Where did the Bahamas come from? Their birth began millions of years ago as a part of the super-continent now known as Godwanaland. Plate tectonics is the study of how this huge land mass broke apart ultimately resulting in the present days continents of the Americas, Africa, and Australia. Also, the Bahama Bank, Cuba, and the West Indies were once a part of this continent.

Island Formation
South America, and Africa. During the rifting process, the 25 degree rotation of the piece of land  land coupled with pull-apart  episodes in the crust created the different types of areas found in the Bahamas such as deep- water channels and shallow water platforms. The original underlying island structure of  the Bahamas consisted of an area of over-lap which fit between North American.
    Then, about 160 million years ago during the Jurassic period, marine sediments were laid down in great quantities. This continuing process has formed the modern island group of the Bahamas.  In fact, during a deep drill test performed at Cay Sal bank, these sediments reached a depth of 5700 meters. While every reason for such a magnitude of sediment deposit is not known, research is in process. The focus of this research is an area called North Andros where sediment deposit is occurring.

Sedimentation
    The geologic matter of the Bahamas besides continental mass is formed of different types of sedimentation. There are two  main ways by which these sediment deposits are presently formed. First, a primitive invertebrate animal known as a Bryozoan - SchizoporeIIa floridana removed dissolved salts from the water and incorporated them into its own skeletal structure. Secondly, there are small particles of limestone which are surrounded by rings of calcium carbonate. This is called an ooid.  A compilation of deposited ooids make up a substance known as oolite which is used in the making of glass, cement and animal foods.

Formation of Limestone
    The term Bahaman Limestone refers to the union of sedimentation, sandy soil, and coral. Such ingredients towards the interior of the islands are the reason for their flat landscape.

Andros
    The dominant rock type present at Andros Island is eoliam oolite with small amounts of bioclastic, pelletal, and reef rock. Different rock cores in Andros have been described such as wackestones, packstones, gainstones, and reefs. The different facies found in the cores show shallow-water rocks supporting the idea that the Bahamas are formed completely out of lithified sediments.
    There are several large creeks which divide different parts of the island. These creeks suggest that Andros was formed by the joining of several smaller islands which were about 10-20 km in diameter.

Blue Hole –  basically any hole with water in it, however, blue holes derived their name from the way the surface water       appears looking down from a plane.

    All Blue holes, including the ones found on Andros Island, are formed from one or more methods of erosion. The entire Bahamas is composed of porous limestone with deposits of calcium carbonate.  Were large portions of the rock have been eroded is called a ‘Karst.’  Over millions of years of erosion deep extensive cave systems have formed.
 

1. The altering of the sea level due to glacial and interglacial periods
2. Carbon dioxide laden rain-water seeping through porous limestone causing chemical dissolution of the calcium carbonate
3. Dissolution of the calcium carbonate by hydrogen sulfide found at particular levels of the water column.  When organic matter decomposes a byproduct created is hydrogen sulfide, which is introduced either from the surface or marine life that flows into the caves with the tides.

    Blue holes are classified into a number of types both by how they formed and were they are located. There can be found an example of each type of Blue hole on or around Andros Island.
 

1. Sinkholes - large blue holes seen best from the air.  Characteristically they do   not have many caves but usually they do feature stalactites and   stalagmites. (50 to 150m in diameter and 50 to 100m in depth)
2. Lens Based Blue Holes – Typically they are the longest of the Blue Hole   types featuring extensive cave systems that are highly decorated.   The water in the hole separates out by density and the fresh water   layer at the surface takes on a lens shape. (Also known as flank   margin caves)
3. Fault Line or Fracture – These systems tend to follow parallel to fault lines,   fractures, and deep-water offshore canyons.  Fault line/Fracture   caves have a tendency for being the deepest type of cave.    (frequently reach depths of over 100m)

Inland Blue Hole – The surface opening of the hole is located inland but the   actual type of hole can be sinkhole, lens based, or fault line.
 
 

Marine/Ocean Blue Holes – can be any of the three geological types with   tidal influences but having the entrance below sea level.
 
 

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