A document by Hongliang Lu. Click on the document to view its contents.

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 determine absolute time and to calibrate cyclostratigraphy-based anhysteretic remanent magnetization intensity variations to establish precessional frequencies in the growth strata record. Incremental tilting rates were calculated between selected horizons over ~5.24 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. Shallow-dipping bedding intrinsically modulated the initial rates of folding for the first 25˚ of limb tilt until 38.9 Ma. Then, halotectonics in the Paleogene Jaca Basin extrinsically modulated accelerating folding rates for the next 42˚ of folding, until ~37.5 Ma. Finally, forelimb-steepening leading to geometric strain hardening and blunted folding rates for the last 21˚ of fold tightening and causing a thrust fault to cut the anticline’s core. Folding ended at Pico del Aguila ~35.9 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.