ON THE RELATIONSHIP BETWEEN EXCURSIONS AND NORMAL SECULAR VARIATION

Recently, the pattern of paleomagnetic secular variation (PSV) surrounding paleomagnetic field excursions has been determined for seven excursions over the last 380 ky of the Brunhes Normal Polarity Chron. Good quality excursion records always appear to be associated with a broad decrease in paleointensity. In all cases, the PSV angular dispersion increases abruptly by a factor of two at the start of the lower paleointensity interval and decreases abruptly at the end. The doubling of PSV angular dispersion occurs with only modest (<10%) decrease or increase in paleointensity. These abrupt changes indicate some significant non-linear change in dynamo conditions. In some cases, anomalous PSV precedes excursions by up to 20 ky and displays a waveform pattern that seems to continue into the excursion waveforms themselves.