Fractional Preservation of Transgressive Coastal Lithosomes on Atlantic Continental Shelf: ABSTRACT

Abstract

Migration of coastal environmental lithosomes across the continental shelf is a response to the latest Quaternary rise of the sea. Preservation of fractions of the transgressive sequence is dependent on depth of erosion, which is a function of impinging wave energy, sediment supply, resistance to erosion, and rate of relative sea-level change. Materials deeper in the column have a greater potential for preservation. The relative sea-level curve for Delaware, based on C14-dated basal peats, rises smoothly from 25 m below present from 10,000 years B.P. to the present at a decreasing rate with time. Shells and peats 9,000 to 10,000 years old on the shelf are 40 m deeper, suggesting an east-southeast shelf tilt, tectonically or hydro-isostatically induced. Sea-leve rise results in rates of coastal retreat of 102 m/year for 10,000 years B.P., 101 m/year for 5,000 years B.P., and 100 m/year at present. In a model of constant volume of net erosion per unit length of coast, a much smaller depth of erosion applies early in the transgression, allowing a greater preservation potential. Changes in wave climate, sediment supply, and downwarping across the shelf also apply. Recovered sediments, seismic profiles, and recognized morphic features indicate better preservation of shoreline elements on the outer shelf, and more planing off and reworking on the inner shelf. Similar analysis of Delaware Bay indicates that it too follows such a model, in changing from a dendritic fluvial system to a broad estuary. End_of_Article - Last_Page 675------------