Denver Basin

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The Denver Basin, sometimes also called the Denver-Julesburg Basin (after Julesburg, Colorado), or the D-J Basin, is a geologic structural basin centered in eastern Colorado in the United States, but extending into southeast Wyoming, western Nebraska, and western Kansas. It underlies the Denver-Aurora Metropolitan Area on the eastern side of the Rocky Mountains.

The basin consists of a large syncline of stratified Paleozoic and Mesozoic sedimentary rock layers, running north to south along the east side of the Front Range from the vicinity of Pueblo northward to Wyoming. The sag is deepest near Denver, where it reaches a depth of approximately 13,000 (3900 m) ft below the surface. The basin is strongly asymmetric: the Dakota Sandstone outcrops in a "hog-back" ridge near Morrison a few miles west of Denver, reaches its maximum depth beneath Denver, then ascends very gradually to its eastern outcrop in central Kansas.

According to current geologic theory, the basin starting forming as early as 300 million years ago, during the Colorado Orogeny that created the Ancestral Rockies. Rocks formed during this time include the Fountain Formation, which is most prominently visible at Red Rocks and the Boulder Flatirons. Tha basin was most likely further deepened in Tertiary time, between 65 and 45 million years ago, during the Laramide orogeny that created the modern Colorado Rockies. In particular, the uplifting of the Rockies in the Front Range caused the crust near Denver to buckle downward on the eastern side, deepening the basin. The basin later became filled with erosional sediment from the Rockies. The Front Range peaks rise approximately 22,000 ft (6600 m) from the floor of the basin under Denver.

The deep part of the basin near Denver became filled with Tertiary sandstone and conglomerate, a layer now called the Denver Formation. In the regions to the north and south of Denver, however, increased stream erosion wore away the uppermost layers of sandstone, revealing the parts of the underlying Cretaceous Pierre Shale to form wide valleys along the South Platte and Arkansas rivers known as the Colorado Piedmont.

Contents 1 Natural resources 1.1 Petroleum 1.2 Groundwater 1.3 Cement 1.4 Coal 1.5 Construction aggregate 1.6 Gold 1.7 Dimension stone 1.8 Uranium 2 References

[edit] Natural resources

[edit] Petroleum

The basin itself forms a petroleum province. Oil and gas has been produced from the Denver Basin since the discovery of the Boulder oil field in Boulder County, in 1901.

The great majority of Denver Basin oil and gas fields produce from Cretaceous sandstones, although the Permian Lyons Sandstone is also a producer. Oil has also been produced from Pennsylvanian limestones in the Nebraska part of the basin.

The Wattenberg Field, one of the largest natural gas deposits in the United States, is a basin-centered gas field just north of the Denver metropolitan area. The field has produced more than 4.0 trillion cubic feet (TCF) of natural gas from the J Sandstone, Codell Sandstone, Niobrara Formation, Hygiene Sandstone, and Terry Sandstone (all Cretaceous).[1][2].

Biogenic natural gas is recovered from shallow gas fields (less than 3,000 feet) of the Fort Hays Limestone member of the Niobrara Formation in Yuma, Phillips, and Washington counties of northeastern Colorado and Cheyenne and Sherman counties of northwestern Kansas.[3] To date, 2,900 wells have produced 470 billion cubic feet (13,000,000,000 m³) of gas. Drilling is currently very active, and the play is expanding into Perkins, Chase, and Dundy counties, Nebraska.^[1]

• Kansas Geological Survey: Geological Overview of the Niobrara Chalk Natural Gas Play
• 2002 USGS Assessment of Oil and Gas Resource Potential of the Denver Basin Petroleum Province of Colorado, Kansas, Nebraska, South Dakota, and Wyoming

[edit] Groundwater

The upper formations of the Denver Basin are aquifers that serve as important sources of water supply in the region.[4][5][6] Increasing rates of water withdrawal have raised concerns about sustainability of yields from Denver Basin aquifers.[7]

Colorado Geological Survey: Sedimentary Rock Aquifers: Denver Basin

[edit] Cement

Raw materials are mined from the Niobrara Formation and Pierre Shale and made into cement at the Cemex plant near Lyons, Colorado.

[edit] Coal

Bituminous coal has been mined by underground methods in the Denver Basin, at Superior and Louisville, Colorado and other locations along the western edge of the basin.^[2] The coal comes from the Cretaceous Laramie Formation.^[3] Mining began in the late 1850s and stopped in 1979.

Large lignite deposits are present in the Paleocene Denver Formation in the central part of the basin, in a north-south belt east of Denver and Colorado Springs, in Adams, Arapahoe, Elbert, and El Paso counties.[8] Some mining was done from about 1886 to 1940, but was reportedly minor.[9]

[edit] Construction aggregate

Sand and gravel for construction are a major mineral resource in the Denver Basin.

[edit] Gold

Small amounts of gold have been mined from sands and gravels in the Denver area since the Pikes Peak Gold Rush of 1858. Some sand and gravel pits still recover gold in their washing operations. See main article Gold mining in Colorado.

[edit] Dimension stone

The Lyons Formation provides flagstone from quarries in Boulder and Larimer counties, along the western edge of the basin.

[edit] Uranium

A small amount of uranium ore has been mined from the Dakota Sandstone at Morrison, Colorado, where the sandstone is impregnated with petroleum.^[4] Uranium is known to exist in roll-front type deposits in the Denver Basin, but the basin has never been a major source of uranium.^[5]

See main article Uranium mining in Colorado

[edit] References

1. ^ Peggy Williams, Shallow DJ gas, Oil and Gas Investor, Mar. 2007, p.51-54.
2. ^ Paul E. Soister (1978) Geologic setting of coal in the Denver Basin, in Energy Resources of the Denver Basin, Denver: Rocky Mountain Association of Geologists, p.153-159.
3. ^ D. Keith Murray (1980) Coal in Colorado, in Colorado Geology, Denver: Rocky Mountain Association of Geologists, p.210-211.
4. ^ Robert J. Wright and Donald L. Everhart (1960) Uranium, in Mineral Resources of Colorado First Sequel, Denver: Colorado Mineral Resources Board, p.363.
5. ^ Louis J. O'Connor and Bruce D. Smith (1978) Magnetic and electrical study of a roll-front uranium deposit in the Denver Basin, Colorado, in Energy Resources of the Denver Basin, Denver: Rocky Mountain Association of Geologists, p.153-159.

• Roadside Geology of Colorado, Halka Chronic, Mountain Press Publishing Company, Missoula, Montana (1980).