek to destroy (btw, I’m referring to folks with advanced degrees – those for whom the process of learning should be understood and appreciated). Anyway, that ideal of how wonderful it can be to experience the unknown and discover a more robust understanding of the world, layer by layer, is, sadly, uncommon. Having a few ppl with whom those experiences can be had without the annoyance of swatting away empty arrogance or ignoring the idiocy, is priceless.
This is how we know what we claim* to know and what we rely on to make moment-to-moment cost/benefit analyses. Observability, Repeatability, Predictability... three legs of the three-legged stool of Knowledge, without all three of which the stool is unstable and The Book Of Knowledge is not amended. Each leg is necessary; no one or two are sufficient.
It's like the Fire Triangle. All three sides are required for a triangle. And all three - Fuel, Oxygen, Source-of-ignition - must be present for fire to occur.
*spoiler alert: knowing does not imply certainty. Past results do not guarantee future outcomes; but, in the absence of clairvoyance, they're all we've got and the message in the movie, 'Oh, God! (1977)' George Burns, John Denver, was "You have everything you need to make it work. It's up to you."
Hey Heather,
I'm a H.S. Biology/Gen. Science teacher, but I have a BS in Geology from KU. Being from Kansas, marine sedimentary rocks are something we are rather used to studying, as the Bahamas look a lot like what Kansas looked like during the Pennsylvanian and Cretaceous periods (shallow marine ecosystem). Shallow marine ecosystems are characterized by sandstones/limestones. Deeper marine rocks are typically your mudstones/siltstones/shales.
To start, the ocean floor is made of is an igneous extrusive rock known as basalt, that forms in midocean ridges where ocean plates are pulling themselves apart. As that rock migrates away from the MOR due to convection currents below the crust, it accumulates sediment that is a mixture of very finely grained minerals and biotic content, which forms the sedimentary rock shale. This occurs in a deep ocean environment. As the ocean floor approaches continents, we see shallowing/sedimentation from continental material due to erosion/deposition of our fluvial systems (rivers) and wave action on the continent itself. If you look at a relief map of the southern US and the Bahamas, you can see that long shore drift (unidirectional erosion caused by waves) has carried sediment from the continent to the SE, forming the underwater peninsula that Florida and the Bahamas are a part of. This would likely mostly be sandstone, and would provide a shallow marine ecosystem to form those limestones/cross bedded sandstones. Keep in mind that 12kya, sea level was several hundred feet lower, and much of this area would've been above water, and before the last million years or so, it would've been about where it is today. Oscillating sea level will have different areas either exposed to the elements to form paleosol or karst, in shallow water to form limestones/sandstones, or in deep water forming shales/siltstones, depending on the time period whichever rock layer in question was being deposited.
My assumption based on what I'm able to read in the abstract/figures is that each island is probably somewhat unique depending on it's location within this marine setting, so each island will likely have a different sequence of rock, even if the general pattern remains for the region.
So, that all said, discussion on the rock types described in the paper you shared (again, I'm only able to see the abstract and figures).
Bioclastic/Oolitic limestones. Bio clastic just means life rock...essentially. It's just saying that the limestone formed from bits of dead sea creatures. Oolitic limestone is formed when concentrations of CaCO3 and the environmental conditions are primed for oolites to form. Oolites are precipitates that form little tiny spherical balls of CaCO3 that look like everlasting gobstoppers or hail stones. Typically a piece of sand works as the starting point, and then concentric layers of CaCO3 forms around that grain. This occurs in very warm, very shallow marine areas, like, well, the Bahamas. As life accumulates over time, so too does it's CaCO3, and you get a build up of that material on the ocean floor enough to form layers of rock.
Eolian cross bedded sandstones form above ground. Typically, eolian sandstones are formed in deserts and arid conditions, but in this case, likely the dunes beachside. Paleosols are ancient soils, calcite and karst surfaces form from erosion. Karst topography is a very special type of erosionary surface that occurs to limestone/dolomite. It's how caves and sinkholes form, as the rock dissolves in solution. These are all types of rock indicative of being exposed to the elements for long periods of time.
So, from what I can gather, due to continental erosion, this region is a shallow marine area. This set the stage for the buildup of organic material in the form of CaCO3 and limestone. As sea levels lowered, it would expose the the shallower areas and you would get paleosol/karst form. As sea level rose, limestones/sandstones would once again build. This was likely an oscillating buildup of erosion/deposition over 10s of millions of years.
