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Exhaustive similarities in terminal Ediacaran--Ordovician cover sequences between tectonic inliers in the Appalachian-Caledonian (A-C) orogen define the Avalonian terrane from coastal northeast North America through southern Britain to Belgium. However, Barr et al. effectively block inclusion of the Mira belt (Mb) in Avalonia by masking a long-documented trans-Avalonian succession under locally defined lithostratigraphic names that prove to be confusing homonyms of themselves. Earlier revisions of Mira belt stratigraphy allow assignment of the Mira belt to a precise location in the Avalonian strike-slip regime--on the marginal-inner platform transition just as the northern Antigonish Highlands and southeast Burin Peninsula. The Mira belt is a tectonic inlier not a 'terrane' in the A-C orogen. Key words: Avalon, Cape Breton Island, Ediacaran, Cambrian, depositional history, sequence stratigraphy, Introduction Accurate reconstruction of Avalonia is key to resolving controversies of early-middle Paleozoic terrane models of the Appalachian--Caledonian (A-C) orogen and in syntheses of global paleogeography. The long appreciated similarity [...]

The Avalonia microcontinent has diagnostic terminal Ediacaran-Ordovician lithostratigraphy, depositional sequence architecture, and igneous activity that extends for 2000+ km reflecting epeirogeny related to the Avalonian transform fault. Avalonia records an abrupt early Middle Cambrian (late Wuliuan) change from green, purple, or light grey to overlying black, dark grey, and brown facies in platform and off-platform areas (Meguma, North Wales). This change within one trilobite zone marks onset of ca. 26 m.y. of shallow-marine anoxia/strong dysoxia lasting into the Ordovician with Hatch Hill oxygenated mid-water zone (OMZ) onlap onto the shelf. A Bakken model (new, based on the middle Paleozoic Bakken Formation) is applied to shallowshelf-shoreline organic-rich mud deposition. Erosion of greenish Avalonian depositional sequence (Ads) 7 was followed by Ads 8 tilting, volcanism, debris flows, and bentonite deposition on a cryptic unconformity in SE Newfoundland. The early Middle Cambrian age of the Ads 7-8 boundary is obscured by referring the lower Manuels River Formation and Cristallinium cambriense Zone to the younger Drumian Stage. Ads 8 has thin ashes in coterminous British and North American Avalonia where erosion and subaerial exposure with caliche development preceded onlap of upper Middle or Upper Cambrian Ads 9 black muds and sands. The green-black change emphasizes Avalonian unity; it precludes multiple Avalonian 'micro-terranes' or assigning parts of Avalonia to West Gondwana or 'Ganderia' (the Little River, Brookville, and Bras d'Or 'terranes' are part of the Avalonian marginal platform). Coeval green-black transitions and similar later Cambrian faunas show comparable paleoenvironments in Avalonia and Baltica. Key words: Cambrian-Ordovician, Avalonia, sequence stratigraphy, epeirogeny, oceanic oxygenation, Bakken model, Introduction Avalonia is a major tectonostratigraphic unit with uppermost Ediacaran-Ordovician sedimentary rock-dominated successions that form the core of the Appalachian-Caledonide orogen (Fig. 1). The Avalon zone is bounded by fault-juxtaposed, [...]

The Cambrian olenid trilobite Peltura Milne-Edwards, 1840 is widespread in the Furongian strata of the Cambrian continents of Baltica and Avalonia, and has played a significant role in biostratigraphic zonations for both regions. Despite this importance, the genus is poorly known in Avalonian Canada. New collections from the Chelsey Drive Group on Cape Breton Island, Nova Scotia, yielded numerous sclerites of a new species, Peltura hutchinsoni sp. nov., that may also occur in the Parabolina lobata Zone of Baltica. Archival specimens from Sweden and Norway allow the revision of Peltura scarabaeoides (Wahlenberg, 1821)and Peltura acutidens Brögger, 1882, respectively. Key words: Cambrian, Furongian, Avalonia, Baltica, Trilobita, Peltura Le trilobite olénidé cambrien Peltura Milne-Edwards, 1840 est répandu dans les strates furongiennes des continents cambriens de Baltica et d'Avalonia et a joué un important rôle dans les zonations biostratigraphiques des deux régions. En dépit de son importance, ce genre est méconnu dans la partie canadienne d'Avalonia. De nouveaux prélèvements du Groupe de Chelsey Drive, dans l'île du Cap-Breton (Nouvelle-Écosse), ont produit de nombreuses sclérites d'une nouvelle espèce, Peltura hutchinsoni sp. nov., qui pourrait aussi être présente dans la Zone àParabolina lobata de Baltica. Des spécimens d'archives de Suède et de Norvège permettent une révision de Peltura scarabaeoides(Wahlenberg, 1821)et Peltura acutidens Brögger, 1882, respectivement. [Traduit par la Rédaction] Mots-clés : Cambien, Furongien, Avalonia, Baltica, trilobites, Peltura, Introduction Peltura Milne-Edwards, 1840 is one of the more widespread olenid trilobite genera in Upper Furongian ('Stage 10') successions of Avalonian Britain (e.g., Lake 1917; Allen et al. 1981) and [...]

