GIS and Palaentology integrated application for the recognition of tsunamigenic events in Doñana National Park

Abstract

The present work aimed to characterize the actual and past environments at Doñana National Park (SW Spain) throughout the study of benthic foraminifera assemblages at two drill holes (cores C and D, from Ruiz et al., 2004) and twenty surface samples, as well as to recognize and confirm the occurrence of extreme energy events (storms/tsunamis) around 2165 yrs B.P. (215 yrs BC). The studied tsunamigenic beds have between 8 to 26 cm in Core C and 40 to 10 cm in Core D. Almost all the variables studied in the present work concur with previous works on tsunamigenic layers found worldwide. These variables include the foraminifera species found in the tsunamigenic layer, the composition of sand beds (suggesting strong waves and currents), the presence of reworked molluscs, marine foraminifera taxa, high values for planktonic/benthic ratio, and high Shannon H, Fisher Alpha and Species richness diversity indexes. In our case the diversity index that evidences the most the occurrence of a tsunami seems to be Fisher Alpha, which value is much higher than the other registered in both cores. Regarding foraminifera species, results with relative abundance >1% were considered in the present work, rather than abundances >5% as used by many authors. These results show the presence of marine foraminifera at the tsunamigenic layers, and their absence in the remaining records, which appeared extremely important for the recognition of the occurrence of these high energy events. From the twenty surface samples studied, only eight presented foraminifera content, which did not allow to compare the actual environments with the palaeoenvironments recorded in Cores C and D. Finally, ArcGIS software and Geosoft Target extension helped the micropalaeontological study, enabling to confirm the palaeoenvironmts description made for Doñana National Park by other authors, as well as the occurrence of palaeotsunamis in this area.