Geologic evolution of the Peña Flexure, Southwestern Pyrenees mountain front, Spain

Abstract

The sedimentary and tectonic evolution of Oligocene continental growth strata of the Peña flexure records the development of a thrust-related anticlinorium and foreland-dipping molasse along the Southwestern Pyrenees mountain front. We exploit the coupling of uplift, the production of accommodation space, and resultant synorogenic sedimentation to explore the interplay of processes accompanying thrust faulting. A new magnetic polarity strata through ~3400 m of continuous pre and syn-growth strata near the town of Sos del Rey Católico, Spain shows coordinated deposition and deformation. The ChRM data reside mostly in magnetite. Correlation to the Geomagnetic Polarity Time Scale suggests our measured stratigraphic section spans from 33.2 Ma (ChronC12r) in the Middle Campodarbe Formation to 23.4 Ma (chron C6C) at the top of the Bernués Formation. Shallowing in dip of the growth strata up-section is related to coeval slip on a mountain front backthrust. The onset of growth strata deposition and fault slip at this position along the Pyrenees mountain front occurred at about 28.6 ± 0.1 Ma. Folding rates calculated from the growth strata at the resolution of the polarity chrons (0.15–1.12 Myr), varies from 03˚/myr to 35˚/myr.