Rockmagnetic and reversal stratigraphy in terrestrial depositsRecovering fault slip rates in growth strata

Resumo

This study develops a high-resolution chronostratigraphy age model based on magnetic susceptibility to determine folding rates recovered from Eocene-Oligocene growth strata of the Berga Conglomerate Group, NE Spain. The syntectonic Berga Conglomerates were sampled for rock magnetic, magnetostratigraphy, and cyclostratigraphy analyses. Analysis of rock magnetic measurements indicates a mixed mineral assemblage with both paramagnetic and ferromagnetic minerals. Reversal magnetic stratigraphy constrains the time frame of folding. Time series analysis of magnetic susceptibility variations shows statistically significant power in expected orbital frequencies. The onset of deformation was at 33.85 Myr and the end of deformation is unconstrained but is younger than 31.06 Myr. Deformation and sediment accumulation rates were unsteady at 20 kyr time scales. Deformation rates range from 0-100 °/Myr and modeled fault slip predicts variable displacement rates ranging from 115-265 m/Myr. Because folding rates are variable and appear to be separated into long periods of quiescence punctuated by rapid changes, it seems that deformation in this region is not driven by changes in sediment supply, but rather by changes in tectonic activity.