Four unconformity-bounded quartzose fluvial sequences filled the Athabasca Basin between about 1760 Ma and 1500 Ma, each with distinct subbasin architecture, grain-size distribution, and paleocurrent directions. Maximum thickness of the Athabasca Group at any one place is about 1500 m, although much has been eroded and the aggregate stratotype thickness is 3800 m. Sequence 1 is Fair Point Formation (conglomeratic Lobstick and pebbly quartz arenite Beartooth members). Sequence 2 begins with conglomeratic Read Formation in the east and sandy Smart Formation in the west, overlain by Manitou Falls Formation (conglomeratic Bird, sandy Collins, and clay-intraclast-rich Dunlop members in the east and centre; sandy Warnes Member to the southeast and pebbly sandy Raibl Member to the northeast). Sequence 3 includes the Lazenby Lake Formation (conglomeratic Hodge, sandy-muddy Clampitt, pebbly Shiels, and sandy Larter members), and the Wolverine Point Formation (mudstone-rich Brule and sandy Claussen members). Sequence 4 comprises Locker Lake Formation (pebbly Snare, conglomeratic Brudell, and pebbly Marsin members), Otherside Formation (pebbly Archibald and sandy Birkbeck members), Douglas Formation quartz arenite and carbonaceous mudstone, and Carswell Formation stromatolite and oolite with minor basal siliciclastic interbeds.

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The eastern margin of the Kechika Graben in the vicinity of Muncho and Moose lakes, northeastern British Columbia, contains Middle Cambrian rift-related strata herein named the Mount Roosevelt Formation. The formation conformably overlies a quartzite package equivalent to the uppermost clastic unit of the informal late Early Cambrian Gataga group (Bonnia-Olenellus zone) and is conformably overlain by a thick, unnamed carbonate sequence of Middle Cambrian age (Plagiura-Poliella zone). The Mount Roosevelt Formation is subdivided into three members. The lowermost member is characterized by oöid-bearing siltstone and sandstone, interbedded with dolostone, limestone, and hematitic conglomerate. Conformably above this, the middle member is a thick sequence of polymict cobbly pebble conglomerate. The upper member includes karstified dolostone, calcareous-cemented conglomerate and sandstone, and limestone. Collectively the Mount Roosevelt Formation reflects alluvial fan delta progradation into a transgressive marine environment. Deposition occurred in an active fault-controlled basin, located on the eastern margin of the Kechika Graben adjacent to the Muskwa High. Basin initiation in the late Early Cambrian coincided with the reactivation of pre-existing regional faults. High rates of subsidence during the initial phase of extension were accommodated on these faults, which provided a locus for fan delta deposition. Continuing high rates of subsidence limited basinward fan delta development. Deposition of the formation ended with base-level transgression in the early Middle Cambrian that drowned the fan deltas and the adjacent Muskwa High and allowed development of the Kechika Trough above the older graben system. Résumé :Située à proximité des lacs Muncho et Moose dans le nord-est de la Colombie-Britannique, la bordure est du graben de Kechika contient des strates, ici nommées la Formation de Mount Roosevelt (Cambrien moyen), qui sont reliées à la distension. La formation repose en concordance sur un ensemble de quartzite équivalent à l'unité supérieure, clastique, du groupe de Gataga, informel, datant du Cambrien précoce (zone à Bonnia-Olenellus); elle est recouverte en concordance par une épaisse séquence de carbonate, sans nom, datant du Cambrien moyen (zone à Plagiura-Poliella). La Formation de Mount Roosevelt est subdivisée en trois membres. Le membre inférieur est caractérisé par des siltstones et des grès à oolites, interstratifiés avec des dolomies, des calcaires, et des conglomérats hématitiques. Par-dessus, en concordance, le membre du centre est composé d'une épaisse séquence de conglomérat grenu, hétérogène et caillouteux. Le membre supérieur comprend de la dolomie karstifiée, du conglomérat et du grès à ciment calcaire, et du calcaire. Dans son ensemble, la Formation de Mount Roosevelt est le reflet de la progradation d'un delta alluvionnaire en un environnement marin de transgression. La déposition a eu lieu dans un bassin contrôlé par des failles actives situé sur la bordure est du graben de Kechika, voisi...

Three unconformity-bounded formations of the Athabasca Group were examined in the Maybelle River - Net Lake area. The lowermost, Fair Point Formation (FP) is here subdivided into lower (FP1) and upper (FPu) conformable members. Fair Point Formation lower member comprises local, massive to planar-bedded siltstone beds interpreted as shallow lake deposits in fault-controlled paleovalleys, interbedded and overlain by matrix- and clast-supported pebble conglomerate and pebbly sandstone deposited by high-velocity streams forming a prograding alluvial plain. Fair Point Formation upper member (FPu) is massive to crossbedded, coarse-grained sandstone, also interpreted as a prograding alluvial plain. Manitou Falls Formation (MF) comprises a lower, crossbedded, medium- to coarse-grained sandstone (unit MFc) and an upper, ripple-crosslaminated, medium-grained sandstone (unit MFd). These are equated to proximal units in Saskatchewan and record relatively low-velocity, distal, braided-river-system tracts. The uppermost, incompletely preserved Lazenby Lake Formation is massive, ripple-laminated, convolute-bedded, pebbly sandstone with sedimentary characteristics as in the Manitou Falls Formation, and records deposition by low-velocity, braided streams.