Triassic Keuper evaporites have long been recognized as the main detachment level for thrusting in the Pyrenean fold-and-thrust belts. The deformed Late Cretaceous to Eocene foreland basin of the Southern Pyrenees has structures and stratal geometries that can be interpreted as related to salt tectonics (e.g. unconformities, rapid thickness variations, long-lived growth fans, overturned flaps), although they have been overprinted by shortening and thrusting. Based on field observations and published maps, we build new structural cross-sections reinterpreting two classic transects of the Southern Pyrenees (Noguera Ribagorçana and Noguera Pallaresa river transects). The sequential restoration of the sections explores the variations of structural style, addressing the role of halokinesis in the tectonic and sedimentary development. In the Serres Marginals area, we propose that salt pillows and diapirs started developing locally during the Mesozoic pre-orogenic episode, evolving into a system of salt ridges and intervening synclines filled with early synorogenic sediments. Rapid amplification of folds recorded by widespread latest Cretaceous-Palaeocene growth strata is taken as marking the onset of contractional folding in the area. During the Pyrenean compression, folding mechanisms transitioned from dominantly halokinetic, to a combination of buckling and differential sedimentary loading. Squeezing of salt diapirs and thrust welding occurred as salt ridges were unroofed. We provide new field observations that lead to a reinterpretation of the regional structural development and contribute to the debate of the role of salt tectonics in the Pyrenees.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5287737

The northern margin of the Organyà basin (Southern Pyrenees) has a complex structure in which syn-rift Lower Cretaceous carbonates flank a wide Keuper evaporite province, featuring the leading edges of the basement-involved thrust sheets of the Pyrenean antiformal stack. Recent observations show that Keuper diapirs and salt walls grew during the Cretaceous extensional episode, conditioning the development of differentiated depocenters and minibasins. The role of salt tectonics during the Pyrenean orogeny has not been addressed in previous structural studies, but present-day cross-sections indicate a Keuper evaporite-bearing vertical thickness of up to 3000 m in the Senterada-Gerri de la Sal area. We infer that salt migration was a determinant mechanism in triggering a gentle northward tilting of the Organyà basin during the Eocene-Oligocene, recorded in the La Pobla de Segur and Gurp syn-tectonic conglomerates in a basin-wide progressive unconformity and a large north-directed onlap, opposite to the main sedimentary influx direction. Contemporaneously, salt migration, promoted by conglomerate differential loading, enabled the sinking and rotation of the unrooted Nogueres thrust units (têtes plongeantes). We use new and published structural data for the Lower Cretaceous margin of the Organyà basin, combined with structural and clast provenance data from the Cenozoic alluvial fan conglomerates of La Pobla and Gurp, to understand the Lutetian to late Oligocene evolution of the northern margin of the Central South-Pyrenean Unit. The tectono-sedimentary evolution of this area and the salt evacuation patterns are closely related to the exhumation history of the stacked Paleozoic thrust sheets of the Pyrenean hinterland to the north. In this study we correlate the movements over a mobile substratum and the paleogeographic changes of conglomeratic basins at the toe of an exhuming orogenic interior.

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In the present paper, the fossil record of the archosaurs (dinosaurs, crocodylomorphs and pterosaurs) of the southern Pyrenees before the CretaceousePalaeogene (KePg) transition is revised. On the basis of this fossil record, a well-dated succession of dinosaurs and other archosaurs is established within polarity magnetochrons C30 and C29r. Almost 150 sites with dinosaur remains have been identified, containing hadrosauroid ornithopods, titanosaur sauropods and theropods, as well as egg sites and tracks. Fossil remains of dinosaurs and other archosaurs are abundant in C29r, disappearing abruptly near the top of the "Lower Red Garumnian" unit of the Tremp Formation. Thus this should be located very close to, or coinciding with the KePg boundary. These data suggest that the disappearance of the dinosaurs and other archosaurs was geologically abrupt in the southern Pyrenees, but to date there is no incontrovertible evidence of the presence of the impact level that marks the CretaceousePalaeogene boundary. Interestingly, what is highlighted in the southern Pyrenees is that the vertebrate-rich upper Maastrichtian continental sites were replaced by similar sedimentological facies characterized by the virtual absence not only of dinosaurs but also of any vertebrate remain throughout the lower Palaeocene. This could mean that the Danian terrestrial ecosystems of the southern Pyrenees took longer than other areas of the world to recover their biodiversity after the KÀPg extinction event.

<p>The Kimmeridge Clay Formation is a mudrock-dominated succession deposited during the Upper Jurassic –Kimmeridgian and Lower Tithonian stages– in a shallow shelf environment, below fair- weather wave base. With a maximum thickness of 712m onshore, and 1400m in the northern North Sea, the formation has several intervals of bituminous shales, rich in organic matter, that make it a major oil source rock in the North Sea.</p> <p>In the Late Jurassic, north-western Europe was part of the Laurasian Seaway, a shallow marine area underlain by a system of interconnected extensional basins. In Britain, sedimentation of the Kimmeridge Clay Formation took place in two main depo-centres; the onshore Wessex and Weald basins and adjacent Channel Basin in southern Britain, and the East Midlands Shelf and adjacent Cleveland Basin in north-eastern Britain, extending offshore into the North Sea. These depo-centres were bounded by normal fault systems. with significant syn-depositional activity associated with  Late Jurassic crustal extension allowing  development of thick sedimentary successions in the hangingwalls of these structures.</p> <p>The sedimentary patterns of the Kimmeridge Clay formation are rhythmic, with intervals of mudstones, organic-rich mudstones and carbonate-rich stone bands, that give characteristic inflection patterns to wireline logs. These patterns are very similar across the Wessex and Weald basins but differ slightly from those of the East Midlands Shelf and Cleveland Basin; perhaps a consequence of compartmentalisation of accommodation space by the Anglo-Brabant Massif.</p> <p>We present a new correlation of borehole geophysical logs (gamma & sonic) and associated thickness maps and structural maps for the Kimmeridge Clay Formation. They reveal lateral changes in thickness that reflect the influence of underlying basin structure on patterns of deposition and post-depositional erosion.</p>