GEOLOGICAL DEVELOPMENT, ORIGIN, AND ENERGY MINERAL RESOURCES OF THE WILLISTON BASIN, NORTH DAKOTA by LEE C. GERHARD, SIDNEY B. ANDERSON, JULIE A. LEFEVER, and CLARENCE G. CARLSON MISCELLANEOUS SERIES 63 Reprinted from The American Association of Petroleum Geologists Bulletin No.8, v. 66 NORTH DAKOTA GEOLOGICAL SURVEY (AugllSt. 1982), p. 989-1020. 36 Figs., 1 Table. Don L. Halvorson, State Geologist The American Asso~iation of Petroleum Geologists Bulletin v. 66, No.8 (Auguu 1982), P. 989-1020, 36 Figs., I Table Geological Development, Origin, and Energy Mineral Resources of Williston Basin, North Dakota} LEE C. GERHARD,' SIDNEY B. ANDERSON,' JULIE A. LEFEVER,> and CLARENCE G. CARLSON' ABSTRACT part of the basin during Absaroka sequence deposition, a product oferosion ofAncestral Rocky Mountain orogenic The Williston basin of North Dakota, Montana, South structures. Continental and shallow marine clastic sedi­ Dakota, aud south-ceutral Canada (Manitoba and Sas­ ments were deposited during Zuni sedimentation until katchewan) is a major producer of oil and gas, lignite, Cretaceous deeper marine environments were estab­ and potash. Located on the western periphery of the lished. Laramide orogenesis to the west provided detritus Phauerozoic North American craton, the Williston basin that was deposited in Ouvial, deltaic, and marginal has undergone only relatively mild tectonic distortion marine environments, regressing to the east. Major lig­ during Phanerozoic time. This distortion is largely re­ nite deposits are part of this postorogenic regressive rock lated to movement of Preca mbrian basement blocks. body. Sedimentary rocks ofcratonic sequences Sauk through Major structures in the basin, and the basin itself, may Tejas are present in the basin. Sauk (Cambrian-Lower result from left-lateral shear along the Colorado­ Ordovician), Tippecanoe (Ordovician-Silurian), and Wyoming and Fromberg zones during pre-Phanerozoic Kaskaskia (Devonian-Mississippian) sequence rocks are time. Deeper drilling in the basin has revealed several largely carhonate, as are the major oil- and gas­ major structures and given indications of others. Most producing formations. Absaroka (Pennsylvanian­ structures probably resulted from renewed movement or Triassic) and Zuni (Jurassic-Tertiary) rocks have more "tensing" of pre-Phaneroroic faults. Meteorite impact clastic content, but carbonates are locally important. events have been suggested as the origin for one or more Clastics of the Zuni sequence (Fort Vnion Group) contain structures. abundant lignite. Tejas (Tertiary-Quaternary) sequence rocks are not significant in the production of minerals or INTRODUCTION energy, although glacial sediments cover much of the region. Recent successful oil exploration and development in the Oil exploration and development in the Vnited States Williston basin have clearly demonstrated the inadequacy of portion of the Williston basin since 1972 have given im­ previous tectonic and sedimentologic models of the basin to petus to restudy basin evolution and geologic controls for predict occurrences of mineral and fuel resources. The energy-resource locations. Consequently, oil production in North Dakota, for instance, has jumped from a nadir United States portion of the basin has sustained oil develop­ ofl9 million bbl in 1974 (compared to a previous zenith of ment during the last half of the 1970s that is remarkable in its 27 million in 1966) to 32 million hbl in 1979 and 40 million definition of previously unrecognized structures, discovery bbl in 1980. Geologic knowledge of carbonate reservoirs of new producing zones, and high success rates. The largest has expanded accordingly. single segment of the basin is the North Dakota portion (Fig. Depositional environments throughout Sauk, Tip­ I), which includes the deepest part of the basin and the pecanoe, and Kaskaskia deposition were largely shallow thickest Phanerozoic section. The wildcat success rate in marine. Subtidal and even basinal environments were North Dakota has steadily increased from 250/, in 1977; 28% developed in the basin center, but sabkha deposits were in 1978; 33% in 1979; to 36% through the first 6 months of abundant near the basin periphery. Evidence ofsubaerial 1980, whereas the recent national average was 15 to 18% for a weathering was commonly preserved in structurally high areas and on the basin periphery, especially in upper similar period (Johnston, 1980; Fig. 2). Although South Kaskaskia rocks. Some pinnacle reefs were developed in Dakota and Montana also sustain active programs, their Kaskaskia deposition. morphologically similar to the success rates are lower; Montana has the second most suc­ Silurian pinnacle reefs of the Michigan basin. cessful active drilling program in the