Abstract Biostratigraphic analyses of ostracod shells from the late Oligocene to early Miocene local Waitakian Stage stratotype at Trig Z, North Otago, and early Miocene local Otaian stratotype at Bluecliffs, South Canterbury, has extended ostracod zonation previously limited to the late Oligocene up into the early Miocene. Two zonation boundaries are recognised, defined by the first appearance of Cytherella magna n. sp. immediately above the main shellbed at Trig Z within the mid‐Waitakian, and the first appearance of Trachyleberis? retizea, an event within the lower Otaian occurring 35.2 m above the FAD Ehrenbergina marwicki foraminiferal marker event for the base of the Otaian Stage. These and other ostracod events observed have the potential to enhance stratigraphic resolution close to the Waitakian/ Otaian boundary, where correlation based on other fossil groups is problematical. Changes in ostracod abundance and composition throughout the Trig Z section reflect changes in paleodepth in an overall sh...