Barremian—Aptian (Early Cretaceous) dinoflagellate cysts from the Scotian Margin, offshore eastern Canada
Notice bibliographique
Résumé
The Scotian Margin is located in offshore Nova Scotia, Atlantic Canada, and includes a well-developed succession of Mesozoic strata that accumulated during the opening of the North Atlantic Ocean following the breakup of Pangea. Biostratigraphic studies of Mesozoic–Cenozoic strata along the Scotian Margin began in the early 1970s and focused on zonation schemes for each fossil group. Subsequent work, however, has emphasized an event-stratigraphic approach, combining palynologic with micropaleontologic and nannofossil events, as well logs and seismic horizons. Extensive taxonomic treatment of Late Cretaceous and Cenozoic palynomorphs from the Scotian Margin were also undertaken, but did not extend to the Triassic to Early Cretaceous interval. Thus, our present aim is to develop a detailed taxonomic review and a comprehensive event-stratigraphic scheme for this earlier interval of the Scotian Margin based mainly on palynology, integrated with macrofossil, nannofossil and sequence stratigraphic analyses. In our initial research, we are focusing on Lower Cretaceous conventional cores, including studies at the Panuke B-90 well. Data from sedimentary facies, including macrofossil and ichnofossil assemblages, suggest that, up from the base of the section studied there is an initial, regressive transition from a shelfal (neritic) to a mainly estuarine-brackish setting. The regressive trend is followed by a transgressive trend through most of the Upper Member of the Missisauga Formation, culminating in a return to fully marine conditions near the base of the overlying Naskapi Member. The presence of the dinoflagellate cyst (dinocyst) species Muderongia microperforata and Palaeoperidinium cretaceum, considered tolerant to low-salinity waters, indicates a brackish-estuarine setting in much of the Upper Member of the Missisauga Formation. However, the relatively abundant and rich dinocyst assemblages in specific intervals within this member indicate frequent fluctuations in and out of the estuarine complex, with intermittent connections with a fully marine environment. The dinocyst assemblages and key bioevents recorded in this study indicate a Barremian age for the Upper Member of the Missisauga Formation in Panuke B-90. This includes the co-occurrence of Odontochitina operculata and Tenua anaphrissa at the base of the section, indicating a probable early Barremian age, and higher, the Cerbia tabulata abundance is a reliable bioevent for the late Barremian to early Aptian interval. The palynological data confirm also an early Aptian age for the overlying Naskapi Member of the Logan Canyon Formation, based on the presence at its base of the age-diagnostic ammonite Deshayesites sp. Near the boundary between the Missisauga and Logan Canyon formations, the δ13C isotope ratio results show a negative carbon isotope excursion and subsequent recovery, which we interpret as the Cretaceous Oceanic Anoxic Event 1a (OAE1a, or Selli Event). At the onset of the event, dinocysts show a relatively high abundance and species richness; but this trend changes upwards, and at the top of the Selli Event both abundance and species richness decreases and Cerbia tabulata temporary disappears. Based on the above results, our ongoing study of the Panuke B-90 conventional cores and coeval successions will contribute to a comprehensive event-stratigraphic framework for the Scotian Margin.
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 | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,002 | 0,002 |
| Études des sciences et des technologies | 0,002 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,005 | 0,001 |
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 ».