Post Creek Formation named for Post Creek Cutoff, Pulaski Co., southern IL. Type section is in banks of Post Creek Cutoff, immediately south of the Joppa to Grand Chains Hwy, center of T15S, R2E, sec. 2 (center), Bandana 7.5-min quad, Pulaski Co. Consists of poorly sorted heterolithic gravels and sand, clay, and silt previously assigned to late Cenomanian Tuscaloosa Formation (Smith and Johnson, 1887) or "Tuscaloosa Formation" of other workers more recently dated as Santonian to middle Eocene. Palynological data indicates middle to late Campanian age for deposits in southeastern MO and southern IL assigned to this unit. Extension into western KY cannot be documented at this time. Unit is overlain by Coffee Sand and underlain by Little Bear Formation. Late Campanian age is based on presence of SEMIOCULOPOLLIS sp. A of Tschudy (1975), TRUDOPOLLIS VARIABILIS, OSCULAPOLLIS PERSPECTUS, CHOANOPOLLENITES CONSANGUINEUS, C. TRANSITUS, EXTREMIPOLLIS VISUS, and VACUOPOLLIS MUNITUS, a notably different assemblage from type Tuscaloosa in AL. Tschudy (1975) noted that these species were present only in strata of Campanian or younger age in Mississippi embayment. Unit lacks OSCULOPOLLIS AEQUALIS, PSEUDOPLICAPOLLIS SERENA, and TRUDOPOLLIS sp. A if Tschudy (1975), all of which are present in younger, late Campanian (to perhaps early Maastrichtian) Coffee Sand overlying Post Creek Formation. COMPLEXIOPOLLIS is conspicuously absent in Post Creek and provides additional support for assignment of middle to late Campanian age; this genus is common in pre-Campanian strata of Mississippi embayment. Report includes measured section, generalized geologic map, and fossil data.

Source: GNU records (USGS DDS-6; Reston GNULEX).