Deadwood Formation (Cambrian-Ordovician)

Regional Geological setting and Previous Studies

The Deadwood Formation represents the deepest stratigraphic interval within the North Dakota portion of the Williston Basin, reaching depths of approximately 16,000 feet True Vertical Depth (ftTVD) in Western North Dakota with maximum formation thickness of 900 ft in Billings County (Anderson, 1988). It was deposited during the Late Cambrian to Early Ordovician (LeFever et al., 1987). The Deadwood Formation is mainly comprised of mixed siliciclastic-carbonate sequences in North Dakota (LeFever et al., 1987) and has been extensively studied and described by Carlson (1960), Lochman-Balk and Wilson (1967), Anderson (1988), and Sarnoski (2015). The Deadwood Formation unconformably overlies the Precambrian basement and is unconformably overlain by the Black Island Formation (Fig. 1).

Fig. 1. Stratigraphic Column of the Deadwood Formation
 

During deposition of the Deadwood Formation deposition in Late Cambrian, the North Dakota’s portion of the Williston Basin (Fig. 2) experienced cratonic subsidence accompanied by a gradual eustatic transgression, punctuated by episodes of minor regression that progressively overstep and onlap the cratonic platform (LeFever et al., 1987; Burgess, 2019). The depositional systems of the Deadwood Formation during this time included, but were not limited to, beach, foreshore to shoreface, tidal flats and channels, and shallow marine transition zones (Anderson, 1988). The deposition of the Deadwood Formation concluded in Early Ordovician time due to relative sea-level fall which may have been caused by change in stress fields (Leighton and Kolata, 1990).
 

Fig. 2. Paleogeographic map during Late Cambrian (Left) and Early Ordovician (Right) of the Williston Basin (Blakey, 2013). Red outline showing present-day North Dakota border.
 

As observed in Fig. 3, Subsurface observations suggest that the Deadwood Formation initially subsided in an elongated pattern during its early deposition but gradually transitioned into a more circular geometry in its later stages (LeFever, 1987).
 

Fig. 3. Regional depth map of Deadwood Formation. Obtained from 297 wells with Deadwood Formation marker.
 

Early work by Carlson (1960) divided the formation based on recognizable presence of 3 (three) lithologic units, a basal sandstone, intermediate carbonate and shale unit, and upper sandstone. As additional well data became available, Anderson (1988) was able to use Gamma Ray (GR) logs to informally divide the formation into six distinct lithostratigraphic units, designated as Member A through Member F. This distinction is based on “traceable” gamma-ray log characteristics, that, in the Deadwood Formation, represent variations in radioactivity attributable primarily to clay content and glauconite content (Fig. 4).
 

Fig. 4. Typical well log response and type log of the Deadwood Formation. Example from well NDGS #6228 Zabolotny No. 1-3-4-A (LeFever et al., 1987)
 

Deadwood Formation Depositional System

Anderson (1988) described the range of depositional systems within the Deadwood Formation in Fig. 5 as follows:

Fig. 5. Schematic depositional model of the Deadwood Formation (Anderson, 1988)
 

During Late Cambrian, from Member A – B, the Deadwood Formation is interpreted to have formed in a range of shallow marine to marginal marine settings, including beach and barrier island, braided fluvial, foreshore to shoreface, and tidal flat to tidal channel environments (Stanley, 1984; Mescher and Pol, 1985; Driese et al., 1981; Hiscott et al., 1984). Member B, characterized by abundant glauconite, has been interpreted as representing deposition in low-energy subtidal lagoons and tidal sand flats, based on analogous glauconitic sandstones and conglomerates from the Black Hills (Stanley, 1984; Lochman-Balk, 1970). The absence of desiccation features in the subsurface supports a dominantly subtidal lagoonal setting for Member B (Sepkoski, 1982).

By the Early Ordovician, from Member C – F, the region’s latitude had shifted, placing it in a tropical climate characterized by high rainfall and low evaporation (Ross, 1976). The siliciclastic and carbonate successions form asymmetrical vertical sequences that reflect the progradation of a siliciclastic shoreline and back-barrier environment over a shallow shelf and distal carbonate shoal.
 

