A novel selective extraction of barite, and its application to eastern Mediterranean sediments

A sequential extraction method (BASEX) was developed to determine the different Ba fractions in sediments. Calibration of BASEX with pure barite and a home-made mixed mineral standard showed that barite is separated from all other major Ba containing mineral phases, such as clay minerals and Fe and Mn oxides. This method permits the direct determination of sedimentary barite content and of the Ba/Al ratio of clay, and is, therefore, a useful tool in palaeoclimatic studies. Application of BASEX to eastern Mediterranean sediments, including sapropel S1, revealed that the enrichment in Ba concentrations observed in this sapropel consists predominantly of barite. The relationship of barite-Ba with organic carbon in sapropel S1 sediments appears to be independent of water depth, of organic matter fluxes and of the sedimentation rate for cores ranging from 2150 to 3300 m water depth. Apparently, organic carbon remineralisation has been virtually absent in the water column deeper than 2150 m. This might have been caused by suboxic to anoxic conditions present in the deep eastern Mediterranean basin during the formation of sapropel S1. Because of the constant relationship between barite and organic carbon in sapropelic sediments, we suggest that the barite content can be used to quantify the initial organic carbon content of the sediment in the oxidised sapropel interval.