basin. Clastic sediments were transported into the southern Oil and gas are not the only mineral and energy resources @1982. The Amencan ASSOCiation of Petroleum Geologists All nghts Ing our efforts. In particular. James H. Clement of Shell Oil Co.; Cooper reserved. Land, consultant; and Walter Moore of the University of North Dakota have 'Manuscnpt received, July 10, 1981, revised and accepted, Apn114, 1982. been Instrumental in construction of our ideas and approach. Other col­ 2North Dakota Geological Survey. Present address Union Texas Petro­ leagues and students who have contributed to this summary are Randolph leum Company, Denver, Colorado Burke. Diane Catt, Tom Heck, John Himebaugh. Peter Loeffler, Tom 3North Dakota Geological Survey, University Station, Grand Forks, North Obelenus, and Nancy Perrin. Support for some of the original studies of Dakota 58202. depositional systems and reservOIr geology came from the North Dakota 4North Dakota Geological Survey. Present address: OIl and Gas DiVISion, Geological Survey, the Carbonate Studies Laboratory of the University of North Dakota Industrial Commission, Bismarck. North DaKota. North Dakota, and from a grant by the U.S. Geological Survey (14-08· Many of our colleagues, students, and cooperating SCIentists have spent 0001-G-591). All of the support is gratefully acknowledged. extensive amounts of time discussing ideas. providing data. and redirect- 989 990 Williston Basin, North Dakota of the basin. Lignite reserves are huge and are actively being basin penetrated Precambrian rock at l5,340 ft (4,676 m); the explored and utilized. Rich potash resources are being mined deepest oil production is from 14,343 ft (4,372 m) in the in Saskatchewan and a mine has been announced for western Ordovician Red River Formation (Mesa 1-13 Brandvik, Dunn Manitoba. In North Dakota and Montana, potash resources County, Nonh Dakota). are potentially far more valuable than the lignite, but are not Rocks deposited during all periods of Phanerozoic time are yet being mined. Halite is being mined near Williston, North present in the basin (Fig. 3). Paleozoic rocks are mainly Dakota, from depths of 8,000 ft (2.438 m) making it proba­ carbonates, followed by the dominantly clastic Mesozoic and bly the world's deepest salt production. The halite deposits Cenozoic rock sequence. Sloss's (1963) sequence concept is are vast, being approximately 1,700 mi' (7,086 km'). particularly useful in the study of these rocks. serving to Coincident with energy development, interest in water "package" major transgressive cycles of continental scale resources (for energy transportation) and the overall regional with accompanying sediment deposition. For this reason, economic significance of the basin has led to an extensive discussions of stratigraphic units and their significance to study of basin geology, with numerous programs of investi­ deciphering the structural evolution of the Williston basin are gation under way. Programs of the Nonh Dakota Geological organized by sequences. Survey, the U.S. Geological Survey, Depanment of Energy, Few regional studies of Williston basin rocks have been and several oil companies deserve particular note; much of published. Several important contributions used extensively the information in this summary is derived from these in this paper are the papers of Poner and Fuller (1959), sources. Carlson and Anderson (1966), the various papers presented in The Williston basin is a slightly irregular, round depression the Geologic Atlas of the Rocky Mountains (Mallory, 1972 a, in the western distal Canadian shield. Structural trends within b), and Macauley et al (1964). Several unpuhlished works of the basin reflect major directional changes in the structure of oil company geologists are also used in this paper, especially the Rocky Mountain belt (Fig. 2). Several writers have those of lames Clement (personal commun., oral dis­ hypothesized a wrench-fault system for control of basin cussions, 1975-80). geometry and structure (Thomas, 1974: Brown, 1978), al­ Several cycles of interpretive writing are evident in the though those studies did not integrate sedimentary depo· literature about the Williston basin. Each proceeds from an sitional facies and porosity development infonnation. equivalent cycle ofmineral or fuel development activity. This Approximately 16,000 ft (4,875 m) of sedimentary rocks cycling of activities is common to most petroleum provinces. are present in the deepest part of the Williston basin, south­ The Williston basin is in its third cycle of oil development east of Watford City, Nonh Dakota. The deepest well in the now and is rapidly increasing oil production. Most of the United States pan of the Williston basin is contained in Nonh Dakota; its statistics