Lacustrine and Fluvial-Deltaic Depositional Systems, Fort Union Formation (Paleocene), Powder River Basin, Wyoming and Montana

Ayers, Jr. W. B.

doi:10.1306/94886c90-1704-11d7-8645000102c1865d

Cited by 18 publications

(3 citation statements)

References 24 publications

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“…The slake durability tests indicated stronger rock (93% durability index) from the Wasatch Formation compared to a durability index of 89% for rock from the Fort Union Formation. Such results align with the presence of substantial sandstone in the Wasatch Formation [26] compared to the higher content of shales and mudstones in the Fort Union Formation [44]. Correspondingly, the grain size distribution analysis indicated a greater fraction of claysized particles (7.6%) present in the Fort Union waste rock.…”

Section: Waste Rock Characterizationsupporting

confidence: 77%

“…Large concentrations of Al and silicon (Si) were present in the Wasatch and Fort Union waste rock, reflective of the dominant aluminosilicate minerals that compose these fluvial and lacustrine deposits [20,26] (Figure 4). Larger concentrations of redox-sensitive elements of Fe and Mn were present in the Fort Union waste rock, which are indicative of the lowenergy paleoenvironments associated with certain units of the Fort Union Formation [43,44]. The slake durability tests indicated stronger rock (93% durability index) from the Wasatch Formation compared to a durability index of 89% for rock from the Fort Union Formation.…”

Section: Waste Rock Characterizationmentioning

confidence: 95%

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Leachate Experiments to Evaluate Weathering of Waste Rock for Backfill Aquifers in Restored Coal Mine Pits, Powder River Basin, USA

Martin,

Langman

2023

Geosciences

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Restoration of open-pit mines may utilize waste rock for landscape reconstruction, which can include the construction of backfill aquifers. Weathering and contaminant transport may be different in backfill aquifers compared to the surrounding aquifer because of newly available mineral surfaces and transportable nano- to micro-scale particles generated during mining. Waste rock from the Cordero Rojo open-pit coal mine in the Powder River Basin was exposed to benchtop leachate experiments for 20 weeks at temperatures of 5 °C and 20 °C. Collected leachate was analyzed for Eh, pH, specific conductance, alkalinity, and cation and anion concentrations as unfiltered and 0.45-μm and 0.2-μm filtered concentrations. During the experiment, leachate Eh and pH substantially varied during the first 55 days, which corresponds to a period of high specific conductance (>1000 µS/cm) and alkalinity (>200 mg/L). Correspondingly, anion and cation concentrations were the largest during this early weathering stage, and the filter fractions indicated multiple forms of transported elements. After this early weathering stage, column leachate evolved towards a weathering equilibrium of neutral, oxidizing, and low solute conditions indicated by positive Eh values, pH near 7, and specific conductance <500 μS/cm. This evolution was reflected in the decline and stabilization or non-detection of metal(loid) concentrations reflective of a shift to primarily bulk aluminosilicate weathering when coal- and salt-associated elements, such as arsenic, cadmium, and selenium, were not detected or at minimal concentrations. Over the course of the experiment, the solute trend of certain elements indicated particular weathering processes—cadmium and nanoparticle transport, selenium and salt dissolution, and arsenic and pyrite oxidation. The mining of overburden formations and use of the waste rock for backfill aquifers as part of landscape reconstruction will create newly available mineral surfaces and nanoparticles that will weather to produce solute concentrations not typically found in groundwater associated with the original overburden.

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Section: Waste Rock Characterizationsupporting

confidence: 77%

Section: Waste Rock Characterizationmentioning

confidence: 95%

Leachate Experiments to Evaluate Weathering of Waste Rock for Backfill Aquifers in Restored Coal Mine Pits, Powder River Basin, USA

Martin,

Langman

2023

Geosciences

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“…Most of the previous work in the Powder River Basin has been focused in the northwestern, central, and southern parts of the basin (for example, Stone and Calvert, 1910;Rogers and Lee, 1923;Bryson and Bass, 1971;Ayers, 1986;Hanley and Flores, 1987;Warwick and Stanton, 1988;Rice and Flores, 1991;Nichols and others, 1992;Brown, 1993;Nichols, 1994;Rice and others, 2002;Nichols, 2003;Vuke and others, 2007). In the northeastern corner of the Powder River Basin near the Miles City Arch, the coal fields were intensely studied at the turn of the century for their mineral potential (Leonard, 1907;Collier and Smith, 1909;Bowen, 1910;Herald, 1910;Rogers, 1911;Calvert, 1912).…”

Section: Lithostratigraphymentioning

confidence: 99%

Magnetostratigraphy of the Lebo and Tongue River Members of the Fort Union Formation (Paleocene) in the northeastern Powder River Basin, Montana

Peppe¹,

Johnson²,

Evans³

2011

American Journal of Science

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We analyzed paleomagnetic samples and documented the stratigraphy from two sections near Miles City, Montana to determine the geomagnetic polarity stratigraphy and to constrain the age and duration of the Lebo and Tongue River Members of the Fort Union Formation in the northeastern Powder River Basin. The resulting polarity sequence can be correlated to subchrons C29n-C26r of the geomagnetic polarity time scale. By interpolating measured sediment accumulation rates from the base of C28r to the top of C27n, and then extrapolating to the top of the Tongue River Member and the bottom of the Lebo Member, we developed two age models to estimate the durations of the Lebo and Tongue River Members. Based on the first model, which uses different sedimentation rates for the Lebo and Tongue River Members, we estimate the duration of deposition of the Lebo to be between 1.30 and 1.74 million years and of the Tongue River to be between 1.42 and 1.61 million years. Using the second model, which uses the same sedimentation rate for the Lebo and Tongue River Members, we estimate the duration of deposition of the Lebo to be between 1.33 and 1.76 million years and of the Tongue River to be between 1.00 and 1.25 million years. Our results indicate a decrease in sediment accumulation rates in C27r, which is likely the result of a 0.26 to 0.62 million-year long depositional hiatus in the middle of C27r, represented by the Lebo-Tongue River contact. This unconformity occurs ϳ2 million years earlier than previously suggested and is likely contemporaneous with unconformities in the Williston Basin and in southwestern Alberta, suggesting that it may be regionally significant.

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Paleocene lakes of the central rocky mountains, Western United States

Yuretich

1989

Palaeogeography, Palaeoclimatology, Palaeoecology

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Lacustrine and Fluvial-Deltaic Depositional Systems, Fort Union Formation (Paleocene), Powder River Basin, Wyoming and Montana

Cited by 18 publications

References 24 publications

Leachate Experiments to Evaluate Weathering of Waste Rock for Backfill Aquifers in Restored Coal Mine Pits, Powder River Basin, USA

Leachate Experiments to Evaluate Weathering of Waste Rock for Backfill Aquifers in Restored Coal Mine Pits, Powder River Basin, USA

Magnetostratigraphy of the Lebo and Tongue River Members of the Fort Union Formation (Paleocene) in the northeastern Powder River Basin, Montana

Paleocene lakes of the central rocky mountains, Western United States

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