Fases geoquímicas de Fe y Mn en sedimentos del noreste del margen continental Atlántico de España: procesos diagenéticos y sedimentarios

This study aims at apprehending the major forcing factors which govern the spatial and vertical Mn and Fe distributions in six cores from the Galician continental margin. Spéciation by chemical leaching experiments in selected cores from the three main morphogenetic units defined by Ercilla et al., 2005 in the study area, helps to understand their chemical behaviour during early diagenesis in this environment. Several sequential extractions protocols were combined in order to assess the distribution bound to amorphous oxyhydroxides, crystalline oxides, carbonates, sulphide and residual phases. The distribution and chemical behaviour of Mn and Fe differ significantly. Low chemical mobility of iron in the sedimentary record is illustrated by relatively uniform depth profiles and an important proportion (76 % , on average) in the residual chemical phase. Conversely, Mn is mostly present in reducible phases and bound to carbonates. The strong dependence of Mn distribution on chemical conditions is expressed by a marked enrichment in the oxic layers of the sediment