Sedimentary Facies, Depositional Environment and Sequence Stratigraphy of the Upper Devonian-Lower Carboniferous Bakken Formation in the Southeastern Corner of Saskatchewan

Liya Zhang
Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
[email protected]

The Upper Devonian-Lower Carboniferous Bakken Formation is one of the most important oil-producing units in Saskatchewan.In the southeastern corner of Saskatchewan, the Bakken Formation unconformably overlies either the Big Valley Formationorthe Torquay Formation, andis conformably overlain bytheSouris Valley Formation,typically consisting of themiddle sandy to siltymemberand the upper black shale member.According to detailed coreanalysis, the Bakken Formation is divided into eight facies: facies1 (black shale); facies2 (greyish green, highly bioturbated siltstone); facies 3(interbedded dark grey, highly bioturbatedsandy siltstone and light grey, micro-hummocky cross-stratified/parallel-laminated very fine-grainedlowersandstone); facies 4 (interbedded light grey, very fine-grained lower sandstone and siltstone); facies5 (dark yellowish green,sandy siltstone); facies6 (interlaminated light grey, very fine-grainedlower sandstone and dark grey,muddy siltstone); facies7 (light grey, green and beige, wavy-beddedvery fine-grainedsandstone); and facies8 (light grey,high-angle planar cross-stratifiedvery fine-grainedto fine-grained sandstone). Thisstudy suggests that the deposition of Bakken occurred in two different paleoenvironmental settings: open marine (facies 1 to 5) and brackish-water marginal-marine (facies 6to 8). The base of the marginal-marine interval is represented bya sequence boundary (coplanar surface or amalgamated sequence boundary and transgressive surface). This sequence boundary is of regional importance because it allows correlation with the Bakken succession in south-central Saskatchewan. This study supports recent paleoenvironmental re-interpretation of the Bakken Formation in nearby areas, indicating that this unit, particularly the marginal-marine interval, represents a complex facies mosaic.

AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects