M. E. Hopkins and J. A. Simon
The Abbott Formation of the McCormick Group (Kosanke et al., 1960, p. 30, 44) is named for Abbott Station on the Illinois Central Gulf Railroad, Pope County.
The type section is exposed along the Illinois Central Gulf Railroad (5, 6, 7, 18, 19, 11S-5E).
Two marine limestones in southwestern Indiana (the Fulda and Ferdinand Members) and the Lead Creek Limestone Member in western Kentucky occur in strata equivalent to the lower part of the Abbott Formation in Illinois, as the associated coal floras show. The Abbott Formation is equivalent to the uppermost part of the Caseyville Formation and the lower part of the Tradewater Formation in western Kentucky and to the upper part of the Mansfield and essentially all of the Brazil Formation in Indiana.
Extent and Thickness
The Abbott Formation has a maximum thickness of 300-350 feet in southern Illinois, but in western Illinois even where it is well developed it is generally less than 100 feet thick.
The Abbott Formation overlies the Caseyville and extends from the top of the Pounds Sandstone Member to the top of the Bernadotte Sandstone Member of western Illinois, which has been correlated with the Murray Bluff Sandstone Member of southern Illinois (fig. P-2). In subsurface, both the top and base of the Abbott are commonly difficult to determine. Only the sandstones and some of the coals have been named. In southern Illinois the Abbott overlaps the Caseyville Formation northward and is the basal formation of the Pennsylvanian System throughout most of the state outside the area of Caseyville strata. The Abbott is overlain by the Spoon Formation, which overlaps it in northern and northeastern Illinois and on some prominent anticlinal structures.
The Abbott Formation is similar to the Caseyville Formation in being composed primarily of detrital rocks, but it differs from the Caseyville in containing thicker, more widespread coals and in the character of the sandstones. The sandstones in the Abbott are generally finer grained, thinner in maximum development, contain more interstitial clay and mica flakes, and have no more than a few quartz granules and pebbles. These characteristics are transitional; the lower sandstones in the Abbott more closely resemble those in the Caseyville and the upper are similar to the impurer sandstones of the overlying Spoon Formation. Abbott shales are similar to those of the Caseyville but are in general less sandy. About half of the formation is shale; no named limestone units occur in the Abbott Formation. Calcareous sandstones, sandy limestones, and a few shale units contain marine fossils locally.
KOSANKE, R. M., J. A. SIMON, H. R. WANLESS, and H. B. WILLMAN, 1960, Classification of the Pennsylvanian strata of Illinois: Illinois State Geological Survey Report of Investigations 214, 84 p.
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