GRAVITY SURVEY OF A BURIED TRIASSIC RIFT BASIN, BERTIE COUNTY, NORTH CAROLINA
Bibliographic record
Abstract
The North American rift margin includes of a series of Triassic rift basins along the eastern seaboard of the United States and Canada. This continent-scale rift basin system is comprised of complex and variable geometries that can be generalized into regions with similar structural, deformational, and sedimentary characteristics. Rift basins provided accommodation space for organic-rich Triassic age sediments that may be source rocks for natural gas and petroleum. Most of the known basins are exposed at the surface and relatively easy to access, but a few buried basins have been identified beneath coastal plain strata. I used primarily geophysical methods to study a buried Triassic rift basin in Bertie County, North Carolina, recently discovered from a deep core sample that documented Triassic sedimentary rocks buried underneath approximately 300 meters of Cretaceous and younger, sediments and sedimentary rock. Approximately 30 meters of Triassic strata were recovered from the well, but basement rock was not reached leaving the overall thickness of the basin undetermined. I used a gravity survey to constrain the dimensions and geometry of the basin and surrounding rock bodies at depth. Data processing, modeling, and integration with preexisting data was accomplished using Oasis:Montaj software. The buried basin creates a maximum gravity anomaly of approximately 7 mGal. Modeling of the data suggests the basin is generally elongate, SW to NE, and has maximum dimensions of approximately 15 km wide, 50 km long, and as much as 2.5 km deep (basin infill). In cross section, the basin is asymmetrical and wedge-shaped, with a NW margin that dips steeply SE and a SE margin that dips more shallowly NW. The Bertie basin is deepest to the south and was likely hydrogeologically open in that direction. Previous datasets have been derived from analysis of the cores at the North Carolina Geologic Survey and include whole rock geochemical analysis, thin sections, and magnetic susceptibility. Interpretation of the geochemical data suggests the Triassic strata are derived from a continental island arc, and thin section analysis suggests a provenance of recycled orogenic material. The rocks classified as Triassic tend to have lower magnetic susceptibility than the overlying Cretaceous rock. One interpretation of these data is a change in sediment provenance from late-stage Triassic basin infill to the overlying Cretaceous strata. The Bertie Basin is located in the Southern Segment of the North American rift margin, suggesting that its geometry and stratigraphy should reflect regional trends and exhibit characteristics similar to other southern rift basins. The characteristic geometry of basins in the Southern Segment generally includes narrow to medium size (10 to 25 km across), fault-bounded, half-grabens with no or very subtle growth structures. The Bertie Basin may be part of a series of basins or a sub-basin within a larger basin due to sequential, domino-style faulting during rift migration. Higher extensional rates and faster rift migration within the Coastal Plain province may be related to its reduced dimensions. Burial underneath Coastal Plain strata may also have helped to preserve the Bertie Basin's original geometry and size which allows for improved constraints on initial tectonic conditions and structures, sedimentary deposition, paleo-environments, and processes related to supercontinent 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 | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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".