Charles Formation Research Articles

Mississippian Sedimentation and Oil Fields in Southeastern Saskatchewan

Marked facies changes occur in the Mission Canyon and lower part of the Charles formation (Mississippian) in southeastern Saskatchewan. Northeastward from the basinal area, four successive environments of deposition with characteristic rock types and fossils may be mapped as follows. 1. Basin: dark brown-gray argillaceous limestone containing scattered white crinoid columnals, black bituminous shale partings, and brownish gray chert. 2. Open marine shelf: cream-white fossiliferous-fragmental and chalky limestones containing crinoids, bryozoans, brachiopods, and zaphrentid corals. 3. Barrier bank: cream-white precipitated limestones including pisolitic, oolitic, pseudo-oolitic, and lithographic types. Fossils include abundant algae and few scattered gastropods. 4. Lagoon: cream-white chalky argillaceous limestone containing ostracods, earthy to sucrosic secondary dolomite and anhydrite. Evaporitic (primary?) dolomites occur in the upper Charles as a result of basin-wide evaporitic conditions. These typically dense (cryptocrystalline) and non-porous dolomites are closely associated with anhydrite. Factors which control porosity in the limestones include sorting of fossil debris or precipitated calcareous grains, submarine erosion and re-deposition of partially lithified calcareous muds, solution, dolomitization (?), fractures, compaction, and infilling of pores by calcite, anhydrite, or chert. Stratigraphic trap oil accumulations occur where permeable units of the Mission Canyon and Charles are truncated and overlain by pre-middle Jurassic redbeds. Factors affecting oil accumulation include the presence of the following. a. Permeable reservoir beds at or near the unconformity. b. Anhydrite filling pores where the permeable reservoir beds are truncated by the pre-Jurassic erosion. c. Anhydrite beds conformably overlying and underlying the permeable units and thus form a roof and floor for the reservoir beds. d. Topography of the Mississippian erosion surface. Mississippian strata in the oil-producing area of southeastern Saskatchewan are characterized by the following. 1. Relatively steep dips (40-60 feet per mile) as compared with dips of 10-20 feet per mile in much of southwestern Saskatchewan. 2. Relatively rapid truncation (15-40 feet per mile) as compared with an average of approximately 5 feet per mile in southwestern Saskatchewan. 3. Relatively saline waters (50,000-150,000 parts per million of chloride ion content) as compared with 100-8,000 parts per million in southwestern Saskatchewan. In exploration for new trends or extensions of known producing areas, important consideration should be given to the distribution of permeable rock facies within individual stratigraphic units. In addition, it is possible to predict the location of topographically high trends as the various lithologic types are differentially resistant to erosion. For example, the precipitated barrier bank limestones End_Page 94------------------------------ are relatively resistant to weathering and form topographic ridges in the Nottingham field. The lower limit of oil accumulation within reservoir beds may be determined by the location of a spill point, in turn controlled by the downdip limit of lagoonal anhydrite floors.

Stratigraphy of Madison Group of Montana and Wyoming: ABSTRACT

Lithologic sequences characterized by distinct evaporite cycles are recognized in the Madison group of Montana and Wyoming. Throughout the basinal area of Montana and North Dakota, the End_Page 421------------------------------ cycles are represented by vertical variations from oolitic-fragmental and normal marine limestone (or dolomitized equivalents) to evaporitic rocks including anhydrite, locally halite, and associated cryptocrystalline or dense carbonates. Within the Wyoming shelf, the cycles exhibit only partial development in which the evaporitic interval is thinly represented by primary cryptocrystalline or dense dolomite. Dolomitized limestones (fine to coarse crystalline dolomites) generally form the marine intervals in the shelf areas. By recognition of these lithologic cycles, the Lodgepole, Mission Canyon, and Charles formations may be correlated to their respective eroded edges in Wyoming, South Dakota, and north-central Montana. Mississippian sedimentation commenced earliest in the Williston basin and central Montana trough with the deposition of black shales (Bakken formation) followed by dense limestones and shales (lower Lodgepole). Preceding and accompanying the initial marine transgression on the Wyoming shelf, minor terrestrial to near-shore marine clastic deposition took place in the Black Hills area (Englewood formation). Widespread marine deposition formed normal marine and fragmental-oolitic limestones which were subject to dolomitization in the shelf areas (upper Lodgepole, lower Pahasapa, and Guernsey formations). Marine limestone and dolomite sedimentation, interrupted by two episodes of evaporite precipitation, resulted in the development of the Mission Canyon formation and the superjacent evaporites of the basal Charles, and their equivalents in the Pahasapa formation of the Black Hills area. Restoration of normal marine conditions and development of a complex evaporite cycle followed (Charles formation, excluding basal evaporites and uppermost few beds of the Pahasapa). Big Snowy clastics were deposited in Chester time in the basinal areas of Montana. In areas to the south, pre-Amsden, pre-Minnelusa, or pre-Pennsylvanian weathering and erosion affected the Mississippian beds. In north-central Montana, pre-Middle Jurassic erosion strongly truncated the upper Madison strata. Oil occurrence in the Madison group is related to the two main provinces of deposition. In general, the oil from the basinal or limestone province is of relatively high gravity, whereas that from the dolomite or shelf province is of much lower gravity. End_of_Article - Last_Page 422------------

Mississippian Madison Group Stratigraphy and Sedimentation in Wyoming and Southern Montana

