Geochemistry Of The Late Devonian 'Punctata' Event In The Western Canada Sedimentary Basin
Bibliographic record
Abstract
Carbonate deposits straddling the Early-Middle Frasnian (Late Devonian) transitional interval at the isolated Miette carbonate platform in the Western Canada Sedimentary Basin were studied geochemically to better understand the paleoceanographic changes that had taken place regionally during the global 'punctata Event' Earth-system perturbation, characterized by the short-term (<0.5 M.y.) yet wide-spread eutrophication of epeiric environments and the deposition of organic carbon-rich facies.This event occurred while the evolution of terrestrial forests entered a rapid, near exponential phase of diversification and expansion, thus altering nutrient-cycling between the terrestrial and marine realms through a transient increase in the intensity of pedogenic weathering.I've attempted a reconstruction of the chemostratigraphic variance of (1) bioproductivity, paleoredox and detrital elemental proxies, of ( 2 ) isotopic records ( 5 13C (carb & org>; 5 15N org) , and of (3) related parameters, including TOC, magnetic susceptibility (MS) and the abundance and mineralogy of acid-insoluble carbonate residues, and interpreted these within the context of regional sequence stratigraphy and paleogeography against the background of global geobiological events.Analytical methods and standards were developed for measuring low (<10 ppm) concentrations of crucial proxies in carbonates (down to 1-2 ppm) by WD-XRF, and were verified by a diversity of statistical tests and analyses.Evaluation of chemostatigraphic trends revealed that eutrophication and geochemical anomalies associate strongly with a 3rd-order transgression (Ilc1) and increased detrital input in the lower punctata Zone.Factor analyses were thus applied to constrain the influence of 1) siliciclastic input vs. 2) the development of benthic anoxia (explaining 55 and 35% of total variance, respectively) on trace element excursions, but also to 3) assess the extent to which MS records within the stratigraphy track the clastic input.Mineralogical controls on MS variance were determined by XRD analyses of acid-insoluble limestone residues, and a multivariate linear regression model was found to account for 97.7 % of total variance as a function of variable admixing of illite, pyrite, quartz and feldspars, in turn variably diluted by the total carbonate content.Dedication To B. Charlotte Schreiber, for years of mentoring, caring support, and friendship V This work is a collection of four individual manuscripts arranged chronologically in the order in which they evolved.The exception is Chapter 2 which focuses on the development of Xray fluorescence spectroscopic (XRF) methods for measuring low abundances (0-100 ppm) of various trace element proxies in carbonate lithologies, for which certified standard reference materials from institutions such as the USGS and NIST are lacking.These methods have been improved upon following the initial trace element study on the punctata Event in the WCSB presented in Chapter 3 (Sliwiriski et al., 2010) through the use of synthetic, in-house carbonate trace element standards and refinements of the original XRF calibrations.The acquisition by University of Alaska Fairbanks' (UAF) Advanced Instrumentation Laboratory (AIL) of PANalytical's PROTrace XRF trace element standards and analytical software (UAF Technology Advisory Board grant to Sliwinski and Severin, April 2011) has further facilitated refinements andverifications of preexisting methods (taliwihski et al., 2012).In order to not disrupt the flow of the punctata Event story in Chapters 3, 4 and 5, I've placed this chapter on methods development at the onset of the compilation (Chapter 2).Variations in the minor and trace element geochemistry of marine sedimentary strata are interpreted as proxies for changes in 1) oceanic bioproductivity (e.g.Ni, Cu, P, Ba, Zn), 2) relative influxes of terrigenous siliciclastics into depositional basins (e.g.Al, Si, Ti, K, Cr, Zr, Co), and 3) for changes in the dominant benthic redox conditions (e.g.U, Mo, V, Ni/Co, U/Th, V/Cr, V/(V+Ni); Edwards, D., and Burgess, N.D., 1990.
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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 | 0.003 |
| Science and technology studies | 0.004 | 0.002 |
| Scholarly communication | 0.002 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".