LATE QUATERNARY PALEOVALLEY MORPHOLOGY AND FILL CHARACTERISTICS REVEAL VARYING MODES OF FORMATION AND EVOLUTION FOR SIZE-EQUIVALENT ESTUARINE SYSTEMS IN NORTH CAROLINA

Core and seismic data were obtained from three coastal-plain estuaries in eastern North Carolina to investigate their evolution over the last glacio-eustatic cycle. Studied systems are less than 2 km wide and situated in proximity to the last interglacial shoreline: 1) The Newport connects to a watershed draining ~210 km² of coastal plain landward of the Sangamon shoreline; 2) The North originates at the Sangamon shoreline and lacks a drainage basin; and 3) the Scuppernong, draining ~400 km² of shallow terrain seaward of the Sangamon shoreline, serves as tributary to the Albemarle system.

The North and Scuppernong paleovalleys are V-shaped and filled with muddy and sandy Holocene bay sediments, respectively. Widening of the Scuppernong valley at its juncture with the Albemarle and sandier bay-fill deposits suggest substantial transgressive paleovalley-flank ravinement by wave action, attributed to combined fetch; abrupt shallowing of the valley upstream of the juncture suggests that once the knickzone became uninfluenced by combined drainage the Scuppernong lacked discharge to equilibrate its longitudinal profile. The Pleistocene surface below the North comprises a network of gullies which developed during sea-level regression in absence of perennial drainage. In contrast, the terraced Pleistocene surface below the Newport houses a single meandering thalweg containing basal fluvial deposits.

Our data showcase three primary modes of paleovalley formation and evolution for the Newport, North, and Scuppernong systems, respectively: 1) fluvial incision, 2) gully-network formation, and 3) tributary base-level effects on knickpoint migration during sea-level regression and valley-flank modification during sea-level transgression.