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TitleOrigin of enigmatic beds in Proterozoic sandstone, Athabasca Basin, Saskatchewan, Canada
AuthorPercival, J BORCID logo; Bosman, S A; Venance, K E; Hunt, P A; Ramaekers, P; Jefferson, C W
SourceMicro et Nano Scientiæ Mare Magnum, XIV International Clay Conference, Book of abstracts, volume 1, Oral sessions; by Associazione Italiana per lo Studio delle Argille; 2009 p. 192
Alt SeriesEarth Sciences Sector, Contribution Series 20080583
MeetingXIV International Clay Conference; Castellaneta Marina; IT; June 14-20, 2009
NTS64E; 64L; 64M; 74E; 74F; 74G; 74H; 74I; 74J; 74K; 74L; 74M; 74N; 74O; 74P
Areanorthern Saskatchewan
Lat/Long WENS-112.0000 -102.0000 60.0000 57.0000
Subjectsigneous and metamorphic petrology; sedimentology; sandstones; tuffs; clays; breccias; drillholes; quartzarenites; uranium deposits; Athabasca Group; Athabasca Basin; Manitou Falls Formation; Proterozoic
ProgramSecure Canadian Energy Supply
Released2009 01 01
AbstractThe Athabasca Group in northern Saskatchewan and Alberta fills a 100,000 km2, 1400 m+ thick basin with four sequences of fluvial conglomeratic sandstone with minor shale and carbonate. In 2000-2004 the basin was the focus of a multi-disciplinary, multi-agency study (EXTECH IV) to improve the framework geology and exploration technologies for unconformity-associated uranium deposits. The Saskatchewan Ministry of Energy and Resources has continued to revise, redefine and reposition the lithostratigraphic units of the Athabasca Group in building a 3-D basin model. During field activities in 2007 an unusual bed was observed in a drill core near the top of the Manitou Falls Formation of the Athabasca Group. The medium to dark grey, thinly laminated, friable and clay-rich bed with gradational upper and lower contacts is in strong contrast to the underlying and overlying layers of very fine- to medium-grained competent sandstone and interbedded siltstone. Preliminary petrographic analysis shows poorly sorted, angular quartz grains with minor to trace mica, zircon fragments, K-feldspar, amphibole, tourmaline, rutile, magnetite, alumino-phosphate minerals and irregularly-shaped clay-rich, soft-sediment deformed intraclasts set in a fine-grained matrix. The intraclasts enclose angular grains of quartz. The angularity of the quartz grains and the variable grain size suggest a possible explosive (volcanic or impact?) origin. Thus, this unit may represent a new tuffaceous layer in the Manitou Falls Formation, or an intraformational breccia of unknown origin. Alternatively, or in addition, it may have been hydraulically fractured during far-field tectonism. During the 2008 field season, several beds in another drillhole located about 40 km away, were observed to show similar field characteristics to the 2007 sample. These samples also appear to be stratigraphically correlative despite their distal location. Both the 2007 and 2008 layers are marked by strong gamma-ray peaks (suspected thorium).
Typically the Upper Manitou Falls Formation (MFd) is a well-rounded medium- to fine-grained quartz arenite with about 1-3% dickite matrix with abundant clay intraclasts dominated by dickite. The 2007 sample contains illite (+ minor kaolinite/dickite) as the matrix clay with deformed siltstone and mudstone intraclasts. However, this layer does not contain the classic devritified glass shards that typify tuffaceous sediments. On the other hand, the felted mass of the matrix clay, the presence of primary minerals such as amphibole (hastingsite composition) and K-feldspar (orthoclase), magnetite and an illitic signature (based on SWIR and SEM analysis) in the matrix provide evidence for an unusual origin. In contrast, the 2008 samples contain rounded quartz grains, pyrite and have a matrix dominated by kaolinite and dickite, closer to the typical MFd composition. This research focuses on determining the origin of these enigmatic interbeds.

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