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TitleSignificance of the chemistry and morphology of diagenetic siderite in clastic rocks of the Mesozoic Scotian Basin
AuthorPe-Piper, G; Piper, D J WORCID logo
SourceSedimentology 2019 p. 1-28,
Alt SeriesNatural Resources Canada, Contribution Series 20190255
Mediapaper; on-line; digital
File formatpdf (Adobe® Reader®); html
ProvinceNova Scotia; Eastern offshore region
NTS10; 11B; 11C; 11F; 11G
AreaAtlantic Ocean
Lat/Long WENS -61.0000 -57.0000 46.0000 43.0000
Subjectsmarine geology; sedimentology; geochemistry; mineralogy; siderite; diagenesis; cementation; crystallization; recrystallization; continental margins; bedrock geology; lithology; sedimentary rocks; clastics; sandstones; shales; mudstones; carbonates; conglomerates; mineralogical analyses; textural analyses; electron microscope analyses; electron probe analyses; statistical analyses; cluster analyses; geochemical analyses; cadmium geochemistry; magnesium geochemistry; manganese geochemistry; iron geochemistry; crystallography; morphology, crystal; formation water; formation fluids; veins; lithofacies; sedimentary environments; stable isotope studies; carbon isotopes; oxygen isotopes; paragenesis; burial history; offshore wells; core samples; geological history; Scotian Basin; Phanerozoic; Mesozoic; Paleozoic; Carboniferous; Mississippian
Illustrationslocation maps; photographs; photomicrographs; tables; ternary diagrams; plots; schematic representations; cartoons
ProgramOffshore Geoscience
Released2019 08 24
AbstractSiderite (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.
Summary(Plain Language Summary, not published)
This study summarises and interprets the distribution of the mineral siderite in the Scotian Basin where it is an important indicator of the evolution of fluids (including hydrocarbons) in the basin.

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