Bathymetry of the Puerto Rico Trench

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Abstract
The Puerto Rico Trench extends for about 400 mi in a generally east‐west direction 80 mi north of Puerto Rico and has a five to ten‐mile wide “flat” floor 4350 fm deep. The Trench is separated from the Nares Basin to the north by a 2900‐fm divide, and is roughly paralleled to the south by a series of seamounts which form an interrupted ridge from 2700 to 3700 fm deep. South of this ridge are basins, 4000 to 4100 fm deep, which may drain into the Trench through San Juan Canyon. The Trench floor has two kinds of sediment in alternating layers up to several meters thick: (1) layers of abyssal red clay with low carbonate content, which is “mormal” at this great depth, and (2) anomalous layers of highly calcareous sands showing excellent graded bedding and shallow water benthonic fossils. The layers of anomalous sand are attributed to the action of turbidity currents, which may have transported the sediment from neighboring island platforms down submarine canyons and deposited it in the Trench, rather than to former shallow water conditions in the Trench.

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