The Nanggulan section in south central Java comprises open marine sediments and volcanic deposits of Eocene� Oligocene age that accumulated in a marginal basin within the young Sunda Arc complex. A new borehole captures the stratigraphy and showcases the exceptional preservation of calcareous microfossils across an apparently complete Eocene� Oligocene Transition (EOT), a time interval significant for the initiation of continental-scale glaciation on Antarctica. Low-resolution benthic and planktonic foraminifera oxygen and carbon stable isotopes (δ18O and δ13C) record increasing δ18O and δ13 C in the basal Oligocene, allowing correlation to global records. Isotopic values imply warm temperatures and relatively high nutrients along the SE Java margin. The Nanggulan EOT is a valuable archive for reconstructing ocean�climate behaviour and plankton evolution and extinction in the Indo-Pacific Warm Pool. The borehole also adds to understanding of the early stages of Sunda Arc volcanism. © 2021 The Author(s).