Observations on the Paleoecology and Formation of the “Upper Shell” Unit, Lee Creek Mine
Geology and Paleontology of the Lee Creek Mine, North Carolina, I
The "Upper Shell" unit at the Lee Creek Mine (Pliocene age, maximum thickness 3 m) is remarkable for its concentration of well-preserved mollusk shells in a sparse quartz sand matrix, and it is dominated by several species of bivalves, with many shells articulated. The unit can be subdivided into three bivalve assemblage zones characterized by associations of dominant species. Zone 1 is dominated by Mercenaria mercenaria, an infaunal, shallow- to medium-burrowing, siphonate clam. Zone 2 is characterized by an epifaunal bivalve assemblage that includes Glycymeris americana, Argopecten eboreus, Anomia simplex, and Ostrea meridionalis. Thin but highly concentrated accumulations of Argopecten and Anomia form distinct layers within zone 2. Zone 3 is marked by a return of Mercenaria mercenaria accompanied by specimens of Geukensia sp. and an increase in oyster shells. The characteristics of the zones of the "Upper Shell" unit strongly suggest that these shell beds were formed by a series of localized catastrophic events that produced mass mortality of the molluscan assemblages, rather than by processes of gradual shell accumulation. The disappearance of Mercenaria mercenaria from the sequence may have been due largely to the inability of juveniles of this species to penetrate a shell pavement formed immediately after a mass mortality event. Return of Mercenaria mercenaria in zone 3 marks a change in bottom environmental conditions in the area. The overlying "Shell Hash" unit contains the bivalve Corbicula densata, representative of lower salinity conditions. This unit consists primarily of shell material reworked from the underlying "Upper Shell" unit and probably represents an accumulation formed in an estuarine tidal channel.
Curran, H. Allen and Parker, Patricia L., "Observations on the Paleoecology and Formation of the “Upper Shell” Unit, Lee Creek Mine" (1983). Geosciences: Faculty Publications, Smith College, Northampton, MA.