Abstract
The silt-sandy and sandy deposits dating from the Neogene and the Quaternary have been studied along a wide littoral area, between the mouths of the rivers Tinto and Guadalquivir (Province of Huelva, Spain). Mineralogical analysis (granulometric, X-ray diffraction, etc.) and quartz grain microtextures, allow for the separation of four «sedimentary sets», which in turn can help to stablish a more detailed chronology. The lowest part on the studied series corresponds to the «Fm. Huelva sands» considered to be from the Lower Pliocene (Civis et al., 1987), in which calcium-sodic feldspars dominate over potassic feldspars, and smectite and iHite dominate over kaolinite in a infratidal sedimentation environment. Above, the Plio-Quaternary «Fm. Bonares sands» can be observed. These sands have been divided into two units: The «Lower Unit», in which the feldspar proportion of is similar to that of the lower deposits but in which there is a predominance of smectite over other clay minerals, in an infratidal to intertidal sedimentation environment; and the «Upper Unit» in which the mineralogical proportions change, with potassic feldspars and kaolinite predominating and smectite lacking, in an intertidal sedimentation environment. Upwards in this unit, some paraconglomerates appear in which the mineralogical characteristics of the matrix are similar to those of the «Upper Unit». The mineralogical, textural and environmental change between these two units is interpreted as a possible variation in climatic and geodynamic conditions of the basin during the Pliocene-Pleistocene transition.
Highlights
The lowest part on the studied series corresponds to the «Fm. Huelva sands» considered to be from the Lower Pliocene (Civis el al., 1987), in which calcium-sodic feldspars dominate over potassic feldspars, and smectite and iHite dominate over kaolinite in a infratidal sedimentation environment
Sorne paraconglomerates appear in which the mineralogical characteristics of the matrix are similar to those of the «Upper Unit»
The mineralogical, textural and environmental change between these two units is interpreted as a possible variation in climatic and geodynamic conditions of the basin during the Pliocene-Pleistocene transition
Summary
En las muestras correspondientes a los niveles H-5 y H-6 de Palos de la Frontera y H-lO YH-ll de cantera de la gasolinera, consideradas asimismo «Fm. Arenas de Bonares» por los autores antes mencionados, la fracción arenosa sigue siendo una subarcosa próxima a las cuarzoarenitas, con predominio de cuarzo monocristalino, pero en cambio puede observarse la disminución del porcentaje de feldespatos calco-sódicos, pasando a ser dominantes los potásicos El estudio al M.E.B. de los granos de cuarzo de la matriz de los paraconglomerados nos revela que son muy semejantes a los de la «Fm. Arenas de Bonares» infrayacentes, salvo que en algunos casos se han observado marcas del medio fluvial y pequeños «depósitos» de sílice globulosa en caras planas, indicadores, asimismo, del medio fluvial (Le Ribault, 1980; Legican et al, 1989).
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