Basement-involved thrusting, salt migration and intramontane conglomerates: a case from the Southern Pyrenees

Abstract

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.

Reconstructing the Iberian Salt‐Bearing Rifted Margin of the Southern Pyrenees: Insights From the Organyà Basin

“…All these observations indicate that halokinetic movements promoted shallow water deposition and highly mobile substrate along the Senterada salt wall throughout Barremian‐Albian time. The redeposited Triassic rocks found toward the top of the Lluçà Formation have been previously interpreted as a salt sheet derived from the Senterada salt wall (Burrel et al., 2021). Certainly, the flap of Nargó mapped along the eastern side of the Flamisell valley suggests an acceleration of the subsidence during early Albian time that eventually led to salt extrusion along the Senterada salt wall.…”

“…In the South‐Central Pyrenees, the importance of Jurassic to Late Cretaceous salt tectonics has received increasing attention in recent investigations that unambiguously demonstrate the role of diapiric processes in constraining the Mesozoic tectono‐sedimentary evolution of the area, including those at: Cotiella (López‐Mir et al., 2015; McClay et al., 2004; Ramos et al., 2020), Sopeira and Sant Gervàs (Burrel, 2020; Gannaway Dalton et al., 2022; López‐Gómez et al., 2019; Muñoz et al., 2018; Saura et al., 2016), and Upper Pedraforca (Saura et al., 2016). This collection of relatively small basins, each containing several kilometres of salt‐controlled sediments, defines a diapiric domain, named as Diapiric Province in Southern Pyrenees (Saura et al., 2016) and Senterada Salt Province (Burrel, 2020; Burrel et al., 2021), that stretches at least 120 km parallel to the fold and thrust belt.…”

Fault Gouge Dating in the Spanish Pyrenees: Fault Ages, Thrust Propagation Sequence, Wall‐Rock Provenance, and Thermal Constraints

“…The Axial Zone antiformal stack in the interior portion of the central Pyrenees consists of 4 thrusts, successively the Nogueres, Gavarnie, Orri, and Rialp thrusts (Munoz, 1992; Teixell et al., 2018). The Nogueres (56.4 ± 1.3 Ma) and the Gavarnie (36.5 ± 1.4 Ma) thrusts were active in‐sequence, although the closeness in age of the Gavarnie gouge age to Priabonian (37.7–33.9 Ma) growth strata associated with the Orri thrust indicates the Gavernie and Orri thrust may have been active essentially simultaneously (Burrel et al., 2021). Several sets of thermochronometer data similarly suggest that a significant pulse of tectonically driven exhumation occurred in the central Axial Zone region around 35 ‐ 25 Ma, linked to growth of the antiformal stack and local out‐of‐sequence thrusting in the interior portion of the range as the orogenic wedge thickened (Bosch et al., 2016; Fitzgerald et al., 1999; Gibson et al., 2007; Jolivet et al., 2007; Labaume, Meresse, Jolivet, Teixell, & Lahfid, 2016; Metcalf et al., 2009; Sinclair et al., 2005; Waldner et al., 2021).…”

Translation, collision and vertical‐axis rotation in the Organyà and Montsec minibasins (South‐Central Pyrenees, Spain)

“…The salt wall is enclosed between the leading branches of the foreland‐dipping basement thrusts and the stiff Mesozoic limestones of the Prada monocline (Séguret, 1972). Elongated, squeezed diapirs and welds are flanked by Cretaceous growth‐strata and Jurassic strata are often missing (Burrell et al., 2021).…”