Millennial‐ to submillennial‐scale features of the Matuyama‐Brunhes geomagnetic polarity transition from Osaka Bay, southwestern Japan

Abstract

A high‐resolution magnetic record of the Matuyama‐Brunhes (MB) reversal transition was obtained from homogeneous marine clay in a 1700‐m core from Osaka Bay. The transition stretches over a core length of 6.4 m and yields four short reversal episodes. Two predate the main MB boundary (MBB), and two postdate it. We made diatom analyses of sediments to estimate relative sea level changes and constructed an age model by correlation with the astronomically calibrated marine oxygen isotope curve. The age model shows the short reversal episodes, with durations of <1 kyr, occurred at 4–5 kyr intervals within stage 19, and the MBB occurred about 5 kyr after the sea level highstand corresponding to isotopic event 19.3. It also shows the paleointensity minimum of 15–20% of the postreversal mean occurred at about 6 kyr before the MBB and another minimum at about 1 kyr after. Four virtual reverse‐to‐normal polarity boundaries found in this study suggest different ages for the MBB could be observed in lava flow studies. Some millennial‐ to submillennial‐scale transition features found in this study are compatible with the previous numerical simulations of geomagnetic field reversal.