The rubidium, strontium, strontium-isotope system in deep-sea sediments: Argentine Basin

Silicate fractions of deep-sea, continental shelf, and estuary sediments from uppermost layers of the Argentine basin and contiguous regions were analyzed for rubidium and strontium concentrations and for strontium-isotope composition. These data give areal indications of sediment provenance but may be equivocal owing to elemental and isotopic variability caused by hydrodynamic processes such as winnowing and differential sedimentation. Plotted on an isochron diagram, however, the data form an envelope of points with characteristic slope. Samples from the adjacent Plata estuary form a separate envelope with a different slope. Samples from the area in which mixing of Plata and Argentine basin material may occur fall between these fields. The slope and approximate initial ratio (87Sr/86Sr at Rb/Sr=0) of the arrays can be used to calculate an ‘apparent age’ for these modern sediments, which is a complex integrated function of the geologic ages, rock types, and weathering processes operative in the source areas of the sediments. Within the analytical and sampling errors the ‘apparent age’ of sediments south of the Plata estuary are indistinguishable as to southern Argentina or Antarctic Ocean provenance.