Contractional salt tectonics and role of pre-existing diapiric structures in the Southern Pyrenean foreland fold–thrust belt (Montsec and Serres Marginals)

Abstract

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 Merluza Graben: How a Failed Spreading Center Influenced Margin Structure, and Salt Deposition and Tectonics in the Santos Basin, Brazil

“…This approach can be applied to other basins to better constrain regional to local variations of sub-salt fault activity relative to salt deposition and tectonics, commonly a challenging task in present-day passive margins such as the Gulf of Mexico, the South Atlantic, Nova Scotia, NW Africa as well as the North Sea, Barents Sea, and the Red Sea. This approach can also be used to understand and restore depositional salt thicknesses and sub-salt fault activity in fossil hyperextended margins that are now inverted as part of orogens such as in the Alps, Pyrenees (cf., Benoit et al, 2020;Burrel & Teixell, 2021;Célini et al, 2020;Decarlis et al, 2014;Ducoux et al, 2021;Ford & Vergés, 2021;Roca et al, 2011). Moreover, constraining the regional context and variability of salt deposition and sub-salt fault activity can afford an improved understanding of the pre-and post-salt structural framework as well as of the distribution of presalt reservoirs and source-rocks.…”

Assessing the Internal Uppermost Crustal Structure of the Central Pyrenees by Gravity‐Constrained Cross Sections

“…This relationship could point to a lateral westward migration of the Triassic evaporites due to differential loading prior to the Cenozoic Alpine compression and probably to an increase in early diapirism to the West (e.g., Saura et al., 2016). Unraveling the pre‐compressional thickness variations of the Triassic evaporites inside the Pyrenean range constitutes a difficult task due to the subsequent development of compressional structures and possible across‐ and/or along‐strike evaporitic flows during its syn‐rift, post‐rift, and compressional stages (e.g., Burrel & Teixell, 2021; García‐Senz, 2002; Santolaria et al., 2016; Storti et al., 2007). A visualization of the volumes of Triassic evaporites at depth based on gravity data could help to solve the pre‐compression scenario.…”

Structural evolution of the superimposed Provençal and Subalpine fold-thrust belts (SE France)

“…During shortening, the pre-existing halokinetic structures were generally reactivated, localizing preferentially the shortening in the cover. The initial geometry of these pre-existing halokinetic structures can be strongly modified during the contractional deformations as documented, for instance, in the Pyrenees (Saura et al, 2016;Labaume and Teixell, 2020;Burrel and Teixell, 2021), in Provence (Angelier and Aubouin, 1976;Espurt et al, 2019b), in the Alps (Dardeau et al, 1990;Granado et al, 2018;Célini et al, 2020Célini et al, , 2021, in the Zagros (Callot et al, 2007(Callot et al, , 2012, and in the eastern Carpathians (Tămaș et al, 2021). Shortening induces the lateral and vertical evacuation of the mobile evaporitic material.…”