The article critiques Álvaro et al.'s (2023) model of Avalonia's depositional history, arguing that it inaccurately applies a rift/half-graben model to a region better described by a strike-slip regime. It also discusses errors in terrane boundary definitions, stratigraphic correlations, and the regional extent of Avalonia, emphasizing the need for accurate bio- and chronostratigraphic correlations to reconstruct Avalonian and Caledonian Highlands deposition.

No basis for controversy exists in the naming of a global, strongly negative, uppermost Cambrian carbon isotope (δ13C) excursion. The HERB Event (HERB) has met the standards for chemostratigraphic units (i.e. consistent biostratigraphic brackets, content and concept) since 1992. By comparison, the TOCE excursion morphed through four temporally distinct δ13C events with spike-like nadirs that shifted temporally through the uppermost Cambrian until its synonymization with HERB (2006–12). In 2018, TOCE became a prolonged interval with very early onset and enveloped HERB – meaning five TOCE homonyms have been unambiguously defined and figured. HERB lies in the high-diversity ptychaspid biomere (trilobites) and below the ptychaspid extinction. But, data on it were used in TOCE's 2006 proposal and in later iterations (2008, 2012) to show it (1) higher, both at and above the ptychaspid extinction; (2) at the level of HERB (2012, 2018); and (3) even extending well below HERB (2018). TOCE fails the recommendations for a formal chemostratigraphic unit. Its relationship to latest Cambrian biotic turnover includes equation with extinction and high-diversity intervals. One TOCE homonym is a synonym, albeit junior, of HERB. [ABSTRACT FROM AUTHOR]

Terminal Ediacaran–late early Cambrian deposition, faunas and passive margin evolution of the north Indian margin are recorded in the Nigali Dhar syncline succession. Restudy of the upper Tal Group (upper lower Cambrian Koti Dhaman Formation, KDF) ichnofauna from the Khud-Drabil section reduces it to 18 confidently named forms. The lower KDF (Lower Quartzite Member) Cruziana-Rusophycus assemblage is in subtidal (not intertidal) sandsheet facies. The overlying black Shale Member (SM) records trans-East Gondwanan deepening, not intertidal facies, in the Palaeolenus Zone. The SM, with low diversity Planolites-Palaeophycus assemblage, is overlain by subtidal (not intertidal) sandsheet facies of the middle KDF (Arkosic Sandstone Member, ASM) with shallow burrowers and furrowers (Gordia marina assemblage, new; Cruziana ichnofacies). KDF faunas with Cruziana and Rusophycus are similar to coeval, shallow marine associations elsewhere in Gondwana and NW Laurentia. Interpretation of a second KDF section 20 km from Khud-Drabil has confused an understanding of Lesser Himalaya geologic evolution as it claims Ordovician Cruziana species in the ASM and an angular SM–ASM unconformity caused by the Cambrian–Ordovician boundary Kurgiakh orogeny. However, upper lower Cambrian microfaunas occur in and above the ASM, while the angular SM–ASM unconformity is consistent with submarine sliding. KDF-type ichnofaunas do not show a tropical location of Avalonia, which has the distinctive lithofacies and biotas of a high-latitude continent unrelated to Gondwana. [ABSTRACT FROM AUTHOR]

New U–Pb radioisotopic ages on early Cambrian volcanic zircons condition a high-resolution Bayesian age model that constrains the first occurrences and zonations of West Gondwanan archaeocyaths and trilobites in southern Morocco. The oldest archaeocyaths in the Tiout Member of the Igoudine Formation (519.71 + 0.26/− 0.35 Ma) are c. 6 Ma younger than the oldest Siberian archaeocyaths. The oldest Moroccan trilobite fragments, from the lower member of the Igoudine, are constrained to 519.95 + 0.43/− 0.40 Ma. The succeeding Issendalenian Stage (i.e. Hupetina antique – Eofallotaspis tioutensis – Fallotaspis plana – Choubertella – Daguinaspis trilobite zones) spans c. 1.5 Ma (519.78 + 0.26/− 0.37 Ma to 518.43 + 0.25/− 0.69 Ma). Identifiable Moroccan fallotaspidids and bigotinids, among Earth's oldest trilobites, occur above a positive δ13C excursion dated with our age model at 520.27 + 0.59/− 0.57 Ma, and correlated with the IV excursion peak within the lower range of Siberian Atdabanian Stage trilobites (Repinaella Zone). This excursion is the best standard for a Cambrian Series 2 base. The oldest West Gondwana trilobite fragments are c. 1 Ma younger than those in Siberia and c. 0.5 Ma older than the oldest Avalonian trilobites (Callavia Zone). This diachrony means a trilobite first appearance datum is an inappropriate chronostratigraphic base for Cambrian Series 2. Taxonomic differences in the oldest trilobites between Cambrian palaeocontinents are in accordance with trace fossil evidence for the group's appearance possibly as late as c. 530 Ma in the Cambrian Evolutionary Radiation. Coeval 519–517 Ma dates from Avalonia (cool-water siliciclastic shelf) and West Gondwana (tropical carbonate platform) sections with distinct macrofaunas emphasize these successions were latitudinally separate by the late Ediacaran Period. [ABSTRACT FROM AUTHOR]