DISCUSSION AND CONCLUSIONS 



The comparison of remote and direct observations has created 

 a synthesis of sedimentary environments for the Maine inner 

 shelf. Figure 16 summarizes some of the major characteristics 

 which we have found using all of these techniques. The rock 

 margin example figured here is based primarily on dives at 

 Halfway Rock, in Casco Bay. Along rock margins sediments are 

 swept clear by waves and tides. Anemones, sponges and other 

 organisms cling to the rocks. Rocks are dislodged from the 

 outcrop and carried through joint chutes or directly down the 

 face to a talus pile. The talus is probably partially a relict 

 on deeper outcrops, when the greater energy available from waves 

 at lowered sea levels was available to dislodge rock fragments. 

 We have not observed well-rounded beach pebbles, however. The 

 talus pile of rock fragments adjoins a coarse apron composed of 

 gravel and shells, primarily mussels ( Modiolus modiolus ) , and 

 accumulates at the base of steep faces around islands and shallow 

 ledges. The carbonate fragments appear fresh, and probably 

 represent a continuing balance of supply of shells from 

 productive shallower regions versus corrosion in the cool 

 seawater. Locally, till crops out on the sea floor. It is 

 identifiable by large, well-rounded boulders at the surface. 



The paleodelta example (Figure 16) is based on the Kennebec 

 paleodelta in western Sheepscot Bay, observed at eight dive sites 

 of fourteen kilometers cumulative extent. Sand and gravel are 

 reworked periodically by storm waves and tides, sweeping away 

 muddy pelagic drape. The coarse sediment is a relict of lowstand 

 paleodelta deposits reworked from upstream glaciof luvial sources. 

 The surface is formed into sand waves, ripples, sand streaks, and 

 the large-scale rippled scour depressions. Thus, this surface is 

 a palimpsest, with a imprint of modern processes over the relict 

 deltaic and transgressive littoral paleoenvironments. During 

 transgression, some of the sand has been reworked into the modern 

 Reid Beach and Popham Beach barrier systems. There is little 

 evidence for extensive transport of sand off the edge of the 

 paleodelta into the deeper basins: the transition zone from sand 

 to mud is a few tens of meters in most cases. 



The basin example (Figure 16) is a composite based on dives 

 in Casco Bay, Sheepscot Bay, and New Meadows Bay. The basin 

 floor is soft mud with abundant bioturbation. There are frequent 

 drag marks from trawls. The dominant natural processes on the 

 basin floor are evidently bioturbation and quiet pelagic 

 settling. Any turbidity currents or slumping must be infrequent 

 or localized, since the abundant burrows and shells at the 

 surface suggest a slow accumulation rate. Natural gas has been 

 noted at depth in most of the nearshore basins, with pits 

 possibly produced by seepage in Penobscot Bay and New Meadows 

 Bay. The pits observed by submersible in New Meadows Bay, 

 referred to as pockmarks, are shallow and actively reworked by 

 lobsters, crabs, and most likely by fish. They are circular to 

 elliptical, with scalloped edges. The sediment within the pits 



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