Late Miocene—Early Pliocene Paleomagnetic Stratigraphy, Paleoclimatology, and Biostratigraphy in New Zealand

Abstract

The paleomagnetic stratigraphy, biostratigraphy, and paleoclimatology have been studied in two marine sections of late Miocene to early Pliocene age in New Zealand. A total of over 850 separately oriented cores were collected from 270 sites. The Blind River section (41°43′ S.) is now adjacent to the southernmost subtropical (temperate) water mass, but planktonic foraminifera indicate that the area was covered by subantarctic water during much of late Miocene and early Pliocene time. The Mangapoike River section (38°55′ S.) records temperature oscillations mainly within the subtropical water mass during late Miocene–early Pliocene age, with perhaps one subantarctic interval during latest Miocene time. The Miocene-Pliocene boundary in New Zealand has consistently been placed at the first evolutionary appearance of Globorotalia puncticulata at the boundary between the late Miocene Kapitean Stage and the early Pliocene Opoitian Stage. This boundary lies within sediments deposited during the Gilbert Reversed Epoch between the Nunivak Event (base at 4.14 m.y. B.P.) and the Gilbert C Event (top at 4.33 m.y. B.P.) in both sections. Thus, the Miocene-Pliocene boundary, as recognized in New Zealand, is dated as 4.3 ± 0.1 m.y., which appears to be slightly younger than the type (International) Miocene-Pliocene boundary in Italy (4.9 to 5.1 m.y.). Biostratigraphic ranges of planktonic foraminifera between New Zealand and the Mediterranean differ in detail, perhaps due to different paleo-oceanographic histories. A major cooling episode during the early Gilbert Reversed Epoch is recorded at Blind River and Mangapoike River. This cooling is more pronounced in the southern section examined, where it is represented by the occurrence of a central subantarctic planktonic foraminiferal assemblage. In the northern section, cooling was also pronounced, although of shorter duration, represented by a probably northern subantarctic assemblage. The Miocene-Pliocene boundary in Europe has still only been dated indirectly by means of non-Mediterranean sections. Interpretation of late Cenozoic paleomagnetic data from Mediterranean deep-sea cores collected from Glomar Challenger is rejected.