The Chapel Island Formation of Newfoundland (Canada) revisited: integrating ichnologic and sedimentologic datasets to unravel early metazoan evolution
Notice bibliographique
Résumé
The Chapel Island Formation (CIF) is a 1000+ m-thick, mainly siliciclastic succession that is well exposed along the coastline of Burin Peninsula, southeastern Newfoundland, eastern Canada. The CIF contains an outstanding record of latest Ediacaran-early Cambrian trace fossils with some intervals rich in small shelly fossils, and in 1992 the Fortune Head section was ratified by the International Commission on Stratigraphy (ICS) and the International Union of Geological Sciences (IUGS) as the Global Stratotype Section and Point (GSSP) for the Cambrian System. This was the first system-level GSSP defined primarily on the basis of trace fossils, a decision that evoked considerable discussion among the geological community. This thesis represents the first modern study of the sedimentology and the first taxonomic appraisal of the trace fossils since the original studies that proposed the GSSP in the 1980’s. More than 1700 m of CIF strata were logged in the sea cliffs of Burin Peninsula at Fortune Head, Fortune North, Grand Bank Head, Lewin’s Cove, Little Dantzic Cove, and Point May. A revision of the sedimentology permitted the description and interpretation of fourteen sedimentary facies composing five facies association (FA), which are interpreted to be deposited in: (1) mud-flat, mixed-flat, sand-flat, and tide-dominated or -influenced embayments (FA-A); (2) middle and lower shoreface (FA-B); (3) offshore transition, upper offshore, and lower offshore (FA-C); (4) shelf (stricto sensu) (FA-D); and (5) carbonate subtidal and intertidal environments (FA-E). An extensive trace-fossil dataset was built from careful field observations and provided a comprehensive record of bioturbation intensity (1596 data points on vertical bioturbation, 1481 data points on bedding plane bioturbation) and of trace-fossil metrics (3162 data points on burrow width, 1473 data points on burrow depth). In addition, a comprehensive revision of the trace-fossil composition (3508 trace fossils identified) allowed the description of twenty-eight ichnogenera and fifty-one ichnospecies, which correspond to cf. Allocotichnus dyeri, Archaeonassa fossulata, Arenicolites aff. carbonaria, Arenicolites isp., Bergaueria perata, B. cf. radiata, Circulichnis ligusticus, C. montanus, Cochlichnus anguineus, C. luguanensis, Conichnus conicus, Cruziana problematica, Curvolithus multiplex, C. simplex, Curvolithus isp., Dendroidichnites aff. irregulare, Didymaulichnus miettensis, Dimorphichnus isp. A, Dimorphichnus isp. B, cf. Dimorphichnus isp., ?Diplocraterion isp., Gordia marina, Gyrolithes gyratus, G. scintillus, Halopoa imbricata, Helminthoidichnites tenuis, Helminthopsis abeli, H. hieroglyphica, H. tenuis, Monomorphichnus bilinearis, M. lineatus, M. needleiunm, Monomorphichnus isp., Palaeophycus annulatus, P. tubularis, Palaeophycus isp., Psammichnites gigas circularis, P. cf. saltensis, Rosselia socialis, Rusophycus avalonensis, Rusophycus isp. A, Rusophycus isp. B, Saerichnites kutscheri comb. nov., Teichichnus rectus, Torrowangea rosei, Treptichnus bifurcus, T. coronatum, T. pedum, T. pollardi, Trichichnus linearis, and Trichichnus isp. Sectioning and polishing of 47 lithic samples from throughout the CIF showed that the sediment mixed layer that characterizes modern oceans developed through a series of steps that took place in the early Cambrian rather than in the Silurian as previously advocated. The main evolutionary innovations took place in the offshore environment with three paleoecologic stages that comprised: (1) an Ediacaran matground ecology, with surficial and very shallow infaunal grazing organisms living on and within microbially bound seafloors; (2) a Fortunian matground/firmground ecology, with a burst in behavioural and anatomical innovations and the first evidence of colonization of the shallow-tier; and (3) a late Fortunian/Cambrian Age 2 mixground ecology, with the development of a shallow mixed layer and deeper discrete burrows of the transition layer. Evaluation of outcrop quality based on accessibility, lateral and vertical continuity of beds, stratigraphic completeness, and type of exposure, demonstrated that Fortune Head, Fortune North, Grand Bank Head, and Little Dantzic Cove represented the best suited section to perform trace-fossil analyses, whereas Lewin’s Cove and Point May suffered from exposure biases affecting their trace-fossil records. The Ediacaran-Cambrian boundary interval was also studied in detail at Fortune Head, Grand Bank Head, Lewin’s Cove, and Point May, and the base of the Cambrian was placed confidently at the first appearance of trace fossils of the Treptichnus pedum Ichno-Assemblage Zone. This study demonstrates that only through detailed, comprehensive, and integrative approaches, can research provide new empirical evidence that further unfold our understanding of the history of animal life on Earth.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,002 |
| Méta-épidémiologie (sens strict) | 0,001 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,004 | 0,010 |
| Études des sciences et des technologies | 0,003 | 0,002 |
| Communication savante | 0,003 | 0,001 |
| Science ouverte | 0,001 | 0,002 |
| Intégrité de la recherche | 0,000 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».