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 4.5 kilometres (2.8 miles).
The limestone forming the Banks of the Great Bahama Sea has accumulated over a long period, likely starting in the Cretaceous period and potentially even earlier during the Jurassic. Today, this layer reaches a significant depth under the bank, exceeding 4.5 kilometers (2.8 miles).