STABLE ISOTOPIC ANALYSIS REVEALS EVIDENCE FOR GROUNDWATER-SEDIMENT-ANIMAL INTERACTIONS IN A MARGINAL-MARINE SETTING
Bibliographic record
Abstract
Abstract We use isotopic analyses of authigenic siderite and calcite cements within Rosselia socialis burrows from shoreface deposits in the Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada, to reveal the early cementation history of the burrow and geochemical conditions of the initial sedimentary environment. Within the Horseshoe Canyon Formation, two forms of the Rosselia burrows are present: bulbous in situ burrows, and transported, spindlelike burrows, which display similar internal shaft diameters but smaller overall size compared to in situ forms. Transverse, incremental sampling of calcite and siderite cements in the Rosselia burrows reveals symmetrical isotopic deviation in δ13C and δ18O around the burrow core, representing accretionary records of evolving pore-water conditions. The number of isotopic deviations recorded in bulbous specimens is equal to those observed in spindle-shaped burrows, suggesting that in situ and transported burrows underwent similar periods of cementation. Cementation, however, was limited during each accretionary event in the spindle-shaped burrows, making them more susceptible to transport by storm waves because of their small size. Early cementation of Rosselia, thus, took place very close to the sediment-water interface at depths where storm waves could rework sediments (i.e., less than 1 m sediment depth). The enriched δ13C values for calcite and siderite (3.06-9.45‰ PDB [Peedee belemnite]) suggest that cement precipitation followed bacterially mediated decomposition of the organic matter concentrated within Rosselia in the zone of methanogenesis. Oxygen isotope compositions are enriched also, ranging in siderite from 17.5‰ to 29.4‰ SMOW (standard mean ocean water) and in calcite from 16.8‰ to 23.0‰ SMOW, and are more akin to the composition of subsurface groundwater than marine waters. Freshwater discharging through shoreface sediments explains the δ18O isotopic signature of calcite and accounts for the early diagenetic precipitation of siderite in shallow marine sediments. In addition, the coexistence of authigenic calcite and siderite cements was most likely controlled by variation in the mixing ratio of meteoric and marine fluids related to variable discharge rates for the freshwater aquifer.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 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 teacher head, 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".