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Evidence for Extensional Rollover Subbasins and Salt Withdrawal Minibasins Adjacent to the Aulet and Adons Diapirs, Spanish Pyrenees

Abstract

The Aulet and Adons diapirs in the south-central Pyrenees have been interpreted as either salt rollers or passive diapirs derived from Triassic Keuper evaporites. They are flanked by upper Albian to Turonian synrift to postrift strata in three tectonostratigraphic domains (Sopeira, Faiada, Sant Gervàs) variously interpreted as extensional rollover subbasins or salt withdrawal minibasins. Pyrenean shortening resulted in contractional megaflaps in at least the Sopeira and Sant Gervàs domains. 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 basin framework for interpreting the kinematics of megaflap rotation.

The Sopeira domain, south of the Aulet diapir, contains subvertical Aulet Fm. preserving an expanded shoreface succession of bioclastic limestones with minimal depositional facies or thickness changes and no evidence of passive diapirism. However, large blocks of lower Aulet Fm. are preserved within upper Aulet Fm. on the lateral margin of the basin and interpreted as slump blocks. These data suggest the Sopeira domain evolved as an extensional rollover subbasin adjacent to a salt roller. The Sant Gervàs domain, south of the Adons diapir, contains completely overturned Santa Fe reefal facies. The subsurface geometry is uncertain, but an extensional rollover origin of the Sant Gervàs domain best explains the salt-sediment relationship and most realistically allows for later rotation to completely overturned. The Llastarri fault zone, between the Sopeira and Sant Gervàs domains, was first part of the N-S trending lateral margin of the older Sopeira basin with numerous slump blocks, then the lateral footwall of the younger San Gervàs basin. Finally, the Faiada domain, west of the Adons diapir, comprises Santa Fe inner platform facies with diapir-derived detritus and halokinetic sequences, which indicates it has at least some component of salt withdrawal adjacent to a passive diapir, even if the basin is largely extensional. By resolving the origin and early extensional history of these domains and salt bodies through sedimentologic and stratigraphic analysis, structural analysis can be applied to determine the kinematics of contractional salt tectonics and megaflap rotation during the Pyrenean Orogeny.