Diagenetic behavior of the rare earth elements in Santa Barbara Basin sediments

Much research has been conducted on the rare earth elements (REE) in various solid phases with the attempt to try and link measured REE distributions to the environmental conditions of deposition. A complicating factor of such studies is the role of diagenesis on the rare earths, a process that is still not well described. Although there have been several investigations on the rare earth elements in pore fluids to characterize the diagenetic behavior of the REEs, this data set only represents estuarine environments and needs to be expanded to other marine systems to not only improve our understanding of porewater lanthanide behavior, but to also improve our knowledge of the geochemical cycling of these elements. We have conducted a detailed investigation of the REE in porewaters of the Santa Barbara Basin where porewater samples were collected from three different locations in the Santa Barbara Basin, each characterized by different bottom water oxygen concentrations. These locations (the upper rim of the basin (water depth = 230m), the slope of the basin (water depth = 550m), and the center of the basin (water depth = 590m)) were sampled to test the behavior of the REE under various sedimentary redox conditions. Measurements were also made on major and minor elements to constrain the redox conditions at each site. Here we present our data for the REE in pore fluids and discuss its behavior in terms of 1) the diagenesis of Fe-Mn oxides, 2) correlations with other porewater constituents, and 3) the types of processes that may occur within the sediment column (e.g., diagenetic release and/or authigenic uptake) and to what extent they may occur.