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TitleAlbitisation of detrital feldspars in the Scotian Basin: implications for the thermal evolution of the basin
LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorPe-Piper, G; Yang, X
SourceGeological Survey of Canada, Open File 7117, 2014, 496 pages, Open Access logo Open Access
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
File formatpdf
ProvinceEastern offshore region
AreaScotian Shelf; Scotian Basin; Sable Sub-basin; La Have platform; Abenaki Sub-basin; Orpheus Graben; Laurentian Sub-basin
Lat/Long WENS -64.0000 -53.0000 45.0000 43.0000
Subjectsigneous and metamorphic petrology; marine geology; sedimentology; sandstones; lithology; petrography; sedimentary petrology; detrital minerals; albite; albitization; detritus; potassium; feldspar; plagioclase; thermal alteration; thermal history; diagenesis; paragenesis; Lower Cretaceous; scanning electron microscopy; electron microscope analyses; sedimentary facies; lithostratigraphy; Peskowesk A-99 well; Louisbourg J-47 well; Kegeshook G-67 well; Mesozoic; Cretaceous
Illustrationslocation maps; photomicrographs; stratigraphic columns; tables
ProgramOffshore Geoscience
Released2014 02 14
AbstractDiagenesis of K-feldspar and plagioclase are among the most significant changes occurring in sandstones during burial diagenesis. Sixteen representative samples at various depths from eight exploratory wells in the Scotian Basin were selected for detailed study of the diagenesis of the detrital feldspars, to evaluate the roles played by sedimentary facies (which influence porosity and permeability), geographic location (controlling the type of detrital supply), burial depth, temperature and salinity as recorded by fluid inclusions, and the structural setting of the sandstones. K-feldspar authigenesis starts at ~1900 m depth as K-feldspar overgrowths on detrital K-feldspars, or as cement that fills fractures in fractured K-feldspars, and continue to 3000 m. Albitization of Kfeldspar also starts at ~1900 m, with diagenetic albite following weakness paths and at greater depths, K-feldspar disappears through dissolution and/or replacement by ferroan calcite ± ankerite. K-feldspars disappear between 3,800 and 4,500 m. Detrital plagioclase is either oligoclase or albite. Early patches of diagenetic albite in detrital albite grains give way with depth to albite pseudomorphs or partially dissolved albite grains, containing large pores. Albite pseudomorphs predate late ankerite cement. Detrital oligoclase is first replaced at depths >3,700 m by diagenetic albite as overgrowths or irregular patches with straight crystal outlines. Diagenetic albite is much more abundant in thick sandstone units than in thin sandstone beds with interbedded mudstone, probably because such sandstones were pathways for flux of basinal fluids. It is more abundant, in the same facies and depth, in the Thebaud-Glenelg fields, where fluid inclusions in silica and carbonate cements are ~21% NaCl compared with the eastern part of the basin where fluid inclusions are ~10% NaCl and probably a little cooler. Dissolution of K-feldspar seems predominantly controlled by burial depth, but is most severe in permeable thick sandstone units.
Summary(Plain Language Summary, not published)
This report documents in detail the development of secondary porosity in the Scotian Basin through the alteration of feldspars. It takes advantage of the presence of feldspars in grains of volcanic rocks. It provides an interpretation of the effect of temperature, pressure and fluid flow on changes in feldspars. A related journal paper will explore the broader implications of this data.

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