The Paleoproterozoic upper Gowganda Formation, Whitefish Falls area, Ontario, Canada: subaqueous deposits of a braid delta

Abstract

The upper Gowganda Formation is part of the Paleoproterozoic Huronian Supergroup (ca. 2.5–2.2 Ga) of the north shore of Lake Huron. The upper Gowganda Formation rests with sharp conformable contact on glaciogenic rocks of the lower Gowganda Formation and is gradational with cross-bedded sandstones of the overlying Lorrain Formation. At the southern margin of the Huronian fold belt, in the Whitefish Falls area, the upper Gowganda Formation is 380–750 m thick, and consists of four coarsening-upward cycles from 30 to 300 m in thickness. Each is comprised of the succession (a) laminated argillite deposited from suspension on the prodelta, (b) argillite and cross-laminated sandstone laid down on the delta front by normal fluvial input and flood episodes, (c) fine-to coarse-grained, cross-bedded sandstone formed as distributary-mouth sand sheets influenced by shallow marine processes. Abundant soft-sediment deformation indicates rapid sedimentation and (or) contemporaneous fault-related seismicity. Erosional contacts between cycles resulted from marine reworking as sediment supply diminished. Each coarsening-upward cycle is interpreted as the subaqueous deposits of a braid delta that prograded into a moderately wave-influenced, tectonically active marine basin. In some respects, the succession of the deltaic deposits is comparable to those formed during the postglacial evolution of the Mississippi delta, but it is likely that the fluvial regime at the time of deposition of the Gowganda Formation was dominantly braided.