AN EOCENE (BARTONIAN) REMNANT ON THE CAPE FEAR ARCH IN THE UPPER COASTAL PLAIN OF NORTH CAROLINA

A small Eocene outlier occurs in the Upper Coastal Plain at Paint Hill, southern Moore County, North Carolina. Located near the axis of the Cape Fear Arch, well above the toe of the Orangeburg Scarp (inland limit of Pliocene transgression) ~18 miles further to the southeast, the informal Paint Hill beds (PHB) are ~50’ thick and the top is ~600’ above msl. These strata record Eocene deposition not generally recognized so far inland in NC.

Poorly exposed and altered from acidic groundwater, the PHB consist of alternating thin to thick beds (~1-10’+-) of moderately cohesive to indurated, tan to yellowish-brown, opaline claystone with minor quartz sand, wavellite-cemented quartz sandstone, and minor quartz conglomerate. Fish scales and fragmentary cranial bones and vertebrae are abundant, and a trichiurid tooth (cutlassfish) and mold of a ray dermal denticle are present. Other fossils include abundant burrows, rare decapod chelipeds, turtle shell, silicified domal cheilostome bryozoans (Osthimosia), and infrequent, poorly preserved pectinid molds. Siliceous wood and plant leaf impressions are uncommon. The PHB can be dated as Bartonian (~41.2 Ma to ~37.8 Ma; Gosport Formation age) by the presence of well-preserved tooth molds of the carcharhiniform shark, Abdounia claibornensis.

The PHB overlie the Upper Cretaceous Middendorf Formation. Loose eolian sands of the Pleistocene-Holocene Pinehurst (?) Formation locally overlie and drape the flanks of the outlier. Unconsolidated surficial gravel units, north of the PHB near Carthage, central Moore County, record post-Bartonian energetic fluvial downcutting into the Cretaceous Middendorf Fm. This is presumably in response to crustal uplift on the Cape Fear Arch. The location, elevation, lithic character, and age of the PHB constrain the position of the updip Bartonian shoreline and the timing of uplift, with subsequent regional erosional removal of much of the Upper Cretaceous and most of the Paleogene strata.