Tracking the long-term evolution of geomagnetic secular variation from tiny wiggles in marine magnetic profiles

Details Tracking the long-term evolution of geomagnetic secular variation from tiny wiggles in marine magnetic profiles Tracking the long-term evolution of geomagnetic secular variation from tiny wiggles in marine magnetic profiles

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmgp33a..03b&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #GP33A-03

Computer Science

Databases

1517 Magnetic Anomalies: Modeling And Interpretation, 1521 Paleointensity, 1522 Paleomagnetic Secular Variation, 1560 Time Variations: Secular And Longer, 3005 Marine Magnetics And Paleomagnetics (1550)

Scientific paper

Knowledge of the ancient geomagnetic secular variation is principally restricted to the past few million years. As a consequence, it has been very difficult to assess a connection between the secular variation regime and the magnetic reversal frequency as initially suggested by McFadden et al. (1991). Marine magnetic measurements exhibit coherent short wavelength anomalies (or "tiny wiggles") that are superimposed on the broader polarity-interval anomalies. Recent high-resolution magnetic measurements acquired near the seafloor demonstrated that most tiny wiggles do reflect paleointensity fluctuations recorded by the oceanic crust (e.g. Gee et al., 2000; Pouliquen et al., 2001, Bowles et al., 2003). Although these studies were limited to a few areas and to short periods of time, they show that the sequence of tiny wiggles offers a unique way for constraining the long-term evolution of secular variation. Hence, the purpose of our study was to perform an exhaustive investigation of tiny wiggles over a long period of time in order to study their temporal distribution as a proxy for secular variation. To this end, we performed a careful inspection of sea-surface marine magnetic profiles selected from worldwide databases within the Indian and Pacific Oceans for the period 83-41 Ma. Many tiny wiggles were isolated by comparing stacks of profiles computed within widespread study areas. Modelling of those anomalies confirms that most tiny wiggles are likely ascribed to past fluctuations of the paleointensity rather than undetected short polarity events. We observe that tiny wiggles are ubiquitous and uniformly distributed throughout this long period of time, which may indicate a nearly constant secular variation regime while the magnetic reversal frequency markedly varied from zero during the Cretaceous Normal Superchron (~118-83 Ma) to about 2-3 reversals per Myr at ~40 Ma. These results motivate testing if the pattern of variation continues throughout the Cretaceous Normal Superchron which is characterized by the absence of magnetic reversal during ~35 Myr. To answer these questions, we are acquiring new high-resolution magnetic data across the Cretaceous Quiet Zone on the eastern flank of the Mid-Atlantic ridge (cruises Magofond3 held during Summer 2005 and Magofond3bis planned for Fall 2008).

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