High-precision U-Pb zircon ages on SE Newfoundland tuffs now bracket the Avalonian Lower–Middle Cambrian boundary. Upper Lower Cambrian Brigus Formation tuffs yield depositional ages of 507.91 ± 0.07 Ma (Callavia broeggeri Zone) and 507.67 ± 0.08 Ma and 507.21 ± 0.13 Ma (Morocconus-Condylopyge eli Assemblage interval). Lower Middle Cambrian Chamberlain’s Brook Formation tuffs have depositional ages of 506.34 ± 0.21 Ma (Kiskinella cristata Zone) and 506.25 ± 0.07 Ma (Eccaparadoxides bennetti Zone). The composite unconformity separating the Brigus and Chamberlain’s Brook formations is constrained between these ages. An Avalonian Lower–Middle Cambrian boundary between 507.2 ± 0.1 and 506.3 ± 0.2 Ma is consistent with maximum depositional age constraints from southwest Laurentia, which indicate an age for the base of the Miaolingian Series, as locally interpreted, of ≤ 506.6 ± 0.3 Ma. The Miaolingian Series’ base is interpreted as correlative within ≤ 0.3 ± 0.3 Ma between Cambrian palaeocontinents, although its exact synchrony is questionable due to taxonomic problems with a possible Oryctocephalus indicus-plexus, invariable dysoxic lithofacies control of O. indicus and diachronous occurrence of O. indicus in temporally distinct δ 13C chemozones in South China and SW Laurentia. The lowest occurrence of O. indicus assemblages is linked to onlap (epeirogenic or eustatic) of dysoxic facies. A united Avalonia is shown by late Early Cambrian volcanics in SW New Brunswick; Cape Breton Island; SE Newfoundland; and the Wrekin area, England. The new U-Pb ages revise Avalonian geological evolution as they show rapid epeirogenic changes through depositional sequences 4a–6.

纽芬兰东南部凝灰岩的高精度 U-Pb 锆石年龄现在涵盖了阿瓦隆阶中下寒武统边界。上下寒武统 Brigus 组凝灰岩的沉积年龄为 507.91 ± 0.07 Ma（Callavia broeggeri 带）、507.67 ± 0.08 Ma 和 507.21 ± 0.13 Ma（Callavia broeggeri 带） a> 组合与缺氧相的重叠（表成或海平面）有关。新不伦瑞克省西南部早寒武世晚期的火山显示出一个统一的阿瓦隆尼亚；布雷顿角岛；纽芬兰东南部；以及英格兰的雷金地区。新的 U-Pb 年龄修正了阿瓦隆期地质演化，因为它们通过沉积层序 4a-6 显示出快速的表成变化。O 出现次数最低。 indicusC 趋化带中。 13 位于华南和西南劳伦大陆时间上不同的 δ O。 indicus 和历时出现O。 indicus-丛，恒定的缺氧岩相控制Oryctocephalus indicus 区域）。分隔布里格斯和张伯伦布鲁克地层的复合不整合面仅限于这些年龄之间。阿瓦隆阶中下寒武统边界介于 507.2 ± 0.1 和 506.3 ± 0.2 Ma 之间，与西南劳伦大陆的最大沉积年龄限制一致，这表明苗岭系基底的年龄（根据当地解释）≤ 506.6 ± 0.3 Ma。苗岭系的基底被解释为寒武纪古大陆之间的相关性在 ≤ 0.3 ± 0.3 Ma 范围内，尽管由于可能存在分类学问题，其确切的同步性值得怀疑Ma） =7>Eccaparadides bennetti 区）和 506.25 ± 0.07 Ma（Kiskinella cristata组合间隔）。中下寒武统张伯伦布鲁克组凝灰岩的沉积年龄为 506.34 ± 0.21 Ma（Morocconus-Condylopyge eli