Quaternary geology of the Northern Great Plains

• Main Authors: Wayne, William J., Aber, James S., Agard, Sherry S., Bergantino, Robert N., Bluemle, John P., Coates, Donald A., Cooley, Maurice E., Madole, Richard F., Martin, James E., Mears, Brainerd, Jr, Morrison, Roger B., Sutherland, Wayne M.
• Format: Text
• Language: unknown
• Published: DigitalCommons@University of Nebraska - Lincoln 1991
• Subjects: Earth Sciences; Arctic; Hudson Bay; Pacific; Hudson; Alden; Black Hills
• Online Access: https://digitalcommons.unl.edu/geosciencefacpub/563; https://digitalcommons.unl.edu/context/geosciencefacpub/article/1572/viewcontent/Wayne_1991QdNorthern_Gt_Plains.pdf

The Great Plains physiographic province lies east of the Rocky Mountains and extends from southern Alberta and Saskatchewan nearly to the United States-Mexico border. This chapter covers only the northern part of the unglaciated portion of this huge region, from Oklahoma almost to the United StatesCanada border, a portion that herein will be referred to simply as the Northern Great Plains (Fig. 1). This region is in the rain shadow of the Rocky Mountains. Isoheyets are roughly longitudinal, and mean annual precipitation decreases from about 750 mm at the southeastern margin to less than 380 mm in the western and northern parts (Fig. 2). Winters typically are cold with relatively little precipitation, mostly as snow; summers are hot with increased precipitation, chiefly associated with movement of Pacific and Arctic air masses into warm, humid air masses from the Gulf of Mexico. Vegetation is almost wholly prairie grassland, due to the semiarid, markedly seasonal climate. The Northern Great Plains is a large region of generally low relief sloping eastward from the Rocky Mountains toward the Missouri and Mississippi Rivers. Its basic bedrock structure is a broad syncline, punctuated by the Black Hills and a few smaller uplifts, and by structural basins such as the Williston, Powder River, and Denver-Julesburg Basins (Fig. 3). Its "surface" bedrock is chiefly Cretaceous and Tertiary sediments, with small areas of older rocks in the Black Hills, central Montana, and eastern parts of Wyoming, Kansas, and Oklahoma. During the Laramide orogeny (latest Cretaceous through Eocene), while the Rocky Mountains and Black Hills were rising, synorogenic sediments (frequently with large amounts of volcanic ash from volcanic centers in the Rocky Mountains) were deposited in the subsiding Denver-Julesburg, Powder River, and other basins. From Oligocene to Miocene time, sedimentation generally slowed with declining tectonism and volcanism in the Rocky Mountains. However, since the later Miocene, epeirogenic uplift, probably ...