The architecture of oceanic plateaus revealed by the volcanic stratigraphy of the accreted Wrangellia oceanic plateau
Bibliographic record
Abstract
The accreted Wrangellia fl ood basalts and associated sedimentary rocks that compose the prevolcanic and postvolcanic stratigraphy provide an unparalleled view of the architecture, eruptive environment, and accumulation and subsidence history of an oceanic plateau.This Triassic large igneous province extends for ~2300 km in the Pacifi c Northwest of North America, from central Alaska and western Yukon (Nikolai Formation) to Vancouver Island (Karmutsen Formation), and contains exposures of submarine and subaerial volcanic rocks representing composite stratigraphic thicknesses of 3.5-6 km.Here we provide a model for the construction of the Wrangellia oceanic plateau using the following information and visualization tools: (1) stratigraphic summaries for different areas of Wrangellia; (2) new 40 Ar/ 39 Ar geochronology results; (3) compilation and assessment of geochronology and biostratigraphy for Wrangellia; (4) compiled digital geologic maps; (5) an online photographic archive of fi eld relationships; and (6) a Google Earth fi le showing the mapped extent of Wrangellia fl ood basalts and linked fi eld photographs.Based on combined radiometric (U-Pb, 40 Ar/ 39 Ar, K-Ar), paleontological, and magnetostratigraphic age constraints, the Wran-gellia fl ood basalts were emplaced during a single phase of tholeiitic volcanism ca.230-225 Ma, and possibly within as few as 2 Myr, onto preexisting submerged arc crust.There are distinct differences in volcanic stratigraphy and basement composition between Northern and Southern Wrangellia.On Vancouver Island, ~6 km of high-Ti basalts, with minor amounts of picrites, record an emergent sequence of pillow basalt, pillow breccia and hyaloclastite, and subaerial fl ows that overlie Devonian-Mississippian (ca.380-355 Ma) island arc rocks and Mississippian-Permian marine sedimentary strata.In contrast, Alaska and Yukon contain 1-3.5-km-thick sequences of mostly subaerial high-Ti basalt fl ows, with low-Ti basalt and submarine pillow basalts in the lowest parts of the stratigraphy, that overlie Pennsylvanian-Permian (312-280 Ma) volcanic and sedimentary rocks.Subsidence of the entire plateau occurred during and after volcanism, based on late-stage interfl ow sedimentary lenses in the upper stratigraphic levels and the presence of hundreds of meters to >1000 m of overlying marine sedimentary rocks, predominantly limestone.The main factors that controlled the resulting volcanic architecture of the Wrangellia oceanic plateau include high effusion rates and the formation of extensive compound fl ow fi elds from low-viscosity, high-temperature tholeiitic basalts, sill-dominated feeder systems, limited repose time between fl ows (absence of weathering, erosion, sedimentation), submarine versus subaerial emplacement, and relative water depth (e.g., pillow basaltvolcaniclastic transition). 1 Supplemental Google Earth File.ALL Wrangellia fi les.This .kmzfi le consists of georeferenced information that is designed to be viewed with the satellite imagery in Google Earth.The Google Earth application is available for free download at http://earth.google.com/.Information about Google Earth can be found at this web address.Please use the most current version of Google Earth for viewing these fi les (version 5.0 as of June 2009).The Supplemental Google Earth File contains ten separate folders: (1) Mapped Wrangellia fl ood basalts.This is a red transparent layer that shows the distribution of the Wrangellia fl ood basalts in Alaska, Yukon, and British Columbia.The map was derived from data in Wilson et al. (1998, 2005), Israel (2004), Massey et al. (2005a, b), and D. Brew (2007, written commun.).(2) Major faults in Alaska and Yukon.(3) Major faults in southwest BC.These folders show the location of faults in parts of Alaska, Yukon, and BC.These fi les were fi ltered from original fi les found at the following locations: Alaska from http://www.asgdc.state.ak.us/;Yukon from in Israel (2004); BC faults from Massey et al. (2005a, b).(4) Alaska sample locations.(5) Yukon sample locations.(6) Vancouver Island sample locations.These fi les show the locations, sample numbers, and fl ow type of samples of Wrangellia fl ood basalts collected during fi eld work.(7) Alaska Range photograph locations.(8) Wrangell Mountains photograph locations.(9) Yukon photograph locations.(10) Vancouver Island photograph locations.These four folders contain small versions of georeferenced photographs.Multiple photographs are referenced to a single coordinate.Therefore, in order to view all of the photographs from a single coordinate it is necessary to open the subfolders for each region in the My Places menu so individual photographs can be selected and viewed.Zooming in also helps to distinguish photograph locations.These photographs and others can be viewed in higher resolution online at the following link
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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 | 0.001 |
| 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 | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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".