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TitreSignificance of the chemistry and morphology of diagenetic siderite in clastic rocks of the Mesozoic Scotian Basin
AuteurPe-Piper, G; Piper, D J W
SourceSedimentology 2019 p. 1-28,
Séries alt.Ressources naturelles Canada, Contribution externe 20190255
Documentpublication en série
Mediapapier; en ligne; numérique
Formatspdf (Adobe® Reader®); html
ProvinceNouvelle-Écosse; Région extracotière de l'est
SNRC10; 11B; 11C; 11F; 11G
Lat/Long OENS -61.0000 -57.0000 46.0000 43.0000
Sujetss l dérite; diagenèse; cimentation; cristallisation; recristallisation; marges continentales; géologie du substratum rocheux; lithologie; roches sédimentaires; roches clastiques; grès; schistes; mudstones; carbonates; conglomérats; analyses minéralogiques; analyses de textures; analyses par microscope électronique; analyses par microsonde électronique; analyses statistiques; analyses d'ensemble; analyses géochimiques; géochimie du cadmium; géochimie du magnesium; géochimie du manganèse; géochimie du fer; cristallographie; morphologie cristalline; eau de gisement; fluides de formation; filons; lithofaciès; milieux sédimentaires; études des isotopes stables; isotopes de carbone; isotopes d'oxygène; paragenèse; historique de l'enfouissement; puits sous-marins; échantillons carrotés; antécédents géologiques; Bassin Néo-Écossais; géologie marine; sédimentologie; géochimie; minéralogie; Phanérozoïque; Mésozoïque; Paléozoïque; Carbonifère; Mississippien
Illustrationslocation maps; photographs; photomicrographs; tables; ternary diagrams; plots; schematic representations; cartoons
ProgrammeGéoscience en mer, Analyse de bassin et ressources géoscientifiques
Diffusé2019 08 24
Résumé(disponible en anglais seulement)
Siderite (FeCO3) is a widespread minor diagenetic mineral in clastic sedimentary basins. Although eodiagenetic authigenesis of siderite is well-known, siderite formed during burial diagenesis shows habits and chemical compositions that are poorly understood. This study tests the hypothesis that diagenetic siderite cements in sandstones in the Scotian Basin, offshore eastern Canada, show systematic variability in chemistry and habit that is a response to recrystallization and changing composition of basinal fluids. Mineral textures were determined from backscattered electron images, and chemistry mostly from electron microprobe analyses. Five chemical types of siderite are identified using k-means cluster analysis, based on the amount of substitution of Ca, Mg and Mn for Fe. Eodiagenetic microcrystalline coated grains, concretions and intraclasts in sandstones are principally Fe-rich siderite and locally have recrystallised to blocky equant crystals. Mesodiagenetic Mg-rich siderite partly replaced these equant crystals and also framework mica and K-feldspar grains, showing textural evidence for coupled dissolution-reprecipitation. Slender Mg-rich siderite rhombs (lozenges, bladed or wheat-seed siderite) have precipitated before and after the formation of quartz overgrowths in geochemical microenvironments. Magnesium substitution reflects Mg-rich formation waters resulting from smectite to illite conversion. Equivalent Ca-rich siderite occurs where sandstones overlie a Jurassic carbonate bank. Late Mn-rich siderite has complex textures resembling those of Mississippi-Valley type ores, with spheroidal rims, a honeycomb-like mesh and concentric infill around secondary pores. It also occurs in veins or replacing intraclasts, post-dating late ferroancalcite cements in sandstones that show strong dissolution by hot basinal brines. The Ca, Mg and Mn content of diagenetic siderite, coupled with textural evidence for recrystallization, can thus be used to track changes in ambient formation fluids. Siderite habits and chemistry described from the Scotian Basin are found in many clastic basins, suggesting that the observed recrystallization textures and variation in chemical type are of broad application.
Résumé(Résumé en langage clair et simple, non publié)
Cette étude résume et interprète la répartition de la sidérite dans le bassin Scotian, où ce minéral est un indicateur important de l¿évolution des fluides (y compris les hydrocarbures).