River chemistry reveals a large decrease in dolomite abundance across the Phanerozoic
Bibliographic record
Abstract
The abundance of dolomite in ancient carbonate sediments, and its apparent rarity today, has important implications for the coupled Ca-Mg-C-cycles in seawater and global climate. Despite its importance, there are large differences between published records of dolomite abundance vs. geologic age, mainly due to complexities in adequately sampling heterogeneous bedrock. We overcome this issue by using dissolved Mg 2 and Ca 2 measurements in rivers draining carbonate-bearing bedrock. Because rivers weather broad areas, this approach integrates the geochemical composition of much larger volumes of carbonate compared to sample based methods. The average Mg/(Ca Mg) molar ratio in rivers declines with decreasing bedrock age, from 0.44 at 485 million year old (Ma) to 0.14 at 5 Ma, suggesting a decreasing percentage of dolomite in carbonate sequences across the Phanerozoic Eon. These data are hard to reconcile with any model that relies only upon oscillatory drivers to explain the dolomite abundance record, such as sea level or episodic expansions of ocean anoxia, and have important implications for the oceanic Mg cycle.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| 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".