Formation and tectonic evolution of the Yukon-Koyukuk Basin, Alaska
Bibliographic record
Abstract
The Yukon-Koyukuk Basin (YKB) is a large wedge-shaped depression south of the Brooks Range orogen in Alaska. It consists of two sub-basins, the northern Kobuk-Koyukuk Basin and the southern Lower-Yukon Basin, separated by remnants of the Koyukuk Arc Terrane. In the Late Jurassic, this arc began colliding with the Arctic Alaska continental margin, resulting in Brookian orogeny. Hypotheses for YKB formation vary from a forearc-backarc setting to formation during post-collisional lithospheric extension of the Brookian hinterland. Although this point remains debated, part of YKB development is clearly related to Brookian orogenesis. While the beginning of the collision is well constrained by synorogenic deposits on the northern side of the Brooks Range, the evolution of the YKB remains unclear. To test which model best describes basin formation and to better assess basin evolution, this thesis investigates the sedimentary units deposited within it. Sediments are effective in recording orogenic evolution, documenting progressive mountain belt denudation, linking erosional detritus to distinctive source areas, constraining depositional ages through U-Pb mineral dating, and more. This PhD thesis characterizes YKB sedimentary units using point counting of framework grains (quartz, feldspars, lithics) in thin section to determine composition, degree of transport, and maturity, and, together with new paleocurrent data, defines sediment dispersal patterns. Heavy mineral analysis further refines provenance and associated source regions. U-Pb analyses of volcanic and detrital zircons provide absolute age constraints and define shifts in sediment supply from early volcanic- to later metamorphic-dominated input. Zircon trace element chemistry provides insight into magmatic sources and allows evaluation of tectonic environments in which magmas formed. Integrated data suggest active sedimentation of deposits with distinct volcanic input characterized by strong continental contribution at ~138 Ma (Valanginian), consistent with the forearc-backarc model rather than the extensional scenario. This was followed in the late Early Cretaceous (~112 Ma, Albian) by deep-marine turbiditic deposits with strong metamorphic input from the surrounding highlands, later overlain by more proximal conglomeratic deposits at ~100 Ma. During the Late Cretaceous, inferred east-west convergence between the North American and Eurasian plates possibly caused additional uplift of the Ruby Terrane. Its enhanced erosion marked a major provenance shift, with sediment supply moving from the Brooks Range in the northern Kobuk-Koyukuk Basin to the Ruby Terrane in the southern Kobuk-Koyukuk Basin and eastern Lower-Yukon Basin. Increased Ruby Terrane uplift further confined the southern Kobuk-Koyukuk Basin, resulting in rapid infill and deposition of fluvio-deltaic deposits. In addition, a structurally controlled valley cutting across the Koyukuk Arc Terrane funnelled sediment to the backarc basin, leading to the deposition of slurry beds and directly connecting the forearc and backarc domains. Comparisons with modern systems such as the Banda Arc-Timor and Luzon Arc-Taiwan highlight strong similarities in tectonic setting, metamorphic grade, volcanic geochemistry, and basin stratigraphy. These parallels improve understanding of sedimentary basins formed in arc-continent collisional settings, providing fundamental insights for refining models of their formation and evolution.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".