Sedimentation on an early Proterozoic continental margin under glacial influence: the Gowganda Formation (Huronian), Elliot Lake area, Ontario, Canada

Abstract

ABSTRACTEight continuous cores up to 150 m long and spaced an average of 200 m apart yield a detailed local insight into the composition and architecture of an ancient continental margin sequence, the Gowganda Formation (early Proterozoic: Huronian) near Elliot Lake, Ontario. Nearby outcrops of similar facies provide important supplementary data on sedimentary structures.Continental glaciers provided an abundant supply of coarse debris but, apart from rafting of debris by floating ice, played little or no part in Gowganda sedimentation. The basal 50 m of the Gowganda Formation in the drill‐hole area represents a continental slope depositional system. It consists mainly of gravelly and sandy sediment gravity flow deposits, interbedded with minor rain‐out units of diamictite, and argillite containing dropstones. Ten types of sediment gravity flow deposit are distinguished. An overlying submarine‐channel depositional system, 10–50m thick, consists of hemipelagic argillites containing dropstones and showing deformation structures. These are interbedded with well‐sorted channel‐fill sandstones. Submarine point bars 4·5 m thick (identified in nearby outcrops) demonstrate a meandering channel geometry. This channel‐fill sequence probably formed during a period of high sea‐level and reduced sediment supply, but the relationship to ice advance‐retreat cycles is unclear. The subsurface sequence is completed by a blanket of massive rain‐out diamictites up to 55 m thick, and a younger slope sequence of sediment gravity flow diamictites and sandstones.The stratigraphy is quite different in outcrop section 10 km to the west of the drill‐holes, suggesting the presence of major lateral facies changes and/or internal erosion surfaces within the Gowganda Formation. This complexity of stratigraphy and depositional processes is probably a feature of many ancient glacial units, and points to the advisability of not making climatic or tectonic interpretations from a few generalized or composite sections.