Espectroscopía de infrarrojos de la fracción arcillosa de la sucesión sedimentaria del yacimiento paleontológico de Húmera (Cuenca de Madrid)

Resumen

The results of the spectroscopic analyzes, corresponding to the mid-infrared spectral range, of samples of the clay fraction obtained from the eight stratigraphic levels described in the paleontological site of Húmera (west of Madrid city) are described. This area shows a special interest because of the taphonomic characteristics observed in previous studies, which indicate processes of early diagenesis and pose unknowns about the ionic exchanges between the mineral phases of the sediments and the fossils they house. Therefore, mineralogical and geochemical studies are important to establish and clarify the trans- formation processes between mineral phases and fossils. It is observed that the sediments are formed by phyllosilicates, quartz and feldspars, as well as minor amounts of calcite. Several clay minerals are distin- guished, among which various phases of the dioctahedral smectites series (montmorillonite-beidellite) stand out, showing different cations in octahedral positions. Kaolinite and micas (di and trioctahedral) are also present. The coexistence of different types of smectites could indi- cate various transformation processes from pre-existing minerals (in- herited from the source area) or the presence of mixed-layer minerals. These results are in accordance with sedimentary media of alluvial fans and lakes, in an environment with contrasted hydric seasonality