Elwood Atherton, Charles Collinson, and Jerry A. Lineback
The Cypress Sandstone (Engelmann, 1863, p. 189-190) is named for Cypress Creek, Union County.
The type section of the Cypress Sandstone is in bluffs along the creek about 6 miles southeast of Anna (T12 and 13S-1E).
The name Ruma, now abandoned, was given to equivalent strata in Randolph County (S. Weller, 1913).
Extent and Thickness
The Cypress and the Tar Springs Sandstone are the thickest and most persistent sandstone formations of the Chesterian Series. In the central part of southern Illinois, the Cypress is generally well over 100 feet thick, and it reaches 200 feet thick (fig. M-37). It thins outward from that area, and it is only 20-30 feet thick near the outcrops in southern Randolph County.
The Cypress Sandstone varies from thick bodies of sandstone to shale and sandy shale interbedded with some thin beds of sandstone. The massive sandstone in the Cypress is white to light gray, fine to medium grained, angular, and generally friable. It makes up about half of the formation and typically is in a single body at the base of the formation. Some wells encounter two sandstone bodies, usually in the lower part of the formation, and others, mostly in the north and southwest but sporadically elsewhere, encounter only shale. Typically the upper part of the Cypress is more shaly than the lower, and commonly 5-30 feet of shale or sandy shale occurs at the top. Locally a few thin beds of sandstone lie immediately below the overlying Beech Creek Limestone. Sandstone beds near the top are generally cemented with calcite or dolomite. The shale in the Cypress is largely dark greenish gray, but some of the top beds are green, and a moderately persistent bed of red shale occurs about 10 feet below the top of the formation. In Randolph County in western Illinois, where the Cypress is almost entirely shale, the formation includes a considerable proportion of red and green shale. Beds of gray or green siltstone are present in the upper part of the Cypress, and a thin, dark green, quartzitic siltstone occurs near the top. Coal beds a few inches thick are sporadically present near the top of the Cypress, especially near its southern limit. The base of the Cypress and, to a lesser extent, surfaces in the middle part of the formation tend to parallel underlying structure more closely than they do the overlying Beech Creek Limestone, which suggests slight warping during Cypress time.
Plant fossils, including Lepidodendron trunks, are present in the Cypress.
ENGELMANN, HENRY, 1863, On the Lower Carboniferous System as developed in southern Illinois: St. Louis Academy of Science Transactions, v. 2, part 1, p. 188-190.
WELLER, STUART, 1913, Stratigraphy of the Chester Group in southwestern Illinois: Illinois Academy of Science Transactions, v. 6, p. 118-129.
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