Paleomagnetic Secular Variation Records From the Post-Glacial Tahiti Coral Reef

Abstract

IODP Expedition 310 recovered more than 600 m of Post Last-Glacial-Maximum (LGM) coral reef framework rocks from the current reef tract surrounding the island of Tahiti. Six sites (12 holes) were sampled for paleomagnetic studies on the south side of the island, termed the Maraa reef tract, and five sites (12 holes) were sampled for paleomagnetic studies on the north side of the island, termed the Tiarei reef tract. The sampled framework rocks are ∼8,000–15,000 cal. YBP in age based on more than 300 radiocarbon and uranium-series dates. We have recovered paleomagnetic inclination and relative paleointensity records from all of these holes with an average sampling interval of ∼100–200 years. These paleomagnetic records are correlatable across all holes of each reef tract. Combining all of the paleomagnetic data let us build a composite paleomagnetic record for each tract, which is correlatable between tracts in their interval of temporal overlap. The paleomagnetic records are synchronous between the two tracks and are consistent with Late Quaternary paleomagnetic records from Australia/New Zealand. This is the first detailed paleomagnetic record from a coral reef environment and one of few late Quaternary paleomagnetic records from the Southern Hemisphere Pacific region. The paleomagnetic results also are distinctive in that they provide replicate evidence for three short (∼100 years) intervals of anomalous inclinations with values that approach reversed polarity. These may be magnetic field excursions or some different kind of anomalous paleomagnetic secular variation.