GEOLOGY, HYDROLOGY AND PEAT FORMATION IN CHOWAN SWAMP 



Kaplan et al. (1978) discuss geology of the area based on 

 Richards (1950). The following interpretation is based on the more 

 recent work of Oaks and DuBar (1974) . 



Geology of the upland portion of the Sand Banks area, 

 forming the escarpment bordering Chowan Swamp s is described in the 

 discussion of the Chowan Sand Ridge natural area later in this 

 report. Most of the adjacent topographic features of the natural 

 area were formed during the Sangamon, Similarly, the floor of the 

 basin which contains Chowan Swamp probably corresponds to a late 

 Sangamon floodplain of the Chowan River. This was the period in 

 which the river carved the two large meander bends which can be 

 seen south of Eure and Gatesville. The mesic islands in Chowan 

 Swamp are probably f luvial/estuarine sands deposited earlier in 

 the Sangamon and reworked during late Sangamon high stands of the 

 sea. 



The history of the peat deposits supporting swamp vegetation 

 along the Chowan River has not been investigated. Peat formation 

 in the Dismal Swamp began about 8,900 years ago, some time after 

 the end of the Wisconsin (Oaks and Whitehead 1979). The Chowan 

 Swamp peats may be much more recent. 



During the Wisconsin, the Chowan and its local tributaries 

 carved channels to an unknown depth below the present surface, as 

 indicated by holes in their channels 10 to 20 feet or more below 

 present sea level. Not until 5,000 years ago did post-Wisconsin 

 sea levels reach -20 feet MSL in this area (Oaks and DuBar 1974) , 

 perhaps initiating peat formation and sedimentation in the lower 

 levels of the river valley. 



Peats investigated in the present study range from very 

 shallow, where they feather out onto the fluvial sand ridges 

 composing the mesic islands and upland borders, to at least 10 

 feet below sea level at the mouth of Bennett's Creek. The total 

 extent and greatest depth in the area are unknown. As sea level 

 continued to rise, peat deposits apparently kept pace, spreading 

 over the inundated floodplain. Not until about 3,200 years ago, 

 did sea level reach -13 feet, enough to initiate peat formation 

 at the lowest levels. Therefore, it is presumed that most of the 

 modern peat deposit underlying Chowan Swamp is no more than about 

 3,000 years old. 



Sea level rise continued until about 1185 years ago, at 

 which time it was 4 feet above the present level. This was 

 followed by recession of relative sea level to about -6 feet 725 

 years ago. Sea level has risen since that time to its present 

 elevation. 



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