Steinlöchner, Jörg (2003) Struktur und Zusammensetzung von oberflächennahen Sedimenten aus dem Vorriff-Bereich der Cay-Sal-Bank und aus der zentralen Floridastraße. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 60, XXXIII pp.

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Abstract

As contribution to post-cruise analytical work on R/V SONNE cruise SO 164 seafloor samples, analyses of grain size distribution and composition of the sand-sized fraction, and investigation of the sedimentary structures have described the recent depositional regime in the southern Florida Straits. The Cay Sal Bank, Bahamas, is the main supplier of carbonate sand whose influence decreased with distance from the platform. The medium and coarse sand contents of surface samples from the Cay Sal side can be related to bottom currents in the Florida Strait. The sample from the channel trough showed a higher amount of sand in general, but the influence of the platform was weaker as indicated by the high proportion of planctonic organisms of the coarse fraction. The sand content of samples from the Florida side was comparatively low. This difference and the low mean sortable silt value in samples from the trough and from the Florida Slope point to an antisymmetrical current profile. This evidence is corroborated by a previous hydrographical survey spanning the same transect across the southern Florida Strait. With reference to the morphology and setting of the study area, the depositional environment of the Florida Straits well compares to a fluviatile meander system. This way, the Florida slope with its accumulation of finegrained sediment can be interpreted as point bar, and the platform of the Cay Sal Bank with its steep slopes and the apron of coarse, washed debris can be seen as chute bar. The carbonate content of the samples was high as expected with the Florida Ramp of calcareous muds on one side, and the Cay Sal carbonate platform on the other side. There was, however, a pervasive terrigenous proportion in the surface samples of up to 17 %. This component was most likely of clay or fine silt in size, because neither in the analysis of the sand-sized particles, nor in the SEM investigations of the silt fraction terrigenous compounds were found. The short piston core SO 164-15-2 from the trough center showed at least one coarse-grained carbonate turbidite. A positive grading in the base of the layer can recognize this turbidite. According to the oxygen isotope stratigraphy, this may have been deposited during Termination I and thus during a transgressive phase. The turbidite mainly compose of platform detritus, which is mobilized during the flooding of the platform. The turbidite buried glacial, probably autochthonous, pelagic foraminiferal sands.

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