The Geochemistry of Qatar Coastal Waters and its Impact on Carbonate Sediment Chemistry and Early Marine Diagenesis
Notice bibliographique
Résumé
Abstract The southern margin of the Arabian Gulf is a “classic” shallow-water, evaporative, carbonate-producing setting. The sediments and early diagenetic products creating the “Great Pearl Bank” of the United Arab Emirates to the east and accumulating in the coastal regions of Qatar to the west have long been studied as modern analogs for ancient evaporitic carbonate deposits of the rock record. An integrated study measuring the chemistry of Qatar subtidal coastal waters, evaporating tidal-pond waters (to halite saturation), and meteoric pond waters was undertaken encompassing both the dry (fall) and wet (winter/spring) seasons of 2016–2017. Measured parameters included temperature, pH, dissolved oxygen, and alkalinity, as well as major-ion (Na+, Ca2+, Mg2+, K+, Sr2+, Cl–, and SO42–) and stable-isotope (δ18O and δD) composition. Initial concentration by evaporation (to ∼ 90 practical salinity units (psu)) is interpreted to drive minor diagenetic aragonite precipitation. Further evaporation initially causes minor aragonite dissolution followed by gypsum and halite precipitation. One pond showed evidence of ongoing replacive dolomitization interpreted to be driven by H2S formation and oxidation in association with microbial breakdown of organic matter. The stable-isotope composition of water in restricted ponds is a function of the degree of evaporation and dilution by meteoric waters during the wet season. Unexpectedly, beyond 350 psu, δ18O and δD continue to rise reaching values greater than 12 and 60‰, respectively. The slope of the δ18O–δD regression line exhibits no differences between dry and wet seasons. During collection of coastal waters (up to ∼ 90 psu), live Pirenella cingulata (previously Cerithidea cingulata) gastropods were collected and their shells analyzed for δ18O and δ13C, as well as Sr2+ and Ca2+ concentration. The δ18O of water and Pirenella from the same sample site exhibits a strong correlation (R2 ≥ 0.85) with a slope of ∼ 1, suggesting that the shells may be a useful chemical archive for the isotopic composition of past oceans. The δ18O and δ13C of the shells correlate positively, likely reflecting greater sequestration of 12C into organic matter in more restrictive evaporative settings. The intercept of the δ18O and δ13C correlation shifts between dry and wet seasons, and is interpreted to reflect average seawater temperature differences during recent growth. There is also a strong correlation (R2 ≥ 0.85) between shell δ18O and measured water salinity, reflecting their mutual control by degree of evaporation. The Sr2+ content of the gastropods does not correlate well with any measured oceanographic parameter, or show evidence of systematic seasonal change.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,002 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 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 tête enseignante, 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 ».