sequence is capped by an erosional unconformity down to at least 

 65 m below present sea level (Belknap, 1987; Belknap et al., 

 1987a, b), and overlain by Holocene littoral, deltaic, and marine 

 basin deposits in various locations. 



The events which produced this sedimentary sequence began 

 with glaciation of the Gulf of Maine, prior to 20,000 years 

 before present (yrs. B.P.), when the Late Wisconsinan Laurentide 

 ice sheet extended to Georges Bank (Schlee and Pratt, 1970). 

 Deglaciation was underway by 18,000 yrs B.P. (Hughes et al, 1985; 

 Denton and Hughes, 1981). Schnitker (1975, 1986) suggested that 

 the early stages of deglaciation occurred with an ice shelf in 

 the Gulf of Maine. This ice shelf or a tidewater ice margin was 

 grounded just offshore of the present coast by 14,000 yrs. B.P. 

 (Smith, 1985; Stuiver and Borns, 1975), at which time it became a 

 tidewater calving embayment (Belknap et al., in press). 

 Deglaciation through tidewater calving continued until 13,000 to 

 12,500 yrs. B.P., while the sea onlapped present coastal Maine up 

 to the marine limit 60-132 m above present sea level (Thompson 

 and Borns, 1985). Sea level then fell rapidly (Figure 2; Belknap 

 et al., 1986, 1987b; Schnitker, 1974) to 55-65 m below present as 

 glacioisostatic rebound dominated. The rebound was greater to 

 the northwest, tilting the highstand shorelines. A low 

 stillstand occurred around 9500 + 1000 yrs. B.P., as isostatic 

 rebound and eustatic rise became equal, producing shorelines 

 ( Shipp et al., in press). Over the past 8000-9000 years the 

 inner shelf has experienced a transgression, with relative sea 

 level rising at a decreasing rate. Thus, the study area has 

 undergone deglaciation, deepwater marine onlap, regression with 

 its accompanying littoral and fluvial erosion, and finally the 

 ongoing marine transgression with littoral and inner shelf 

 processes of sediment redistribution. 



Maine is in a cool temperate locale, with continental and 

 oceanic regimes competing to produce a variable climate. Long- 

 term wind and wave data for the central Gulf of Maine are 

 summarized in Figure 3, from Summary of Synoptic Meteorological 

 Observation (SSMO) statistics (USNWSC, 1975). Prevailing winds 

 during summer are from the southwest, prevailing winter winds are 

 northwest, and dominant storm winds are easterly or 

 northeasterly ( Fef er and Schettig, 1980). Waves with the longest 

 period and greatest height are generated by winter storms, and 

 thus come from the east and northeast, while the greatest 

 exposure to fetch is from the southeast. Storm waves of 8-10 sec 

 period and 3-4 m height are common during extratropical cyclones 

 ("northeasters"), comprising 3.4% of the February waves in the 

 central Gulf of Maine (USNWSC, 1975). Hurricanes, however, are 

 rare (<5% annual probability: Fefer, and Schettig, 1980). Pearce 

 and Panchang (1983, Figure 24) calculate the 50-year significant 

 wave height to be 9.3-9.8 m off central coastal Maine, while the 

 annual significant wave height is 3 m. Mean annual deepwater 

 wave height is 1.13 m (Figure 3), while the August value is 0.68 

 m and the February value is 1.53 m. Tides are meso- to 

 macrotidal, increasing in spring range from 3.1 m in Portsmouth 



146 



