Petrology and Sedimentation of Huronian Arenites, South of Espanola, Ontario

Abstract

The five arenaceous lithostratigraphic units of the Huronian sequence recognized in the Espanola–Willisville area are the Mississagi, Espanola, Serpent, and the Lorrain Formation, as also the intercalated zone which forms the uppermost subdivision of the Gowganda Formation.The bulk of the Huronian arenites is a mixed assemblage of fine, medium, and coarse subarkose, and arkose which are either poorly sorted, muddy fine-to-medium grained (Mississagi, calcareous Espanola, lower Serpent) and muddy medium-to-coarse grained (lower and middle Lorrain), or, moderately well-sorted, medium-to-coarse grained (middle and upper Serpent and intercalated zone). There is, however, one unit in the upper part of the Huronian sequence (uppermost Lorrain) which is a brilliant white supermature quartzarenite. Among the notable petrographic features are a lower quartz – feldspar ratio, rock fragments of metasedimentary and metavolcanic origin, and occasionally occurring rounded quartz. The feldspathic debris for these arenites was derived largely from the older granitoid rocks similar to the 'Algoman granite' of the Canadian Shield to the north of the study area and partly from the supracrustal rocks infolded in the granitoid terrain. Dominance of plagioclase (oligoclase ?) over potassic feldspar and their overall freshness in the arenites may suggest that the source rocks by and large were not deeply weathered,An integrated analysis of lithologie association and sedimentary characters, including texture and mineralogy of the arenites, possibly indicates a near-shore depositional environment (? fluviatile-deltaic) for several Huronian arenites (Mississagi, Serpent, intercalated zone, and middle and upper Lorrain); some may be deltaic-marine (lower part of lower Lorrain). Calcareous Espanola was perhaps deposited beyond the shoreline partly in deeper waters and partly in shallow turbulent environment. Likewise, clean white quartzarenite of top Lorrain may represent deposition in the turbulent fore-shore zone (beach or shelf).