Ángel Sánchez Bellón

Geochemical characterization of sedimentary basins by statistical analysis: The Mio-Pliocene sequences of the Vera Basin, SE Spain

Abstract The origin and history of sedimentary rocks can be deciphered from the trace elements in their clay minerals. The inheritance from weathering profiles is detected by the analogy in trace-element amounts of the Principal components analysis (PCA) was used to find the relationships among the chemical elements, the minerals and the parent rocks, and to select the most discriminating elements. Sr, Ni, Cr, Cu, Co, V, Sc and Zn appeared so to be representative of the clay fractions and the parent rocks, and were therefore selected to obtain information about the parent rocks of the sediments. A hierarchical ascending classification (HAC) was performed with these elements, it regroups samples with similar geochemical characteristics. Graphical comparison of mean geochemical composition among HAC groups provided a better identification of inherited similarities between some sediments and the parent rocks. Most of the clay minerals in the sediments appeared so to have been formed by weathering of the metamorphic basement. Only one laminite sample from Cuevas de Almanzora section in the north of the basin was identified as formed by weathering of volcanic rocks. Volcanic weathering fluids enriched some clays from the Coscojar, Garrapancho and Garrucha sections in Sr. Some Cu and Zn enrichments acquired during early diagenesis are also evidenced by graphic comparisons. B and Mg contents were used to indicate paleoenvironments. They distinguished two different sedimentary environments, separated by a paleogeographical high situated at the site of Garrapancho Hill. Higher B contents in the southern part of the basin indicate a more marine environment than in the north composed of several subbasins with different salinities correlated with varying inputs of fresh water. The Mg contents are always higher in the north, suggesting a more confined environment. The sediments in the south were deposited in higher-energy environments as shown by the presence of olistostromes whereas in the north marls and clayey laminites suggest a calmer and more monotonous environment.

Assessment and suggestions for improvement of soils with different uses in a sector of Montesinho Natural Park, Portugal

The main objective of this study is to evaluate the quality of four soils with distinct uses and managements (pasture, cereal, chestnut and oak) to check whether their use is appropriate and propose improvements. The investigation took place at Vilar de Ossos, a sector of Montesinho Natural Park in northeast Portugal. Results were obtained from field work and laboratory analyses of more than 25 parameters (textural analysis, nitrogen, phosphorous and potassium contents, cation exchange capacity and cation saturation percentage, pH, organic matter, stoniness, useful soil depth, drainage, etc.). An estimation of erosion was also made following the universal soil loss equation. Pasture and oak registered low values on soil erosion while cereal and chestnut had medium values in the same parameter. With the data obtained, we made soil evaluations according to the Agrologic Classes and the Riquier Bramao and Cornet systems. Results indicate that only chestnut soil had low qualities for farming, and that cereal soils needed a change of use. Finally, based on the assessments, recommendations to improve soil quality have been made. For the pasture soil, the proposal is to put the focus on the nutritional values. In the cereal soil, conservation tillage is proposed. In the chestnut soil, stopping the current plowing technique is suggested and, in the oak soil, which is a natural soil, the proposal is to leave it in its current state.