INTRODUCTION 



The inner shelf of the Gulf of Maine is characterized by 

 heterogeneous bottom types, ranging from rocky outcrops to sandy 

 slopes and soft muddy bottoms. The distribution of these 

 environments is related to a combination of glacial and deglacial 

 processes, changes in relative sea level, and nearshore 

 sedimentary processes which have acted over the past 14,000 

 years. The purpose of this paper is to describe some aspects of 

 the distribution of these sediments and the sedimentary processes 

 that have formed them, as determined from a combined manned 

 submersible and remote sensing/sampling study. 



For the past six years our marine geology-sedimentology 

 group at the University of Maine has undertaken detailed 

 sedimentological investigations of the inner shelf using high- 

 resolution seismic reflection profiling, side-scan sonar 

 surveying, grab sampling, and limited coring. Since 1984, we 

 have used NURP submersibles to compare direct observations with 

 this remotely collected data. The study has evolved from an 

 observational approach to, in 1987, an experimental one in which 

 sediment traps and metric arrays were deployed for the analysis 

 of bedform movement and suspended sediment fluxes. The seismic 

 and sediment sampling have allowed detailed determination of late 

 Quaternary stratigraphy, relative sea-level changes, 

 paleogeography, and sediment distribution. The addition of 

 direct observations and experiments from submersibles has allowed 

 us to make preliminary inferences concerning sedimentary 

 processes involved in sediment movement and long- and short-term 

 rates of redistribution. The model developed suggests that the 

 inner shelf of the Gulf of Maine is a complex, mixed process 

 zone. The sediments are a palimpsest (see: e.g., Swift et al., 

 1972), showing evidence of former processes such as glaciation, 

 which brought the sediments to the area, but also manifesting 

 more recent reworking. This reworking was caused by fluvial and 

 littoral processes during sea-level changes, by waves, tides, and 

 mass-movement in the inner shelf environment, and by biological 

 activities of bioturbation, formation of mats, and in situ 

 production of carbonate. 



Geologic Setting 



The inner shelf of the northern Gulf of Maine (Figure 1) is 

 underlain by Pre-Cambrian to Paleozoic metamorphic rocks and 

 Paleozoic to Mesozoic igneous intrusive rocks ( Osberg et al., 

 1985). The bedrock is overlain by Quaternary sediments, which 

 have been described primarily by seismic stratigraphy (Belknap, 

 1987; Belknap et al., 1987a, b; Birch, 1984; Kelley et al., 1986, 

 1987a, b; Knebel, 1986; Knebel and Scanlon, 1985). The bedrock is 

 directly overlain by thin till, with occasional moraines. These 

 are covered by glaciomarine sediments, which are offshore 

 equivalents of the Presumpscot Formation (Bloom, 1960, 1963). 

 The glaciomarine sediments are muddy, with thin sand lenses and 

 interfingering stratified subaqueous outwash. The glaciomarine 



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