Not being an expert in the region, I can't give you too many more specifics than that, but that's the more general explanation.
I too have had the opportunity to snorkel in the Caribbean - such a wide array of spectacular sights! But your story has me laughing at my own experience birding just yesterday. We have white-throated sparrows on our property and I noticed a color variation which I presumed to be gender-related (think cardinals, mallards, heck nearly every duck where the male has much more attractive plumage). So I googled it 🤦 and was pleasantly surprised to find out that the color variations occur in both sexes and is more indicative of an aggressive/territorial behavior (hey, I'll make sure our nest is secure) versus a more nurturing behavior (hey, I'll make sure the kids get fed). Typically they form mating pairs with opposite color patterns which works well, but sometimes they are left with only a similar colored mate and their family raising efforts are less than ideal. So not what I was expecting ... in fact, it was such the opposite of what I was expecting that I shall never forget it. Or maybe, I was just intrigued to learn about something other than Covid?
But I whole-heartedly agree with your recommendation to spend time outside just observing and asking questions (such a completely worth-while endeavor which sadly is overlooked in our modern concrete world). I truly do enjoy marveling at what is known while still being cognizant of the much greater unknown.
Heather,
You are right, there is a huge literature on the geology of the Bahama Islands. Much of the work was done by (or sponsored by) petroleum companies from the 60’s onward. Petroleum geologists saw the Bahamas as a modern analog for limestone reservoirs around the world. One unique aspect of the Bahamas in the presence of large oolite shoals. Oolites are almost perfectly spherical carbonate sand grains that are precipitated in agitated seawater. They are not common in the modern coastal environments, but are major oil reservoirs around the world.
I am a retired petroleum geologist. Early in my career, I had the option to take a company training class to the Bahamas, to learn about these carbonate sands and reefs. At the time, I opted out since I had babies, and I thought I could go later. Alas, these trips didn’t survive the low oil prices in the 80’s. I am currently working on a PhD in geology. A few years ago, I had the opportunity to take a class in the Bahamas. We saw many of the classic localities on Andros Island (the big island), with Paul Harris as our guide (he did his Ph.D. in 1979 on the oolite banks at the north end of the island). It was like a pilgrimage. Even though I came back covered with many insect bites, it was so fantastic to see the carbonate rocks forming under my feet. I recommend looking at the Bahamas with Google Earth. You can see the oolite shoals forming in many areas around the Bahamas where you have strong waves or tidal action.
Thoroughly enjoyed vicariously experiencing your trip to the islands – a much needed respite from this corporate drudge. About the ability to think through a novel unknown... it's heart-rending how so many colleagues do exactly what you seek to avoid, which is only expressing what you think you know by regurgitating what has been fed to you in an advanced learning institution, or doing a quick internet search, then regurgitating that surface level pablum as having achieved some sort of SME status. Diving in, metaphorically or not, to the unknown yields emotionally / intellectually resistant, dead-eyed fear, and / or future retribution from the purported SME’s. Does it shore-up their internally felt incompetence? Nope - but the cycle invariably continues. It’s difficult being inquisitive and having fun hypothesizing to reach a better understanding when presented with novel unknowns and getting it wrong until further research can be undertaken, when the knee-jerk impulse of those around you is to seek to destroy (btw, I’m referring to folks with advanced degrees – those for whom the process of learning should be understood and appreciated). Anyway, that ideal of how wonderful it can be to experience the unknown and discover a more robust understanding of the world, layer by layer, is, sadly, uncommon. Having a few ppl with whom those experiences can be had without the annoyance of swatting away empty arrogance or ignoring the idiocy, is priceless.
This is how we know what we claim* to know and what we rely on to make moment-to-moment cost/benefit analyses. Observability, Repeatability, Predictability... three legs of the three-legged stool of Knowledge, without all three of which the stool is unstable and The Book Of Knowledge is not amended. Each leg is necessary; no one or two are sufficient.
It's like the Fire Triangle. All three sides are required for a triangle. And all three - Fuel, Oxygen, Source-of-ignition - must be present for fire to occur.
*spoiler alert: knowing does not imply certainty. Past results do not guarantee future outcomes; but, in the absence of clairvoyance, they're all we've got and the message in the movie, 'Oh, God! (1977)' George Burns, John Denver, was "You have everything you need to make it work. It's up to you."