Geology and coal resources of the Minot region, North Dakota

Abstract

The Minot region includes about 2,800 square miles in north-central' North Dakota, extending from the Souris River on the north to the Missouri River on the south and from the western border of Ward County on the west to Anamoosej. Sheridan County, on the east. The divide between the Souris and Missouri Rivers, which is also the dividebetween drainage to Hudson Bay and the Gulf of Mexico, follows a belt of hummocky topography which is about 20 miles wide and trends northwestward acrossthe central part of the Minot region. The surface of the region southwest of the divide is a plateau trenched to a depth of 200 feet or more by the valleys of the Missouri River and its tributaries. The northeastern part of the region fs a plain* sloping gently to the northeast and bordered on the north by the valleys, 100 to 200 feet deep, of the Souris River and the Riviere des Lacs. About 250 feet of soft buff to gray sandstones and shales of the lower part of theFort Union formation, of Eocene (Tertiary) age, are exposed along the Missouri River and probably 150 feet or more of these sedimentary rocks are exposed at places in the higher parts of the area. -The Fort Union is also exposed in placesalong the Souris River, the Riviere des Lacs, and some of their deeper tributaries. Pleistocene glacial deposits, 1 to 200 feet thick, form a widespread surface cover in the high central part of the region and consist of sand, gravel, boulders, and clay. Similar deposits of the same age with a somewhat smaller thickness, 10 to 50 feet, cover most of the northern part of the region. The hummocky divide in the centralpart of the region is formed by the Altamont moraine, of late Wisconsin (Pleistocene) age. The interstream divides of the country southwest of the Altamont moraine are covered with a thin veneer of drift of earlier than late Wisconsin age and late Wisconsin outwash. The present course of the Missouri River in this portion of the Minot region was established! and incised in the Missouri Plateau in Pleistocene time. The sloping plain on the northeast side of the Altamont moraine marks the site of the southwest margin of the glacial Lake Souris. The history of this lake as recorded in the northeast corner of the Minot region is revealed by beaches at levels of 2,100 down to 1,600 feet above sea level, by deltas, and by intricate abandoned channels that drained the lake. During the higher stages of Lake Souris the beaches followed the front of the Altamont moraine and probably extended from the vicinity of Dogden Butte northwestward beyond the northern border of North Dakota, but at the low stages the lake was confined to the lower levels of Souris Valley and extended northward: from the vicinity of Drake and Minot to the junction of the Souris and AssiniboineRivers, in Manitoba. 43 44 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1938-39 Coal of lignite rank is found at several horizons in the Fort Union formation. Although several of these coal beds were found and measured, only six are of sufficient thickness and persistence to trace consistently along the outcrop and to . trace by means of records of the deep wells that have been drilled in the region. These six coal beds average more than 4 feet in thickness; the Coteau bed, in the northeastern part of the region, is 13 feet thick for considerable distances; the Burlington bed, in the northwestern part of the region, and the Garrison Creek bed, in the southwestern part, attain thicknesses of 10 feet in some places. Several localities are indicated where stripping of the Coteau bed, the Garrison Creek bed, and the Minter bed (in the southwestern part of the region) may be commercially feasible. The estimated reserves of coal in the Minot region are 18,094,592,000 tons. A test well drilled for oil near Des Lacs and another well just outside the southeast corner of the region were reported to have obtained showings of oil and gas but failed to obtain commercial production. The rocks in the region are practically flat-lying, and no indication of structural features favorable for oil accumulation was found. INTRODUCTION The Minot coal region includes most of Ward and McLean Counties and parts of Mercer, Sheridan, and McHenry Counties, in northcentral North Dakota. It includes an area of approximately 2,800 square miles extending from the Riviere des Lacs and the Souris River on the north to the Missouri River on the south and from the vicinity of Berthold and Makoti, near the west border, to the vicinity of Drake and Anamoose, on the east border. The location of the Minot region is shown on figure 11. Coal fields whose locations are shown on figure 11