Bahama Banks
From Wikipedia, the free encyclopedia
The Bahama Banks are the submerged carbonate platforms that make up much of the Bahama Archipelago. The term is usually used to refer to either the Great Bahama Bank around Andros Island, or the Little Bahama Bank of Grand Bahama Island and Great Abaco, which are the largest of the platforms. Other banks are the Caicos Bank of the Caicos Islands, the Cay Sal Bank north of Cuba, and the wholly-submerged Silver Bank north of the Dominican Republic.
[edit] Geologic History and Structure
The limestone that comprises the Banks has been accumulating since at least the Cretaceous period, and perhaps as early as the Jurassic; today the total thickness under the Great Bahama Bank is over 4500 meters.[1], [2] As its limestones were deposited in shallow water, the only way to explain this massive column is to estimate that the entire platform has subsided under its own weight at a rate of roughly 3.6 centimeters per 1,000 years.[3]
The waters of the Bahama Banks are very shallow; on the Great Bahama Bank they are generally no deeper than 25 meters.[4] The slopes around them however, such as the border of the Tongue of the Ocean in the Great Bahama Bank, are very steep. The Banks were dry land during past ice ages, when sea level was as much as 120 meters lower than at present; the area of the Bahamas today thus represents only a small fraction of their prehistoric extent.[5][6] When they were exposed to the atmosphere, their limestones were subjected to chemical weathering that created the caves and sinkholes common to karst terrain, resulting in structures like blue holes.[7]
