The geomagnetic field at the Proterozoic-Paleozoic boundary and lower-mantle plumes

Data on the amplitude of variations in the direction of the geomagnetic field and the frequency of reversals in the Vendian-Cambrian are presented. It has been established from these data that (a) distributions of variations in the direction of the geomagnetic field S _p are bimodal (modes 9° and 11°); (b) the maximum of the average amplitude S _p takes place by 5–10 Myr later than the Vendian-Cambrian boundary; (c) S _p tends to increase as plume epicenters are approached; and (d) the plume formation is more often confined to intervals with different frequencies of geomagnetic reversals than to the interval of a stable state of the geomagnetic field without reversals (Vendian hyperchron). The listed features of the geomagnetic field behavior are repeated near all boundaries of geological eras of the Phanerozoic.