LATE LUDLOW AND PRIDOLI (SILURIAN) FORAMINIFERA FROM THE HENRYHOUSE FORMATION, ARBUCKLE MOUNTAINS, OKLAHOMA

The Ludlow to Pridoli (Silurian) Henryhouse Formation (Hunton Group) consists of argillaceous wackestone and mudstone with some beds of skeletal wackestone and packstone. The lower part of the Henryhouse Formation is separated from the upper part by an unconformity corresponding to the mid-Ludfordian Lau Event. The contact with the overlying Haragan Formation corresponds with the Klonk Event and an abrupt change to a Lochkovian (Early Devonian) fauna of brachiopods, trilobites, and conodonts. This work focuses on foraminifers found in samples taken for conodont study from the upper part of the Henryhouse Formation at sections P1 and 9-10 in the Arbuckle Mountains of south-central Oklahoma and comprising the interval between the Lau and Klonk Events. The lower part of section 9-10 above sample 4A contains conodonts characteristic of the post-Lau event: Ozarkodina snajdri, O. crispa, and Zieglerodina species. The appearance of the late Pridoli conodont species Oulodus elegans detortus in section P1 indicates that this section is stratigraphically higher than section 9-10. The foraminifers Hyperammina leptalea, Lagenammina cucurbita, and Thurammina sphaerica occur in section 9-10 in samples 4A-8A, disappear in samples 9 through 11, and are present rarely above this interval. In contrast, the pseudocolonial foraminifers Sorosphaera? tricella, S.? multicella and S.? subconfusa increase in both abundance and in chamber number higher in section 9-10 (samples 9 through 12B). The foraminiferal species Thuramminoides sphaeroidalis ranges through both sections, but most species, including Hyperammina leptalea, Lagenammina sphaerica, L. cucurbita, Thurammina limbata, Th. stelliformis, and Sorosphaera? subconfusa do not persist into the strata of section P1. Instead, section P1 has the first appearance of the attached foraminifer Tolypammina tortuosa. Also, in section P1, the pseudocolonial species Sorosphaera? multicella becomes attached to its substrate, increasing the size of its chambers, and decreasing their number.