Late Devonian and Early Mississippian Bakken shales are important source rocks to the oil accumulations in southeastern Saskatchewan. However, to date there is lack of knowledge concerning the mineralogy and lithology of the Bakken shales, which may impact the source effectiveness and heterogeneity of the Upper and Lower Bakken shales. This research investigates the mineralogy and lithology of the Bakken shales in southeastern Saskatchewan based on results from detailed core and rock thin-section examination, scanning electron microscope-back-scattered electron imagery and energy-dispersive spectrometry analysis (SEM-BSEI/EDS), and X-ray diffraction analysis (XRD) of sixty-eight selected samples from seven wells. Based on the mineralogy and texture of the Bakken shales, the Upper and Lower Bakken Formation members have been subdivided into six distinct lithologies. Laminated carbonaceous shales (Lithologies 4, 5, and 6) are preserved in anoxic environments of quiet, stratified water below the wave base – Lithofacies association A, and the degree of textural lamination lessens towards storm wave base; non-laminated shales (Lithologies 2 and 3) formed under a still water environment of moderate depth, transiting anaerobic to dysaerobic conditions – Lithofacies association B; highly bioturbated Lithology 1 with the presence of Chondrites isp. and Thalassinoides isp. deposited in a moderately agitated to quiet, shallow marine environment at the lower shoreface to offshore environment – Lithofacies association C. In addition to high content of organic matter, the mineral assemblages identified in the Bakken shales include: a) a detrital assemblage mainly comprising quartz, feldspar, mica and heavy minerals; b) detrital clay minerals with minor authigenic clays; c) a mixture of detrital and authigenic carbonate minerals (primarily dolomite and calcite); and d) other minerals of minor abundance (pyrite, sphalerite, anhydrite, and apatite). This study has determined that the basin centre generally has less abundant quartz and feldspar with a higher clay mineral content than the eastern margins of the basin. In addition, there is an inverse correlation between the abundance of quartz and feldspar and the clay mineral content. The content of quartz and feldspar in the Lower Member is slightly more abundant than those from the Upper Member. Correspondingly, the Lower Bakken contains a lower total organic carbon (TOC) content than the Upper Bakken in the study area. These stratigraphic and regional differences in the distribution and abundance of quartz and feldspar, clay minerals, carbonate minerals, TOC, and their correlations suggest the processes affecting deposition in the Bakken Shale could be: (1) A clastic influence from nearby landmasses. The detrital quartz and feldspar were probably deposited in near shore, high energy environments closer to the source area. (2) The rate of siliciclastic sedimentation affected the preservation of organic matter. (3) The concentration of organic matter demonstrated similar hydrodynamic properties to clay minerals, which are likely to accumulate in the deeper water, lower energy environments far away from the basin margins. Key words: Bakken shale, source rock, lithology, mineralogy, depositional environment, southeastern Saskatchewan, Williston Basin, Mississippian-Devonian.