Importance of Tidal-Inlet Sedimentation in Barrier-Island Systems: ABSTRACT

Barrier-island complexes, long thought to be composed largely of inlet-fill material deposited during migration, have been shown by recent work in geomorphology, stratigraphy, and petrology to contain only 10% tidal-inlet sediments. Geomorphology of the North Carolina Outer banks barrier-island complex, as determined from recent aerial photographs, indicates that tidal inlets and their deposits comprise only 13 of the 120 mi between Beaufort and Nags Head. These 13 mi of inlets and inlet fill represent only 10.8% of the barrier-island system. Furthermore, geomorphic study of the earliest to most recent USCGS charts shows that tidal inlets and their deposits never have accounted for more than 10-11% of the barrier-island complex. Washover fans, tidal deltas, lagoon deposits, dunes, and beaches appear to be of far greater importance. To confirm volumetric percentages of tidal-inlet deposits, 80 holes were drilled and 178 bottom samples collected from Pamlico Sound and the Atlantic shelf. Grain-size analyses made by settling-tube techniques indicate that tidal-inlet sediments are distinct. Standard deviation versus mean plots allows the best separation of fields. These subsurface studies clearly define the limits of tidal-inlet sedimentation and indicate that only 10% of the total sedimentary complex consists of such deposits. We must conclude, therefore, that (1) inlet-fill sedimentation is minor in the depositional framework of these barrier systems, and (2) tidal-inlet systems do not migrate significantly in the formation of these barrier islands. End_of_Article - Last_Page 839------------