Formation of Interdigitate Patterns on Martian Alluvial Fans
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Bibliographic record
Abstract
Introduction: Alluvial fans are semi-conical accumulations of sediment that develop at the base of slopes where channelized flows decelerate and spread laterally due to a change in gradient. Flow deceleration triggers sediment deposition, gradually building up a mounded or semi-conical fan shape. Terrestrial alluvial fans are constructed by a multitude of processes that range between two end-members: (i) low-density fluidal flows (riverine flows) and (ii) high-density sediment-gravitydriven flows (debris flows). As a key component of landscape evolution modeling and natural hazard research, terrestrial alluvial fans have been widely investigated from both academic and engineering research contexts. Several recent investigations have documented alluvial fan-like deposits on Mars [1, 2]. Collectively, these studies have documented fan characteristics consistent with fluid and gravity-driven alluvial sedimentation. However, many aspects of Martian fan formation remain poorly understood including the source and amount of fluid involved in mobilizing the flows. In this study we describe interdigitate patterns of lobate deposits on Martian alluvial fans and propose that they result from high-density, sediment-laden flows (debris flows). We compare the interdigitate fans with terrestrial analogs and draw implications for Martian alluvial fan development. Interdigitate fans on Mars: Using two MOC narrow angle images (R13-02920 and E11-04033), we have identified interdigitate patterns on fans at the base of south-facing crater walls (Figs. 1 and 2). In the first image (R13-02920; Fig. 1), the crater rim is characterized by a series of closely-spaced alcoves with feeder channels that extend partway down the slope. The upper feeder channels are broader and consist of multiple gullies that merge downslope to form a single channel above the fan apex. The feeder channels are up to 250 m wide and between 400-700 m long. The boundary between the lower portion of the feeder channels and the apex of the alluvial fans is diffuse. In some cases levees extend a short distance from the feeder channels onto the proximal fan. The fan surface is comprised of an overlapping (interdigitate) pattern of lobate deposits and largely devoid of channels, suggesting that the most recent phase of fan development involved upslope aggradation and backfilling. Lobate deposits on the proximal fan are much smaller than those along the medial and distal portions. Consequently, the proximal fan has a higher density of these deposits. The size of the lobate deposits range between 2-80 m wide and between 10200 m long. The second MOC image (E11-04033; Fig. 2) shows an alcove with a fan branching out onto the crater floor. The arcuate ridges at the base of the crater (inset; Fig. 2) resemble protalus ramparts [3]. The fan has an interdigitate pattern of lobate deposits. Similar to their counterparts in Fig. 1, the lobes decrease in size towards the fan apex. The size of the lobes ranges between 4-25 m wide and 15-60 m long. Like Fig. 1, the fan surface is not dissected by channels, suggesting upslope aggradation.
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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 | 0.000 | 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) | 0.000 | 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 it