22 



BIOLOGICAL REPORT 31 



The retreat of the two adjacent glacial lobes did 

 not occur in concert. The Buzzards Bay lobe and 

 the Cape Cod Bay lobe met approximately at the 

 location of the Cape Cod Canal. The Buzzards Bay 

 lobe began retreating before the Cape Cod Bay 

 lobe, uncovering a break in the moraine at the point 

 where they joined. With the later melting of the Cape 

 Cod Bay lobe, water was able to flow through the 

 break where the canal is now located, across the 

 outwash, and into Buzzards Bay. In later years, two 

 streams with headwaters less than one kilometer 

 apart inhabited the old glacier outlet, separated by 

 a sandy ridge: the Scusset River flowing northeast 

 into Cape Cod Bay and the Manamet (or Monu- 

 ment) River flowing southwest into Buzzards Bay. 

 No more than 9. 1 m above sea level, these valleys 

 became a natural area for later construction of the 

 Cape Cod Canal. 



2.2. A Marine Bay 



The rapid warming about 1 4,000 years B.R that 

 caused the retreat, thinning, breakup, and final dis- 

 appearance of the ice sheets did not end the ice- 

 driven morphological alterations of the New En- 

 gland surface. When the water trapped in that ice 

 returned to the oceans a relatively rapid rise in sea 

 level occurred. During the past 1 8,000 to 1 0,000 

 years ocean levels rose 60- 1 20 m with levels about 

 7,000 years B.R at 7-10 m below present (cf. 

 Emery and Aubrey 1991). In the region of Cape 

 Cod, this rise in sea level resulted in the flooding by 

 Atlantic Ocean waters of Cape Cod and Buzzards 

 bays and Nantucket, Vineyard, and Long Island 

 sounds. As relative sea levels rose, Martha's Vine- 

 yard and Nantucket became islands, and the lower 

 deposition between the terminal and Buzzards Bay 

 moraines became the sounds. The lower topogra- 

 phy of what became Buzzards Bay is probably a 

 result of a combination of events, starting with sub- 

 aerial erosion during a period of extremely low sea 

 level in the late Tertiary ( Veatch 1 906). insufficient 

 deposition (being at the margin of the Wareham pit- 

 ted plain), and erosion due to meltwaters from the 

 later retreat of the Cape Cod Bay lobe. Whatever 



the cause, rising sea level flooded current Buzzards 

 Bay about 5,000-6,000 years B.R 



The historic rate of relative sea-level rise (the 

 combination of eustatic or ocean surface rise and 

 changes in the land surface due to subsidence or 

 uplift) can be ascertained by radiocarbon dating of 

 reefs, deltaic deposits, intertidal peats, and so forth. 

 One such study using intertidal peats collected at 

 the peat/till contact was conducted in Barnstable 

 Marsh only 1 km from Buzzards Bay. Since the 

 peat was generated by salt marsh plants, which only 

 grow in intertidal wetlands, it acts as a tracer for 

 historic relative sea level. It appears from this method 

 (Fig. 2.3) that the early rapid (0.003 m/year) rise in 

 relative sea level continued until about 3.500 years 



12 10 8 3 6 4 2 



Time (10 years BP) 



Fig. 2.3. Age of peat at depths relative to the 4000-year 

 B.P datum Scale on right shows assumed eustatic rise 

 in sea level (Inset: Curve B is subsidence of coast of 

 eastern Massachusetts; Curve C is subsidence from Cape 

 Cod to Virginia Curves A, B, and C correspond to main 

 figure) From Redfield (1967). 



