Sedimentary facies in the Archean Timiskaming Group and their tectonic implications, abitibi greenstone belt, Northeastern Ontario, Canada

Abstract

Listen

Translate article

The Archean Timiskaming Group occupies two east-west trending belts in the southeastern part of the Abitibi greenstone belt in northeastern Ontario, and unconformably overlies a thick sequence of submarine mafic-to-felsic volcanic rocks. Within the Timiskaming Group four sedimentary facies are included in a Non-marine Association, which is dominated by pebble-cobble conglomerate and sandstone of braided river origin. Smaller amounts of floodplain, lacustrine, and eolian deposits are also present. A Resedimented Association consists of four other facies, and includes graded and ungraded conglomerates, sandy turbidites, sandy and silty, laminated turbidites, and oxide iron-formation. These facies represent deposition within submarine fans. Paleocurrent patterns in the Timiskaming Group were established using sedimentary structures, and orientations of gravel-sized clasts and sand grains. These data suggest multiple paleoslopes. Lateral and vertical facies changes between the Non-Marine Association and Resedimented Association are abrupt, and there are no indications of intervening shallow, marine deposition. Various lines of evidence suggest that for the Timiskaming Group fluvial rock bodies represent remnants of volcanic islands, which were separated by deep-water marine basins receiving turbidites and resedimented conglomerates. The vertical sequence defined by submarine volcanic rocks, overlain by Non-marine Association rocks and subaerial volcanic rocks, and capped by components of the Resedimented Association is termed an up-down sequence. Rapid subsidence within the up-down sequence is interpreted to result from foundering of volcanic islands. Depositional environments in the Timiskaming Group and in other Archean greenstone belts in Canada contrast with sedimentary environments from Archean greenstone belts in South Africa, where paralic deposition appears to be widespread. This suggests small, unstable continental fragments in the Canadian Shield during the Archean, and larger, more stable continents in the South African Shield for this time period.