Depositional environment of the Gowganda Formation (Precambrian) at the south end of Lake Tamigami, Ontario

Abstract

ABSTRACT The Gowganda Formation is world-famous as evidence for Precambrian glaciation. As many features of tillites are similar to those of turbidites, the time seemed ripe for a re-examination of the evidence for its origin. The formation was studied in detail as it is exposed across the southern half of Lake Timagami, Ontario. Two main rock-types, conglomeratic graywacke and argillite-quartzite, alternate three times throughout the 10,000 ft of Gowganda exposed in the area. Conglomerate characterized by granite clasts occurs sporadically along the basal contact. Present attitudes of the formation in the area are initial. The mountainous pre-Gowganda topography was not controlled by basement structure. Most of the evidence points to a glacial origin. A pre-Gowganda glaciated surface of considerable extent is reported. The basal conglomerate is fluvial--possibly outwash. The conglomeratic graywacke is tillite deposited by glacial ice advancing from the northeast quadrant. The argillite-quartzite is an interglacial, flysch-like facies probably deposited in a cool, shallow-water environment with considerable ice-rafting. The periglacial lake or sea was characterized by frequent small-scale turbidity currents triggered by slumping of the unconsolidated sediment on the mountainous pre-Gowganda topography. Paleocurrent features in the argillite-quartzite correspond to the pre-Gowganda topography.