The Sabiñánigo Sandstone Succession, Jaca Basin, Southern Pyrenees, NE-Spain : A Depositional Model

The Eocene Sabiñánigo Sandstone Succession (SSt-Succession) forms part of the sedimentary infill of the Jaca Basin, which evolved as a piggyback basin in front of the emerging Pyrenean orogeny. Foreland basins in general, and their siliciclastic deposits in particular, are not only of scientific but also of common economic interest, due to their outstanding relevance for hydrocarbon exploration. Furthermore, the SSt-Succession is of great scientific interest, as it takes over a challenging position within the Jaca Basin. It forms the transitional part from deep marine to continental deposition, promising to reveal some insights on the depositional processes affecting the Jaca Basin. Thus, the scientific research was driven by the general interest in the genesis of the SSt-Succession, and how it fits into the Pyrenean realm, e.g. how basin formation was triggered by the Pyrenean orogeny. Therefore, the SSt-Succession was scrutinized from different points of view, integrating distinct approaches, and analytical methods, with the working process described in this case study. The SSt-Succession is exposed within two distinct ridges, showing excellent outcrop conditions, with lateral and vertical stratigraphic surfaces, that can be traced physically and optically over large distances. But they are lacking any marker horizon between both ridges that enables to easily link-up both exposure sites situated at the northern and the southern limb of the Basa Anticline. Therefore, the sediments of the SSt-Succession have been processed in detail to get a data set that enables to construct a time-calibrated framework of each exposure site. This in turn allows connecting both exposure sites and developing a depositional model of the entire SSt-Succession. Different techniques were applied within this study to characterize the sedimentary succession of the Sabiñánigo Sandstones. It considers gamma ray logs together with standard lithological profiles. In addition, to constrain the previous sedimentary overburden, covering the SSt-Succession, low-temperature thermochronology has been applied. Spectral gamma ray analyses were used to refine standard facies analysis and to support sequence stratigraphic correlation within the SSt-Succession. Detailed facies analyses and gamma ray spectrometry studies were combined, revealing a pattern of returning facies types, large-scale facies associations and related vertical stacking patterns. On the basis of the generated data set a scheme of facies types and corresponding facies associations was established, comprising various lithologies, ranging from argillaceous siltstones rich in Nummulites up to coarse-grained sandstonesand conglomerates. This allowed to deduce the depositional setting of the SSt-Succession, reaching from transitional offshore to delta plain environments, and enabled to characterize the sedimentary evolution of the Sabiñánigo Delta system, and thus, to elucidate driving mechanisms controlling the depositional processes. This study greatly benefits from a wide data set that allows interpreting the deposits of the SSt-Succession from different points of view and to integrate the applied methods into a time calibrated model. It, therefore, was possible to identify two progradational sequences as well as to examine the depositional history of the SSt-Succession and to reveal corresponding driving mechanisms. The SSt-Succession reflects a process response system that connects the evolution of the Pyrenean Orogeny with sedimentary deposition in the southern Foreland basin (Jaca Basin). The development as a piggyback basin is stored in the sedimentary archive. The first stage of evolution clearly identifies a partly developed delta, whereas the sedimentary sequence of the second stage indicates a fulldeveloped delta. In the early stage, the moving piggyback basin was filled from the emerging Boltaña Anticline in the east, and during the second stage from the newly uplifted Axial Zone in the north