Paleomagnetic records of secular variation from Lake Michigan sediment cores

Continuous measurements of the natural remanent magnetization of six cores from central Lake Michigan have been made, using a cryogenic magnetometer designed to permit the passage of long cores through its sensing region. The output of each of the three-component sensors is deconvolved with the appropriate system response function and combined to yield continuous records of inclination, declination and intensity with a resolution of approximately 6 cm. The paleomagnetic record extends to about 13,500 years B.P. and includes two features which may be excursions of the earth's field. Other features may be correlated between different cores, and the magnetic sequence is, in general, consistent with the stratigraphic sequence. There is an indication of a repeated sequence of field changes, which is somewhat reminiscent of the solar field cycle.