Sedimentology, ichnology, and stratigraphy of the Sparky, Waseca, and McLaren Alloformations, West-Central Saskatchewan, Canada

The Lower Cretaceous Sparky, Waseca, and McLaren alloformations (Upper Mannville Group) of west-central Saskatchewan comprise an interval up to 60 m thick, consisting of weakly consolidated sandstones, shales, heterolithic bedsets and minor coals deposited in shallow-marine to coastal plain/delta plain environments. Thirteen facies are recognized. These facies are grouped into six spatially recurring facies associations. Facies Association 1 (FA1) corresponds to sediments deposited below fairweather wave base but above storm wave base. Facies associations 2 and 3 (FA2 and FA3) coarsen upward and represent the progradation of wave- and storm-dominated shorefaces as well as mixed river- and wave-influenced deltas, respectively. Facies Association 4 (FA4) commonly displays fining-upward successions, interpreted as distributary channel or fluvio-estuarine deposits, depending upon their stratigraphic context. Facies Association 5 (FA5) is broadly similar to FA2, but is ichnologically distinct. The succession is characterized by low-diversity, impoverished trace-fossil suites with variable bioturbation intensities that are interpreted to record deposition in shallow brackish-water bays. Facies Association 6 (FA6) successions are interpreted as coastal plain/delta plain deposits. Upper Mannville strata can be separated into parts of two depositional sequences. The main deposits of the lower sequence comprise two highstand systems tracts (HST), corresponding to the Sparky Alloformation and the Lower Waseca Allomember. The base of the Lower Waseca marks the onset of a transgressive systems tract (TST). A maximum flooding surface (MFS) marks the end of transgression and the resumption of progradation for the remainder of the Lower Waseca. Following highstand progradation a relative base-level fall produced a subaerial unconformity, which marks the base of the upper sequence. Fluvial valley incision led to sediment bypass, and deposition of forced regressive and lowstand shoreface and delta complexes of the falling stage systems tract (FSST) and lowstand systems tract (LST) towards the northern part of the study area. TST accumulation is largely confined to estuarine infill of the incised valleys of the Upper Waseca Allomember. The Upper Waseca is separated from the McLaren Alloformation by a maximum flooding surface (MFS). The overlying McLaren Alloformation marks a return to regional shoreline progradation, and corresponds to a highstand systems tract (HST).