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The Aulet and Adons diapirs are exposures of Triassic Keuper evaporites in the Ribagorça Basin in the south-central Pyrenees. The diapirs have been alternatively interpreted from mapped structural relationships as either passive salt diapirs or extensional salt rollers. Correspondingly, the associated diapir-flanking minibasins have been interpreted as either salt-withdrawal or extensional-rollover minibasins, respectively. New field mapping, stratigraphic sections, petrographic analysis, correlation diagrams, and drone photography characterize the depositional facies and stratal architecture of the flanking Sopeira, Sant Gervàs, and Faiada minibasins (upper Albian to lower Santonian synrift to postrift strata), which in turn, constrains the origin and evolution of each salt body and associated minibasins. Each minibasin displays unique facies patterns and stratal thicknesses that reflect depositional systems evolving in response to spatially and temporally variable extension, salt evacuation, and passive diapirism during the Pyrenean rift and postrift phases. The Sopeira minibasin developed in the late Albian with significant localized subsidence, but it remains inconclusive if the bounding Aulet diapir originated as a passive diapir or a salt roller. The Llastarri fault zone, previously interpreted as a salt weld, separates the Sopeira minibasin from the primarily extensional Sant Gervàs minibasin, and is reinterpreted here as a remnant salt ridge, as it lacks evidence for passive diapirism. The Sant Gervàs minibasin remained relatively uplifted until the middle to late Cenomanian, along with the Faiada minibasin. Evidence for passive diapirism in the Faiada minibasin, including diapir-derived detritus and composite halokinetic sequences, indicate salt evacuation into the bounding Adons passive diapir. Integration of detailed sedimentologic and stratigraphic analyses with interpretations of basin formation and structural development provides better resolution of the earlier phases of gravity-driven extension and loading-driven salt movement of the Aulet and Adons diapirs; these insights help constrain structural interpretations and reconstructions of Pyrenean shortening and megaflap development in the Ribagorça Basin. Sedimentological and stratigraphic evidence for or against passive diapirism need to be integrated into structural interpretations, especially when precursor salt structures are obscured by subsequent contraction. This well constrained basin framework demonstrates the effects of inherited extensional structures and passive diapirism on Pyrenean shortening and megaflap rotation.

The interplay between sedimentation and salt rise around a diapir results in distinct geometries that can be used to determine the structural and stratigraphic history within a basin. Using new geologic mapping, measured stratigraphic sections, and subsurface interpretations of seismic and well logs, we describe circum-diapir stratal geometries and deformation at the Sinbad Valley salt wall in the proximal, northeastern Paradox Basin, southwest Colorado (USA). We interpret these geometries in the context of newly recognized halokinetic features and salt-associated deformation (megaflaps, counterregional faults, intrasalt inclusions), present a revised stratigraphic and salt tectonic history of Sinbad Valley diapir, and compare these proximal features to those at the distal Gypsum Valley diapir and infer local versus regional controls on their formation. The deposition of conglomerates within the Paradox Formation, now preserved as intrasalt inclusions in the center of Sinbad Valley, record early elevation of the Uncompahgre Uplift. Subsequent differential sedimentary loading resulted in initiation of passive diapirism during the late Pennsylvanian through the latest Triassic/Early Jurassic, facilitated by movement on a NE-dipping, listric, counterregional fault that extends for >22 km southeast of the diapir. Exposures of a steeply dipping stratal panel of late Pennsylvanian-aged Honaker Trail Formation along the southwestern flank of Sinbad Valley are interpreted as a megaflap, a preserved remnant of the diapir roof that was folded into a vertical position by drape-folding during passive salt rise. Significant lateral changes in the surface geometry and depositional facies of the megaflap define four structural domains that may result from a combination of radial faulting and varying degrees of folding via limb rotation or limb rotation with minor hinge migration. Using key differences between Sinbad Valley and Gypsum Valley salt walls in regard to the megaflap facies, timing of megaflap formation, and the presence of a Paradox Formation conglomeratic intrasalt inclusion, we conclude that salt wall position (i.e., proximal versus distal) within a basin influences the characteristics of some of these features, whereas the timing of other features (e.g., megaflap formation) appears to be similar throughout the basin suggesting a more regional control.

This study documents the growth of a megaflap along the flank of a passive salt diapir as a result of the long-lived interaction between sedimentation and halokinetic deformation. Megaflaps are nearly vertical to overturned, deep minibasin stratal panels that extend multiple kilometers up steep flanks of salt diapirs or equivalent welds. Recent interest has been sparked by well penetrations of unidentified megaflaps that typically result in economic failure, but their formation is also fundamental to understanding the early history of salt basins. This study represents one of the first systematic characterizations of an exposed megaflap with regards to sub-seismic sedimentologic, stratigraphic, and structural details. The Witchelina diapir is an exposed Neoproterozoic primary passive salt diapir in the eastern Willouran Ranges of South Australia. Flanking minibasin strata of the Top Mount Sandstone, Willawalpa Formation, and Witchelina Quartzite, exposed as an oblique cross section, record the early history of passive diapirism in the Willouran Trough, including a halokinetically drape-folded megaflap. Witchelina diapir offers a unique opportunity to investigate sedimentologic responses to the initiation and evolution of passive salt movement. Using field mapping, stratigraphic sections, petrographic analyses, correlation diagrams, and a quantitative restoration, we document depositional facies, thickness trends, and stratal geometries to interpret depositional environments, sequence stratigraphy, and halokinetic evolution of the Witchelina diapir and flanking minibasins. Top Mount, Willawalpa, and Witchelina strata were deposited in barrier-bar-complex to tidal-flat environments, but temporal and spatial variations in sedimentation and stratigraphic patterns were strongly influenced from the earliest stages by the passively rising Witchelina diapir on both regional (basinwide) and local minibasin scales. The salt-margin geometry was depositionally modified by an early erosional sequence boundary that exposed the Witchelina diapir and formed a salt shoulder, above which strata that eventually became the megaflap were subsequently deposited. This shift in the diapir margin and progressive migration of the depocenter began halokinetic rotation of flanking minibasin strata into a megaflap geometry, documenting a new concept in the understanding of deposition and deformation during passive diapirism in salt basins.