MULTI-BASIN CARBON ISOTOPE CORRELATION OF THE IREVIKEN, MULDE AND LAU EXCURSIONS (EASTERN NORTH AMERICA): A COMPREHENSIVE SEQUENCE STRATIGRAPHIC SYNTHESIS

The Silurian Wenlock-Pridoli interval of eastern North America contains a dynamic stratigraphic record that includes carbonate platforms with periodic reef build-ups, red-green-black shales, thick clastic wedges, and up to 900 m of evaporites locally. Despite more than a century of study, the exact age relationships of much of this complex succession remain uncertain. Facies distributions in this interval differ markedly from those of the underlying Llandovery as the early Sheinwoodian onset of the Salinic Orogeny triggered major tectonic reorganization into four depositional basins with different environmental characteristics. The resulting stratigraphic complexities, combined with the paucity of index fossils, have resulted in uncertain chronostratigraphic correlation between basins. Ultimately, this uncertainty has crippled efforts to decipher the signatures of the Silurian global ocean-atmosphere chemical events that are recorded in this succession.

Over the last decade we have endeavored an ambitious initiative to establish a robust sequence stratigraphic model for the Wenlock-Pridoli strata across 1.5 million km² of eastern North America, built upon synthesis of previous biostratigraphic studies and generation of a new δ¹³C_carb data set seamlessly integrated with previously published data. This effort has included the study of more than 100 subsurface cores, over 100 outcrops and the collection and analysis of over 10,000 samples. More than twenty-five new δ¹³C_carb profiles arranged in transects across the Illinois, Michigan, Ohio and Appalachian basins unravel complex stratigraphic relationships and define the exact stratigraphic position of the Ireviken, Mulde and Lau excursions. This regional framework of chemostratigraphic correlation resolves many longstanding uncertainties about the exact age of Silurian rocks and for the first time permits the direct study of cause-and-effect relationships between different features recorded in this succession. The δ¹³C_carb, sequence stratigraphic, and time-specific facies patterns together support a unified model of long-lived environmental stability punctuated by upheavals of the ocean-atmosphere chemical system that transformed the Paleozoic world.