Studies of Recent sediments in coastal Delaware show complex sediment-distribution patterns resulting from lateral and vertical movements of successive environments of deposition over a Pleistocene unconformity. Recent sediments are infilling a drowned topography with a local relief of 70 ft and possibly up to 125 ft eroded on highly variable Pleistocene sediments. Identification of the Pleistocene surface is a problem. However, it may be recognizable as a soil zone or intermixture of marsh clay with Pleistocene sands at the unconformity; it also may be recognized on the basis of radiocarbon dates.

Larger depositional features forming around eroding Pleistocene headlands and infilling the estuaries include characteristic depositional shoreline environments, such as spits, dunes, baymouth bars, an intermeshing network of tidal deltas, nearshore marine erosional-depositional sand and gravel, and the bays or estuaries and fringing Spartina and Distichlis marshes which form the westernmost edge of the transgressive units. The thickness and areal extent of the sedimentary bodies are controlled largely by the morphology of the Pleistocene unconformity. A large part of these Recent sedimentary units is being eroded by the transgressing Atlantic Ocean.

Cores of sediment taken under the shallow bays, such as Rehoboth, Indian River, and Assawoman Bays, and in the fringing marsh environment, show that the depositional units are thin, highly irregular in areal extent, extremely variable in thickness, and difficult to project. Sedimentary processes active in the shallow bays include shoreline marsh erosion and the formation of thin, possibly ephemeral, beach-dune complexes consisting of clean, well-sorted sand having typical beach and dune sedimentary structures. They are anomalous in that they are completely surrounded by Spartina marshes on the landward side and extremely muddy sand grading into dark gray lagoonal mud on the bay side. It appears that distinctive sedimentary structures, and sediment size-sorting relations such as those hat characterize the larger more common sedimentary units of the coastal area may be formed in miniature at the very thin edge of transgression and may lead to considerable confusion in the interpretation of sediments of this type in the geologic record.

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