that such material is being deposited today in any part of the study 

 area. 



c. Sand . The widespread sand blanket occurring off the northern 

 part of the study area was considered Holocene by Willett, et al. (1972). 

 One core obtained for the ICONS study (core 152) contained lignite and 

 plant fragments 14 feet downhole under a typical fine sand sequence similar 

 to the fine sand in the northern part. This material yielded a radio- 

 carbon age of 12,000 years (±250 years) B.P. which places deposition of 

 the overlying sand in the Holocene. Foraminifera in the 14-foot section 

 of sand above the dated layer indicate that this layer was deposited in 

 an open marine nearshore setting similar to its present locale. 



Information obtained in this study supports the supposition of Willett, 

 et al. (1972), Oldale, Uchupi, and Prada (1973), and Setlow (1973) that in 

 most places, there are at least two distinct sediment subunits of the trans- 

 parent layer, and that these subunits have recognizable acoustic signatures. 

 Both acoustic facies are sometimes greenish-gray mud, but also, notably 

 off Nantasket Beach, the upper facies with strong internal reflectors 

 may consist of sand. It is not known whether this sand is time-correlative 

 with the upper unit of greenish-gray mud or if the sand was deposited at 

 a later time, possibly after a period of erosion. The latter possibility 

 is most likely since lithology and fauna of the sand suggest an energetic 

 open-marine environment unlike the probably depositional environment of 

 the silt and clay. 



Sand or sand and gravel appear to be common where low mounds overlay 

 the transparent reflector. These mounds with their smooth-rounded contours 

 are distinct from the raised bottom created by outcrops of the basement 

 reflector which is characterized by irregular and angular surface topo- 

 graphy. Little information is available on the mounds, but some may be 

 relict shoreline or nearshore deposits- dating from the late transgressive- 

 regressive sequence of Kaye and Barghoom (1964) . If so, topographic 

 highs in the transparent reflector are promising features for further 

 exploration for suitable beach sand. The extensive sand and gravel 

 deposits of the prime project NOMES area appear to be an example of the 

 relationship between morphology and sediment types. 



3. Modem Sedimentation . 



Since relative sea level approached its present stand about 3,000 

 years ago, sedimentation has been most active along the present coastline. 

 Sediments eroding from headlands are being distributed to beaches, spits, 

 and the adjacent sublittoral shoreface zone. 



There appears to have been little modem sediment accretion during 

 this time. The widespread skin of gravel and boulders covering much of 

 the area is a relict deposit of the Holocene transgression-regression 

 sequence that remains unburied in most places (Willett, et al . , 1972). 

 In addition, the greenish-gray clay is considered a Pleistocene or relict 



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