Paleoecology and paleoenvironmental trends immediately prior to the end-cretaceous extinction in the latest maastrichtian (66Ma) frenchman formation, Saskatchewan, Canada
Notice bibliographique
Résumé
The fossil-rich deposits of the latest Maastrichtian Frenchman Formation (66Ma) of Saskatchewan, Canada, contain a complete, continuous record of terrestrial vertebrate diversity in the last half-million years prior to the end-Cretaceous mass extinction. The objective of these studies was to recover biodiversity patterns at the level of the ecological community, and to explore the paleoenvironmental and paleoclimatic variables that influenced these patterns. The primary study locality for this research was the East Block of Grasslands National Park (GNP) in southern Saskatchewan. The first chapter of this thesis is review of paleoecology: what it is, why it is important, and how it is studied. The second chapter is a survey of the depositional environments in the Frenchman Formation in GNP, based on 23 mapped stratigraphic sections, as well as on sediment and paleosol (ancient soil) samples. Stratigraphic surveys revealed a series of repeated depositional cycles, each likely linked to an uplift and subsistence event. Based on these cycles, the Frenchman Formation was divided into seven lithostratigraphic units, across which paleoecological and paleoenvironmental trends could be more easily assessed. Paleoclimate data was determined using x-ray florescence (XRF) analysis of paleosol samples collected from two of the stratigraphic sections. No significant temporal trends in mean annual temperature or precipitation were recovered, although other sedimentological indicators imply that small-scale or seasonal climate fluctuations did occur. In Chapter 3, a second set of paleoclimate estimates is presented, with these estimates derived from plant macrofossil (leaf) physiogamy found in two Frenchman Formation paleofloral sites. Climate estimates were calculated using leaf margin analysis (LMA) and the Climate Leaf Analysis Multivariate Program (CLAMP), and compared with other paleoclimate estimates for the Western Interior Basin. The LMA and CLAMP estimates were not significantly different from those derived from the paleosol analyses, and were broadly similar to estimates from coeval sites in Montana and Wyoming. Based on the presence of inertinite (fossil charcoal) in one paleofloral site, the marked disparity in floral diversity between the two sites was suggested to be reflective of ecological succession following a disturbance by fire. Chapter 4 explores trends in vertebrate diversity throughout the Frenchman Formation, based on some 7400 fossils from 38 vertebrate microsites. Fossils were collected, along with the lithostratigraphic information necessary to place them in a chronological context, and were sorted, identified and catalogued. Temporal variations in alpha (within-site) and beta (among-site) diversities were explored. On the level of the ecological community, no significant overall trends in vertebrate diversity were recovered, although small-scale biodiversity patterns were discovered. A distinct turnover in turtle family diversity was found, coinciding with an increased occurrence of coastal-like taxa in the upper part of the formation. These diversity trends may be linked to increased brackish-water conditions associated with the Cantapeta Advance, a marine transgression described from coeval deposits in Wyoming. This study lends support to the catastrophic theory of the end-Cretaceous extinction, and underlines the importance of exploring both local and regional driver of paleodiversity. Furthermore, it demonstrates that focusing on the pre-extinction diversity patterns of single vertebrate groups (i.e. dinosaurs) can be misleading, as the group diversity can fluctuate independently of the overall diversity. These results have important implications for our understanding of the timing and cause of the Cretaceous mass extinction on local scales, and demonstrate the benefits of assessing paleodiversity patterns on multiple ecological levels.
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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 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,002 | 0,004 |
| Études des sciences et des technologies | 0,001 | 0,001 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,001 | 0,001 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 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 ».