Figure 13. Dark 

 tidal creeks on 

 marsh on the left 

 is older accord to 



areas represent the distribution of pond holes or pannes and 



the high marsh at Barnstable, Cape Cod (Redfield 1972). The 



apd in the foreground where fewer of these features are found 



1^ 



C dating, 



water may evaporate, leaving salt 

 deposits that limit the vegetation. 

 Several processes may be responsible 

 for these features, including the 

 blockage of drainage creeks by 

 slumping of the banks, the evolution 

 of high marsh from patches or lines of 

 slough marsh growing together, the 

 decay of surface turf because of poor 

 drainage ("rotten spots"), and the 

 accumulation of "trash." The pond 

 holes appear to be relatively stable 

 over the short term because the depth 

 of standing water in them (0.5 to 1 m 

 or 1.6 to 3.2 ft) is usually great 

 enough to prevent the spread of 

 Spartina rhizomes (Redfield 1972), but 

 their disappearance from the older 

 portions of the marsh (Figure 13) 

 suggests that most of them are an 



ephemeral 

 1960). 



part of the marsh (Chapman 



MARSH SEDIMENTS 



Marshes along the Atlantic coast 

 may receive sediment from rivers, from 

 the nearshore zone, and from relic mud 

 deposits on the 

 (Mead 1969; Phleger 

 sediment source 

 important for many 



continental shelf 



1977). The latter 



is particularly 



of the coastal 



marshes along the Northeastern United 

 States, where the supply of new 

 terrigenous sediment is low. The 

 mechanism responsible is a landward 

 flow of bottom water across the shelf. 

 In areas where marshes have formed 

 behind barrier spits, large amounts of 



19 



