An improvedMid Tertiary ostraeodstratigraphyhasbeenobtainedfrom detailed samplingof
four outcrop sectionsof Kokoamu Greensandand overlying Otekaike Limcstunein the South I s l a n d , N e w Z e a l a n d . T h e s e c t i o n si n c l u d e t h e s t r a t o t y p e sa n d r e f e r e n c es e c t i o n sf o r t h e N e w ZealandDuntroonianandWaitakianStagesCI..ateOligocen¢to Early Miocene).
Threekeyevolutionaryeventsprovidethemainbasisforcorrelationofthesections,andallow recognitionof four zones. Theseeventsare, from oldesto youngest:the first appearanceof C~theralison amiesia, t abouttheWhaingaroan/DuntrooniaSntageboundary;thelastappearance o f A g r e n o c y t h e r e ?s e m i v e r a , t o g e t h e r w i t h a m a j o r f a u n a l r e p l a c e m e n t i , n t h e l o w e r D u n t r o o n i a n ; and the first appearanceof Trachyleberisfilletti sp. nov. at the Duntroonian/WaitakianStage boundary. The lowerboundaryoftbe lowermostzoneandupperboundaryof theuppermoszt one arenotdefinedsincetheyoccurbeyondthelimitsofthesequence. Thiscorrelationisconsistent withthatprovidedbyforaminiferaandenhancestratigraphicarlesolutionparticularlythroughthe DuntroonianStage.
Changesin relativeabundanceandspeciescompositionthroughoutthesequencearesimilar in the sectionsstudiedand are consideredto be controlledby faciesand water depth. An outer shelf fauna in the lower part of the Kokoamu Greensandis replacedin the upper Kokoamu Greensandby a relativelyshallowmid shelffaunawhichpersistsinto theOtekaikeLimestone. In theupperWaitakianpartof theOtekaikeLimestoneaninnershelfenvironrr~ntis indicated.
Fivenewspeciesareproposed:Cytheralison spinosasp. nov.,Qztheralisonparafavasp.nov., Rugocythereis reticulatasp. nov., Trachyleberisfilletti sp. nov. and Vitjasiella dulplicispinasp. nov.