The Transgressive Barrier-Lagoon Coast of Delaware: Morphostratigraphy, Sedimentary Sequences and Responses to Relative Rise in Sea Level
John C. Kraft, Michael J. Chrzastowski, Daniel F. Belknap, Marguerite A. Toscano, Charles H. Fletcher, III, 1987. "The Transgressive Barrier-Lagoon Coast of Delaware: Morphostratigraphy, Sedimentary Sequences and Responses to Relative Rise in Sea Level", Sea-Level Fluctuation and Coastal Evolution, Dag Nummedal, Orrin H. Pilkey, James D. Howard
Download citation file:
Transgressive barriers of the embayed Atlantic and Gulf coast are generally similar in overall form, processes, and landward migration in response to relative sea-level rise, but they vary greatly in potential sources and volume of sand supply. Delaware's transgressive barriers vary in thickness from 25 m to less than 5 m; dunes may rise to 20 m above sea level, whereas barrier-spit and inlet sand reach depths of 10–18 m below sea level. Widths vary between 0 m at eroding headlands and 4–6 km near tidal delta and spit complexes.
A complete Holocene paralic sequence for Delaware includes a basal sand and/or gravel overlain by marsh, lagoon, and barrier lithosomes. Shoreface erosion, as the barrier lithosome moves landward, occurs to an average depth of 10 m, with about 50% of eroded sediment derived from Holocene and Pleistocene lagoonal mud outcrops. Since the suspended material is carried out of the shoreface, its removal requires a re-evaluation of the volumetric model commonly inferred from the Bruun mechanism. Also, the third dimension of longshore transport of coarse material needs to be considered.
As transgression continues, the ravinement surface exposes lagoonal sediments, marsh mud, irregularly shaped basal remnants of the Holocene barrier lithosome, or varied Pleistocene strata. These are then blanketed by varying thicknesses of inner-shelf sand. Ultimately, the transgressive barrier and associated paralic environments migrate landward to peak interglacial positions where the entire transgressive record may be preserved. A relatively complete vertical sequence of transgressive coastal lithosomes might also be preserved at the outer edge of the continental shelf at glacial sea-level minima. Thus, the optimal chance for total preservation of a transgressive coastal lithosome sequence lies at the extremes, landward at the peak interglacial when eustatic sea-level rise stops and the coastal lithosome sequences become stranded, and possibly on the outer edge of the shelf as deglaciation begins and there is rapid rate of sea-level rise.
Figures & Tables
Sea-Level Fluctuation and Coastal Evolution - This Special Publication is the result of a symposium in honor of W. Armstrong Price held at the first SEPM Midyear Meeting at San Jose, California, on August 12, 1984. The factors controlling relative sea-level change along our shores are varied and, at best, imperfectly understood. Yet, the relative rate of change is what controls shoreline erosion, the arrangement of sedimentary facies of the coastal zone, and the character of deformities within the coastal stratigraphic record. Therefore, these papers address sea-level changes, shoreline responses, and the controls on the three-dimensional geometry of the consequent lithosomes; in short, the architecture of the coastal depositional systems.