Silurian System

Type area and use of name in the Illinois Basin: The Bailey Limestone was named for exposures of argillaceous limestones and shales along the Mississippi River between Bailey's Landing and Red Rock Landing in Perry County, Mo. (E. O. Ulrich as published by Buckley and Buehler, 1904, p. 110). The Bailey was then considered to be Early Devonian in age. After Collinson and others (1967, p. 940) delineated the general distribution of the Bailey in the Illinois Basin, its occurrence in the southwestern Indiana subsurface, in an area of about eight-county size, was detailed by Becker (1974, p. 27 and various illustrations). Although Silurian conodonts had been discovered in a part of the Bailey in Illinois (Collinson and others, 1967, p. 940), Becker (1974) treated the formation as mostly Devonian in age and included as its top part a few tens of feet of white medium- to coarse-grained pure bioclastic limestone as had been the practice in Illinois.

This upper limestone has been found to have Devonian conodonts and also to coextend with the Backbone Limestone (Lower Devonian). It was removed, as a classificatory matter, from the Bailey by Becker and Droste (1978, p. 3-4). This reassignment left the Bailey of Indiana wholly within the Silurian System. This classification was also adopted by Droste and Shaver (1980 and in preparation).

Description: The Bailey consists of drab, neutrally colored limestones and some dark- gray limestone. They are mostly very fine grained, somewhat cherry, and slightly dolomitic. The bottom part of the Bailey is lithologically transitional to the Moccasin Springs below, but the conformable contact is placed at the top of the blackish dense dolomitic shale and dark greenish-gray limestone of the Moccasin Springs. The top of the Bailey is placed at the base of the whitish granular bioclastic Backbone Limestone as noted above. This contact appears to be conformable in deeper basin areas but may be unconformable in the more distal basin area. Middle Devonian rocks unconformably overlie the Bailey in a small part of its area of occurrence.

The Bailey has a reef-and-bank facies consisting of light-colored granular, rather pure carbonate rocks that are distributed in so-called pinnacle reefs, in coalesced reef masses, and as reef detritus that helps to make up the feature called the Terre Haute Bank. (See Droste and Shaver, 1980, fig. 7.) Insofar as known, the Bailey reef rocks are upward continuations of reefs that began to grow in the St. Clair Limestone and the Moccasin Springs Formation.

The Bailey has a more or less vertical cutoff boundary with upper Wabash rocks along the basin margin of the Terre Haute Bank. Its non reef thickness is as much as 375 feet (114 in) but reaches zero in its northern occurrence in Indiana, where the Bailey is erosionally truncated below Middle Devonian rocks. (See the cross sections in Becker and Droste, 1978, and Droste and Shaver, in preparation.)

Correlation: Like an the formations in the Bainbridge Group, some diachroneity along contacts may apply to the basin-to-shelf relationships among these rocks as well as to the equivalent section eastward ranging upward from the Salamonie Dolomite and culminating in the Wabash Formation. (See the suggestion of this circumstance in Droste and Shaver, 1980, fig. 4.) These general statements on correlation may be made, however: The Bailey of Indiana has coextension with the Bailey in the Illinois Basin parts of Illinois and Kentucky. In Illinois the highest Bailey rocks as generally defined there are Devonian in age and therefore are younger than the Bailey of Indiana. (See Shaver and others, 1985, for depiction.) In Kentucky am equivalent of the lower Bailey of Indiana is called the Decatur Limestone. Northeastward in Indiana and northward and some westward in Illinois, upper Wabash rocks (Kokomo, Kenneth, and Liston Creek members) and upper Racine rocks respectively are correlative of the Bailey of Indiana.

Fossil data for the subsurface Bailey are sparse, but Silurian conodonts (Collinson and others, 1967) and Silurian ostracods (Schwalb, 1975; Droste and Becker, 1978, p. 4) have been found in Illinois and Kentucky. These fossils and the principles of sequence stratigraphy suggest that the Bailey ranges from about late Ludlovian through Pridolian in age (Cayugan in the American standards).