SEDIMENTOLOGIC AND SEQUENCE-STRATIGRAPHIC CHARACTERIZATION OF SALT-RELATED BASINS AND MEGAFLAPS AT THE AULET AND ADONS DIAPIRS, SPANISH PYRENEES

The Aulet and Adons diapirs in the Ribagorça Basin of the south-central Pyrenees have been variously interpreted as either salt rollers or passive diapirs derived from Triassic Keuper evaporites. They are flanked by upper Albian to Santonian synrift to postrift strata in three tectonostratigraphic domains (Sopeira, Faiada, Sant Gervàs) interpreted as extensional-rollover subbasins or salt-withdrawal minibasins. Pyrenean shortening resulted in contractional megaflaps in at least the Sopeira and Sant Gervàs domains, but the alternative models have significant implications on interpretations of subsurface geometries and megaflap rotation. We use sedimentologic and stratigraphic analysis to: 1) resolve if the Aulet and Adons diapirs evolved as salt rollers or passive diapirs; 2) determine if the Sopeira, Faiada, and Sant Gervàs domains evolved as extensional-rollover subbasins or salt-withdrawal minibasins; and 3) establish a conceptual basin framework for the Ribagorça Basin. The Sopeira domain, south of the Aulet diapir, contains subvertical Aulet Fm. preserving an expanded wave-dominated carbonate ramp shoreface succession of skeletal limestones showing broad facies and thickness changes in the lower Aulet Fm., minimal variations in the upper Aulet Fm., and no evidence of passive diapirism. These data suggest the Sopeira domain evolved by some amount of gravity-driven extension, but it remains inconclusive if the Aulet diapir was a salt roller or a passive diapir. The remnant Llastarri salt ridge, which also lacks evidence for passive diapirism, separates the Sopeira domain from the primarily extensional Sant Gervàs domain, south of the Adons diapir. Finally, the Faiada domain, west of the Adons diapir, comprises an expanded succession of Santa Fe to Agua Salenz Fm. with diapir-derived detritus and halokinetic sequences, which indicate it has a component of salt evacuation adjacent to the passive Adons diapir, even if the basin was initiated by extension. With better resolution of the earlier phases of gravity-driven extension and passive salt movement, the subsequent impact of these inherited structures on contractional salt tectonics and the timing and kinematics of megaflap rotation during the Pyrenean Orogeny can be addressed and clarified.