Madison group sediments accumulated in two depositional realms: a basinal, predominantly limestone province in Montana and adjoining Dakotas; and the Wyoming shelf, characterized by prominent dolomitization on the south. The belt of transition in southern Montana and adjoining limestone and shale deposition took place in the Idaho geosynclinal trend. Southeastward to the Cambridge arch, Madison group sediments were affected by increasing amounts of pre-Pennsylvanian erosion in Wyoming and western South Dakota. Mississippian sediments are absent from a part of southeastern Wyoming. Early, medial, and late stages of sedimentation may be differentiated on the basis of lithologic cycles or sequences developed in the Madison group. Early sedimentation was characterized by deposition of the approximate Lodgepole formation and equivalents, Guernsey, Englewood, and lower Pahasapa formations. Deposition commenced earliest in the Williston basin and central Montana trough with the development of black shales, followed by dense limestone and shales; minor terrestrial to near-shore marine clastic sedimentation in the Black Hills area commenced somewhat later, preceding and accompanying the initial marine transgression on the Wyoming shelf. Widespread deposition of normal marine and fragmental oolitic limestones (mainly dolomitized equivalents in the shelf areas) occurred. hoaling was prominent, and as a result local minor restricted deposition took place. Marine limestone and dolomite sedimentation, modified by two episodes of evaporite precipitation, occurred during medial Madison group time. Mission Canyon carbonates containing an intermediate evaporite zone and overlain by the prominent basal Charles evaporites constitute the resulting middle unit. Evaporitic deposition was characterized by the precipitation of anhydrite and halite in the basinal areas at the north. Southward, progressively less restriction is demonstrated by the disappearance of halite, thinning of anhydrite, and the development of primary dense carbonate zones. Late sedimentation was characterized by restoration of normal marine conditions and development of a complex evaporite cycle (Charles formation, excluding basal evaporites). Big Snowy clastics were deposited in Chester time in the northern basinal areas. In other areas, pre-Amsden or pre-Pennsylvanian to pre-Middle Jurassic erosion had varying effects on the Madison group surface. Limestone reservoirs in the basinal areas of Montana and North Dakota, and dolomites in northwestern Wyoming yield group oil. Optimum facies changes and post-depositional tectonic effects make the madison group an excellent prospective unit in many areas. End_Page 2170------------------------------

Case History of East Poplar Field, Roosevelt County, Montana: ABSTRACT

The discovery well for the East Poplar field was completed in March, 1952. On December 1, 1954, there were 53 producing oil wells in the field which had proved approximately 15,000 acres to be productive. The field is located on a large, northwest-southeast anticline. Oil is obtained from limestone beds in the Charles formation of Mississippian age. The accumulation is partly controlled by porosity variations. During the first 11 months of 1954, more than one out of every 5 barrels of oil produced in Montana came from the East Poplar field. End_of_Article - Last_Page 531------------

Ellis, Amsden, and Big Snowy Group, Judith Basin, Montana

Strata lying between the top of the middle Mississippian Madison limestone and the base of the Upper Jurassic Morrison formation in an area in central Montana are described and correlated. Sixteen columnar outcrop sections and six well sections are presented on three plates to show the lateral extent, thickness, and lithologic character of the Jurassic Ellis formation, the lower Pennsylvanian Amsden formation, the upper to middle Mississippian Big Snowy group. The Big Snowy group, which is divided into the Heath, Otter, Kibbey and Charles formations in descending order, contains marine, fluvial and estuarine facies. It lies disconformably on the Madison in the southern part of the area. The upper marine limestone strata of the Amsden overlaps successively lower Amsden redbeds and the upper part of the Big Snowy group. The Ellis is a transgressive marine deposit. While it rests on a Jurassic evaporite series in the eastern part of the area, the Ellis also overlies the Amsden, each member of the Big Snowy group, and the Madison at other localities. The regional diastrophic history as revealed by this stratigraphic study includes the following: post-Madison-pre-Big Snowy uplift, post-Big Snowy-pre-Amsden folding, middle Amsden movement, post-Amsden-pre-Gypsum Springs (lower Ellis) uplift, middle Upper Jurassic movement, Laramide folding, Tertiary uplift.

Cambrian formations and sections in part of Cordilleran trough

Field and laboratory studies have shown that the older type Cambrian sections in Nevada, Utah, and Wyoming are not usable for correlation, and that published faunal lists are incomplete and partly erroneous. In 1936 and 1937, fossils were accurately zoned in seven remeasured sections: Pentagon, Prairie Reef, and Scapegoat, Montana; Wind River Canyon, Wyoming; Blacksmith Fork and House Range, Utah; and Highland Range, Nevada. The terms DuNoir and Gallatin are not applicable to the Wind River Canyon section which is now divided into the Depass (Albertan) and Boysen (Croixan) formations. The St. Charles (Croixan) formation in the original Blacksmith Fork section is redefined, as the upper 827 feet contain Ordovician fossils. The name Tatow limestone is applied to the youngest Waucobian rocks in the House Range. The upper 370 feet of the original Pioche shale in the Highland Range contains Albertan species and is named the Comet shale, the name Pioche being retained for the 600 feet of Waucobian rocks underlying the Comet and resting upon the Prospect Mountain formation. Few Middle Cambrian formations south of Montana can be correlated on evidence from fossils, other than the basal Ute with the Chisholm and Gordon, the upper Howell with the Damnation, and, doubtfully, the Wheeler and Marjum with the Pentagon. The Kochaspis upis fauna in the Steamboat limestone of Montana seems to be younger than the Marjumia-Neolenus fauna in the upper part of the Marjum limestone in the House Range.