Extinction and recovery of benthic foraminifera across the Paleocene–Eocene Thermal Maximum at the Alamedilla section (Southern Spain)

A complete succession of lower bathyal–upper abyssal sediments was deposited across the Paleocene–Eocene Thermal Maximum (PETM) at Alamedilla (Betic Cordillera, Southern Spain), where the benthic foraminiferal turnover and extinction event associated with the negative carbon isotope excursion (CIE) across the PETM have been investigated. Detailed quantitative analyses of benthic foraminifera allowed us to distinguish assemblages with paleoecological and paleoenvironmental significance: pre-extinction fauna, extinction fauna, survival fauna (including disaster and opportunistic fauna) and recovery fauna. These assemblages have been associated with significant parts of the δ13C curve for which a relative chronology has been established. The correlation between the benthic turnover, the δ13C curve, the calcite and silicate mineral content, and sedimentation rates, allowed us to establish the sequence of events across the PETM.At Alamedilla, the benthic extinction event (BEE) affected ~ 37% of the species and it has been recorded over a 30-cm-thick interval that was deposited in c.a. 10 ky, suggesting a gradual but rapid pattern of extinction. The beginning of the BEE coincides with the onset of the CIE (+ 0 ky) and with an interval with abundant calcite, and it has been recorded under oxic conditions at the seafloor (as inferred from the benthic foraminiferal assemblages and the reddish colour of the sediments). We conclude that dissolution and dysoxia were not the cause of the extinctions, which were probably related to intense warming that occurred before the onset of the CIE.The BEE is immediately overlain by a survival interval dominated by agglutinated species (the Glomospira Acme). The low calcite content recorded within the survival interval may result from the interaction between dilution of the carbonate compounds by silicicate minerals (as inferred from the increased sedimentation rates), and the effects of carbonate dissolution triggered by the shoaling of the CCD. We suggest that Glomospira species (disaster fauna) may have bloomed opportunistically in areas with methane dissociation, in and around the North Atlantic. The disaster fauna was rapidly replaced by opportunistic taxa, which point to oxic and, possibly, oligotrophic conditions at the seafloor. The CCD gradually dropped during this interval, and calcite preservation improved towards the recovery interval, during which the δ13C values and the calcite content recovered (c.a. + 71.25 to 94.23 ky) and stabilized (> 94.23 ky), coeval with a sharp decrease in sedimentation rates.