Iron oxide mineralogy in late Miocene red beds from La Gloria, Spain: rock-magnetic, voltammetric and Vis spectroscopy analyses

Free ferric oxides of a red bed series were analyzed by rock-magnetic techniques (IRM component analysis) and by two less traditional methods: visible spectroscopy and voltammetry. All three methods have low limits of detection, making them suited for this type of analysis. The red bed samples studied contained clay minerals, quartz, and calcium carbonate as major constituents. Free Fe oxides occurred at a concentration of 0.3–2.1%, i.e. in the majority of the samples below the detection limit of X-ray powder diffraction. The combination of the employed analytical techniques enabled to characterize the mineralogy of free ferric oxides and to estimate the ratio of goethite and to hematite. This ratio changes substantially within the section that probably indicates paleoclimatic changes.