YPRESIAN/LUTETIAN (Y/L) PALEOENVIRONMENTS IN SE SPAIN: INFERENCES FROM BENTHIC FORAMINIFERA

Benthic foraminifera in the Fortuna section (Betic Cordillera, Southern Spain) were used to reconstruct changes in palaeoproductivity and oxygenation as part of a study to define a Global Stratotype Section and Point (GSSP) for the base of the Lutetian Stage (early/middle Eocene, ~ 49 Ma). The most common taxa in the upper-middle bathyal assemblages include Cibicidoides spp., Lenticulina spp., Osangularia spp., Clavulinoides angularis, Gaudryina spp. and Dorothia spp., and include highly fluctuating relative abundances of Globobulimina spp. (up to ~45-65%), which are in recent oceans characteristic of areas of high primary productivity and associated low oxygen conditions in bottom and/or pore waters. The Y/L boundary occurs in one of the intervals with a high relative abundance of Globobulimina spp., which is characterized by low species richness, a negative carbon isotope excursion (~-2‰) and a high relative abundance of Aragonia aragonensis. Other intervals with abundant Globobulimina spp. do not have A. aragonensis. Early Cenozoic climate is characterized by a long-term warming from mid-Paleocene to initial early Eocene, followed by cooling starting in the early middle Eocene. The Paleocene/Eocene Thermal Maximum (PETM) was a superimposed, short-lived hyperthermal event, during which deep-sea temperatures increased by 5 to 6^oC, during which there was a ~3‰ negative carbon isotope excursion. Benthic foraminiferal species including A. aragonensis show short-term peaks in relative abundance just after the PETM and in the overall period between ~61.5 and 49 Ma. We suggest that the Y/L A. aragonensis peak accompanied by a negative carbon isotope excursion could be a hyperthermal event of lesser magnitude than the PETM, possibly caused by methane hydrate dissociation. Methane hydrate dissociation could have been caused by sea-level fall, and may have triggered increased activity of chemosynthetic bacteria serving as food supply for such species as A. aragonensis.