U-Pb Zircon Dates from North American and British Avalonia Bracket the Lower–Middle Cambrian Boundary Interval, with Evaluation of the Miaolingian Series as a Global Unit

Ed Landing, Mark D. Schmitz, Stephen R. Westrop, Gerd Geyer

Research output: Contribution to journalArticlepeer-review

Abstract

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 13 C 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.

Original languageAmerican English
JournalGeosciences Faculty Publications and Presentations
StatePublished - 1 Sep 2023

Keywords

  • Lower Cambrian
  • Miaolingian
  • Middle Cambrian
  • Newfoundland
  • U-Pb dates

EGS Disciplines

  • Earth Sciences
  • Geophysics and Seismology

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