The Eocene–Oligocene Transition in Nanggulan, Java: lithostratigraphy, biostratigraphy and foraminiferal stable isotopes

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 δ¹³C 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 behavior 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.