Search

The Tinto and Odiel rivers (SW Spain) drain from a vast sulfide mining district and join at a 20-km-long estuary that enters the Atlantic Ocean. In this work, the contents of rare earth elements (REE) and fractionation in Neogene–Holocene sediment cores from La Fontanilla cove (Tinto estuary) were studied. The sediments were collected from a depth of 18 m at different distances from the recent river flow and were analyzed for new information on the temporal development of the REE load in the sediment column. Results show that the ∑ REE is higher in the finer sediments and during periods of mining activity from prehistoric to recent times. Marine influence appears to increase the light REE (LREE) relative to the heavy REE (HREE). The REE patterns of these estuarine sediments show convex curvatures in the MREE relative to the LREE and HREE, indicating the presence of acid-mixing processes between the fluvial waters affected by acid mine drainage (AMD) and seawater, as well as the precipitation of poorly crystalline mineral phases. Significant positive Eu anomalies were found in ebb-tide channels and marsh deposits, which can reflect the mineralogical composition and/or a strong localized salinity gradient combined with organic matter degradation. Sedimentological characteristics of the deposits appear to play the main role in accumulation and fractionation of the REE. [ABSTRACT FROM AUTHOR]

The elemental content—mainly trace elements—of samples from two boreholes (PLN, CM) with evidence of tsunamiites, located in the Doñana National Park (SW Spain), were studied. The geochemical variations of the REE, LILE, HFSE, and other elements (Al, Ti, S, Na, Br, Sc, Co, Cr) were interpreted according to the mineralogy present in the samples. The results obtained show the geochemical complexity of the estuarine paleoenvironments, in this case with the existence of three Holocene-age tsunamigenic deposits (around 4.25, 3.56 and 2.2–2 kyr BP). The statistical analysis of the samples' geochemistry, by means of linear correlation and factor analysis, made it possible to differentiate two associations. The first is representative of an inherited mineralogy (REE-Y-Rb-Sr-Cs-Th-U-Hf-Al-Ti-Co-Cr-Sc); the second includes elements (Br-Na) linked to mineral formation under evaporite conditions (halite). The trace element geochemistry of sediments thus becomes an excellent tool to identify tsunamiites in the studied zone, especially those elements that are clear proxies for marine incursions (Na, Br, Sr) and high energy events (Hf, Ti). The parent area of the provenance of the materials is mainly of felsic composition. [ABSTRACT FROM AUTHOR]