Long-term variations of the geomagnetic field, observed in the palaeomagnetic record, have the potential to shed much light on the evolution of Earth's deep interior. With a geomagnetic field characterised by anomalous directions and ultra-low intensities, the Ediacaran period (635-538 Ma) is a time of special interest. Steep and shallow directions, leading to virtual geomagnetic poles (VGPs) separated by angles of up to 90° and very close in age could have recorded a geomagnetic field switching between axial and equatorial dipole-dominated states. Alternatively, the field may simply have been highly nondipolar and subject to rapid reversals. Palaeointensity determinations of units that record the anomalous directions could potentially help to discriminate between morphologies but the spatial and temporal distribution of palaeomagnetic data require improvement. Here we present new palaeointensities from 6 dykes from the western end of the Grenville Dyke swarm that recorded directionally anomalous geomagnetic fields around ∼585 Ma. Results from double-heating Thellier experiments failed to satisfy the used selection criteria, but successful microwave Thellier, Shaw and pseudo-Thellier experiments lead to palaeointensities that show field strength values of 2.9 ± 2.2 μT and corresponding virtual dipole moments of 0.3-$1.7\times {10}^{22}$ A m². These field strengths are an order of magnitude weaker than the present-day field. VGPs grouping in two distinct clusters with almost identical angular dispersions of VGPs ($S_{\mathrm{B}}=18.5$° and 18.9°) may argue for the presence of an equatorial dipole. In contrast, the palaeointensities associated with the steep and shallow components are indistinguishable. Although based on a low number of results, this observation, together with the overall very large VGP dispersion may rather support that the Grenville Dykes have recorded enhanced secular variation linked to a highly unstable and rapidly reversing field.

在古地磁记录中观察到的地磁场的长期变化有可能为地球深部内部的演化提供更多线索。由于地磁场以异常方向和超低强度为特征，埃迪卡拉纪（635-538 Ma）是一个特别有趣的时期。陡峭和浅的方向，导致虚拟地磁极 (VGP) 的角度高达 90°，并且年龄非常接近，可能记录了轴向和赤道偶极子主导状态之间的地磁场切换。或者，该场可能只是高度非偶极，并且会快速逆转。记录异常方向的单位的古强度确定可能有助于区分形态，但古地磁数据的空间和时间分布需要改进。在这里，我们展示了来自格伦维尔堤坝群西端的 6 个堤坝的新古强度，这些堤坝记录了大约 585 Ma 的定向异常地磁场。双加热 Thellier 实验的结果未能满足使用的选择标准，但成功的微波 Thellier、Shaw 和伪 Thellier 实验导致古强度显示场强值为 2.9 ± 2.2 μT，相应的虚拟偶极矩为 0.3- 在这里，我们展示了来自格伦维尔堤坝群西端的 6 个堤坝的新古强度，这些堤坝记录了大约 585 Ma 的定向异常地磁场。双加热 Thellier 实验的结果未能满足使用的选择标准，但成功的微波 Thellier、Shaw 和伪 Thellier 实验导致古强度显示场强值为 2.9 ± 2.2 μT，相应的虚拟偶极矩为 0.3- 在这里，我们展示了来自格伦维尔堤坝群西端的 6 个堤坝的新古强度，这些堤坝记录了大约 585 Ma 的定向异常地磁场。双加热 Thellier 实验的结果未能满足使用的选择标准，但成功的微波 Thellier、Shaw 和伪 Thellier 实验导致古强度显示场强值为 2.9 ± 2.2 μT，相应的虚拟偶极矩为 0.3-$1.7\times {10}^{22}$阿 米²。这些场强比现在的场弱一个数量级。VGPs 分成两个不同的簇，VGPs 的角色散几乎相同（${秒}_{\mathrm{乙}}=18.5$° 和 18.9°）可能会证明存在赤道偶极子。相比之下，与陡峭部分和浅层部分相关的古强度是无法区分的。尽管基于少量结果，但这一观察结果以及整体非常大的 VGP 离散度可能更支持 Grenville Dykes 记录了与高度不稳定且快速反转的磁场相关的增强的长期变化。