STRATIGRAPHIC REVISION AND HIGH-RESOLUTION CHRONOSTRATIGRAPHIC CORRELATION OF THE SILURIAN BAINBRIDGE GROUP, ILLINOIS BASIN

The Illinois Basin contains a thick succession of poorly exposed Silurian strata, which, until recently, have been assigned to stratigraphically lumped formations and correlated only approximately at the series level. Recent work on the Schlamer #1 Core and several outcrops reveals the lithostratigraphic character and biostratigraphic content of the units, and demonstrates that they capture a series of global change events (Ireviken, Mulde, and Lau positive carbon isotope excursions). This new knowledge will enable stratigraphic revision and high-resolution global chronostratigraphic correlation of these strata. The ‘Bainbridge Formation’ should be revised as a group, with the former members elevated to formational status. The Bainbridge Group should contain the Seventy-Six Shale (uppermost Telychian-lowermost Sheinwoodian), St. Clair Formation (Sheinwoodian-Homerian), and the Moccasin Springs Formation (Gorstian-Pridoli). It is overlain by the Bailey Formation (?Pridoli-Devonian) and unconformably underlain by the Sexton Creek Formation (Aeronian-?Telychian). The Seventy-Six can be correlated into Arkansas, where it could replace the confusing term “’button shale’ of the Cason Fm.” The Moccasin Springs Fm. should be composed of four members: Greens Ferry, Sheppard Point, Lithium (new), and Randol members. Global series and stage boundaries can be correlated using integrated conodont-graptolite-carbon isotope bio-chemostratigraphy.