Abstract

Sequence boundaries and maximum flooding surfaces of the Cherokee Group (Middle Pennsylvanian) in Southeastern Kansas lie within marker intervals (MI) that comprise up to 5 repeated lithologic units (LU): underclay, coal and an overlying dark gray to black shale, each of cm-dm thickness. A caprock, impure limestone or sandstone _1 dm thick, may separate coal and dark shale. Underclay may overlie cemented, bleached, sideritic shale or siltstone, perhaps a lower horizon of the gleyed paleosol of the underclay. Distinctive log signatures of these units, which originate in several unrelated depositional environments at different times during sea-level fluctuation, make the MI easily traceable, unless eroded.

The transgressive systems tract of a sequence comprises coal, cap rock, part or all of the dark gray to black shale, and valley-fill successions of sandstone and shale, with the sequence boundary following the top of the underclay or base of the valley fill. The maximum flooding surface lies within the dark gray to black shale LU. The bulk of each sequence consists of 2-10 m of dark gray to light gray shale, heterolithic strata, and rippled sandstone, commonly in coarsening upward successions. These units contain some trace fossils and very sparse body fossils of normal marine organisms and form progradational or regressional deposits of the high stand systems tract.

Overall the Cherokee Group is transgressive, reflecting a long-term rise of relative sea level, but with numerous higher order sequences. It contains 22 sequence boundaries, some of which have very wide extent, and others are only local. The wide-ranging sequences correspond generally to those described previously by Ross and Ross (1987).