SEDIMENTOLOGICAL ANALYSIS OF THE UPPER GOWGANDA FORMATION AT WHITEFISH FALLS: A PALEOPROTEROZOIC LATE STAGE RIFT-BASIN INFILL?

The Gowganda Formation (part of the Huronian Supergroup, 2.2-2.4 Ga) is a succession of Paleoproterozoic sedimentary rocks that outcrops along the northern shore of Lake Huron and is well exposed in the area of Whitefish Falls, Ontario. The lower member of the Gowganda Formation consists of interbedded diamictite, conglomerate, sandstone and argillite, and is interpreted to record sedimentation by mass flow processes on a steep and active subaqueous depositional slope. This presentation focuses on the upper member of the Gowganda Formation at Whitefish Falls which is characterized by thick successions of sandstone, laminated mudstone and interbedded sandstone and mudstone. Sandstone facies are dominated by ripple cross lamination and record deposition by unidirectional traction currents. Rare beds of SCS sandstone suggest deposition in relatively shallow water depths (probably less than 40m), along a coastline affected by substantial storm waves. Massive, horizontally laminated, graded and deformed sandstones record deposition by sand rich turbidity currents and mudstone facies are interpreted as fine grained turbidites. Interbedded sandstones and mudstones record intermittent influx of sandy turbidites into an environment dominated by mud deposition. The ubiquitous presence of soft sediment deformation features suggests rapid deposition of both coarse and fine grained sediment in an environment prone to seismic shock. Occasional outsize clasts in fine-grained facies indicate rafting of debris by ice bergs or seasonal ice flows and a cool to cold climate depositional setting. In sum, the upper Gowganda Formation at Whitefish Falls appears to record subaqueous deposition in a tectonically active setting characterized by steep depositional slopes and supplied with substantial amounts of sand and mud from fluvial or deltaic source areas. The overall succession of facies types recorded by the upper and lower Gowganda Formation at Whitefish Falls is consistent with conceptual models describing the tectono-sedimentary evolution of rift basin infills. The sandstone-rich upper Gowganda deposits reflect late stage or post-rift tectonic quiescence in the basin when relatively high rates of sediment supply allowed progradation of shallow marine depositional systems along the basin margin.