ABSTRACT: Following the deep-sea benthic foraminiferal extinction event (BEE) across the Paleocene Eocene Thermal Maximum (PETM), certain groups of agglutinated benthic foraminifera bloomed and dominated the foraminiferal assemblage. In particular, the widespread proliferation of Glomospira, Glomospirella and Repmanina species, known as the “Glomospira acme”, has been recorded in bathyal to abyssal depths of the eastern North Atlantic and Tethys oceans. The Glomospira acme has been traditionally linked to the widespread rise in the calcite compensation depth (CCD) during the PETM, although recent studies suggest that calcite dissolution was not the only factor responsible for the acme. In order to investigate alternative paleoenvironmental causes that may have contributed to the Glomospira acme, we studied the Glomospira spp. abundances, their variations in test sizes, and the provenance of organic matter sources as indicated by lipid biomarkers in the Alamedilla section (southern Spain). Test size analysis for the acme interval reveals a reduction in test size characteristic of rapid population growth and reproduction due to the lack of interspecific competition after the BEE. Biomarkers for terrestrial sources suggest an increased influx of refractory organic matter to the seafloor across the PETM, and particularly during the Glomospira acme. We hypothesize that this influx may have favored the proliferation of detritivorous taxa such as Glomospira spp., which may have fed on refractory organic detritus that was not easily digested by other calcareous or agglutinated species. In summary, we suggest that an increased input of refractory organic matter across the PETM must have exacerbated the environmental stress caused by calcite dissolution and global warming leading to the Glomospira acme.
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