Distribution of Trace Elements in Offshore Sediments of the Orinoco Delta

Surficial sediments from 56 stations on the Orinoco Delta offshore zone were analyzed by x-ray fluorescence spectrometry for aluminum (Al), barium (Ba), calcium (Ca), chromium (Cr), copper (Cu), iron (Fe), hafnium (Hf), magnesium (Mg), manganese (Mn), sodium (Na), nickel (Ni), rubidium (Rb), silicon (Si), strontium (Sr), vanadium (V), zinc (Zn), and zirconium (Zr). The resulting compositional data set was subjected to factorial and cluster analysis. The results demonstrated that two different sedimentary environments could be distinguished: (1) fine-grained sediments with significantly higher concentrations of Al, Cr, Fe, Mn, Rb, V, and Zn, and (2) coarse-grained sediments with significantly higher concentrations of Ca, Hf, Sr, Zr, and Si. On the other hand, Ba, Cu, Mg, Na, and Ni show relatively homogeneous concentrations in the sediments studied. Our results suggest that the calcareous and coarse-grained quartz sand fringe is a transgressive and relict sediment from the last glacial. This fringe, which is parallel with the coastlines, occurs at between 80 and 170 meters of water depth. Presumably all the studied trace elements, except Sr, Hf, and Zr, are adsorbed on clays and/or are associated with oxide-oxyhydroxides of Fe-Mn. Strontium shows a good correlation with Ca, which suggests the presence of carbonates. The high degree of correlation between Zr and Hf suggests a common origin, probably associated with the presence of heavy minerals. The concentrations of the trace elements reported in this work are useful as reliable baselines and can be used for comparison in future sediment studies.