Geomorphology and geologic structure: Straits of Florida

Malloy, R.; Hurley, R.

A bathymetric map of the Straits of Florida was compiled using a 10-fathom contour interval. Except for coastal areas of Cuba and the Bahamas, depth soundings were collected by systematic surveys between 1951 and 1964, using electronic positioning and recording fathometers. Distances between depth sounding lines were: 1 n.m. below, 100 fms north of Miami and below 300 fms elsewhere; 1/2 n.m. to 20 fms; and 1/4 n.m. from 20 to 10 fms. Seismic reflection profiling and previous seismic refraction studies suggest that the main axis of the Northern Straits (west of Little Bahama and Grand Bahama Banks) has formed aseismically, by non-deposition and limited erosion, and that the Southern Straits (north of Cuba) have formed principally by subidence and normal faults along Cuba to form a half-graben with the down-dropped portion tilted toward the south. Downward flexing and subsidence of the strata which form the southern terminus of the Florida Plateau have probably been accompanied by normal faulting, although of less than regional signifcance, along the Pourtales Terrace Escarpment and the Mitchell Escarpment. This subsidence reaches its maximum near Cuba where the Sierra de Jatibonica and the Las Villas normal faults form the major scarps. The thalweg, or axis of greatest depths, of the Southern Straits lies only 17 n.m. north of Cuba in response to the southerly tilted blocks of the Southern Straits. Sediment distribution on the floor of the Straits is strongly influenced by elongate depositional anticlines which occur typically at the base of steep slopes. These anticlines are separated from the scarps by nondepositional troughs which may be formed by contour currents concentrated along the bases of the scarps. The associated sedimentary rises may be formed by periodic spill-over. The surfaces of Pourtales and Miami Terraces are marked with karst-like topograghy, probably true solution and collapse features which formed, or at least have been maintained, subaqueously by the corrosive waters of the Floridan aquifer, effluent in the Straits of Florida. Oceanic reefs, largely branching coral with entrapped sediments, have locally reshaped the morphology of the Northern Straits. Areas of the thalweg of the Northern Straits and Little Bahama Bank are mounded or ridged (or both) with reef topography. The length of the outer edge of the Miami Terrace, including buried extensions north and south, may have been elevated by reef growth, but extensive dredging yielded phosphatic nodules, not coral. Eroded strata crop out on the sea floor along the thalweg of the Northern Straits and in places along the bases of scarps. Abstract provided by author.

Geomorphology and geologic structure: Straits of Florida

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