LATE PLEISTOCENE PALEOENVIRONMENTAL CHANGES IN THE LOWER NEUSE RIVER BASIN, NORTH CAROLINA AND IMPLICATIONS FOR COASTAL EVOLUTION

The coastal plain of eastern North Carolina evolved through the changes associated with late Pleistocene rapid relative sea-level oscillations during Marine Isotope Stages 5 to 2. The sea-level highstand deposits of MIS 5 and MIS 3 have been previously studied in eastern North Carolina; however, certain regions have had little to no data collected, which makes determining the areal extent of late Pleistocene facies and associated depositional environments challenging. To overcome these limitations and better understand the spatial and temporal variation of sea-level fluctuations, geophysical and geological data from the lower Neuse River Basin have been analyzed. These data reveal the presence of multiple paleoenvironments with distinctive facies corresponding to MIS 5a and MIS 5e. The chronological framework, determined using optically stimulated luminescence dating, provides sediment age estimates ranging from 123.5 (± 7.2) ka to 85.7 (± 5.3) ka. Two distinct foraminiferal assemblages were identified. Samples dominated by Elphidium excavatum, Ammonia parkinsoniana, and Elphidium mexicana are overlain by higher diversity samples with the same dominant species but also containing open shelf species, Buccella inusitata, Nonionella atlantica, and Rosalina sp. This foraminiferal record suggests a transgressive inner shelf environment with normal marine salinity during MIS 5e. The boundary between the foraminifera-bearing units (below) and the barren unit (above) is interpreted as the MIS5e/MIS5a boundary. The pollen record indicates cooler conditions in the lowermost samples dated to MIS 5e and warming upward into MIS 5a units. Lithofacies and grain-size statistics support shoreface and inner shelf environments. MIS 5e deposits are characterized by burrowed muddy sands containing bivalve shells overlain by tidally influenced MIS 5a burrowed laminated muddy sands and laminated sandy muds (wavy bedding). Based on the apparent tidal bedding, the MIS 5e unit appears to be inner shelf, whereas the MIS 5a unit is shallower water, potentially coastal tidal flat deposits. The results of this study can be used to understand the regional stratigraphic framework and aid in developing projections of future coastal evolution of North Carolina.