SEDIMENT DYNAMICS OF THE NEARSHORE GULF OF MAINE: 

 SUBMERSIBLE EXPERIMENTATION AND REMOTE SENSING 



Daniel F. Belknap 1 ' 2 

 Joseph T. Kelley 1 ' 2 ' 3 



and 

 Donald H. W. Robbins 1 



Department of Geological Sciences 1 

 and Center for Marine Studies 2 

 University of Maine 

 Orono, ME 04479 



Maine Geological Survey 3 



State House Station 22 



Augusta, ME 043 33 



ABSTRACT 



Observations during submersible dives covering more than 

 thirty linear kilometers of sea-floor have been integrated with 

 seismic reflection profiling, side-scan sonar survey, and grab 

 samples to produce a preliminary model of sedimentary processes 

 on the Maine inner continental shelf. Sediments occur in a 

 complex mosaic which is a composite of sedimentary materials 

 inherited from glacial-deglacial , shoreline, and fluvial 

 environments, and overprinted by modern marine systems (thus, a 

 palimpsest) . A primary control on environments is the position 

 of bedrock ledges and islands. Second are the glacial- 

 glaciomarine sources of sediments. Third is the importance of 

 sea-level lowstand shorelines and the Kennebec Paleodelta, a 

 point source of sand and gravel on the west-central Maine coast. 

 Finally, modern wave and tidal processes, biological activity, 

 and human impact redistribute and rework these sediments. Three 

 main environmental settings are recognized: 1) Rock ledges are 

 swept clear of sediments, but accumulate talus aprons and halos 

 of carbonate-rich coarse-grained gravel around their bases. 2) 

 Nearshore ramp/paleodelta sandy environments are also above storm 

 wave base, and are swept clear of mud (annually?). Their 

 surfaces are reworked into sand waves, sand ribbons, and rippled 

 scour depressions. 3) Basins are filled with thick Quaternary 

 mud, and presently are slowly accumulating fine-grained organic- 

 rich mud, which is bioturbated extensively. These basins are the 

 locus of natural gas deposits, which occasionaly vent to the 

 surface, initiating gas pockmarks that are modified by organisms 

 and currents. Identification of meter to ten-meter scale 

 variability in sedimentary environments implies that great care 

 is required for remote sediment sampling. Similar variability 

 might be expected in benthic biological studies of the area. 



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