Holocene floods in a complex fluvial wetland in central Spain: environmental variability, climate and time

The study of flooding can be complex as it involves dynamic systems (rivers) characterized by high variability in time and space. To minimize the effects of these handicaps, we merge several records from different locations across the hydrographic basin of the Upper Guadiana River (central Spain) and use multiple proxies. The comparison of three nearby cores by means of the facies, stratigraphic correlation and geochemical indexes allows us to differentiate local environmental changes related to the natural behaviour of the system (autocyclic) from those driven by external forcings (allocyclic). The facies and facies sequence analyses allow long-term paleohydrological trends to be reconstructed and parameters that are used to identify flooding events to be determined. Si (proxy for siliciclastic supply) and Ca/S (proxy for water budget/level) show trends that can be related to facies sequences and long-term variations. Si/Al is used as a sorting proxy (transport efficiency). To analyse the relative changes in sediment discharge and transport efficiency, these proxies are compared with water budget level, represented by (Si/Al)/(Ca/S) (sorting vs. water level) and Si/(Ca/S) (siliciclastic discharge vs. water discharge). We were able to define local, major and minor regional flood events/periods and events by relating sequence boundaries to the occurrence of environmental conditions related to high energy events (relative/absolute sorting, water level, sediment discharge) across multiple cores. Comparison to other studies around the western Mediterranean basin allows us to identify common periods of flooding at 9000–8400 cal. BP, 7700–7100 cal. BP, 6400–6200 cal. BP, 4900–3700 cal. BP, 3500–3300 cal. BP, ca. 2600 cal. BP, ca. 2000 cal. BP, ca. 1500 cal. BP and 1000–300 cal. BP. For the long-term evolution, it seems that changes in insolation during the Holocene could have played a role in controlling the hydrology. However, determining the drivers of higher-frequency variation is more challenging due to uncertainties in the chronologies and local differences. Nevertheless, some degree of correlation among these flooding periods and higher frequency changes in irradiance, temperature and NAO is observed.Departamento de Geodinámica, Estratigrafía y Paleontología, Universidad Complutense de Madrid, EspañaInstituto Geológico y Minero de España, Españ