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New Zealand late miocene biostratigraphy and biochronology: Studies of planktic foraminifers and bolboforms at oceanic sites 593 and 1123, and selected onland sections

Using high-resolution suites of core samples, including 940 samples from Deep Sea Drilling Project (DSDP) Site 593 in southern Tasman Sea off western New Zealand, and 353 samples from Ocean Drilling Program Site 1123 in the Southwest Pacific Ocean off eastern New Zealand, this study documents for the late Miocene interval (about 11.6 to 5.2 million years ago) the nature and abundance of planktic foraminifers in these uncomplicated and virtually uninterrupted oceanic sequences. The discovery and documentation of bolboforms at both sites - an enigmatic group of marine calcareous protophytes new to New Zealand - has enabled a highly-refined and integrated planktic foraminiferal and bolboform zonation to be established with 69 well-defined biostratigraphic events - highest and lowest occurrences, acme zones, and coiling zones - that are potentially useful for the correlation and subdivision of the late Miocene in New Zealand. It has also enabled these bioevents to be correlated with the excellent paleomagnetic record at ODP Site 1123 (Wilson et al. in prep.) and age calibrated directly or indirectly with the geomagnetic polarity time scale GPTS-95 (Cande & Kent 1995). This represents a major advance in New Zealand late Miocene biostratigraphy and biochronology and it is the first time a robust late Miocene chronology has been developed entirely from local data. The study also links the major microfossil bioevents established in the offshore records at Sites 593 and 1123 back into selected onland New Zealand sections (730 samples), where the late Miocene is rather poorly resolved, thereby improving our ability to date, correlate, and interpret the paleoceanographic significance of late Miocene events more widely. Reassessment of faunal criteria used for the operational recognition and correlation of the late Miocene Tongaporutuan Stage in onland New Zealand, shows that the current defining faunal criterion for the base of the stage, the lowest occurrence of benthic foraminifers of the Bolivinita quadrilatera group, does not maintain a consistent position with respect to the robust biostratigraphic framework of planktic foraminiferal and bolboform events at Sites 593 and 1123. Consequently, it is proposed that the lower Tongaporutuan Stage boundary should be redefined as the base of the Kaiti Coiling Zone and (secondarily) by the highest common occurrence of Neogloboquadrina mayeri s.l. The redefinition of the Tongaporutuan Stage locates the Waiauan-Tongaporutuan Stage boundary close to the earliest New Zealand occurrences of the B. quadrilatera group. Because all of these events occur near to the base of base of Chron C5n.2n (10.95 Ma), at a stratigraphic level that is about 1.3 million years older than rocks at the base of the Tongaporutuan stratotype in North Taranaki, a new reference section is needed for the base of the stage.
Type of thesis
Crundwell, M. P. (2004). New Zealand late miocene biostratigraphy and biochronology: Studies of planktic foraminifers and bolboforms at oceanic sites 593 and 1123, and selected onland sections (Thesis, Doctor of Philosophy (PhD)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/13214
The University of Waikato
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