New Zealand Journal of Geology and Geophysics abstracts

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Ostracod biostratigraphy of the Oligocene–Miocene (upper Waitakian to lower Otaian) in southern New Zealand

Michael A. Ayress

Ichron Limited
5 Dalby Court
Gadbrook Business Centre
Northwich, CW9 7TN
United Kingdom

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 shelfal depositional setting. A deeper upper slope environment of deposition is indicated by numerous deep-water ostracod species obtained from the Bluecliffs section. These interpretations accord well with data available from other fossil groups.

Keywords  New Zealand; Oligocene; Miocene; Waitakian; Otaian; stage boundary stratotype; Trig Z; Bluecliffs Silt; Otekaike Limestone; Ostracoda; biostratigraphy; paleoecology; systematics

G06001; Received 2 February 2006; accepted 28 June 2006; Online publication date 8 August 2006
New Zealand Journal of Geology & Geophysics, 2006, Vol. 49: 359–373
0028–8306/06/4903–0359  © The Royal Society of New Zealand 2006

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