HIGH-RESOLUTION CHRONOSTRATIGRAPHIC CORRELATION OF UPPER HOMERIAN (SILURIAN) STRATA DURING THE MULDE EVENT, MIDCONTINENT, USA

The upper Homerian Mulde Event, a mass extinction that devastated graptolite diversity, occurred before and during the onset of a major perturbation to the global carbon cycle recorded as a double-peaked positive carbon isotope excursion (CIE). Whereas the Mulde Event and associated CIE are well-documented globally, changes in global sea level associated with the Mulde Event have only been investigated in detail in the West Midlands, England and Gotland, Sweden. A critical step toward understanding both the drivers and results of global climatic change during the Mulde Event is to constrain changes in eustasy. This study integrates carbon isotope chemostratigraphy and conodont biostratigraphy of Homerian strata in Tennessee, Indiana, and Ohio in an effort to determine if a global type-1 sequence boundary is recorded within the ascending limb of the Mulde CIE, and to produce a high-resolution chronostratigraphic framework for Homerian strata in the midcontinent USA.

Six sections from TN, IN, and OH were included in this investigation. Carbon isotope data were collected from five of the sections, and one section was sampled for conodont biostratigraphy. A complete record of the Mulde excursion is now documented in the Laurel and Pleasant Mills formations in Indiana and confirmed in the Wayne Group of Tennessee. These data demonstrate that the Waldron Shale is diachronous across the midcontinent, and that a sequence boundary identified herein from Indiana and Tennessee is the same sequence boundary that occurred during the ascending limb of the Mulde Excursion in the West Midlands and Gotland.