Internal and External Modulation of Folding Rates With 10 4 to 10 5  Year Time Resolutions From Growth Strata, Pico del Aguila, Spain

High‐resolution cyclostratigraphy in growth strata are used to reconstruct unsteady folding rates at the regional‐scale Pico del Aguila anticline, southern Pyrenees, to evaluate deformation modulation. Magnetic polarity stratigraphy was used to calibrate cyclostratigraphy‐based anhysteretic remanent magnetization intensity variations to establish precessional frequencies in the growth strata record. The astronomically tuning was used to determine sedimentation rates and absolute time. Incremental tilting rates were calculated between selected horizons over ∼6 myr of fold growth. Careful treatment of uncertainties enhances confidence that the results are meaningful and results show significant variability in folding rates over time. The acceleration phase of fold growth was variable, punctuated by a prolonged period of tectonic quiescence, and correlated to sedimentation changes in the wedge‐top basin. Low dipping bedding intrinsically modulated the initial rates of folding for the first 25° of limb tilt, until ∼38.86 Ma. Then, halotectonics in the Paleogene Jaca Basin extrinsically modulated accelerating folding rates for the next 45° of limb tilting, until ∼37.42 Ma. Finally, forelimb‐steepening leading to geometric strain hardening and blunted folding rates for the last 17° of fold tightening and causing a thrust fault to cut the anticline's core. Folding ended at Pico del Aguila ∼35.10 Ma. Calculated folding rates varied between 0° ± 5.5°and 90° ± 19°/myr over 100s kyr time increments. Variations in the folding rate of the Pico del Aguila décollement anticline are attributed to both intrinsic modulation as a result of progressive bedding steepening during folding and extrinsic modulation as a result of variable deltaic sedimentation rates in the wedge‐top basin. A high‐resolution age model, with careful consideration to tilting uncertainties, is used to reconstruct deformation rates at Pico del Aguila anticline, Spain. The age model is recovered from sedimentary rocks that were deposited during deformation using magnetic methods. Deformation occurred over 5.95 million years with variable speed. Variations in deformation rate are attributed to both internal and external causes. Variable folding rates, between 0 ± 5.5° and 90° ± 19°/myr over 100s kyr time increments, characterize Pico del Aguila anticline, Spain Deformation rates are modulated by both intrinsic processes and extrinsic processes