The Caribbean Sea Essay Research Paper The — страница 2

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North American plate moved away from the African plate and the Atlantic Ocean became wider. For the whole of this period, the Bahamas has formed a shallow tropical sea. Evaporation from the warm sea surface causes the concentration of calcium carbonate on the water to become very high, so tiny grains of this mineral, ooliths, form and collect on the sea bed. These grains form a rock known as oolite. The Bahama Banks are a platform of oolite several kilometres thick. During the glacial periods, sea level fell, and the Banks became enormous islands. Sand dunes which formed in the ice ages solidified, and remained above sea level when the ice melted and the sea rose again, to form the present-day Bahama islands. To the S, Trinidad and Tobago were joined to the South American

mainland when sea levels were low in the ice ages, hence the richness and variety of their plant and animal life. The boundary between the South American and Caribbean plate actually runs through N Trinidad, so these islands are another earthquake zone. There are also signs of early volcanic activity on Tobago, though not from a geologically recent period. Many Caribbean coastlines are being pushed upwards by earth movements: Barbados, the N coast of Jamaica, NW Haiti for example. Along many of these emergent coastlines, the land rises in a series of steps, each one marking an old coastline and a fossil coral reef. Where the land is being slowly submerged, as along the S coast of Jamaica, in the Bahamas, Antigua, and many of the Windwards, there is an indented coast with many

offshore islands. Some shallow bays in these areas are being filled in by mud and other sediments; this makes interesting wetland wildlife. The Guianas on the South American mainland are by contrast geologically very stable, and are formed of ancient rocks several thousands of millions of years old. Guyana?s gold and diamonds are derived from these ancient rocks. In the coastal belt of the Guianas, however, there is a layer of geologically more recent river-borne and marine sediments over the ancient rocks. This includes fertile silt, disastrously infertile white silica sands, and, below the surface in some areas, valuable bauxite deposits.