Geochemistry Of The Late Devonian 'Punctata' Event In The Western Canada Sedimentary Basin
Notice bibliographique
Résumé
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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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,002 | 0,003 |
| Études des sciences et des technologies | 0,004 | 0,002 |
| Communication savante | 0,002 | 0,000 |
| Science ouverte | 0,001 | 0,001 |
| Intégrité de la recherche | 0,001 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,004 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».