Palaeoweathering events recorded on siliciclastic continental deposits (Albian, Lower Cretaceous) in NE Spain

Abstract

A set of materials from Teruel (NE Spain), which includes a karst bauxite deposit overlain by an Albian (Lower Cretaceous) kaolin-rich clay succession, has been characterized from a mineralogical, textural and geochemical point of view. The materials under study were examined by X-ray diffraction, optical and electron microscopy and by inductively coupled plasma (ICP) optical emission spectroscopy (OES) and mass spectroscopy (MS). The bauxite is pisolitic and predominantly red and the overlying clay succession is mainly made up of grey claystones. Upper-section of the clay succession is a layer with carbonate nodules and scarce pisolith-like particles that can be distinguished. The studied materials are mainly composed of kaolinite, coupled with gibbsite and accessory boehmite in the bauxite. Gibbsite is also identified in the layer with carbonate nodules. Mineralogical data, kaolinite crystallinity and the Chemical Index of Alteration indicate that the layer with carbonate nodules has recorded a weathering event that was not as intense as the one that led to the in-situ formation of the bauxite deposit. The geochemical behaviour of the analysed elements, especially the REEs, also supports the existence of a weathering event recorded in the layer with carbonate nodules, given the similar trends observed in this layer and in the bauxite. The weathering led to REE + Y leaching, with the HREEs being less mobile than the LREEs, and thus the Albian clay succession, except the layer with carbonate nodules, shows a greater potential as source of these strategic elements. The research has revealed that redox fluctuation made a significant contribution to the distribution of Fe and Ce during bauxitization concerning the precipitation of Fe oxides and accessory minerals such as those of the goyazite-crandallite series.