Revised Compilation of the M-anomaly Geomagnetic Polarity Time Scale and its Implications

The current M-anomaly Geomagnetic Polarity Time Scale (GPTS) is mainly based on the Hawaiian lineation set in the Pacific Ocean. This limited basis belies the fact that GPTS assumes that magnetic anomalies represent global reversals. Compiling a GPTS from a broader array of lineation sets from various ocean basins is desirable because correlatability and repeatability supports the global nature of each polarity reversal. We present a new compilation of the M-anomaly GPTS derived from a Pacific-wide set of Mesozoic magnetic anomalies. The anomalies were collected from three lineation sets (Hawaiian, Japanese, and Phoenix) in various parts of the Pacific basin and resampled for subsequent modeling. The analysis was accomplished with 97 profiles grouped into five age ranges (M0-M4, M5-M10, M10N-M15, M15-20, M21-M29). Each age group has on average 18 segments over the three lineation sets. This large number of profiles allows us to compute errors and test coherence in anomaly correlations. Both inversion and forward calculations were applied to estimate polarity reversal boundaries. Polarity block models were established within each lineation set separately to examine anomaly variability. Subsequently, an overall average GPTS was constructed by normalizing and averaging the block models from the three lineation sets. Correlatability and repeatability of most of Mesozoic anomalies are excellent amongst three different lineation sets. The compilation confirms correlatable short-wavelength, small amplitude anomalies within M11, 12, 16, 19, 20, 22, and 25, perhaps indicative of geomagnetic polarity excursions, short reversals, or paleointensity fluctuations. Short-wavelength, small amplitude anomalies around and including M10, as reported in Larson and Hilde (J. Geophys. Res., 80, p. 2586, 1975) are not consistent on all three lineation sets. Hence, they may indicate a regional tectonic origin or local geomagnetic field behavior rather than actual geomagnetic reversals. Further investigation of the M-sequence GPTS will be carried out with additional anomaly sequences from other ocean basins, such as the Argo Abyssal Plain in northwestern Australia and off Morocco Basin in the Atlantic Ocean. This compilation represents a wider analysis of anomalies, which presumably shows global changes in the Earth's geomagnetic field and therefore may be more reliable as a time scale for geological dating applications.