THE PALEOPROTEROZOIC UPPER GOWGANDA FORMATION, WHITEFISH-FALLS AREA, ONTARIO, CANADA - SUBAQUEOUS DEPOSITS OF A BRAID DELTA

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 uppe r Gowganda Formation rests with sharp conformable contact on glaciogen ic 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 up per Gowganda Formation is 380-750 m thick, and consists of four coarse ning-upward cycles from 30 to 300 m in thickness. Each is comprised of the succession (a) laminated argillite deposited from suspension on t he 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-sed iment deformation indicates rapid sedimentation and (or) contemporaneo us fault-related seismicity. Erosional contacts between cycles resulte d from marine reworking as sediment supply diminished. Each coarsening -upward cycle is interpreted as the subaqueous deposits of a braid del ta that prograded into a moderately wave-influenced, tectonically acti ve marine basin. In some respects, the succession of the deltaic depos its 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.