Initiation, Growth, and Contractional Deformation of Minibasins in a Salt‐Bearing Inverted Atlantic‐Type Rifted Margin: The Cotiella Massif (Southern Pyrenees)

Abstract

The study of offshore salt‐bearing rifted margins is commonly limited by seismic data resolution. Through the incorporation of salt‐bearing rifted margins in orogenic belts, some field analogs are still present at the surface. The Cotiella Massif, in the Southern Pyrenees, is an exceptional outcrop of the former Bay of Biscay–Pyrenean Atlantic margin and offers an ideal scenario for describing and studying rifted margin‐related salt structures. Integrating structural field data, detailed geological mapping, drone imagery and digital terrain models, we propose a revised evolutionary model in which salt tectonics began with lower–middle Coniacian reactive diapirism and associated reactive faults, in contrast to previous models that only proposed basinward normal faulting. During reactive diapirism, a relatively thin post‐rift succession broke apart, leading to the formation of two incipient minibasins: the Armeña and Cotiella minibasins. During subsequent passive diapirism, both minibasins evolved differently: Armeña developed mainly as an asymmetric subsiding basin, whereas Cotiella initially recorded more symmetric subsidence followed by major minibasin tilting and asymmetric subsidence without requiring prior basal welding. Alpine shortening subsequently squeezed and, secondarily, welded the diapirs, tilted the minibasins, and incorporated them into the South Pyrenean thrust system as part of the Cotiella Thrust Sheet. This field example documents the early evolution of minibasins in an inverted rifted margin and provides new constraints on the Mesozoic evolution of the Bay of Biscay–Pyrenean Atlantic margin. It also offers a valuable field analogue for refining seismic interpretations of salt‐bearing rifted margins worldwide and provides constraints for interpreting sub‐seismic reactive fault systems.