REGIONAL MIDDLE AND LATE KATIAN (LATE ORDOVICIAN) δ13C CHEMOSTRATIGRAPHY IN NORTH AMERICA: COMPARISON BETWEEN SUCCESSIONS IN IOWA, THE CINCINNATI REGION IN KENTUCKY AND OHIO, AND THE ARBUCKLE MOUNTAINS IN OKLAHOMA

Since the early 1990s, the Hirnantian (latest Ordovician) δ¹³C excursion (HICE) has been investigated in several parts of North America (Anticosti Island, Quebec; the Canadian Arctic; Nevada; the Upper Mississippi Valley; southern Ontario) and is now relatively well known. Likewise, the early Katian Guttenberg δ¹³C excursion (GICE) has been recorded at many localities across Laurentia. However, the middle and late Katian δ¹³C chemostratigraphy remained virtually unknown until 2007 when Bergström and others presented the first stratigraphically complete δ¹³C curve through the Cincinnatian Series in its type area in the Cincinnati region. Recently, δ¹³C data have become available from two other important successions, namely the Viola Springs and Welling formations of the Arbuckle Mountains, Oklahoma and the Decorah Shale, Galena Group, and Dubuque Formation of Iowa. The four post-GICE Katian δ¹³C excursions recognized in the Cincinnati region have been identified also in Oklahoma, where the Kope, Fairview, and Waynesville excursions occur in the lower, middle, and upper parts of the Viola Springs Formation, respectively. The Whitewater excursion is recorded in the Welling Formation. In Iowa, the first three excursions are identified in the middle Dunleith, upper Wise Lake, and upper Dubuque formations, respectively. The Whitewater excursion is expected to be present in a not yet investigated interval in the middle-upper Maquoketa Group. The fact that these excursions, which are tied to conodont and graptolite biostratigraphy, are recognizable over a very large region supports the idea that they are not local but continent-wide, if not global, isotopic events.