RESULTS 



Seismic reflection profiling, side-scan sonar seafloor 

 mapping, sediment grab samples, and submersible crossings form 

 the basis for interpretation of modern sedimentary patterns and 

 processes on the Maine inner shelf. An area of concentration so 

 far has been the Kennebec paleodelta (Belknap, 1985) in western 

 Sheepscot Bay and the surrounding environments (Figure 7) (Belknap 

 et al., 1986; in press 1988). Much of the paleodelta surface is 

 composed of gravelly muddy sand, rich in carbonate shell hash. 

 Seasonal variations of the surface aspect of the Kennebec 

 paleodelta are expected. These may include mud drapes produced 

 after spring runoff and seasonally shiftirg bedforms. Figure 8 

 shows textural analyses of five of the grab samples. There is 

 evidence of progressive winnowing of finer materials, producing a 

 coarser lag near the Kennebec River mouth and finer sands on the 

 distal lobe surfaces. On the whole, however, the primary mode of 

 fine, well-sorted sand is similar to the finer range of beachface 

 sands from adjacent Popham Beach (L.K. Fink, unpublished data) . 

 Detailed analysis of the remainder of the sediment samples is in 

 progress. 



As seen in sidescan records, the sediments on the sandy 

 ramps occur in three major types of appearance: 1) smooth, low 

 reflectivity; 2) rippled surfaces; and 3) large-scale variations 

 in light and dark return, either as streaks or lenticular bodies 

 (Figure 9) . Submersible dives over these features confirm that 

 sidescan return 1 is unrippled muddy sand. Return 2 is clean 

 gravelly sand in large-scale oscillation megaripples. They have 

 straight to sinuous crests and common tuning-fork junctions, 

 short crestlines (continuity 2-10 m) , amplitudes of 20-40 cm, and 

 wavelengths of 0.5 to 2 m. Their crests are symmetrical and 

 sharp or rounded (Figure 10) . Return 3 is difficult to 

 distinguish in the submersible, where direct visibility is 

 usually 5 m or less (video and photos are even more limited) . It 

 is interpreted as being composed of sand waves and/or current 

 furrows and streaks. 



The megarippled sands (return 2) occur in distinct low- 

 relief depressions and near bedrock outcrops (Figure 11) . They 

 occur only on the paleodelta and on other nearshore ramps in 

 Maine, above storm wave base. We interpret these as rippled 

 scour depressions, as described by Cacchione et al. (1984) from 

 central California. Features of this type have been identified 

 in shelf environments as diverse as the northern Bering Sea 

 (Hunter et al . , 1982), western Mexico (Reimnitz et al., 1976), 

 Onslow Bay, North Carolina (Mclntyre and Pilkey, 1969) , the Mid- 

 Atlantic Bight (Swift and Freeland, 1978) , off Long Island 

 (Shipp, 1984), and the Rhode Island shelf (Morang and McMaster, 

 1980) . They are produced by combined oscillatory and 

 unidirectional flow in storm waves and downwelling currents. 

 Black and Healy (1988), however, find similar features in less 

 than 8 m water depth controlled solely by convergence of 

 refracted waves. We suggest bedrock steering and constriction of 



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