The mid-Ludfordian Lau Event and carbon isotope excursion (Ludlow, Silurian) in southern Laurentia - Preliminary results

The mid-Ludfordian Lau Event can be recognized in three areas along the southern margin of Silurian Laurentia in association with a major positive carbon isotope excursion (CIE) and an abrupt turnover in conodont faunas: southern Oklahoma, southeastern Missouri, and western Tennessee. Although the major features of the Lau Event and CIE in southern Laurentia are similar to those described from the Baltic region, each site in southern Laurentia displays a different view of the effects associated with the Lau Event and a possible marine flooding episode coincident with the start of the Lau Event. The Lau Event lies at a disconformity between the lower and upper members of the Henryhouse Formation in southern Oklahoma at which the greater part of the CIE is missing. Diverse, but different offshore conodont faunas occur below (Polygnathoides siluricus/auna) and above (Ozarkodina snajdri fauna,) the disconformity. In the Moccasin Springs Member of the Bainbridge Formation in southeastern Missouri, the CIE and the Lau Event occupy an offshore condensed section of argillaceous strata in which Pseudooneotodus is the dominant conodont taxon. A less diverse Po. siluricus fauna occurs below the Pseudooneotodus interval and a diverse O. snajdri fauna above it. In western Tennessee, the CIE and Lau Event lie within a grainstone unit assigned to the Bob Member of the Brownsport Formation. The Po. siluricus conodont fauna of the underlying Beech River Member disappears within the base of the Bob Member, but very few conodonts occur in the shallow water fades of the upper Bob and overlying Lobelville Member. No evidence of an associated turnover in the diverse macrofauna of western Tennessee has been recognized. Identification of the Lau Event and the CIE in these areas provides an important line of time-effective correlation across southern Laurentia that will allow better placement of poorly timeconstrained stratigraphic units and faunal assemblages in this region.