OSTRACOD BIOSTRATIGRAPHY AND PALEOECOLOGY OF THE KOKOAMU GREENSAND AND OTEKAIKE LIMESTONE (LATE OLIGOCENE TO EARLY MIOCENE), NORTH OTAGO AND SOUTH CANTERBURY, NEW-ZEALAND

An improved Mid Tertiary ostracod stratigraphy has been obtained from detailed sampling of four outcrop sections of Kokoamu Greensand and ov erlying Otekaike Limestone in the South Island, New Zealand. The secti ons include the stratotypes and reference sections for the New Zealand Duntroonian and Waitakian Stages (Late Oligocene to Early Miocene). T hree key evolutionary events provide the main basis for correlation of the sections, and allow recognition of four zones. These evens are, f rom oldest to youngest: the first appearance of Cytheralison amiesi, a t about the Whaingaroan/Duntroonian Stage boundary; the last appearanc e of Agrenocythere? semivera, together with a major faunal replacement , in the lower Duntroonian; and the first appearance of Trachyleberis jilletti sp. nov. at the Duntroonian/Waitakian Stage boundary. The low er boundary of the lowermost zone and upper boundary of the uppermost zone are not defined since they occur beyond the limits of the sequenc e. This correlation is consistent with that provided by foraminifera a nd enhances stratigraphical resolution particularly through the Duntro onian Stage. Changes in relative abundance and species composition thr oughout the sequence are similar in the sections studied and are consi dered to be controlled by facies and water depth. An outer shelf fauna in the lower part of the Kokoamu Greensand is replaced in the upper K okoamu Greensand by a relatively shallow mid shelf fauna which persist s into the Otekaike Limestone. In the upper Waitakian part of the Otek aike Limestone an inner shelf environment is indicated. Five new speci es are proposed: Cytheralison spinosa sp. nov., Cytheralison parafava sp. nov., Rugocythereis reticulata sp. nov., Trachyleberis jilletti sp . nov. and Vitjasiella dulplicispina sp. nov.