Foraminiferal fauna present in the lower Castle Hayne biomicrudite exposure northeast of Wilmington, North Carolina, suggests a depositional environment in a transitional zone between the open-marine outer continental shelf and the upper continental slope. Evidence that supports this assumption is the assemblage of abundant Lenticulina and Globigerina genera, and common occurrence of Uvigerina, Nonion, and Cibicides genera. This typical assemblage indicates a paleodepth of 90-300 m, which is analogous to depth ranges of extant foraminifera of the Gulf of Mexico. Further evidence of an outer-shelf to upper-slope depositional environment is the benthic to planktonic ratio of 4:1, a common ratio found in modern foraminiferal assemblages of the Gulf of Mexico at these depths.
Rare specimens of Textularia and Globulina genera present in the assemblage may have been displaced downslope of their natural habitat via ocean currents or influx of fluvial discharge from the Eocene age Cape Fear River.