We discuss the ages of twelve (clusters of) localities along the northeastern margin of the Kutai Basin (East Kalimantan, Indonesia). These localities form the basis for a large-scale study to improve our documentation of the fossil record of shallow marine environments in the center of maximum biodiversity. We integrated the results of investigations of occurrences of calcareous nannoplankton, (rare) planktonic foraminifera, larger benthic foraminifera, strontium isotope stratigraphy, and magnetostratigraphy. In addition to previously well-documented middle Miocene carbonates, new surface outcrops of early Tortonian- and Messinian-age carbonates are reported.