V. DISCUSSION 



Most of the submarine canyons off the east 

 coast of the United States previously have been 

 regarded as relatively inactive so far as sedi- 

 mentary processes are concerned (Stetson, 

 1949; Shepard, 1965a, p. 327) because they 

 head far out on the shelf in deep water in tec- 

 tonically stable area. This contrasts sharply 

 with submarine canyons in other areas which 

 serve to funnel sediments from shelf areas to 

 the deep sea. Shepard (1965a, p. 322-323) lays 

 particular stress on supply of longshore- 

 drifted detritus to canyons heading close in- 

 shore on tectonically active borderlands, as in 

 the area off southern California. In those can- 

 yons, sediment is transferred from the head to 

 the deep-sea fans at their base by processes 

 which include slumping, creep, sand flows and 

 turbidity currents. The surface texture in the 

 vicinity of these Californian canyons appar- 

 ently reflects the present activity of the pro- 

 cesses outlined above although a thin cover of 

 'pelagic' mud occurs in areas more remote 

 from active channels (Shepard and Dill, 1966, 

 p. 68). A submarine canyon on the northwest 

 Atlantic margin. The Gully off Nova Scotia, 

 which has been described by Stanley (1967) 

 displays a spectrum of processes similar to 

 those observed in canyons on the Pacific mar- 

 gin. 



In the Wilmington canyon area, the sum of 

 photographic observations shows that textural 

 types are more closely related to geographic 

 proximity to the canyon depression and other 

 major features of the slope than to depth per 

 se. However, the distribution of relatively fine- 

 grained bottom surface sediments in the prox- 

 imity of the Wilmington canyon (an observa- 

 tion also made by Stetson, 1949) and the abun- 

 dance of burrowing activity in all but the most 

 shallow portions of the canyon suggest a rela- 

 tively inactive role for sedimentation at the 

 present time. Similarly, the pattern of current 

 movement in the vicinity of the canyon, where 

 examined, shows only minor evidence of axial 

 transport (unlike more active canyons de- 



scribed by Shepard, 1965b; Shepard and Dill, 

 1966; Ross, 1968 and others). 



Photographic evidence, however, must be in- 

 terpreted cautiously in evaluating the role of 

 the Wilmington Canyon in Holocene (post- 

 Pleistocene to modern) sedimentation. It is im- 

 portant to note, for instance, that textural va- 

 rieties at the surface often conceal very differ- 

 ent sediment types just a few millimeters or 

 centimeters below the surface. An examination 

 of cores collected in the same areas as photo 

 Stations 33, 34 and 46 (Fig. 3) indicates that 

 the surface veneer recorded in bottom photo- 

 graphs is generally finer-grained than the sedi- 

 ment lying below it (Stanley and Kelling, 

 1968b). The textural pattern as mapped in 

 Figure 7 is thus a composite reflecting both re- 

 cent depositional activity and, locally, relict 

 (pre-Recent) sediment patterns. These local 

 pockets of relict sediment may represent areas 

 which are not receiving sediments at the pre- 

 sent time or they may indicate removal of the 

 veneer of recent sediment by erosion. 



It is also important to note that the textural 

 map indicates only the most recent sediment 

 activity and masks the results of processes op- 

 erating in the recent past. Examination of the 

 bottom photographs suggests that, at present, 

 benthic organisms are reworking the sediment 

 cover over much of the slope and rise. Cores 

 show distinct laminations of somewhat coarser 

 sediment below a mottled uppermost sediment 

 veneer. This indicates that at most localities 

 periods of active deposition have alternated 

 with quieter periods (perhaps like the present) 

 when the entire sediment horizon is reworked 

 by bottom-living organisms. 



The hypothesis that sedimentation in the 

 Wilmington submarine canyon has been active 

 within the recent past, and perhaps even today 

 on a local scale, is supported by several obser- 

 vations : 



(1) The present study indicates that there 



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