Date of Award


Document Type


Degree Name

Master of Science (MS)



First Advisor

A.M. Cvancara


The geology of the North Beulah, Center, and Glenharold lignite mines in Mercer and Oliver Counties, southwestern North Dakota, were examined. Stratigraphically, all mines lie within the Sentinel Butte Formatiom. The North Beulah Mine lies 70 m below the top of the Sentinel Butte Formation and the Center and Glenharold Mines lie about 80 m above the base of the Tongue River Formation.

Four sedimentary types are recognized arid common to all mines; these are: silt and clay, silty sand, sand, and lignite. The silt and clay were deposited in floodbasins and shallow lakes occupying the lowest parts of the floodbasins. Illite is the most abundant clay mineral · in clay samples from all the mines, followed by smectite and kaolinite. Clay samples from the North Beulah Mine contain a third more smectite than the clay samples from the other mines. Adsorbed calcium and manesium ions on the clay decrease with depth and sodium ions increase with depth in the North Beulah and Center Mines. The silty sand commonly occurs in beds less than 1. 5 m thick that have planar, horizontal strata and small-scale, curved cross-strata. These beds were probably deposited in crevasse-splays across the floodbaslns. The silty sand less commonly occurs in beds 2. 5 to 6. 5 m thick that have climbing ripple cross-strata. These beds were probably deposited in natural levees that developed near dis tributary streams. The sand occurs exclusively in discrete bodies having concave-upward erosional bases and horizontal tops. These bodies have large-scale, trough cross-strata, medium- to large-scale, low- to high-angle, straight cross-strata, and small-scale, curved cross-strata, and were formed by the deposition of lateral bars in low-sinuosity channels that crossed the floodbasins. The sand is subangular lithic arenite. · The lignite has a woody texture and contains large tree stumps and logs. Thin, discontinuous lignite beds less than 50 mm thick are commonly normally faulted with displacements up to 100 mm and thicker lignite beds are folded with amplitudes of up to 4 m. The lignite beds were formed by peat accumulation in forested alluvial backswamps,

The vertical and horizontal associations of low-sinuosity channel deposits, floodbasin deposits, natural-levee and crevasse-splay deposits are characteristic of the distributary-swamp facies of a highly constructive delta.

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