Local and regional geochemical signatures of surface sediments from the Cariaco Basin and Orinoco Delta, Venezuela

We have analyzed the chemical compositions of 87 samples from the Cariaco Basin and 20 samples from the Orinoco Delta, Venezuela, in order to better characterize the fluvial sources of material to the Cariaco Basin. We observe distinctive regional patterns in composition; shelf sediments found near the Tuy River, Manzanares River, the Araya-Margarita region, and in the northern portion of the Unare platform record reproducible compositional differences. However, linear mixing models using only the composition from these rivers do not satisfy the variability observed in modern sediment trap samples collected from the basin. Average trap values are best approximated by mixing upper crust (30%-50%) with local river sources (50%-70% of either the Tuy, Unare, or Neveri Rivers) and eolian dust (<2%). The chemical data suggest a glacial-interglacial switching of sources, with the Tuy-Tacarigua, Unare, and Neveri being more important during glacials, and the larger Tuy and Manzanares being more important during interglacials. The K/Al in shelf sediments (0.14-0.27) spans the range of previously documented glacial to interglacial values (0.16-0.26), and the high Ti/Al found during glacials (similar to 0.052) can perhaps be supplied by some of the local rivers (Ti/Al similar to 0.049-0.106) and not exclusively by Saharan dust. The data and statistical models do not offer support for the presence of any significant Orinoco source.