Mineralogía y geoquímica del sondeo Montemayor-1 (Cuenca del Guadalquivir)

Abstract

This study shows the results of the geochemical and mineralogical analysis of core samples obtained from the Montemayor-1 borehole, located in the lower Guadalquivir basin. The Borehole is 260 meters depth, and includes the Niebla, Gibraleón (Guadalquivir marly clay), Arenas de Huelva and Bonares formations (Upper Miocene - Lower Pliocene in age). X-ray diffraction (XRD) analysis has been performed in bulk and in the <2 μm fractions. It was assessed XR fluorescence, total and organic carbon, scanning electron microscopy (SEM) and TEM with coupled EDS (TEM-EDS). The aim of this study is the characterization and interpretation of the type of components of this sequence and the oscillations in the context of the environmental changes of the Messinian Salinity Crisis described in this period. The mineralogical composition is very uniform, and is mostly represented by made, phillosilicates (illite, dioctahedral smectite, kaolinite, illite-smectite and a trace amount of sepiolite), quartz; calcite; mainly biogenic, dolomite, which increases towards the top of the sequence, and other minor minerals such as plagioclase, gypsum, pyrite and zircon. The chemical composition is also very homogeneous and the small variations observed in the Gibraleón formation can be interpreted as alternations of biogenic carbonates with levels with larger amount of terrigenous components (mainly silicates) and some increasing of illite component mainly in depth.