CORRELATION OF MIDDLE CHEROKEE GROUP CYCLOTHEMS ACROSS NORTHERN MIDCONTINENT USING GONDOLELLA AS A MARKER FOR THE UPPER TIAWAH CYCLOTHEM

The Cherokee Group has long been a source of coal and petroleum in the Midcontinent and is now of interest for coal bed methane. Previous lithostratigraphic correlations of coals have proven unreliable because of their dependence on coal bed thicknesses and inferred positions of discontinuous sandstones. New results from middle Cherokee strata [from the base of the Wier-Pittsburg coal up to the base of the Croweburg coal of the widespread Verdigris cyclothem] have correlated marine cyclothems in cores and outcrops from Oklahoma to Iowa, using the distinctive conodont genus Gondolella. This genus is known only from certain offshore marine shales, and occurs in only one marine unit between the Inola cyclothem in the lower Cherokee and the Verdigris cyclothem in the upper Cherokee.

The type Tiawah Limestone near Claremore, Oklahoma, is part of two cyclothems: the Lower Tiawah cyclothem includes the thin Tebo Coal at the base, the overlying conodont-rich shale and the lower part of the Tiawah Limestone. Above the shallow-water facies in the middle of the Tiawah Limestone, the Upper Tiawah cyclothem includes the top of the Tiawah Limestone and the overlying black shale containing Gondolella, which also occurs above the Scammon Coal of Kansas.

In the type area of the Tebo Coal near Montrose, Missouri, the Gondolella-bearing black shale lies above an “unnamed” coal above the Tiawah Limestone and type Tebo Coal. This coal was left unnamed because it is overlain by a thin sandstone, apparently misidentified as Chelsea [an Oklahoma term], which underlies the type Scammon Coal in Kansas. This coal, however, represents the base of the Upper Tiawah cyclothem and is more likely the Scammon Coal equivalent, while the type Tebo coal and entire Tiawah Limestone here represent the Lower Tiawah cyclothem.

In northeastern Kansas, the Gondolella zone was found in two cores in black shale directly above a coal bed identified as Tebo, which thus more likely is the Scammon, as it is part of the Upper Tiawah cyclothem. The Gondolella zone was found in Iowa in black shale some distance above the Carruthers Coal, which had been correlated with the Tebo Coal of Missouri using palynology, but may be younger than the Tebo, and equivalent to the Scammon.