Continental Breakup, Mountain Building, and the Great Unconformity: The Exhumation History of North America’s Most Iconic Erosional Surface Using Zircon (U-Th)/He Thermochronology
Bibliographic record
Abstract
The Proterozoic and early Paleozoic is a key period in Earth’s history coincident with the amalgamation and breakup of the supercontinent Rodinia, global Snowball Earth glaciations, oxygenation of the atmosphere and deep oceans, and the Cambrian Explosion of biological diversity. However, the global sedimentary record is sparse prior to the Cambrian, making investigations of this time period difficult. Around the globe, Phanerozoic sedimentary rocks unconformably overlie Proterozoic and older igneous and metamorphic “basement” rocks, representing 300 million to over one billion years of Earth history depending on location. On North America, this unconformable contact is called “the Great Unconformity” and is observed across the continent. Despite the limited Proterozoic sedimentary rock record, we can still learn a great deal about processes on Earth’s surface during this time from the rocks that are preserved. This dissertation presents three applications of (U-Th)/He thermochronology to understanding the timing and mechanisms by which rocks were exhumed and eroded to expose Proterozoic basement, create the Great Unconformity, and provide sediment for sedimentary basins. Applications of (U-Th)/He thermochronology to exhumation focus on constraining the timing, magnitude, and associated mechanisms of Great Unconformity exhumation in the Grand Canyon, USA and southeastern Ontario, Canada. New (U-Th)/He thermochronologic data combined with independent field evidence and geochronologic data reveal distinctly different timings of exhumation in these locations. In the Grand Canyon, Great Unconformity exhumation reflects paleotopographic evolution related to Rodinia assembly and breakup. In Ontario, significant exhumation occurs in the Ediacaran to Cambrian, associated with temporally long-lived geodynamic and tectonic processes impacting the Canadian Shield. (U-Th)/He thermochronology is also applied to understanding exhumation of sediment and deposition in the Neoproterozoic Jacobsville Sandstone, located on the Upper Michigan Peninsula, USA and associated with the c. 1090-980 Ma Grenville Orogeny and amalgamation of Rodinia. The dataset presented here suggests at least five periods of exhumation contributing sediment, hinting at surface processes that may have been active on the continental interior of Rodinia.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".