A study of the paleoenvironmental evolution of themiddle Eocene platforms recognized in the westernmost Tethys has been carried out in the well-exposed middle Eocene succession from Sierra Espuña-Mula basin (Betic Cordillera, S Spain). Eight microfacies (Mf1 to Mf8) have been recognized, based mainly on fossil assemblages (principally larger benthic foraminifera), and rock texture and fabric. The fossiliferous assemblage can be
assigned to the ‘subtropical’ heterozoan association or to the low-latitude ‘foralgal facies’, which are dominated by non-framework building, light-dependent biota such as perforate larger benthic foraminifera, coralline algae, and sometimes green algae and solitary corals. Larger benthic foraminifer assemblages, corresponding from euphotic to oligophotic conditions and the large surface showed, suggest a progressive marine ramp under essentially oligotrophic conditions. Eventually, supply of detrital sediments fromthe continent and/or upwelling
currents increases the nutrients of marine waters. Comparisonwith other Tethyan sectors allows stating
that coral-reef buildups (z-corals) were widespread on shallow platforms of the central and eastern Tethys
Ocean, but these were neither of great dimensions nor dominant because of themuchmore dominant presence
of larger benthic foraminifera.Moreover, these coral constructions were completely absents in the westernmost
Tethys. The dominance of larger benthic foraminifera and the absence of z-corals in the westernmost Tethys are
explained by particular paleogeographic features due to the occurrence of a narrowand deep oceanic branch (i.e.,
the Maghrebian Flysch Basin) connecting the Tethys with the Atlantic Ocean. The various issues regarding the
morphological characters and evolution of larger benthic foraminifera in the study area, such as sizes of tests, specific
diversity and/or intraspecific variability, number of appearances and last occurrences during themiddle Eocene
are analyzed and compared with those appearing in other Tethyan sectors. In addition, the early to late
Bartonian boundary is recognized in the study area as critical for the biological change as in other shallow-marine
environments along the Tethys margins.