PALEOECOLOGICAL INTERPRETATION OF TRANSITIONAL ENVIRONMENTS IN EOCENECARBONATES (NE SPAIN)

The paleoecological characteristics of the Eocene shallow-marine carbo nate shelf deposits in. NE Spain, rich in foraminifers and coralline a lgae, are interpreted through analogy with recent counterparts. Microf acies distribution, within three carbonate units of the Eocene Termina l Complex reveals an. overall upward-shallowing and a progressive chan ge from mesotrophic to eutrophic conditions. Microfacies diversity ref lects susceptibility of transitional environments to local variations because small, local morphological or environmental changes can, modif y the nutrient distribution and, consequently, biofacies occurrences. The two biofacies present in the Lower Carbonate Unit indicate a platf orm colonized by a macro-algal vegetation cover, coexisting probably w ith a perennial vegetation and local coralline algal bioherms. Normal marine-salinity waters and a mesotrophic environment prevailed in this unit. The four biofacies present in the Middle Carbonate Unit indicat e a platform where a macro-algal vegetation and coralline algal bioher ms coexisted and/or alternated with cyanobacterial mats. This biofacia l diversity was produced by local variations in nutrient and organic r esources, in salinity and in fresh-water inputs. Finally, the only bio facies present in the Upper Carbonate Unit is characterized by the abu ndance of cyanobacterial mats and indicate more eutrophic conditions a nd meteoric influences.