Grain-Size Controls On the Morphology and Internal Geometry of River-Dominated Deltas
Bibliographic record
Abstract
Abstract: Predictions of a delta's morphology, facies, and stratigraphy are typically derived from its relative wave, tide, and river energies, with sediment type playing a lesser role. Here we test the hypothesis that, all other factors being equal, the topset of a relatively noncohesive, sandy delta will have more active distributaries, a less rugose shoreline morphology, less topographic variation in its topset, and less variability in foreset dip directions than a highly cohesive, muddy delta. As a consequence its stratigraphy will have greater clinoform dip magnitudes and clinoform concavity, a greater percentage of channel facies, and less rugose sand bodies than a highly cohesive, muddy delta. Nine self-formed deltas having different sediment grain sizes and critical shear stresses required for re-entrainment of mud are simulated using Deflt3D, a 2D flow and sediment-transport model. Model results indicate that sand-dominated deltas are more fan-shaped while mud-dominated deltas are more birdsfoot in planform, because the sand-dominated deltas have more active distributaries and a smaller variance of topset elevations, and thereby experience a more equitable distribution of sediment to their perimeters. This results in a larger proportion of channel facies in sand-dominated deltas, and more uniformly distributed clinoform dip directions, steeper dips, and greater clinoform concavity. These conclusions are consistent with data collected from the Goose River Delta, a coarse-grained fan delta prograding into Goose Bay, Labrador, Canada. A reinterpretation of the Kf-1 parasequence set of the Cretaceous Last Chance Delta, a unit of the Ferron Sandstone near Emery, Utah, USA uses Ferron grain-size data, clinoform-dip data, clinoform concavity, and variance of dip directions to hindcast the delta's planform. The Kf-1 Last Chance Delta is predicted to have been more like a fan delta in planform than a birdsfoot delta.
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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 | 0.003 | 0.001 |
| 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 | 0.000 | 0.000 |
| 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 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".