| Summary |
Pleistocene deposits exposed in the Lee Creek mine near Aurora, and penetrated by coring in southern Beaufort County, North Carolina consist of unfossiliferous muds overlain by fossiliferous sands and sandy muds. Co-occurrence of the bivalves Argopecten solarioides and Anadara ovalis in shelly deposits indicates a middle Pleistocene age (molluscan zone 2 of Blackwelder [1981b]) which postdates the James City Formation and predates the Flanner Beach Formation (between 0.5 and 0.2 ma). The "shell bed" is a condensed bed, more specifically a sifted deposit, for which detailed community reconstruction is impossible. The "oyster bed" is a paleo-channel deposit that is partially situ and partially condensed. Each of these "beds" contains fossils derived from a distinctive community (or communities), the precise nature of which has been masked to produce time-averaged fossil associations. Molluscan associations include: 1) Mulinia lateralis, which characterizes fossiliferous muddy sands and shell "pavements"; 2) Mulinia lateralis-Nuculana acuta, found in fossiliferous sandy muds; 3) Crassostrea virginica-Corbula swiftiana, limited to muddy, sandy oyster banks. Foraminiferal associations include: 1) Elphidium excavatum forma clavata-E. limatulum, found with molluscan Association 1; 2) Elphidium excavatum formae clavata and selseyensis, which occurs with molluscan Associations 2 and 3. All associations indicate deposition within a barrier-built estuarine ecosystem. Within the estuarine ecosystem, each deposit represents a specific environment. Fossiliferous muddy sands (molluscan Association 1, foraminiferal Association 1) represent subtidal deposits along the margins of a back-barrier lagoon or estuary mouth. Included shell "pavements" were deposited in the intertidal zone along sandy shoals. Fossiliferous sandy muds (molluscan Association 2, foraminiferal Association 2) accumulated in quieter, perhaps slightly deeper portions of a sound or estuary mouth. Muddy, sandy oyster banks (molluscan Association 3, foraminiferal Association 2) represent subtidal to intertidal deposits within a tidal creek or protected mainland embayment. Underlying unfossiliferous muds represent organic-rich, carbonate-poor channel muds of the estuary mouth and inner sound. Vertical juxtaposition of these deposits requires lateral migration of the appropriate depositional environments. Although the entire sequence is associated with marine transgression, the relationships of strata observed during this study may have been produced either in direct response to an advancing shoreline or by lateral migration of environments parallel to it. |
