First ESR dating of quaternary sediments in Mérida Andes, Western Venezuela

The main objective of this study is to demonstrate that Electron Spin Resonance (ESR) dating of Quaternary sediments can be performed at Venezuelan Laboratory (Laboratorio de Física de la Materia Condensada – Instituto Venezolano de Investigaciones Científicas). The dating was carried out using quartz samples extracted from sedimentary Quaternary fill of three alluvial terraces (Qt12, Qt9 and Qt7) located along the Santo Domingo River (Mérida Andes, Western Venezuela), that have been previously studied and dated by Terrestrial Cosmogenic Isotope (¹⁰Be). The sedimentological characteristics of the Qt9 terrace fill indicate that the transport and sedimentation process of the sediments was under stable and high energy conditions. Our ESR dating suggest a maximum age of 85 ± 16 ka for this terrace, which is consistent with the ¹⁰Be ages previously published. In the case of the Qt12 and Qt7 terraces, field observations suggest a sediment transport process by debris flows, with rapid deposition. In this case, our ESR ages (228 ± 93 ka, 108 ± 33 ka, for Qt12 and Qt7, respectively) seem to be overestimated compared with the ¹⁰Be ages reported in previous studies. These results confirm that the sedimentary material to be used for dating through this technique must be deposited under stable conditions involving long-term sediment transport processes. This will allow the “optical bleaching” of paramagnetic centers to occur before the material is buried, as seems to have happened with the Qt9 terrace sample. The results discussed in this work support the existence of the technological and human resources necessary to carry out numerical dating of Quaternary sediments in Venezuela.