Diatoms of the Fortuna Basin, southeast Spain: Evidence for the intra‐Messinian inundation

Abstract

The Fortuna Basin in southeast Spain, part of the Betic Strait, was one of the connecting pathways between the Atlantic Ocean and the Mediterranean Sea during the late Miocene. The basin contains a remarkable record of Messinian marine sediments. Two well‐laminated, marly, diatomaceous sections were examined: the 1‐m‐thick El Fenazar section (F section) and the 36‐m‐thick Rio Chicamo Diatomite Member (RCD section). Both sections are intercalated with gypsum horizons. The diatoms in the Rio Chicamo Diatomite suggest an Atlantic origin and strong coastal upwelling associated with high productivity. On the basis of event stratigraphy, the diatomites correlate to the intra‐Messinian inundation of the Mediterranean Sea during the Messinian salinity crisis. Four biostratigraphically useful species, Nitzchia jouseae, Thalassiosira oestrupii/T. praeoestrupii, Denticulopsis hustedtii, and Asterolampra acutiloba, occur in the west Pacific between ∼5.35 and 4.5 Ma (lower reversed Gilbert chron). This interpretation places the subsequent Upper Evaporite deposition into the lower reversed Gilbert chron. Our results indicate (1) the existence of a marine connection between the Atlantic Ocean and the Mediterranean Sea through the Betic Strait (southeast Spain) during the Messinian salinity crisis, (2) a possible earlier first appearance of Nitzchia jouseae in the Betic Strait compared to the Atlantic and Pacific oceans according to the stratigraphy of the Fortuna Basin, and (3) the probability that many of the “Tripolilike” and younger diatomites in the Mediterranean are local deposits and diachronous with each other.