Do Montana's Sixmile Creek Cobbles Have Nevada Origins? Evidence for Headwaters of the Miocene Bell River Basin
Bibliographic record
Abstract
The Miocene Sixmile Creek Formation in Montana contains distinctive river cobbles of coarse-grained sandstone and conglomerate that include small grains of black chert, but the source of these cobbles has not been confirmed. The Paleozoic Diamond Peak Formation of Nevada may be one possible source of these cobbles. It is widespread in central Nevada's mountains but is unlike any bedrock formations found in Montana. If cobbles in the Sixmile Creek Formation were derived from central Nevada, the Miocene river that carried them would have had to have crossed the present positions of the Snake River Plain and the Idaho-Montana Continental Divide. The purpose of our study is to test the hypothesis by examining particularly distinctive cobbles along the proposed Miocene river path. We compared cobbles collected from the Sixmile Creek Formation at locations from Nevada to Great Falls, Montana, and compared these to each other and to samples collected from proposed source rocks at Pequot Summit, Nevada. We measured the percentage of black chert grains in each rock sample, as well as the shapes and size ranges of the chert grains. Our results support the hypothesis of a great Miocene river that flowed through Montana from headwaters as far south as central Nevada (Sears, 2014). This would have been possible in the Miocene because tectonics had not yet formed the Snake River Plain and modern Continental Divide. The river implied by this model would have been a tributary to the pre-ice age Bell River basin of Canada, which rivaled the modern Amazon River basin in scale. This research could lead to new understanding of the paleotopography and paleofluvial systems of the western interior of North America.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".