Avalonia: a long-lived terrane in the Lower Palaeozoic?
L. R. M. Cocks, R. A. Fortey, 2009. "Avalonia: a long-lived terrane in the Lower Palaeozoic?", Early Palaeozoic Peri-Gondwana Terranes: New Insights from Tectonics and Biogeography, M. G. Bassett
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Avalonia was undoubtedly an independent terrane throughout the Ordovician, merging with Baltica at about Ordovician–Silurian boundary times (443 Ma). We consider it to have been internally unified throughout the Lower Palaeozoic, and not the two independent ‘East’ and ‘West’ Avalonian terranes of some authors. In the early Ordovician its faunas were certainly Gondwanan. However, its earlier history is controversial: we discuss whether Avalonia split off from Gondwana in the early Ordovician, or whether it left Gondwana in the late Neoproterozoic. We conclude that the varied basement terranes underlying Avalonia were aggregated to the margin of Gondwana before 650 Ma. Some substantial transform movements occurred along the Gondwanan margin between 610 and 530 Ma, but the Avalonian area remained part of core Gondwana until about the end of the Cambrian (490 Ma), when the rift–drift initiation of the opening Rheic Ocean between Gondwana and Avalonia began.
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Following the late Neoproterozoic – early Cambrian breakup of the supercontinent Rodinia, Gondwana evolved as one of the principal continental masses on Earth, embracing most of South America, Africa, Australasia, Antarctica, much of western Europe and parts of Asia. Around its margins were various other terranes that had varying tectonic and biogeographical affinities with the main continental block. This book incorporates a series of reviews and multidisciplinary research papers that together explore the tectonic, palaeogeographical and palaeobiogeographical evolution of the elements that made up the peri-Gondwanan collage. The stratigraphical scope of the coverage embraces the late Precambrian through early Devonian, providing a comprehensive overview of structural, stratigraphical and biological evolution through this significant interval of Earth history. Integration of these various processes throughout the volume will be of broad-based interest to a wide range of geoscientists.