The Zircon Story of the Niger River: Time‐Structure Maps of the West African Craton and Discontinuous Propagation of Provenance Signals Across a Disconnected Sediment‐Routing System
Bibliographic record
Abstract
Abstract The Niger River drains a large part of the West African Craton, where rocks ranging in age from Paleoarchean to recent offer an unexcelled opportunity to map the diverse time structures of sediment sources and provide essential information for provenance diagnoses. In this study, U‐Pb zircon dating is complemented with bulk‐sand geochemical (Zr, Hf, REE) and Nd‐Hf isotope data to pin‐point parent rocks of zircon grains and draw inferences on sediment generation across sub‐Saharan western Africa. In Upper Niger sand, zircon ages pass from exclusively Archean in Guinea headwaters to dominantly Paleoproterozoic in the Inner Delta in Mali, testifying to the progressive dilution by tributary sediment derived from the Birimian domain. Zircon ages abruptly change to dominantly Neoproterozoic downstream of the Inner Delta, becoming indistinguishable from those in Saharan eolian dunes across the Sahel. Most of the sediment generated in the headwaters is thus dumped in the marshlands and bedload is reconstituted downstream by recycling eolian sand. Zircon grains in the Lower Niger yielded virtually the same U‐Pb ages as in Benue sediment, indicating an overwhelming supply from the Benue tributary. In the Niger Delta, however, Archean zircons reappear, and both ε Nd and ε Hf values become notably more negative, indicating extensive reworking of sand deposited along the coastal plain at earlier times of wetter climate, when artificial barriers to the sediment flux did not exist in the upper to middle Niger River catchment.
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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 | 0.002 | 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 | 0.001 |
| 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".