CONODONT FAUNAS AND BIOSTRATIGRAPHY OF THE LINGLE/ST. LAURENT FORMATION FROM THE DEEP SUBSURFACE OF THE ILLINOIS BASIN IN EDWARDS, WAYNE AND WHITE COUNTIES, IL, AND POSEY COUNTY, IN

Woolsey Operating Company (WOC) LLC drilled seven four-inch diameter cores in the southern Illinois Basin that were donated to the Illinois State (ISGS) and Indiana Geological surveys (IGS) in 2022. Most of WOC cores include: the Tournaisian Rockford (Choteau) Fm.; complete sections through the Late Devonian and earliest Carboniferous New Albany Shale; partial sections of the underlying Middle Devonian carbonate platform rocks of the Lingle/St. Laurent formations. We sampled (>70 samples) the platform carbonates of the Lingle/St. Laurent formations and basal Blocher Member of the New Albany Shale in the seven available cores to: document the conodont faunas and sequence, constrain the timing of deposition of the platform carbonates, and determine the timing of carbonate platform drowning recorded by the onset of the Blocher Member deposition.

Lingle/St. Laurent samples yield low to moderately diverse faunas dominated by species of Icriodus, Latericriodus, and Polygnathus, with common scolecodonts and fish teeth and dermal scales. Our samples from the basal Blocher Member (basal New Albany) did not yield conodonts. The Lingle/St.. Laurent fauna includes: Icriodus brevis Stauffer, I. difficilis Ziegler and Klapper, Latericriodus latericrescens latericrescens Branson and Mehl, Polygnathus linguiformis linguiformis Hinde-gamma morphotype of Bultynck, P. timorensis Klapper, Phillip & Jackson, and P. xylus xylus Stauffer. Based on the association of I. brevis, I. difficilis, with P. timorensis in samples in the lower parts of the WOC Sams and Brown cores the sampled Lingle/St. Laurent formations are no older than timorensis Zone, and no younger than ansatus Zone. Samples from the upper Lingle/St. Laurent at and just below the contact with the overlying Blocher Member of the New Albany include I. brevis, I difficilis, L. l. latericrescens, and P. l. linguiformis gamma morphotype and are no older or younger than ansatus Zone. This constrains the age of the overlying Blocher Member as no older than ansatus Zone. This suggest that the marine flooding event that initiated platform drowning and basal Blocher deposition represents the Devonian T-R IIa-1 flooding that initiated basal Cedar Valley Group and lower Tully deposition in the adjacent Iowa and Appalachian basins.