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Re-evaluation of eumetazoan modular coloniality gives a new perspective to Ediacaran–Ordovician animal diversification. Highly integrated eumetazoan colonies (porpitids [“chondrophorines”], pennatulacean octocorals, anthozoans) prove to be unknown in the Ediacaran. Ediacaran Evolutionary Radiation (EER, new term) fossils include macroscopic and multicellular remains that cannot be compellingly related to any modern group. Claims of eumetazoan coloniality in the Ediacaran are questionable. The subsequent Cambrian Evolutionary Radiation (CER, terminal Ediacaran–late early Cambrian) records appearance and diversification of deep burrowers and a relatively abrupt development of biomineralization. The CER began in a transition zone that spans the Ediacaran–Cambrian boundary and includes the final few million years of the Ediacaran. The early CER has pseudocolonial(?) Corumbella that may be related to some Phanerozoic taxa (conulariids) and records appearance of the first macroscopic biomineralised organisms ( Cloudina , Namacalathus , Namapoikea ), which may not be eumetazoans. Modular eumetazoans dominate and define many Ordovician and younger habitats (coral, bryozoan, sabellitid reefs; pelagic larvaceans, salps, early–middle Palaeozoic graptolites), but eumetazoan coloniality largely “missed” the EER and CER. All purported Ediacaran–Ordovician porpitids (“chondophorines”) and pennatulaceans are not colonial eumetazoans. Only in the late early Cambrian (late CER) or early middle Cambrian do a few modular colonial eumetazoans first occur as fossils. These include Sphenothallus (available evidence precludes Torellella coloniality), some corals (colonial “coralomorphs”), and lower middle Cambrian graptolithoids. Modular eumetazoan colonies (corals, graptolithoids) in the late early and early middle Cambrian (late Epoch 2–early Epoch 3) and appearance of mid-water predators (cephalopods, euconodonts) and bryozoans in the late Cambrian–earliest Ordovician (late Furongian–early Tremadocian) are the root for the Great Ordovician Biodiversification Interval (GOBI, new term) and diverse later Phanerozoic communities. [ABSTRACT FROM AUTHOR]

Distinctive uppermost Ediacaran–Ordovician rocks (Avalonian overstep sequence) were key in definition of Avalonia, which comprises large areas of the NE Appalachians and the Caledonian and Variscan mountains (Britain and western Europe). This siliciclastic-dominated cover succession unconformably overlies a Neoproterozoic pre-Avalonian basement collage (arc, continental, oceanic fragments; Gwna-type melanges [now Rhode Island–Maritime Canada–North Wales]). Rather than an arc–transform transition, our new model proposes that the Avalonian basement was amalgamated after inferred late Ediacaran ridge-trench collision that initiated the northerly–southerly trending Avalonian transform fault (Atf, new). Avalonia is commonly regarded as originating as an arc marginal to Gondwana in the early Paleozoic and detached only in the Ordovician. We review multiple lines of evidence that show it was an insular microcontinent; this require revisions of Ediacaran–early Paleozoic paleogeography and plate tectonics models. Detrital zircon isotopic data show an Avalonia–Baltica link to the Neoproterozoic Timanian orogen, with Avalonia a peribaltic, not perigondwanan, terrane. The Avalonian basement detached from Baltica and rotated parallel to the Atf, with its origin similar to the modern Scotia Sea plate (i.e., North Scotia Ridge and transform) by accumulation of Neoproterozoic arc and continental fragments on the transform. Deposition of the cover sequence beginning ca. 552 Ma in pull-apart basins on the basement marked origin of the Avalonia ribbon-microcontinent. The cover succession, with ten unconformity-bounded depositional sequences, extends for ca. 5000 km (eastern Massachusetts–Silesia). Avalonia is bounded on its NW and SE by siliciclastic rocks (i.e., Gander and Meguma belts with an Ordovician arc in Gander) that were continental margin prisms coeval with the overstep sequence. Endemic Avalonian lower Lower Cambrian (Terraneuvian–lower Series 2, ca. 538–510 Ma) faunas, dropstones, absence of archaeocyaths, and minor shallow-water carbonates suggest an isolated location at ≥50° S. Only in the latest Early Cambrian (ca. 506 Ma) do Avalonian faunas show NW African, "Gondwanan" affinities with Avalonia-Gondwana convergence on the Atf. A longer (ca. 28 Ma, Middle Cambrian–Tremadocian) faunal similarity links temperate Avalonia and Baltica as terranes on the same plate. An insular Avalonia is consistent with a Middle Cambrian, ca. 49° S latitude (Cape Breton Island) location—its only reliable Cambrian paleomagnetic datum. Meso- and Paleoproterozoic zircons do not record nearby West Gondwana margins, but were eroded from Avalonian basement. Purported "Ganderian" plutonic zircons and whole rock signatures in SW New Brunswick indicate heterogeneity between Avalonian basement blocks, not a "Ganderia" affinity before a purported transfer of parts of Avalonia to "Ganderia." Coeval extensional and collisional igneous rocks along the Atf is seen in regions of transform faulting and do not allow reference of Avalonian areas to "Ganderia." Avalonia should not be shown as part of West Gondwana or separating from it in the Ordovician. [ABSTRACT FROM AUTHOR]

Abstract: Use of the first appearance datum (FAD) of a fossil to define a global chronostratigraphic unit's base can lead to intractable correlation and stability problems. FADs are diachronous—they reflect species' evolutionary history, dispersal, biofacies, preservation, collection, and taxonomy. The Cambrian Evolutionary Radiation is characterised by diachronous FADs, biofacies controls, and provincialism of taxa and ecological communities that confound a stable Lower Cambrian chronostratigraphy. Cambrian series and stage definitions require greater attention to assemblage zone successions and non-biostratigraphic, particularly carbon isotope, correlation techniques such as those that define the Ediacaran System base. A redefined, basal Cambrian Trichophycus pedum Assemblage Zone lies above the highest Ediacaran-type biotas (vendobionts, putative metazoans, and calcareous problematica such as Cloudina) and the basal Asteridium tornatum–Comasphaeridium velvetum Zone (acritarchs). This definition and the likely close correspondence of evolutionary origin and local FAD of T. pedum preserves the Fortune Head, Newfoundland, GSSP of the Cambrian base and allows the presence of sub-Cambrian, branched ichnofossils. The sub-Tommotian-equivalent base of Stage 2 (a suggested “Laolinian Stage”) should be defined by the I′/L4/ZHUCE δ13C positive peak, bracketed by the lower ranges of Watsonella crosbyi and Aldanella attleborensis (molluscs) and the Skiagia ornata–Fimbrioglomerella membranacea Zone (acritarchs). The W. crosbyi and A. attleborensis FADs cannot define a Stage 2 base as they are diachronous even in the Newfoundland “type” W. crosbyi Zone. The Series 2 base cannot be based on a species' FAD owing to the provincialism of skeletalised metazoans in the Terreneuvian–Series 2 boundary interval and global heterochrony of the oldest trilobites. A Series 2 and Stage 3 (a suggested “Lenaldanian Series” and “Zhurinskyan Stage,” new) GSSP base is proposed at the Siberian lower Atdabanian δ13C IV peak—which correlates into South China, Avalonia, and Morocco and assigns the oldest trilobites to the terminal Terreneuvian Series. [Copyright &y& Elsevier]