EXTENSION OF THE BIOSTRATIGRAPHIC RANGE OF THE GASTROPOD (NEOGASTROPODA) AMULETUM (AMULETUM) FASCIOLATUM (WADE)

The Upper Cretaceous (upper Maastrichtian) Owl Creek Formation is located in the uppermost reaches of the Exogyra costata biostratigraphic zone. Bulk samples collected from this formation have revealed the presence of the gastropod Amuletum (Amuletum) fasciolatum (Wade). Sohl (1964) restricted this species of gastropod to the Exogyra cancellata zone, a subzone located at the base of the E. costata biostratigraphic zone.

Three specimens of this species have been identified, although two may be juveniles. Identification is based on descriptions given by Wade (1926) and Sohl (1964) and associated photographs of this species. This species is not an abundant taxon and until now, has only been identified in the lower parts of the Upper Cretaceous (lower Maastrichtian) Ripley Formation of Tennessee. The three specimens identified were all collected from an outcrop of the Owl Creek Formation located on Owl Creek in Tippah County, MS.

The specimens are not present within the Owl Creek due to reworking, based on three lines of evidence. First, the outcrop does not appear to contain any inclusions of material associated with the Ripley Formation. Underlying the Owl Creek Formation unconformably are the Chiwapa Sandstone and McNairy Sand Members of the Ripley Formation. The Chiwapa Member is described as containing sandy limestones and calcite cemented sandstone and the McNairy Sand Member is described as a loose, medium to coarse grained, micaceous sand with few fossils. In contrast, the Owl Creek Formation is described as a typically fossiliferous, medium gray, silty clay to fine-grained sand. Based on their differing lithologies, inclusions of material from the Ripley Formation were not observed in the Owl Creek Formation. Second, the species in question was previously found in the base of the Ripley Formation, not at the top where it would come into contact with the Owl Creek Formation. Third, the shells are in virtually pristine condition, indicating they were transported minimally. Although the apertures are missing, the surface ornamentation is well preserved with numerous, intricate details easily discernible. Based on these observations, it appears necessary to extend the range of the gastropod Amuletum (A.) fasciolatum (Wade) to include the entire E. costata biostratigraphic zone.