Iron oxide mineralogy in late Miocene red beds from La Gloria, Spain: rock-magnetic, voltammetric and Vis spectroscopy analyses T. Grygar a, * , J. De ˇdec ˇek b , P.P. Kruiver c , M.J. Dekkers c , P. Bezdic ˇka a , O. Schneeweiss d a Institute of Inorganic Chemistry, Academy of Sciences of Czech Republic, R ˇ ez ˇ 250 68, Czech Republic b J. Heyrovsky ´ Institute of Physical Chemistry, Dolejs ˇkova 8, 180 00 Prague 8, Czech Republic c Utrecht University, Paleomagnetic Laboratory, ‘‘Fort Hoofddijk’’, Budapestlaan 17, 3584 CD Utrecht, The Netherlands d Institute of Physics of Materials, ASCR, Z ˇ iz ˇkova 22, 616 62 Brno, Czech Republic Received 26 March 2002; accepted 20 January 2003 Abstract 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. D 2003 Elsevier Science B.V. All rights reserved. Keywords: Fe oxides; Goethite; Hematite; Red beds; Voltammetry; Diffuse-reflectance spectroscopy 1. Introduction The relationship between the mineralogy of ferric oxides in soils and the soil-forming environment is a traditional topic in soil science (Schwertmann and Taylor, 1989; Cornell 0341-8162/03/$ - see front matter D 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0341-8162(03)00023-7 * Corresponding author. Fax: +420-2-20941502. E-mail address: grygar@iic.cas.cz (T. Grygar). www.elsevier.com/locate/catena Catena 53 (2003) 115 – 132