Paleoecology and paleoenvironmental trends immediately prior to the end-cretaceous extinction in the latest maastrichtian (66Ma) frenchman formation, Saskatchewan, Canada
Bibliographic record
Abstract
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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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.004 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".