The Charlevoix area, which is host to an impact structure of Devonian age, straddles the boundaries among crystalline rocks of the Grenville Province, the CambrianOrdovician sedimentary succession of the St. Lawrence Platform, and accreted units of the Appalachian orogen. The area features well-developed supracrustal fault systems attributed to impact cratering. A major fault system oriented from northeast to northwest consists of normal faults marked by cataclastic and gouge breccias and, less frequently, by pseudotachylyte. Detailed mapping of faults both within and outside the Charlevoix impact crater suggests that brittle faulting occurred both before and after impact cratering. Polymictic fault breccias occurring along some supracrustal faults are the clearest evidence of impact-related fault rocks in the Charlevoix area. The St-Laurent fault, trending to the northeast, represents a major structure interpreted as being related to Late Proterozoic early Paleozoic rifting of the Iapetus Ocean. However, the St-Laurent fault crosses the Charlevoix impact crater without major deflection, suggesting post-impact reactivation. The fault systems in the Charlevoix area are interpreted to be pre-impact structures related to the opening of the Iapetus Ocean, most of which have also been reactivated during the Devonian cratering event and in post-impact time, the latter most likely coeval with the Atlantic Ocean rifting in Mesozoic time.
The geology of the Sainte-Marie-de-Beauce-Saint-Sylvestre area depicts a tectonostratigraphic, structural, and metamorphic transition that characterizes the boundary between the external and internal Humber Zone. It also corresponds to a region of reversal in
structural vergence and tectonic transport, i.e. from foreland-directed struc- tures in the northwestern part to hinterland-directed structures in the southeastern part. A series of thrust nappes make up tectonostratigraphic packages that are correlated to various stratigraphic units: the
Sainte-Hénédine, Rivière Filkars, Richardson, and Oak Hill nappes comprise rocks units of the Île d'Orléans, Saint-Roch, Armagh, and Oak Hill groups, respectively. To the southeast, the Bennett Fault separates these nappes from metamorphosed and polydeformed lithologies of
the Rosaire Group and Bennett Schists. The Bennett Fault is a southeast-directed backthrust fault, which best corresponds to the dominant structure representing the boundary between the external and internal Humber Zone.
At the front of the Mackenzie Mountains west of Norman Wells, the Upper Devonian Imperial Formation was deposited by a fan-slope complex that prograded southwest from an eastern basin margin. Laterally extensive submarine fan deposits are composed of intercalated sandstone lobe and lobe fringe deposits. Sandstone lobes are composed of thick-bedded turbidites reflecting high sediment fallout rates. Lobe fringe deposits are thin-bedded turbidites deposited under upper flow regime conditions. Slope facies are shale-dominant, but include turbidites deposited by both fine-grained dilute flows and thin-bedded facies deposited under upper flow regime conditions but low sediment fallout rates. Near the eastern edge of the study area, at Imperial River, shallow marine deposits are preserved above and below slope deposits, a relationship interpreted to record local shelf construction at the basin margin during initial stages of subsidence. Near the western edge of the study area, at Flyaway Creek, Imperial Formation is composed entirely of shale, marking the western extent of well developed base-of-slope submarine fan deposits. In the western area Imperial Formation is overlain by Tuttle Formation sandstone, which marks an increase in the grain size of sediment supplied to the southwestward prograding slope system.
RÉSUMÉDevant les monts Mackenzie, à l'ouest de Norman Wells, la Formation d'Imperial du Devonien supérieur a été déposée par un complexe de cônes de talus qui s'est accumulé au sud-ouest en provenance d'une marge de bassin orientale. Composés de lobes de grès interstratifiés et de dépôts de lobes marginaux, les dépôts de cônes sous-marins sont latéralement extensifs. Les lobes grèseux sont composés de lits de turbidites épais, ce qui reflète des taux de sédimentation élevés. Quant aux dépôts de lobes marginaux, ils sont composés de turbidites en lits minces déposés par un régime d'écoulement énergique. Dans le faciès des talus, le shale prédomine, mais on y remarque également des turbidites déposées par des écoulements à grains fins dilués et des faciès de lits minces déposés en régime d'écoulement énergique, mais avec de faibles taux de sédimentation. Près de la limite orientale du secteur étudié, à Imperial River, des dépôts de mer peu profonde sont préservés au-dessus et au-dessous des dépôts du talus, ce que l'on interprète comme une relation
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