Palaeomagnetic chronology of the evaporitic sedimentation in the Neogene Fortuna Basin (SE Spain): early restriction preceding the 'Messinian Salinity Crisis'

The magnetostratigraphic study of the evaporitic Rio Chicamo section (240 m ) in the Neogene Fortuna Basin (Murcia, southeast Spain) has identified the record of five magnetozones. The most probable correlations with the stand ard geomagnetic polarity time scale (GPTS) imply that the marine evaporitic sedimentation of this basin was not coeval with the Messinian evaporites o f the Sorbas Basin (Almeria, southeast Spain) and the Caltanissetta Basin ( central Sicily) (assigned to the reverse Chron C3r, late Messinian by Gauti er et al., 1994). The marine evaporites and diatomites from the Fortuna Bas in are older (late Tortonian to early Messinian) than the evaporites of tho se basins. The chronological framework for the sedimentation in the Fortuna Basin together with the isotopic data from the sulphates in these evaporit ic units indicate the following. (1) Restriction and confinement in the bas in initiated as early as uppermost Tortonian, leading to deposition of evap orites under mixed (marine-continental) conditions. (2) The subsequent sedi mentation of marine evaporites and diatomites in this basin occurred in a p eriod between the Tortonian and Messinian transition and the early Messinia n: the onset of this sedimentation pre-dates similar sediments of restricte d marine environments in the eastern Betics basins, and possibly of the wes tern Mediterranean region also. (3) Episodes of restriction and reflooding in the basin would have occurred in response to periodic fluctuations of th e oceanic level under local tectonic controls. In the Fortuna Basin, the gl obal base level drop associated with the 'late Messinian Salinity Crisis' w as recorded by the progradation of alluvial fans leading to thick elastic d eposits overlying the youngest evaporites. These observations hint to: (a) the peculiar characteristics and sensitiveness of some of the marginal intr amontane basins in the eastern Betics to reflect structural controls framed in the late Neogene global climatic changes; and (b) the diachronism of th e beginning of the marine evaporitic deposition in the Mediterranean region linked to the salinity crisis during the Messinian. (C) 1999 Elsevier Scie nce B.V. All rights reserved.