Dating the onset of Lower Tagus River terrace formation using electron spin resonance

Abstract

In the Western Iberian Peninsula, staircases of fluvial terraces have been the subject of several recent studies. In particular, many recent publications have focused on the Quaternary fluvial chronostratigraphy of the Lower Tagus Basin. However, there are still doubts with respect to the timing of the first incision into the late Tertiary basin-fill deposits, their upper part already recording a fluvial environment (‘basin inversion’), which was the start of terrace formation. This is because most dating methods are ineffective for this type of deposit (generally without organic and/or volcanic materials). In the last 10 years, new dating methods such as electron spin resonance (ESR) applied to sedimentary quartz now facilitate more accurate chronologies. This paper presents the results of the ESR dating of the older terraces of the lower Tagus Basin, Portugal, with extrapolation on the age of early drainage network evolution. According the results, the oldest fluvial terrace was formed around 900 ka, so the origination of the Portuguese Tagus River terrace system can be attributed to the final part of the Early Pleistocene.