Fossil Hot-Spring Travertine in the Turkana Basin, Northern Kenya
Bibliographic record
Abstract
Abstract The Ngakoringora Ridge is a large (300 m long), linear mound of limestone, dolomitized limestone, and chert that rises abruptly from the desert floor on the southwestern edge of the Lothidok Hills, west of Lake Turkana, Kenya. The origin of the ridge has been controversial. It has previously been considered either a hot-spring deposit or an uplifted holier of pre-Cenozoic marine carbonates. Interpretation has been hampered by the extensive diagenetic alteration of the rocks and the lack of identifiable fossils. A preliminary examination of the ridge morphology and the facies and fabrics of the rocks confirms a hydrothermal origin. The carbonates contain radial calcite fans, micrite-microsparite laminae, stromatolites, coated grains, peloids, intraclasts, Mn-shrubs, and other fabrics that characterize hot-spring travertines. Many of the carbonates have been partly silicified and dolomitized. The ridge is interpreted to be a fissure-ridge travertine, precipitated from thermal waters that discharged along a medial fissure. Fluids flowed laterally from five main mounds that were probably active at different times. Crystal fabrics along the ridge crest are compatible with abiotic precipitation from alkaline spring waters undergoing rapid degassing of CO2. Microbially influenced fabrics, including stromatolites, become more common distally. Silicified plants, filamentous microbial mats, and thin chert beds are locally present in distal slope settings. Plant silicification and chert formation may have taken place in shallow terrace pools from spring fluids undergoing cooling and evaporation. The Ngakoringora Ridge formed after the faulting and tilting that formed the Lothidok Hills, but its age is difficult to constrain. Silicification and dolomitization of the carbonates resulted from contact with hydrothermal fluids, and possibly from circulating ground water or lake water after deposition. Hydrothermal activity in rifts migrates with the evolving structural configuration. In the Kenya Rift, this is evident as a migration of hydrothermal activity toward the rift axis. Fossil spring deposits can provide much useful paleoenvironmental information even though they are of small lateral extent.
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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 | 0.000 |
| 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".