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Morton County Geology

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Water-bearing Formations, continued

Triassic (?) System

Undifferentiated Redbeds

Character--The Triassic(?) redbeds are made up of red siltstone; buff, red, and white sandstone; and a small amount of gypsum. The siltstone is thinly and unevenly bedded, is maroon when freshly exposed, but weathers to a pink or light red, is generally hard, and breaks into irregular chips and nodules. The sandstone is massive and fine-grained, and ranges from white to gray, tan, brown, and red. Test hole 8 (fig. 2) at Point Rock near Cimarron River in sec. 12, T. 34 S., R. 43 W., was drilled 200 feet into the redbeds. The rocks encountered included about 150 feet of maroon siltstone and about 50 feet of buff and red sandstone. Test hole 4, at the south-east corner of sec. 36, T. 31 S., R. 42 W., was drilled 41 feet into Triassic(?) redbeds, of which about 35 feet was red siltstone and 6 feet was buff, brown, and gray siltstone and sandstone. Test hole 6, in sec. 8, T. 33 S., R. 42 W., was drilled through 55 feet of fine reddish-brown sandstone, 49 feet of tan to buff sandstone containing a small amount of gypsum, and 25 feet of maroon-red sandstone, all of which is believed to be Triassic(?) in age. Test hole 7, in sec. 31, T. 33 S., R. 43 W., on the Kansas-Colorado line, penetrated 35 feet of Triassic(?) material of which 9 feet was maroon-red sandstone and 26 feet was fine-grained buff sandstone.

The Triassic (?) redbeds crop out at two places along the Cimarron valley; at Point Rock, on the north side of the river in sec. 12, T. 34 S., R. 43 W., and on the south side of the river in sec. 5, T. 34 S., R. 42 W. A section at Point Rock (pl. 5B) was measured by Perry McNally as follows:

Section of Triassic (?) rocks at Point Rock, sec. 12, T. 34 S., R. 43 W. Feet
7. Sandstone, massive, soft, buff to brown; weathers yellow and yellow-brown8
6. Siltstone, massive, soft, maroon red; weathers pink3
5. Sandstone, massive, hard, gray to brown; weathers yellow brown7
4. Sandstone, fine grained, soft, buff10
3. Sandstone, fine grained, soft, gray; weathers yellow brown2
2. Sandstone, massive, fine grained, orange yellow3
1. Sandstone, fine grained, massive, white9
Base not exposed 

Distribution and thickness--The contact between the Triassic(?) redbeds and Permian redbeds is not definitely established, owing to the lithologic similarity of the rocks of the two systems and to the lack of exposures; therefore the total thickness of the Triassic(?) redbeds is not known. A test hole in southern Hamilton county penetrated 320 feet of redbeds that was probably Triassic (?). A test hole in Cimarron County, Oklahoma, encountered 260 feet of Triassic, and Sanders (1934, pp. 860-870) reports as much as 575 feet of Triassic beds in that area. Along Cimarron River in north-eastern New Mexico the Triassic is more than 600 feet thick (Parker, 1933, pp. 38-51).

Logs of test wells in Morton County indicate that the Triassic (?) underlies only the western half of the county (pl. 6). In Texas county, Oklahoma, however, the formation probably extends farther eastward.

Age and correlation--The redbeds at Point Rock are lithologically very similar to those in the Red Point district in Texas county, Oklahoma, which Schoff (1939, pp. 49-51) and others have called Triassic (?). In 1900 Gould (1900, p. 139) wrote:

it has been demonstrated that the upper part of the problematic Kansas-Oklahoma redbeds is Triassic. Vertebrates taken from the lower part of these beds, in eastern Oklahoma, have been identified by Dr. S. W. Williston as Permian forms similar to those from the Texas Permian. On the other hand, invertebrates obtained from near the top of the redbeds in western Oklahoma are classed as Triassic forms, on the authority of Dr. J. W. Beede and Mr. Charles Schuchert.

The beds at Point Rock and Red Point generally are correlated with the Dockum group of Texas, New Mexico, and Colorado, rocks which are Triassic, probably Upper Triassic. The beds are lithologically similar to the Tecovas formation, the lower part of the Dockum group of the Texas panhandle. The buff and red sandstones encountered in test hole 7 (fig. 2) are similar to the sandstone that caps Two Buttes, in southeastern Colorado about 45 miles northwest of Morton County. Sanders (1934, pp. 860-870) describes the sandstone, locally called "Big sandstone," that caps Two Buttes as a massive cross-bedded medium-grained friable sandstone about 240 feet thick. Generally it is gray to buff, but locally it is reddish. He correlates this sandstone with the Dockum group for the following reasons: (1) It overlies redbeds of probable Permian age. (2) It is correlated by well logs with the Dockum group of Cimarron County, Oklahoma. (3) The Morrison formation rests on progressively older beds toward the east. (4) If the "Big sandstone" is Jurassic, then there is no Triassic. This would raise the question, What happens to the 575 feet of Triassic of Cimarron County, Oklahoma?

Water supply--The Triassic (?) redbeds yield moderate quantities of water to wells in Morton County, including wells 86, 110, 118, and 119. Water from wells in the upper part of the Triassic (?) redbeds is moderately hard as shown by analysis 119 in table 6. Artesian water from well 86 in the lower part of the Triassic (?) was reported to be "strongly alkaline" and artesian water from well 140, which was initially drilled to the Triassic (?) redbeds, was reported to be strongly mineralized. Artesian water has been found in these beds along the Cimarron River valley at depths of 200 to 215 feet and north of the river in R. 43 W. at depths of 250 to 300 feet. Because of the poor quality, however, the water from the lower part of the Triassic (?) redbeds is no longer used.

Jurassic (?) System

Morrison (?) Formation

Test hole 4, at the southeast corner of sec. 36, T. 31 S., R. 42 W., penetrated 28 feet of blue-green clay and marl and 12 feet of blue-green, light-gray, and brown sandstone. These beds occur between the Cheyenne sandstone and the Triassic (?) redbeds and are believed to be a part of the Morrison formation. The color and lithology of these beds are very similar to those of the Morrison formation of southeastern Colorado. The Morrison formation crops out in Cimarron county, Oklahoma; Union county, New Mexico; and at Two Buttes, Baca County, Colorado. At Two Buttes the Morrison consists of 160 feet of green and purple shale, and white sandstone. These beds probably thin eastward and pinch out a few miles east of the Kansas-Colorado line. The beds classed as Morrison (?) probably yield little or no water to wells in Morton County.

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Kansas Geological Survey, Morton County Geohydrology
Comments to
Web version Sept. 2004. Original publication date March 1942.