A new high‐resolution, middle Miocene magnetostratigraphy from western Southland, New Zealand

Abstract

We present an astrochronologically constrained magnetostratigraphic age model for a middle Miocene (16–13 Ma) mudstone succession from the Bryce Burn, western Southland, New Zealand. Fourteen magnetic polarity zones were identified from magnetic remanence measurements. Eleven of the polarity zones can be correlated with the geomagnetic polarity time‐scale using four biostratigraphic tie points. The magnetostratigraphically determined sedimentation rate was verified by conducting spectral analysis of an orbitally paced magnetic susceptibility record which contains obliquity and eccentricity cycles. In the Bryce Burn succession, the Lillburnian/Clifdenian stage boundary (defined at the lowest occurrence of Orbulina suturalis) occurs within Chron C5ADn and is assigned an age of 14.450 ± 0.2 Ma, which is some 650 kyr younger than the current estimate (15.1 ± 0.34 Ma). At least two hiatuses are indicated near the base of the studied succession (between 180 and 280 m; 15.3–14.3 Ma) and these are interpreted to indicate scouring by invigorated ventilation of the deep Pacific during the cryospheric expansion at the beginning of the middle Miocene climatic deterioration.

Keywords:

• middle Miocene
• Clifdenian
• Lillburnian
• magnetostratigraphy
• Orbulina suturalis
• greigite
• Pacific plate rotation