Magnetostratigraphic chronology of late Miocene to early Pliocene biostratigraphic and oceanographic events in New Zealand

Abstract

Successions of uplifted shallow marine sediments in New Zealand were among the first to provide evidence of latest Miocene climatic deterioration and were also among the first onshore successions where late Miocene to early Pliocene magnetostratigraphic records were established. A revised chronology of late Miocene to early Pliocene events has been determined from new magnetostratiigraphic results from two important successions at Blind River and Upton Brook, South Island, New Zealand (lat. 41°45′S, long. 174°05′E). Magnetostratigraphic results from Upton Brook are the fast from strata containing the Kapitean index mollusks and provide the first reliable estimate of the age of the Tongaporutuan-Kapitean boundary. A coherent chronology from Blind River and Upton Brook indicates that two synchronous low sea level and cool paleoclimatic events occurred in the late Miocene Kapitean Stage. This inference is supported from other well-known coeval successions in the New Zealand region. The revised New Zealand chronology supports recent determinations from the Mediterranean that indicate a two-stage Messinian salinity crisis and a 5.2-Ma age for the Miocene-Pliocene boundary. Data from New Zealand, the Mediterranean, and ocean cores around the world suggest that these latest Miocene events are related to glacio-eustatic sea level fluctuations. A 6.05-Ma age for the first occurrence datum of Globorotalia conomiozea indicates that significant diachroneity exists in the placement of this datum between the Southwest Pacific and the Mediterranean, confirming the observation that G. conomiazea is unsuitable for correlation between ocean basins.