Climate and Atlantic sea-level recorded in Southwestern Spain from 6.3 to 5.2 Ma. Inferences on the Messinian Crisis in the Mediterranean

Abstract

The Mio-Pliocene succession of Andalusia on the Atlantic coast (Guadalquivir Basin) is known as one of the former stratotype candidate for the Andalusian Stage, proposed during the seventies as the last stage of the Miocene. Its type section, located in Carmona, a small town east of Seville, has been the subject of mainly stratigraphic, sedimentological and micropaleontological studies. We carried out several field campaigns in this locality from 1987 to 1999, including the drilling of three cored boreholes, which allowed the acquisition of bio- and magnetic-stratigraphic data, and a high-resolution palynological analysis (including pollen, spores and dinoflagellate cysts). The pollen flora and its climatic quantification provided the mean to climatically correlate the section to the oxygen isotope curve from the Montemayor-1 borehole, located about 80 km to the West of Carmona. The variations in the ratio between dinoflagellate cysts and pollen grains were used to identify high and low oceanic levels, the two lowest levels being successively marked by the deposit of a littoral calcarenite (the Calizza Tosca Formation on which the city of Carmona is built) then by a subaerial erosive episode. Based on the correlation with the Montemayor-1 regional drilling, the two major lowering in oceanic levels observed at Carmona are linked with the two episodes of the Messinian Crisis. The interlocking position of the high-energy sandstone deposits inscribed in the Messinian valley leads to an assessment of a drop in the global oceanic level of at least 114 m at the beginning of the paroxysm of the Messinian Crisis. Comparisons are discussed with the amplitude of the Messinian Erosion Surface in the West-Alboran Basin which potentially remained suspended and fed with Atlantic waters during the height of the crisis and isolated from the rest of the almost totally dry Mediterranean Basin. The quantified climate constructed from the pollen records, compared between the Atlantic province and the Mediterranean area, confirms the climatic predisposition of the Mediterranean to desiccation. Atlantic sea-level variations observed in the Guadalquivir region and measured at Carmona suggest that global glacio-eustatism somewhat contributed to the onset and completion of the Messinian Crisis in the Mediterranean Basin.