Electron spin resonance dating of the culminant allostratigraphic unit of the Mondego and Lower Tejo Cenozoic basins (W Iberia), which predates fluvial incision into the basin-fill sediments

Abstract

The Cenozoic basins of western Iberia have a culminant allostratigraphic unit (designated UBS13), which records the beginning of Atlantic drainage and predates the fluvial incision that led to the development of the present drainage networks. However, the available numerical dating is quite limited and mainly restricted to the lowerlevel terrace deposits. Therefore, this study uses for the first time the electron spin resonance (ESR) method to date this culminant unit in the Mondego and Lower Tejo Cenozoic basins of Portugal. The depositional age of this unit is supposed to lie between~3.7 Ma (basal deposits) and~1.8 Ma (uppermost deposits). The Al-centre provided reliable ESR data, but the dates obtained by using the TieLi centre clearly underestimate the burial ages. With reference to the existing independent dating of the Vale Farpado site (3.7-3.6 Ma) at the lowermost basal level of the UBS13 deposits, the ESR (Al-centre) ages of 3.0 to 2.3 Ma obtained for the UBS13 basal and middle deposits give reliable estimates of the burial age. The ESR ages (Al-centre) obtained for the UBS13 uppermost deposits indicate a probable age of~1.8 Ma. Thus, these results are of international significance, in that they constitutes the first numerical ages obtained for the uppermost levels of the Cenozoic basin-fills of western Iberia, which predate the fluvial incision that took place in response to lower Quaternary base levels.

ESR dating applied to optically bleached quartz - A comparison with 40Ar/39Ar chronologies on Italian Middle Pleistocene sequences

“…Our results strengthen the validity of ESR-MC method to accurately date sedimentary successions in fluvial context proposed in previous studies (Tissoux et al, 2007;Bartz et al 2018Bartz et al , 2019del Val et al 2019;Duval et al , 2017Gouveia et al 2020;Kreutzer et al 2018;Mendez Quintas et al 2018;Sahnouni et al 2018). The only discordant sample, Isoletta ESR1, was carried out from extremely coarse and poorly sorted sediments probably of colluvial origin, in which quartz grains could not have been completely bleached, or in relation with a poor dose rate reconstruction in the age calculation process.…”

“…In addition, this Al-centre has a long-life expectancy due to a thermal stability (for temperatures below 100°C) that exceeding six million years (Toyoda et al, 1991). It can thus be used to date samples as old as several million years (Laurent et al, 1998;Gouveia et al, 2020).…”

“…The joint use of the Al and Ti centres, or MC approach, is therefore intended to better estimate the quality of the sediment bleaching during transport. This approach has been used several times in recent years, and several studies have shown its potential in a variety of sedimentary contexts and for periods ranging from the Lower to the Upper Pleistocene (Bartz et al 2018Gouveia et al 2020;Kreutzer et al 2018;).…”

Basin inversion: A worldwide Late Cenozoic phenomenon

“…The overflow of a basin could also occur if water level were to rise during a wetter climatic phase (e.g. Heidarzadeh et al, 2017), as again is envisaged for Iberia (see Cunha et al, 2020). This idea is contrary, and an important alternative, to the common interpretation of fluvial capture, triggered by headward erosion, as the mechanism for endorheic to exoreheic transformation (e.g., Craddock et al, 2010).…”

Estudio de la evolución cuaternaria de un modelado fluvial escalonado intramontañoso mediante índices morfométricos: río Lozoya, Sistema Central Español

“…Along these lines, many studies of the Quaternary landscape evolution of the internal basins of the Iberian Peninsula have been carried out (Silva et al, 1988;Pérez-González, 1994;García-Castellanos et al, 2003;Benito-Calvo & Pérez-González, 2008;Cunha et al, 2008;Benito-Calvo & Pérez-González, 2010;Antón et al, 2012;García-Castellanos & Larrasoaña, 2015;Silva et al, 2017;Soria-Jáuregui et al, 2018;Cunha et al, 2019;Struth et al, 2019;Gouveia et al, 2020;Rodríguez-Rodríguez et al, 2020). Likewise, this paper analyzes the Quaternary landscape geometry and evolution of the Lozoya intramountain basin located in the eastern part of the Spanish Central System (SCS), which presents a complex morphostructural evolution (Figure 1; Hernández-Pacheco 1932;Schwenzner, 1937;Birot & Solè Sabaris, 1954;Gladfelter, 1971;Pedraza, 1978;Garzón Heydt, 1980;Gracia et al, 1988;Pérez-González, 1994;Gutiérrez-Elorza & Gracia, 1997;Silva & Ortiz, 2002;Alonso-Zarza et al, 1993;Vicente et al, 2007;Benito Calvo & Pérez-González, 2010;Vicente et al, 2011;Karampaglidis, 2015;Silva et al, 2017;Karampaglidis et al, 2020).…”