Mineralogy of tuffaceous sediments on the Eyasi Plateau (northern Tanzania): Precambrian basement rocks and Lower Laetolil Beds
Bibliographic record
Abstract
The Eyasi Plateau, located to the southwest of the Crater Highlands in northern Tanzania, is a paleo-anthropological locality, which is well-known for its fossilized remains of animals and human ancestor species (including Australopithecus afarensis). These fossils occur in tuffaceous sediments (~150 m thick, ca. 4.4 to 0.2 Ma), with aeolian tuffs as a dominant rock type. The sediments overlie a Precambrian basement complex consisting of granite, gneiss, amphibolite, garnet amphibolite, and greenschist. At least 24 minerals (with quartz, plagioclase, microcline, amphibole, biotite and epidote being major constituents) are present in the basement rock. The Lower Laetolil Beds are the oldest section of the tuffaceous sediment package and directly overlie the basement. The beds are composed predominantly of authigenic minerals (~60-90 wt% montmorillonite, kaolinite, phillipsite, chabazite, analcime, calcite, and dolomite). Non-authigenic minerals (38 in total) are less abundant and represented by diverse silicate and oxide phases. Chromium-poor Ca-Na clinopyroxenes (diopside to aegirine), calcic garnets (Ti-bearing andradite to schorlomite), titanite and feldspars (labradorite to albite, microcline and sanidine-anorthoclase) are the most common primary silicate phases; Cr-bearing diopside is much less common. Major oxide constituents are magnetite of highly variable composition (including Mg-Al-rich and Cr-bearing varieties), perovskite and quartz. Exceptionally rare oxide phases are magnesiochromite, pyrochlore and zirconolite. The observed minerals association in the Lower Laetolil Beds suggests that non-authigenic minerals derive from several distinct, and not necessarily cogenetic, rock types. The Precambrian basement rocks and phonolite-nephelinite Sadiman volcano appear to represent the principal sources (“basement” and “nephelinitic”, respectively) for primary detritus in the Lower Laetoli Beds. The occurrence of magnesiochromite and Cr-bearing diopside in these sediments implies also the existence of a “basaltic” source, possibly near Lake Manyara, whereas the pyrochlore + zirconolite assemblage is an indication of a “carbonatitic” source (e.g., Oldoinyo Dili carbonatites). For the latter sources to have contributed to the mineralogy of the Lower Laetolil Beds, non-authigenic detritus would have had to endure surface transportation by wind over a distance of at least 70 km.
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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 | 0.002 | 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) | 0.001 | 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".