growing acceptance of glacial theory 

 and sea level rise soon provided a 

 more satisfactory general explanation 

 for the thick deposits of marsh peat 

 (Davis 1910). The development of 

 l^C dating techniques shortly after 

 the Second World War made it possible 

 to begin study of the quantitative 

 relationship between marsh develop- 

 ment, sea level rise, and land 

 subsidence since the last glaciation-- 

 the Holocene Transgression. 



Using radiocarbon-dated material 

 from present-day salt marsh peat as 

 well as from relic peat deposits and 

 other materials on the continental 

 shelves, workers have developed curves 

 relating sea level to the land over 

 the past 35,000 years. While there is 

 some uncertainty in the data and 

 various versions of the curve are 

 offered from time to time (see Emery 

 and Uchupi 1972), the general picture 



suggests a 

 which began 



continued for 

 rapid fall 

 rise in sea 

 8,000 years 



rapid fall in sea level 

 about 20,000 years ago and 



some 5,000 years. This 

 was followed by a rapid 

 level until about 7,000 or 

 ago when the rate of rise 



began to slow appreciably (Figure 1). 

 Virtually all present-day marshes 

 Northeastern United 

 to have become 

 during the past 3,000 

 1972; Rampino 

 average rate 



found in the 

 States appear 

 established only 

 to 4,000 years (Redfield 

 and Sanders 1980). The 



of relative sea level rise during this 

 recent period of marsh building has 

 been about 1 mm/yr in this region 

 (Table 1), and it is commonly thought 

 that marsh development can only take 

 place when the rate of sea level rise 

 is slow. But relic salt-marsh peat 

 has also been found on the continental 

 shelf ranging in age from 5,000 to 

 11,000 years; a period when the 

 average rate of sea level rise may 



THOUSANDS OF YEARS AGO 

 10 15 20 25 



30 



35 



"r~T" 



1'— r 



T — I — f — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — r 



q: 



UJ 50 



2 



CO 



I 





%"^ 



5^ 



s Shells '-^^ 



oolites jp *, 



A coralline algae ? 



ioo|- e salt-marsh peat 



e beachrock 



150 1 — I — I — I — I — I — I — I I I I I I I I I I L__i I 1 I i_ 



1 I 1 I I I 



I I I I I I I I L. 



Figure 1. Sea level relative to the present level on the Atlantic continental 

 shelf during the past 36,000 years (Emery and Uchupi 1972, based on Emery and 

 Milliman 1971). 



