Sedimentation in the Albemarle—Pamlico lagoonal system: synthesis and hypotheses

Abstract

Relative to its size and in terms of its sedimentary processes, the Albemarle-Pamlico Lagoonal system is one of the least studied coastal lagoons in the United States. A synthesis of the current knowledge about sedimentation in the Albemarle-Pamlico system is presented, based on archived data published over the last 30 years and new, unpublished data, collected over the past two years. The literature reflects considerable past research effort on sediment grain size and mineralogy, but very little on sediment dynamics or flux of suspended particulate material. The physiographic complexity of the system, which includes barrier islands, a deep central basin, four river systems and extensive fringing embayments, does not appear to be reflected in the form of sedimentologic complexity. In general, the surficial cover of sediments ranges from medium sands in the inlets and on the shoals of the Outer Banks to fine silts and organic-rich clays in the central basin and embayed river mouths and channels. The transition zones from sands to muds are typically sharp and are usually related to bathymetry. It is concluded that (1) parts of the Albemarle-Pamlico lagoonal system may have high sedimentation rates relative to rates of sediment input and that rapid vertical flux by large aggregates offers an explanation for the fluid-mud deposits that would otherwise be absent, (2) fine-grained sediments that escape the estuarine sediment “trap” are confined to Pamlico Sound by the Outer Banks barrier islands and are simply recycled until finally coming to rest in the deep basin, (3) short-term advective processes are secondary to longer term processes (such as sea-level rise and barrier island migration) in the net advection of Albemarle-Pamlico sediments, and (4) at the present rate of terrigenous sediment input and relative sea-level rise, the Albemarle-Pamlico lagoonal system will never reach a sediment-filled state.