Detailed stratigraphy of the Paleoproterozoic Athabasca Group along the Shea Creek-Douglas River trend and its relationship to the regional stratigraphy of the western Athabasca Basin, Canada

Preliminary analysis of logged sedimentary characteristics from core near Shea Creek, in the western Saskatchewan part of the Athabasca Basin, allowed construction of an initial lithostratigraphic model that bore little resemblance to expected models. Subsequent detailed analysis of sedimentary structures and facies assemblages in these cores led to revisions of this model and establishment of lithostratigraphic subdivisions that can be used independently of existing regional nomenclature. A distinctive basal package of sandstone referred to as the Shea Creek Sequence was delimited from the overlying Manitou Falls Formation, which was previously believed to be the basal Formation in the study area. Following a purely lithostratigraphic subdivision, further regional cores were logged and a sequence stratigraphic approach was applied in order to test sub-basinal correlations. Seven formation-scale third-order sequences were recognized across the western Athabasca Basin. These comprised stacks of 4th order parasequences that stacked to produce characteristics stratigraphic responses to changes in rates of accommodation called systems tracts. Three systems tracts were recognized. The lower low accommodation systems tract represents progradation of parasequences at the onset of basin-development while accommodation rates were low. This is represented by an upward coarsening trend in section. The high accommodation systems tract represents a retrogradation of parasequences as the rates of accommodation increased. This is represented by an upward-fining trend in section. Late low accommodation systems tracts are rare deposited or preserved. These represent a late stage normal regression as accommodation rates became outpaced by sediment supply. Provenance studies may be a valuable tool for correlation, as red cathodoluminescent quartz grains, of possible syn-volcanic origin, are only recognized in the upper units at Shea Creek. The presence of a major 2 nd order sequence boundary in the lower Athabasca Group in Alberta supports the development of at least two sub-basins within the western Athabasca Basin.