Geochronologic analysis of the Fold-thrust-belt Growth within the Argentina Precordillera

Abstract

Foreland basins, gathering sediment from rivers draining adjacent fold-thrust-belts, preserve important records of tectonic and climatic changes such as fault growth, exhumation, continental aridity, and storm intensity. The Bermejo Basin, fed by the Rio Huaco, Rio Jachal, and Rio San Juan, is a broken foreland basin located in the eastern Precordillera, San Juan, Argentina. Fault and fold propagation from the Miocene to present has contributed to erosion, deposition, and burial followed by subsequent exhumation and erosion. Work in the northern section of the basin (Huaco) attributes late-Miocene and Pliocene changes in paleo-erosion rates, to increased continental aridity. However, this interpretation does not consider active thrusting on several faults in the eastern Precordillera, which could also influence sedimentation in the basin. Fault growth and propagation in this region appears to be significant and complex, with out-of-sequence thrusting, back thrusting, and propagation along strike, therefore, we consider that paleo-erosion and depositional signals could be varied across the basin. We use cosmogenic radionuclide (CRN) dating and paleomagnetic stratigraphy in the Rio Jachal and Mogna formations, in the central Bermejo Basin (Mogna) to compare paleo-erosion rates with the northern section (Huaco) to deconvolve signals between tectonic and climate controls on basin sedimentation. Preliminary CRN data reveals that the base of the Mogna fm. near Huaco (north) is 5.15 ± 0.33 Ma and near Mogna (central) is 4.59 ± 0.65 Ma. The northern section age (Huaco) is 2 m.y. older than previously suggested and the central section (Mogna) age is similar to that of previous work. These new results imply there may be a need to reassess the interpretation of continental aridity as the main driver of paleo-erosion rate changes. Anticipated Be10 ages from 25 CRN and paleo-magnetic samples will provide a robust dataset to approach questions about paleo-erosion rate changes in the Bermejo Basin. By comparing our new findings to ongoing work constraining the spatiotemporal changes on the easternmost thrust faults of the Precordillera, we can determine the role faulting may play on basin sedimentation changes and interpreting basin records.