Where Has All the Aragonite Gone? Mineralogy of Holocene Neritic Cool-Water Carbonates, Southern Australia
Bibliographic record
Abstract
Abstract Surficial carbonate sediments on the southern continental shelf of Australia are cool-water in aspect and composed of biogenic particles produced largely during the late Quaternary. Current understanding is that such sediments are calcite-dominated, as were their older Cenozoic counterparts. The Holocene fraction of these sediments in modern open-shelf, neritic environments between 30 and 350 meters water depth is, however, 50% to 80% aragonite. Scant evidence of significant former aragonite in many cool-water carbonate sedimentary rocks implies that most aragonite is lost before such sediments exit the marine diagenetic environment. Although marine dissolution must be taking place in such settings, the conundrum is exacerbated because seawater over the shelf in southern Australia is saturated with respect to aragonite. It is proposed that the aragonite, from skeletons of gastropods, infaunal bivalves, and certain bryozoans, is dissolved in the shallow subsurface, probably as the byproduct of bacterial degradation of sedimentary organic matter. As a consequence, the geological and paleontological record of many cool-water carbonates is strongly biased, and the inferred original calcitic composition of such sediments is the product of early diagenetic taphonomic loss, not selective biogenic productivity. The net result is not only dissolution of aragonite but also neomorphism of Mg-calcite to calcite with a marine geochemical signature. Synsedimentary aragonite loss, by removing CaCO3 that is usually available for calcite cementation during meteoric diagenesis, leads to retarded lithification of these cool-water carbonates until deeply buried. Such removal of a significant carbonate fraction during deposition likely contributes to the low rates of cool-water sediment accumulation.
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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 | 0.000 |
| 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".