From a marsh that was once sea: The geological evolution of Europe's largest biological reserve as told by its benthic foraminifera-a review

Abstract

This paper presents an updated list of benthic foraminifera found in brackish and marine (paleo-)environments of the Do˜nana National Park (SW Spain) from the Lower Pliocene to the present-day. This list, based on published records, includes ninety-four species whose autoecology and temporal distribution in surface sections and continuous sediment cores allow us to infer the palaeogeographic evolution of this Biosphere Reserve over the last millions of years. During the Lower Pliocene, this area was occupied by a wide shallow bay with Nonion faba and Ammonia beccarii as the most representative species. During the Upper Pliocene, there was a transition to terrestrial environments, later dominated by fluvial dynamics for much of the Pleistocene and devoid of these aquatic microorganisms. During the Upper Pleistocene and part of the Holocene, the park was flooded during the MIS-1 transgression and a large lagoon was formed and progressively silted up. At this stage, benthic foraminiferal assemblages were dominated by the brackish species Ammonia morphogroup tepida and Haynesina germanica, which were occasionally replaced by marine species (mainly miliolids) during high-energy events. Currently, benthic foraminifera are mainly represented by Ammonia morphogroup tepida in the temporary lagoons and distributary channels, while Ammonia beccarii is dominant in their marginal marine areas. In summary, there is a clear correspondence between the palaeogeographic evolution of the park and its benthic foraminiferal associations, a review of which contributes to increase the knowledge of its remarkable present and past faunal diversity.