Abstract
Sudden global warming ∼55 Ma is associated with remarkable biotic events among both terrestrial and marine organisms. The marine microplankton were especially affected, with a rapid diversification among tropical planktonic foraminifera, a global acme of the dinoflagellate
Apectodinium complex, and sudden changes in abundance patterns among the calcareous nannoplankton. Additionally, and in contrast with the former two groups, the latter group showed marked provincialism, with the distinctive
Rhomboaster spp.–
Discoaster araneus association (RD) restricted to a broadly crescent-shaped area extending through the Tethys seaway and the North and South Atlantic Oceans. We show here that this geographically restricted association was also temporally restricted. The stratigraphic occurrence of the
Rhomboaster spp.–
D. araneus association is correlative with the earliest Eocene Carbon Isotope Excursion. The relative abundance of this association is highest in the interval of minimum δ
13C values, and sharply decreases as the δ
13C increases toward preexcursion values. We propose that the
Rhomboaster spp.–
D. araneus association constitutes a stratigraphic proxy for the Carbon Isotope Excursion and represents an unique response to the Paleocene/Eocene Thermal Maximum (PETM), with a temporal span on the order of 175 kyr.