Landscape evolution in Africa during the Cenozoic and Quaternary—the legacy and limitations of Lester C. King
Bibliographic record
Abstract
African landscape evolution since 66 Ma reflects interactions among parts of the Earth system from the Core to the Biosphere. We stress changes in those interactions in three events that have dominated landscape development: (i) a climatic revolution when the circumpolar current and the East Antarctic ice sheet first formed ∼37 Ma; (ii) a tectonic revolution at ∼32 Ma dominated by elevation of ∼30 topographic structural swells continent-wide; and (iii) a second climatic revolution in a Northern Hemisphere cooling event (at ∼2.7 Ma) that triggered Sahara desert initiation and the beginning of glacial cycles in the Northern Hemisphere (∼2.15 Ma). We recognize the following distinct features of the great Afro-Arabian continent (∼40 M km2) that show its relationship to Earth structure and processes: deep mantle structure and dynamics, plate motion with respect to that structure, especially plate-arrest (∼32 Ma). The topographic, erosional, geomorphic, and depositional modifications following that tectonic event were strongly influenced by changes around the continent in oceanic and atmospheric circulation that affected the entire continent. Atmospheric circulation changes since ∼34 Ma have involved zonal winds, the ITCZ, desert formation and destruction, the evolution of the persistent (since ∼35 Ma) Antarctic ice sheet, and since ∼2 Ma of the rapidly cycling Eurasian ice sheets. We explain that a widely supported idea that ancient erosion surfaces have survived at high elevations in Africa is the result of a failure to recognize that the present elevations of the continent’s swells are dynamically maintained, but do not display a thermochronological signature because they are young (less than ∼32 My), so that conduction of heat from shallow convection cells has not yet reached the Earth’s surface.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| 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 source (direct Gemma or distilled Codex), 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".