Abstract—The previous paleomagnetic studies of the Upper Vendian Zigan Formation sediments on the western slope of Southern Ural revealed uncommonly numerous magnetic polarity zones (Bazhenov et al., 2016). The dating of magmatic zircons from the tuff interlayer constrained the age of this formation to 547.6 ± 3.8 Ma. The rate of reversals estimated from most general considerations is about 20–30 per Myr which is approximately two to three times higher than the highest reversal frequency in Phanerozoic. In this work, a more accurate estimate of the rate of reversals is obtained from cyclostratigraphic study of the lower red-rock part (74 m) of the Zigan Formation in its continuous section along the Sterlitamak–Magnitogorsk road—the longest one among those previously studied by the paleomagnetic method. The correlation of the detailed cyclostratigraphic studies with the magnetostratigraphic column allowed a more reliable estimation of the reversal rate. The studied section in which we identified 20 reversals was accumulated during 1.6 Myr, i.e., the reversal frequency in this interval was 12–13 per Myr. Our quantitative assessment shows that the previous studies overestimated the geomagnetic reversal frequency by a factor of two. However, even the reversal rate estimated in this study can be regarded anomalously high, and the previous conclusions about the existence of a period with anomalously frequent reversals in terminal Ediacaran 547.6 ± 3.8 Myr ago can be considered validated.

摘要—先前对乌拉尔南部西坡上的文迪安兹干组上层沉积物的古地磁研究显示，不常见的是许多磁极带（Bazhenov等，2016）。凝灰岩夹层岩浆锆石的年代将这一层的年龄限制在547.6±3.8 Ma。根据大多数普遍考虑，估计的逆转率约为每Myr 20–30，这比幻生界中最高逆转频率高出大约2到3倍。在这项工作中，从沿斯特拉塔玛克-马格尼托哥尔斯克公路连续段的子干组下部红色岩石部分（74 m）的旋回地层的地层学研究获得了更准确的逆转率估算值，这是先前研究中最长的一个用古磁方法研究。详细的地层学研究与地磁地层柱的相关性可以更可靠地估算反转速率。在1.6 Myr期间，我们确定的20个逆转的累积研究部分，即在此间隔内的逆转频率为每Myr 12-13。我们的定量评估表明，先前的研究高估了地磁反转频率的两倍。但是，即使在本研究中估计的逆转率也可以被认为异常高，并且先前关于终末期Ediacaran 547.6±3.8 Myr之前存在异常频繁逆转的时期的结论也可以被证实。在1.6 Myr期间，我们确定的20个逆转的累积研究部分，即在此间隔内的逆转频率为每Myr 12-13。我们的定量评估表明，先前的研究高估了地磁反转频率的两倍。但是，即使在本研究中估计的逆转率也可以被认为异常高，并且先前关于终末期Ediacaran 547.6±3.8 Myr之前存在异常频繁逆转的时期的结论也可以被证实。在1.6 Myr期间，我们确定的20个逆转的累积研究部分，即在此间隔内的逆转频率为每Myr 12-13。我们的定量评估表明，先前的研究高估了地磁反转频率的两倍。但是，即使在本研究中估计的逆转率也可以被认为异常高，并且先前关于终末期Ediacaran 547.6±3.8 Myr之前存在异常频繁逆转的时期的结论也可以被证实。