Middle Eocene to Early Oligocene calcareous nannofossils from the Nanggulan Formation, Java, Indonesia

In this article, we document the late Middle Eocene to Early Oligocene calcareous nannofossil assemblages from a new low-latitude site in the south-central region of Java, Indonesia. The studied assemblages are from the Nanggulan Formation, recovered from cores drilled in the Special Region of Yogyakarta. The study focused on a ~60-m succession of marine clays and claystones that were recovered from Corehole NKK1, which includes a near-continuous Eocene–Oligocene section. The Late Eocene palaeolocation of this site was close to the region of the modelled peak sea-surface temperatures of the Eocene Indo-Pacific Warm Pool. Documenting coccolithophore communities from the tropical ocean through an interval of global cooling is important for several reasons. In particular, the Late Eocene to Early Oligocene coccolithophore assemblages of NKK1 include species that are usually only found in younger Oligocene assemblages, suggesting that this region may have been a key location for coccolithophore speciation and a source of increased diversity. Conversely, there were no significant range extensions of Lower or Middle Eocene taxa up-section, suggesting a degree of synchrony in extinctions across the tropical to subtropical oceans. A total of 115 species are documented, and two new species– Coccolithus aspida and Reticulofenestra nanggulanensis–– are described.