BEST OF AAPG: EPISODIC DEFORMATION RATES RECOVERED FROM GROWTH STRATA, PYRENEES (Invited Presentation)

Growth strata are used to recover high-resolution incremental deformation rates in syntectonic strata. The synsedimentary strata preserve the interaction between uplift and sedimentation and require deconvolution of deformational and depositional processes. We used magneto-and biostratigraphy to determine absolute time and to calibrate rock magnetic-based cyclostratigraphy for three regional Paleogene structures near the South Pyrenean mountain front. Incremental folding or fault slip rates were determined for each structure. At Sant Llorenç de Morunys, a fault-propagation fold records uncoupled deformation and depositional rates and folding rates of 0 to 100˚/myr, which resulted from thrusting rates of 115-255m/myr over 3 myr. At Pico del Aguila, the décollement anticline developed for 5.23 myr and records variations in folding rate of 0° to 95°/myrs as a result of episodic thrusting in the fold’s core. Near Sos del Rey Católico, the Peña duplex records the growth of a thrust-related anticline that delineates the southwestern mountain front. Shallowing of the growth strata up-section was related to slip on a mountain front backthrust where deformation and deposition were coupled. Folding rates calculated from the growth strata at the resolution of the polarity chrons (0.42-2.5 myr), varies from 4°/myr to 13°/myr over 10 myr. At each location, our metronome was cyclostratigraphy related to magnetic-mineral concentration variations in the growth strata that were modulated by astronomically forced climate changes. Each fault related-fold recorded episodic deformation at 10⁴ years time scales accompanying depositional rate variations. The marine and continental growth deposits had order of magnitude difference in accumulation rate variability depending on facies and accommodation space development.