Palaeobathymetry and anomalous subsidence at rifted margins: Observations from the magma-rich and magma-poor Nova Scotian margin
Bibliographic record
Abstract
The isostatic evolution and bathymetry of rifted margins depends on thinning of continental crust, the volume of magmatic additions, lithosphere thermal perturbation during rifting and its post-rift re-equilibration, and sediment loading. Additionally, at some margins, bathymetric evolution may also be affected by basin isolation, where eustatic variations are not controlled by global sea-level changes, and mantle plume dynamic uplift and its collapse. The relative influence of these contributors to rifted margin bathymetric evolution varies from example to example.Here we investigate the parameters controlling the palaeobathymetric evolution of the Nova Scotian rifted margin during the early stages of the opening of the Central Atlantic Ocean, following Triassic rifting, salt deposition and early Jurassic continental breakup. We use a 3D flexural backstripping technique which incorporates decompaction and post-breakup reverse thermal subsidence modelling to provide palaeobathymetric predictions through the Cretaceous down to the Late Triassic base salt.Quantitative analysis of seismic reflection and gravity anomaly data together with residual depth anomaly analyses have also been used to determine variations of crustal thickness and crustal type as well as volumes of magmatic addition emplaced during rifting and continental breakup. We show the magma-rich to magma-poor transition of the Nova Scotian margin, characterized by seaward dipping reflectors (SDRs) in the SW, while in the NE mantle is possibly exhumed.Comparison of our palaeobathymetric predictions with seismic observations and palaeoenvironments deduced from biostratigraphy of drill samples are in good agreement over the continental shelf. As expected, discrepancies exist more distally related to salt withdrawal and sediment gravity-driven sliding. Palaeobathymetries predicted seaward, on the first oceanic crust, range from 2 to 2.5 km; values in the range of those observed at young oceanic ridges.The oceanic crust of the SW Nova Scotian margin shows well developed sequences of SDRs. Their morphology resembles that of inner SDRs of volcanic margins like the Norwegian and Greenland margins (North Atlantic), where drilling results indicate that they correspond to lava-flows emplaced near or above sea-level. Our predicted palaeobathymetry of top SDRs at breakup is nearly ~2km deeper than the expected near sea-level. This discrepancy suggests that the subsidence of this thick oceanic crust with SDRs requires an additional mechanism in addition to post-rift thermal subsidence.Mantle plume uplift and collapse likely occurs at volcanic margins and has a long wavelength of the order of 500 km or more. However, the subsidence discrepancy we observe has a shorter wavelength and seems focused along the nascent spreading axis. Thinning of the thick oceanic crust after SDR emplacement by oceanward lateral flow of molten and ductile lower crust is an alternative possibility and may be a common occurrence at volcanic rifted margins after continental breakup.
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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 | 0.000 | 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 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".