Rare earth element distribution in sediments from the Minho river and estuary (Portugal) — a preliminary study

River sediments are composed of a complex mixture of mineral fragments resulting from the weathering of the rocks in the drainage basin of the river, biological material and organic substances; each component shows characteristic concentrations of trace elements. Depending on the sedimentation region and environment, the trace element geochemistry, particularly the REE distribution is an important tool to characterize the origin of the sediments and their sedimentation processes. The importance of these trace elements on riverine, estuarine and marine studies have been reported by several authors (Piper, 1974; Elderfield, 1988; Elderfield et al., 1990). However, the present knowledge on the chemical composition of sediments draining the northwestern Portuguese shelf is very limited and there are no studies accomplished on their rare earth element (REE) distribution. In this study, we report the first results on REE (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu) determined in sediments (using INAA), from the Minho river and estuary and how these data can be used to demonstrate different processes occurring during the river course and particularly at the estuarine environment.