ATLANTIC COASTAL PLAIN AND ADJACENT OCEAN BASIN 



139 



not truly an arch as defined in Chapter 2. The Eocene and Miocene con- 

 tacts with the Cretaceous also reflect the broad nose. The unconformities 

 around the Cape Fear arch indicate the principal times of uplift and ero- 

 sion to have been at the close of the Cretaceous and again at the close of 

 the early Miocene. 



In the New Jersey region Dorf and Fox ( 1957 ) recognize eight trans- 

 gressive-regressive cycles of sedimentation in the history of the Coastal 

 Plain from Raritan ( Upper Cretaceous ) to Cohansey ( close of Miocene ) 

 time (Fig. 10.1). If these prove to be of local extent, then it would be 

 concluded that the continental margin pulsed up and down locally this 

 many times, but if the cycles are found to be widespread and recorded 

 in the Gulf Coastal Plain sediments, then eustatic changes in sea level 

 would be the more probable cause. The subject will be considered in 

 Chapter 41 on the Gulf Coastal Plain. 



known outcrops and well records; and two submarine traverses were run 

 across the continental shelf, one from Woods Hole southward, and one 

 from Cape Henry, Virginia, eastward (section 37 of index map. Fig. 7.1 

 The Cape Henry section is the most significant. Many reflection surfaces 

 were recorded in the sediments above the crystalline floor, and two par- 

 ticularly strong ones were measured by refraction beyond the present 

 shore line. See Fig. 10.5. The seismic data on the crystalline floor are in 

 fair agreement with the deep-well records and indicate that at a point 

 60 miles at sea off Cape Henry the basement would be 12,000 feet deep. 

 The significance of the other two surfaces is not altogether clear. Miller 

 ( 1937 ) suggests that the "unconsolidated" zone consists of Cenozoic and 

 Cretaceous, and the "semiconsolidated" zone consists of Jurassic and 

 Triassic. The surface separating the two is known as the M /one to the 

 geophysicists, and this has later been considered as a reflection horizon 



CONSTITUTION OF CONTINENTAL SHELF AND 

 ADJACENT ATLANTIC OCEAN CRUST 



Composition of Basement 



As a result of seismic refraction studies in the Atlantic Coastal Plain 

 between Virginia and New Jersey, Ewing et al. ( 1939 ) believe that the 

 ^ocks of the crystalline Piedmont, as known in the exposed belt, are also 

 ^present in the basement complex below the Cretaceous. They recognize 

 |the Petersburg granite and the Wissahickon schist into which the granite 

 ijis intrusive, under the unconsolidated sediments east of Petersburg, Vir- 

 ginia, and think they can trace the belts northward through Maryland, 

 ^Delaware, and New Jersey. It would appear, they say, that the Peters- 

 burg granite is a correlative of, or is continuous with, the late Devonian 

 granites of Connecticut and Rhode Island. 



Deposits of Continental Shelf 



■ 



The continental shelf off the Atlantic Coastal Plain has been investi- 

 gated geophysically in the past 12 years, and some interesting results 

 have been obtained (Ewing et al., 1937, 1940). Several seismic traverses 

 were run across the Coastal Plain in order to check the seismic data with 



WOODS HOLE SECTION 



CONTINENTAL SHELF 



sea level 



c « 



STATUTE 



^cojsolk) 



Sf *'C>NS0 L 



- ■"^PL OATEI) 



t**F 



StlUT H 



PAF A L L 













CAPE 



HENRY SECTION 



V- CONTINENTAL 



■HELP 









*•.■ m ' 



o— c 











J 





•"•CONSOLIOHTio L_____-o— — -° A 





MM' 







C R 



VST 



* "•'■<»,. 



-^ 



^"co, 



s O(_l|>ATED 



V 

 \ 





«:■:.* 

















s 



r *-* 





















•oeo' 





















> 











. .. 









■ 300' 







































INI 







STA 



U TE 



M 1 I 



E S 



EAST 



OF 



PET : RS B J RC 





V 



v 















; 



q 











• 



i 



>Q 





o 



r^^o 





• 







Fig. 10.5. Seismic traverses on the Atlantic Coastal Plain and continental shelf, after Ewing. 

 Crary, and Rutherford, 1937. Small circles represent elevations determined by the refraction 

 seismograph. The Cape Henry section is section 37 of the index map of Fig. 7.1. The Woods 

 Hole section runs southward from Woods Hole, Mass. The M Zone is probably a horizon 

 within the Upper Cretaceous. 



