The late Quaternary stratigraphy and geologic history of northeastern North Carolina and southeastern Virginia.

摘要

This study to sought to increase our understanding of the stratigraphy and geologic history of the northeastern North Carolina and southeastern Virginia late Quaternary section. Stratigraphic analysis used data from numerous core holes, outcrops, and ground penetrating radar. Chronology was based on age data acquired using optically stimulated luminescence, amino-acid racemization, Uranium series, and radiocarbon dating techniques. Geomorphic patterns were identified using the NCDOT LiDAR database.Nine primary lithofacies were identified in outcrops and cored late Quaternary sediments and comprise seven coastal plain depositional sequences. However, lithofacies occurrence, distribution, and stacking patterns on interfluves and in paleo-valleys differ. Where not removed by subsequent erosion, depositional sequences on interfluves reflect an upward succession from shelly marine lithofacies to tidal estuarine lithofacies and are bounded below by a marine ravinement surface and above by the modern land surface. However, older depositional sequences in the subsurface are typically bounded above and below by marine ravinement surfaces. Portions of seven depositional sequences were recognized and, based on age and stratigraphic data, interpreted to represent deposition from late middle Pleistocene to present. Sedimentary processes associated each depositional sequence modified and truncated older depositional sequences. The stratigraphic records of the most recent sea-level highstands (MIS 5a and MIS 3) are best preserved. The Suffolk Shoreline is primarily the product of MIS 5a processes. Seaward, the geomorphic character and uppermost sediments that characterize the Pamlico Terrace are primarily a result of MIS 3 processes. Glacio-isostatic adjustment has strongly influenced depositional patterns so that deposits associated with late Quaternary sea-level highstands that did not reach as high as present sea level (MIS 5c, 5a, and 3) according to the equatorial eustatic sea-level record, are uplifted and emergent within the study area.An unexpected record of Holocene processes is indicated by the stratigraphic record associated with organic-rich deposits of the eastern Albemarle-Pamlico Peninsula. Prior to 3 ka, astronomical tides were sufficient to produce ravinement well inland of the present peat-dominated shoreline. Gradual closure of the barrier-island system within the last 2.5 ka resulted in decreasing astronomical tides and freshening of estuarine waters. Decreasing tidal amplitudes promoted first marsh development above the earlier Holocene ravinement surface and then replacement of marsh by forested wetlands as peat accreted in response to rising base level under tidally stable conditions.An increased understanding of the evolution of the region through a series of late Quaternary sea-level cycles enables prediction of the future evolution of the coast. A series of maps and tables characterize this likely future and the impact that it will have on society on a decadal to centennial time scale.