Delaware's coastal zone, both above and below the water line, is a mosaic of relict Delaware Bay and Atlantic shorelines created during different highstands of global sea level. Sediments deposited during oxygen-isotope Stage 5 (approximately 125,000 to 80,000 years before present) and in earlier-Holocene transgressive coastal environments (e.g., lagoon/estuary, estuarine beach, tidal inlet) are currently eroding in the shoreface as the modem shoreline migrates landward and upward through time. In coastal regions that lack significant input of new sediment to the littoral system, the local geologic framework can provide an important context for the interpretation of spatial and temporal trends in long-term erosion. Even where geologic data are abundant, the difficulty lies in providing information synthesized in a manner readily useable by coastal zone managers. High-resolution seismic-reflection profiles, cores, and historical shoreline positions were used to refine the geologic framework and explore ways in which the framework influences the geomerphology and longterm retreat of the modem beach system along the Atlantic coast of Delaware. Examples are presented from Cape Henlopen, where a Holocene sand unit is supplying enough beach-compatible sediment to slow shoreline retreat, and Rehoboth Beach, where a Pleistocene headland appears to be more resistant to erosion than similarly composed Holocene sediments to the north. Visual correlation of long-term shorelinechange rates with a generalized geologic framework indicates that, statewide, the lowest relative erosion rates occur where relict Pleistocene or Holocene shorelines intersect the modern beach system. Geostatistical analyses indicate that although it may be possible to quantify the effects of large-scale transitions in the geologic framework, smaller-scale phenomena are not resolvable with this method. The results of this study can prove useful to coastal managers, scientists, and engineers by providing a scientific basis for modifying methods to calculate past and predict future shoreline change, and a mechanism for incorporating geologic data into the evaluation, design, and monitoring of beach renourishment and other coastal management activities. [ABSTRACT FROM AUTHOR]