Origin and Evolution of Eocene Rock Salts in Pakistan and Implications for Paleoclimate Studies: Insights From Chemistry and Cl Stable Isotopes
Bibliographic record
Abstract
The Kohat Basin (KB) lies on the Himalayan Foothills and is of scientific importance as it directly recorded the closure of the Tethys Sea and the Himalayan collision between India, Asia, and a number of other small plates. During the Eocene, after the collision between the Indian and Eurasian plates terminated the Tethys Sea, thick-bedded marine evaporite sequences developed in the KB. In this study, we combined mineralogy, geochemistry, fluid inclusion and chlorine stable isotope compositions to discuss the origin and evolution of the KB Eocene halite deposits with the ultimate objective of defining the paleoclimate that was prevailing in Asia during the Eocene. Our results showed that halite samples were SO42− rich (225–370.103 ppm) and Br− poor (<3 ppm). Cl−, B+, Mg2+, K+, SO42− and very low Br concentrations as well as the (Br/Cl) ratios indicated that halite resulted of a mixture of solutions with variable compositions and that dissolution, recrystallization and a progressive decrease in dolomitization were the mechanisms leading to the formation of these evaporites. A Br/Cl vs Cl plot revealed that the end members involved were: seawater (sw), saline waters and/or freshwaters. The recrystallization process prevented identifying the primary structures and primary fluid-inclusions. Most of Cl isotope compositions (−0.54‰<δ37Cl < 0.83‰) were within the usual range (0 ± 0.5‰) associated to seawater as the initial source for the halite. The higher isotope compositions (δ37Cl ≥ 0.83‰) comforted the hypothesis of the genesis by mixing of solutions of different origins as well as the involvement of recrystallization. Based on our results, we are proposing the following to explain the regional paleoclimate sequence: 1) shallow water conditions; 2) halite precipitation induced by evaporation, 3) unstable paleoclimatic conditions that resulted in the morphing from an evaporite basin into a terrestrial foreland basin. All these events were controlled by regional tectonic and linked to both the overall uplift times of the NW Indian Craton and the Eocene thermal maximum one during the Eocene-Oligocene period.
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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 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".