present Atlantic and Gulf of Mexico shorelines (Oaks and DuBar 1974). 



Superimposed on these essentially tectonic sea-level changes are higher-frequency 

 fluctuations of a multitude of origins. Periodic formation of continental ice sheets and 

 attendant deglaciations have, at least since the Pliocene and possibly throughout the 

 Cenozoic (Matthews and Pore 1980), been responsible for major sea-level changes on a 

 typical time scale of 10,000's of years. Present sea level appears to be at an elevation 

 comparable to that reached during earlier major interglacials. The latest low stand of 

 sea level occurred at the peak of the late Pleistocene Wisconsin glaciation some 18,000 

 years ago. Early sea level curves (Curray 1965; Milliman and Emery 1968) indicated that 

 this low stand was as much as 130 m below present sea level. Recent work by Dillon and 

 Oldale (1978) and Blackwelder (1980), however, strongly suggests that sea level may have 

 risen much less than 100 m since the late Wisconsin low (Figure I). 



a. 

 Q 



100- 



150 



® Fixed samples 

 • Mobile samples 

 — Proposed sea-level 

 curve; U. S. East Coast 



20 



Years BP X 10^ 



35 



40 



Figure 1. Sea-level curves for the late Quaternary inferred from radio- 

 carbon-dated samples along the east coast of the U. S. (Dillon and Oldale 

 (1978). The most recent curve (dashed) suggests a late Wisconsin low stand 

 of less than 100 m below present sea level. 



Regardless of the absolute magnitude of sea-level rise over the last 18,000 years, 

 this "Holocene transgression" is responsible for the existence of a multitude of coastal 

 sedimentary sequences (deltas, fluvial channel fills, marsh deposits, tidal channel fills) on 

 the present shelf floor (Curray 1965; Swift 1976; Field et al. 1979; Pilkey et al. 1981). At 

 the time of maximum ice retreat, global sea level rose at a rate of about I m/century, a 

 rate which is about four orders of magnitude faster than the long-term tectonically 

 induced global sea-level changes. 



Because the relative abundance of stable oxygen isotopes in deep-sea sediments is a 

 measure of global oceanic temperatures, one can reconstruct a paleo-temperature time 

 series from analysis of deep-sea cores (Figure 2). This curve suggests the existence of 

 numerous glaciations on a time scale of about one every 100,000 years throughout the 

 Pleistocene (Shackleton and Cita 1979). 



165 



