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| Explore Navassa - Geology |
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upper terrace |
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Ancient coral reef sediments that have been raised above sea level by
vertical movements of the earth's crust underlie Navassa. Navassa may have
formed as a small coral atoll, but at the close of the Miocene Period about
5 million years ago, these reefs began to emerge. Emergence resulted in
the alteration of calcium carbonate sediments (aragonite) to
calcium-magnesium carbonate rock (dolomite), the formation of a terrace
around the island, and the beginnings of chemical weathering and cave
formation.
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oolitic phosphate |
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About two million years ago phosphate-rich sediment was
deposited on the island, perhaps guano that was greatly altered to form the
mineral phosphate deposit now found on the surface. The oolitic phosphate
forms a thin veneer overlying and filling karst holes in the dolomite.
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