| Summary: | Physical Characteristics and Resources Geology Many people do not realize the extent to which their activities depend upon their geological and geographical environment. Better than half of the state's fertile soil resulted from continental glaciation; North Dakota's oil and gas resources are the result of geological processes that formed the Williston Basin, millions of years ago; our groundwater is contained in geologic formations; the great coal resources of the western half of the state are the result of geological processes. The list could go on and on. Briefly, rocks of four great eras of geological time occur in North Dakota, although not all are exposed at the surface. Cryptozoic (Archean) rocks are deeply buried and provide the "basement" upon which all other rocks were deposited. Marine sandstones, shales, and limestones of the Paleozoic era were deposited upon these crystalline rocks. Nearly all of North Dakota's oil and gas is produced from rocks of Paleozoic age. Rocks of Mesozoic age contain the dinosaur fossils found in western North Dakota. Cenozoic rocks contain our vast lignite reserves, as well as the glacial deposits that cover much of the surface of the state. After the deposition of the Paleozoic rocks, a great erosion interval intervened and most of the Paleozoic rocks were worn away, particularly in the eastern part of the state. Upon this eroded landscape were later deposited rocks of the Mesozoic era. Some of these rocks, like the famous artesian water-bearing Dakota sandstone, were deposited on land or under terrestrial conditions, whereas others were deposited in a vast seaway, which extended from the Arctic to the Gulf, Dinosaurs lived in North Dakota during this time; their fossils are being excavated today in some parts of the state. Following the deposition of the Mesozoic rocks, continental conditions prevailed throughout North Dakota. During the Cenozoic era, conditions were apparently more moist than they are now and great swamps and forests of conifers and other trees covered much of the state. Great thicknesses of partially decayed vegetable matter that accumulated in these swamps has been changed into widespread lignite coal beds through a combination of the weight of the overlying rocks and the addition of heat. Long after the deposition of the coal, many of these beds were exposed at the surface through the stripping action of erosion by running water. Through spontaneous combustion, or by ignition by lightning or prairie fires, some of these beds started to bum, producing ash and clinker beds found today throughout western North Dakota, The clinker formed due to baking and fusing together of the overlying shale and sand due to the heat of the burning lignite. The process is still going on today. 490 Chapter 10 Physical Characteristics
|
|---|