The Pleistocene Columbia Group in Sussex County, Delaware, has long been identified as a complex of nearshore marine and coastal deposits. However, interpretation of the internal geometry of the sedimentary lithosomes has proved to be difficult because of the extreme variability of these units. Environmental lithosome models of the morphology and internal geometry of the Holocene transgressive shoreline complex along the present Delaware coast provide an analog for the interpretation of the Pleistocene sedimentary sequences.

On the basis of sedimentary structures, lithologic sequences,

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and geomorphology, four linear barrier complexes have been identified within 10 km of the present coast. Each is a transgressive, peak-sea-level barrier complex including barrier and washover sands and gravels, tidal-marsh muds, and fossiliferous lagoonal sands and muds. A regressive sequence of sand and gravel occurs between each barrier. From most landward to most seaward, the barriers were formed at sea levels of about +5.4 m, +4.3 m, +2.8 m, and -1.0 m relative to present sea level. Age estimates based on amino acid racemization for shells within lagoons behind these barriers suggest a Sangamon age for at least the three most landward barriers.

Thus the upper 15 m of the horizontally correlative Pleistocene Columbia Group consists of at least four chronologically discrete, parallel, linear barrier-lagoon complexes formed during multiple marine transgressions and regressions. This interpretation of trends and vertical sequences of nearshore marine and coastal deposits may prove useful in the understanding of other ancient coastal deposits.

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