Deadwood Formation and its relation to subsurface energy resource and storage

Deadwood Formation has remained relatively underexplored due to its low contribution to hydrocarbon production in North Dakota. Of the nearly 50,000 wells drilled in the state, only 297 vertical wells penetrated the Deadwood Formation, and 15 wells (Fig. 6) have produced from the Deadwood Formation/Winnipeg Group, yielding a cumulative production of approximately 500,000 barrels of oil—which accounts for less than 0.01% of North Dakota’s total oil production (Nesheim, 2019).
 

Fig. 6. Cumulative oil production from Deadwood Formation in North Dakota
 

Recently, however, interest in the Deadwood Formation has grown due to its potential for geothermal energy, the presence of helium resources, and feasible CO₂ storage in saline aquifers (Fig. 7).
 

Fig. 7. Distribution of non-hydrocarbon energy resources and subsurface storage projects across North Dakota. Red dots show wells with helium analysis, dark purple boundary shows DEEP Geothermal Project in North Dakota – Saskatchewan border, and dark blue boundary display CO₂ storage projects across Central North Dakota.
 

Helium

In Saskatchewan, the helium potential of the Deadwood Formation was first identified in 1952, with commercial production beginning in 1963. Production has continued intermittently, with the most recent helium wells commencing operation in 2021 (Yurkowski, 2021).

A study by Nesheim and Kruger (2019) demonstrates that helium is present within major productive oil and gas reservoirs of the North Dakota portion of the Williston Basin. The data, originally compiled from the United States Bureau of Land Management (USBLM, 2019) gas database, include 65 total gas samples analyzed for measurable helium concentrations (>0.01%). Of these, 54 samples contained helium concentrations ranging from 0.01% to 0.09%, while the remaining eight samples exhibited concentrations between 0.10% and 0.46% (Fig. 6). The highest helium concentrations were identified within the Cambrian–Ordovician interval, particularly along structural trends such as the Nesson and Antelope anticlines, as well as the Newporte structures.
 

Geothermal

In addition to helium exploration, geothermal development has also been pursued in the Deadwood Formation in the Williston Basin, particularly in Saskatchewan, Canada. As Fig. 7 shows, Deep Earth Energy Production (DEEP) Corporation has drilled five geothermal wells to a depth of 11,500 feet, encountering formation temperatures of 250°F (Murphy, 2021).
 

Carbon, Capture, and Storage (CCS)

The Deadwood Formation has been utilized for CO₂ sequestration in Saskatchewan, serving as a reservoir for the CO₂ injected from SaskPower’s Boundary Dam Carbon Capture Facility (Nesheim, 2019). As of early 2023, the project successfully stored over 500,000 tonnes of CO₂. Deadwood Formation has also been targeted as CO₂ storage target in Carbon, Capture, and Storage (CCS) projects in North Dakota with a few projects as follows; PCOR Partnership (2003), Northwest McGregor Field Validation Test (2010), CarbonSAFE Phase II: North Dakota Integrated Carbon Storage Complex Feasibility Study (2017 – 2020), Roughrider Carbon Storage Hub (2023 – 2025), Project Tundra (2023), CarbonSAFE III (2020 – 2024), Coal Creek Carbon Capture (2023 – 2027). Announced October 21, 2024, the DOE awarded Project Tundra for advancement in CarbonSAFE IV: Site Construction.

Although most ongoing exploration and production activities for helium and geothermal resources within the Williston Basin are currently concentrated in Saskatchewan, the shared basin geometry between North Dakota and Saskatchewan suggests potential resource continuity beyond the country border. Thus, geological studies and exploratory efforts are actively underway in North Dakota to assess the extent of these resource plays and evaluate the feasibility of subsurface CO₂ storage. These investigations aim to determine whether the success observed in Saskatchewan can be replicated in North Dakota.

Last Updated: 04/29/2025.