INTO THE ANCIENT DEEPS: A SEDIMENTOLOGICAL INVESTIGATION OF LAMINATED ARGILLITES AT WHITEFISH FALLS, ONTARIO

The 2.4Ga Gowganda Formation of the Huronian Supergroup in Northern Ontario records shallow to deep water marine sedimentation on a tectonically active extensional basin margin. In the area of Whitefish Falls, Ontario, a thick (approximately 200m) succession of laminated argillites separates two boulder rich diamictite units of the Lower Gowganda Formation which are interpreted to have a glaciogenic origin. Sedimentological examination of the laminated argillite succession identifies several facies types which include finely laminated (<2cm), normally graded silt and claystones, most of which incorporate interbedded rippled sandstone lenses and thin beds to loaded sandstone units up to 50cm in thickness. Normally graded successions of thinly (<2cm) laminated mudstones and siltstones can be correlated throughout the study area. These fine grained facies are interpreted as turbidites that record slow rates of deposition under relatively deep water conditions during periods of tectonic quiescence in the basin. Irregularly spaced beds of rippled sandstone interrupt the laminations and record either sporadic tectonic activity or major storm events. A non-glacial setting is indicated by the general absence of clasts within the argillite succession, with the exception of rare clasts found immediately above the lower diamictite. Localized areas of soft sediment deformation within the argillites provide evidence of slumping and deposition in a slope proximal setting. The laminated argillites of the Gowganda Formation at Whitefish Falls provide an important record of relatively deep water turbidite deposition in a sediment starved rift basin. Reconstruction of the paleoenvironmental conditions in which these argillites formed helps constrain regional paleoclimate along the southern margin of Arctica during the Paleoproterozoic.