SEQUENCE STRATIGRAPHY OF THE WARSAW FORMATION ACROSS THE OSAGEAN-MERAMECIAN STAGE BOUNDARY IN WESTERN ILLINOIS

Sequence stratigraphic investigation of the Osagean and lower Meramecian (Lower and Upper Mississippian, respectively) age Warsaw Formation was undertaken in western Illinois in its type area in near Hamilton and Warsaw, southward to the Grafton and Columbia areas. Most of the Lower Warsaw consists of highstand system tract (HST) developed in arid coastal plain sabkha facies comprising the upper part of the Lower Warsaw Formation in its type area and southeastward into the Grafton area. Paleosols developed on sabkha supratidal channel facies characterize the upper part of the Lower Warsaw in the Grafton area. Shallow subtidal facies characterize the Lower Warsaw in the Columbian area indicating a transition from coastal plain to marine platform between these areas. Thin carbonates and shales of the Upper Warsaw comprise the TST in the type area juxtaposed abruptly over the coastal plain facies in the Warsaw-Hamilton area, whereas the initial marine flooding and thin marine TST facies overly a paleosol horizon in the Grafton area are stratigraphically within the Lower Warsaw at a lower position that previously thought, with a MFS at the Lower-Upper Warsaw contact. Further south the initial marine flooding and maximum flooding surfaces appear to be positioned at the Lower-Upper Warsaw and within the Upper Warsaw in the Columbia area of southwestern Illinois