Permian and Triassic paleosols in the fluvial-lacustrine record of the central Pyrenees Basin, Spain: A stratigraphic tool for interpreting syn-tectonic sedimentary evolution and paleoclimate

Abstract

Paleosols as stratigraphic tools are an established approach in the study of continental basins and offer information on the complex interplay between the factors that control the filling of basins, as the accommodation, deposition, erosion, and climate, which exerts a great influence on the supply rate of sediment and water from the sources to the basin. They are also useful to describe alternating phases of active tectonic movements and quiescence. In highly deformed basins, the differentiation between lithostratigraphic units with very similar facies but different ages may be problematic. In these cases, paleosols are a good distinguishing criterion because they are very sensitive to both climatic and topographic changes and distinct types of paleosols are expected in units deposited under different conditions. On the southern border of the Pyrenees, early Permian terrestrial red-beds were deposited under a transtensive-extensive tectonic context in isolated strike-slip sub-basins affected by syn-sedimentary tectonic activity, which generated internal unconformities of different orders. A generalized extensive tectonics was developed from middle Permian onwards, allowing the incursion of the first Tethys transgression in the Pyrenean Basin during the Middle Triassic. Subsequent Alpine tectonic inversion greatly affected the configuration of the basins, adding to their complexity. In this work, the paleosols observed in the field are described, classified, and interpreted in order to study the link between pedogenesis and the evolution of the landscape under changing tectonic and palaeoclimatic conditions. Grouped into palaeocatenas, the lateral variation of pedotypes across the landscape is used to interpret topography and water table variations, which was explained by variations in climate, available accommodation space, and sedimentary supply. The study of hydrological and climatic conditions was complemented by the identification of the mineralogical composition of the parent material and δ13 C and δ18 O isotopic signatures from the inorganic pedogenic carbonate of paleosols and lacustrine limestones. These continental basins of the Pyrenees were strongly disconnected during the Permian and characterized by several periods of non-deposition and erosion. The results provided herein improve our knowledge of the tectonic and palaeoclimatic conditions of this near equator area of the westernmost peri-Tethys domain during the first stages of the Pangea break-up.