Reworked miospores in the upper paleozoic and Lower Triassic of the northern circum‐polar area and selected localities
Notice bibliographique
Résumé
Abstract Reworking of Devonian, Carboniferous and Permian palynomorphs into the Lower Triassic of western Canada, Yukon, the Canadian Arctic Archipelago and Alaska has been documented by a number of workers. The phenomenon occurs in other northern circumpolar localities, such as East Greenland and the Barents Sea, and was probably widespread. Examples are given from western and eastern Europe, Russia, the Middle East, Pakistan, China, Brazil and Australia. The abundance and diversity of reworked palynomorphs from a number of stratigraphic units of different ages into the Lower Triassic is an important palynostratigraphic phenomenon of chronostratigraphic value. It may be the result of a major regional regression in the late Permian, followed by a widespread marine transgression in the Early Triassic, or it may be due to tectonic activity resulting in eustatic sea‐level rise. Whatever the mechanism, the advancing transgression resulted in erosion of exposed Devonian, Carboniferous and Permian rocks, but by Mid‐Triassic times most pre‐Triassic rocks had been covered by sediment, and the supply of reworked material much reduced. Reworked Devonian taxa belong to a variety of suprageneric groups including cavate trilete spores (lycopsids), acavate trilete spores (ferns) and monolete spores; Lower Carboniferous taxa include cingulate trilete spores. Possibly reworked Upper Carboniferous and Permian pollen includes that of Gymnosperms—Cordaites, conifers, pteridosperms (taeniate bisaccate and polyplicates), and cycads and gnetophytes. Lower Triassic palynomorphs, possibly in situ, may include (sometimes abundant) acanthomorph acritarchs such as Micrhystridium breve, M. setasessitante, M. fragile and Wilsonastrum colonicum. Lack of recognition of reworking has many implications concerning chronostratigraphy, palynostratigraphy, paleoenvironments, paleoclimates, coal petrography, thermal maturity, geochemistry, and chemostratigraphy. For example, if the Upper Permian and Lower Triassic Densoisporites playfordii, D. complicatus, D. nejburgii, Lundbladispora obsoleta and Aculeisporites variabilis are not in situ, but reworked specimens of the Devonian progymnosperm cavate morphon Geminospora lemurata, one has to question the commonly held view that a lycopsid dominated macroflora, with a large biomass, recolonised the land in the Early Triassic. Lower Triassic assemblages in which reworking occurred but has not been recognised may give the impression of palynofloral diversity, whereas low diversity and low abundance would be more consistent with the hostile arid environment of the Lower Triassic. One Upper Permian and Lower Triassic plant entity, well‐adapted to harsh conditions, was the algal cyst Chordecystia chalasta. Nevertheless, some higher plants must have survived the Permian‐Triassic crisis as witnessed by the presence of gymnosperm pollen in the Mesozoic. This is Geological Survey of Canada (Calgary), Contribution no. 2004237.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| 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 | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,001 |
| Communication savante | 0,000 | 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) | 0,000 | 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 tête enseignante, 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 ».