FORAMINIFERA IN THE ALBEMARLE ESTUARINE SYSTEM, NORTH CAROLINA: DISTRIBUTION AND RECENT ENVIRONMENTAL CHANGE

Abstract

This study investigated the surface and subsurface distributions of foraminifera (both live populations and dead assemblages) throughout the Albemarle Estuarine System (AES) to determine the utility of the modern foraminiferal assemblages as models for paleoenvironmental interpretations in this estuarine and barrier island system. Thirty-seven species were recognized in the dead assemblages from 49 stations; 19 species comprised the living populations. Cluster analysis of the dead assemblages defined five biofacies: the calcareous foraminiferal nearshore marine and inlet biofacies, and the dominantly agglutinated foraminiferal estuarine shoal, estuary, inner estuary, and marsh biofacies. Paleoenvironmental reconstruction of three cores from the central Albemarle basin, based on the distribution of dead surface foraminiferal assemblages, recognized the inner estuarine and estuarine biofacies. Radionuclide tracers ( 210 Pb and 137 Cs) provided the geochronologic framework for each core. The westernmost core was capped by the inner estuarine biofacies overlying the estuarine biofacies, indicating either accumulation of a seasonal ephemeral layer of sediment from a lower brackish, upstream environment or increased freshwater discharge since the 1990’s as a result of increased tropical storm and hurricane activity. The two easternmost cores indicated that, in the early 19 th century, Albemarle Sound populations included calcareous foraminiferal species. These taxa were adapted to the higher salinities that resulted from several inlets that were open adjacent to the AES prior to 1828. Taphonomic processes (test transport, test dissolution, mechanical test breakage) are active but, with the exception of test dissolution in a relatively restricted geographic area, they do not significantly alter surficial foraminiferal assemblages in the transition into subfossil assemblages. Thus, foraminiferal distributions are useful for characterizing modern estuarine environments and for interpreting paleoenvironmental changes in sediments deposited over the past few hundred years in coastal North Carolina.