Stratigraphy, sedimentology and tectonic setting of the upper Shaler Group, Victoria Island, Northwest Territories.

摘要

The stratigraphy and sedimentology of the uppermost late Proterozoic Shaler Group (Kilian and Kuujjua formations) in the Minto Inlier, Victoria Island, was investigated in order to better understand conditions of deposition and to place these strata in a regional tectonic context so that they might be compared with models developed for similar strata in adjacent and formerly adjacent areas.;Detailed stratigraphic section measurement, regional correlation and lithofacies analysis reveals that much of the upper Shaler Group was deposited on a tectonically stable, low gradient, shallow marine platform, perhaps within a passive margin or intracratonic seaway (Amundsen-Mackenzie Basin or Embayment). Subtidal to supratidal alternations (cycles) within the Kilian Formation can be correlated for at least 200 km and are attributed to two scales of glacio- and/or tectono-eustatic sea-level fluctuations. Marine deposition and cyclicity was abruptly terminated by deposition of the overlying Kuujjua Formation, a mature quartzarenite interpreted as a low sinuosity fluvial braidplain deposit, which flowed into the Amundsen Basin from the southeast. Intercalated evaporite deposits in both the Kilian and Kuujjua Formations are indicative of a prevailing arid climate.;Unimodal northwesterly paleocurrents, detrital quartz petrography, detrital zircon geochronology and mudstone geochemistry indicate that the river(s) which deposited the Kuujjua Formation may have incorporated detritus from as far away as the Grenville Province, presently 3000 km to the southeast. It also suggests that the extremely high compositional maturity of the quartzarenite may in part be due to extreme humid climate-related weathering in the source area.;Differential tectonic uplift which increased in intensity from southwest to northeast, resulting in a decrease in the rate of basin subsidence and eventual net uplift is recorded by: (1) The abrupt marine to terrestrial transition at the Kilian-Kuujjua contact, (2) pinch out of the uppermost Kilian and Kuujjua formations to the northeast, (3) block faulting and erosional preclusion of some of the uppermost Kilian Formation in the northeast part of the Minto Inlier. Uplift is considered to be a consequence of thermal upwelling which accompanied the arrival of a mantle plume at the base of the lithosphere, prior to the eruption of flood basalts of the Natkusiak Formation, uppermost stratigraphic unit of the Shaler Group.