Bakken formation

Pg. 72-74, figs. 4, 5. Bakken formation. Name applied to basal Mississippian clastic zone (northern Montana, southern Saskatchewan, Manitoba, and northwestern North Dakota). Previously considered basal clastic unit of Lodgepole limestone. Described in type well as (descending): shale, black, very slightly calcareous, 20 feet; sandstone, light-gray to gray-brown, very fine-grained, calcareous, interbedded with minor amounts of gray-brown, cryptocrystalline limestone, 60 feet; shale, black, fissile, very slightly calcareous, 25 feet. Total thickness 105 feet. Correlated with Sappington sandstone of western Montana, and with Exshaw shale and Banff sandstone in the subsurface of southern Canada. Probably older than Englewood formation of the Black Hills, South Dakota, and Wyoming. Excluded from Madison group. Overlies Three Forks formation; underlies Lodgepole formation. Age is Early Mississippian (Kinderhook). Type section (subsurface): depth-interval 9,615 to 9,720 ft, Amerada Petroleum Corp. H.O. Bakken No. 1 well, in SW/4 NW/4 sec. 12, T. 157 N., R. 95 W., Willliams Co., ND. Source: US geologic names lexicon (USGS Bull. 1200, p. 197-198); GNU records (USGS DDS-6; Denver GNULEX). Uses term Englewood formation, instead of Bakken formation, for strata in the Amerada Petroleum Corp., H.O. Bakken No. 1 well, Williams County, North Dakota, in the Williston basin, and elsewhere for the correlative unit in the subsurface of North Dakota. Saskatchewan Geological Society, 1956, Report of the Mississippian Names and Correlations Committee, J.W. Porter (chairman): Saskatchewan Geological Society Field Trip Guidebook Bakken formation of Madison group. Recognized in northeastern Montana, western North Dakota, and adjacent parts of Saskatchewan and Manitoba, Canada. Overlain by Souris Valley Beds of Madison group and underlain by Devonian Qu'appelle group of Baillie (1953). Age is Mississippian. Considered to be Devonian(?) and Early Mississippian age in the subsurface of the central part of the Williston basin and in north-central Montana [on the Central Montana uplift and Sweetgrass arch?]. In earlier reports, assigned to the Devonian(?) and Mississippian. Consists of two radioactive black shales separated by light-gray sandstone, siltstone, or dolomite. Disconformably overlies Three Forks formation. Unconformably underlies Lodgepole limestone. Not deposited on southern and eastern margins of Williston basin. Ballard, F.V., 1963, Structural and stratigraphic relationships in the Paleozoic rocks of eastern North Dakota: North Dakota Geological Survey Bulletin, no. 40. Overlain conformably in eastern North Dakota by the Bottineau interval (new) of Madison Group. Kume, Jack, 1963, The Bakken and Englewood Formations of North Dakota and northwestern South Dakota: North Dakota Geological Survey Bulletin, no. 39. Redescribed well cuttings from type well in Williams County, North Dakota, in Williston basin. Revised the thickness of the middle sandstone unit (to 45 feet) and the lower shale unit (to 40 feet). Isopach maps show thickness and extent of the upper and lower shale units, and the medial sandstone unit in western North Dakota, Williston basin. Lithologic descriptions given for several wells in North Dakota, including the type and reference wells. Lower shale unit considered to be equivalent or nearly equivalent to lower shale unit of Englewood Formation in the Black Hills, South Dakota. Overlain by Lodgepole Formation of Madison Group; underlain by Three Forks Formation. Age is Early Mississippian. Designated reference section as the cored interval from depths of 10,035 to 10,095 ft in the Socony Vacuum Oil Co., C. Dvorak No. 1 Well, in SE/4 NE/4 sec. 6, T. 141 N., R. 94 W., Dunn Co., [ND], in the Williston basin. [Misprint (GNU records, USGS DDS-6; Denver GNULEX): Reference section is in North Dakota, not South Dakota.] Sandberg, C.A., and Klapper, Gilbert, 1967, Stratigraphy, age, and paleotectonic significance of the Cottonw