activity (neocurrent patterns) and to infer the 

 dominant current trends in the area of study. 

 Most of this evidence is derived from an exam- 

 ination of current-formed sedimentary struc- 

 tures, principally ripple marks, and the atti- 

 tude of certain marine organisms, principally 

 worm tubes, on the compass-orientd photo- 

 graphs (Table II). The paterns of dominant 

 current movement in the Wilmington Canyon 

 and adjacent continental shelf, slope and rise 

 are depicted on Fig. 8. 



The form of ripple marks (straight, sinuous, 

 interference types) and the orientation of dom- 

 inant crests were recorded, and the direction of 

 steeper faces was measured wherever possible. 

 The vertical position of the camera and slight 

 oblique illumination employed, however, made 

 this determination impossible in some in- 

 stances. A two-directional trend is depicted in 

 those cases where symmetrical ripple-marks 

 are present or where the appearance of sym- 

 metry does not allow interpretation of the 

 sense of current transport. The mean value of 

 current direction or trend has been determined 

 for each station ; this value, in some cases, rep- 

 resents the orientation of current patterns 

 measured over as much as two miles of sea 

 floor. In several cases the large number of pho- 

 tos obtained over an extensive distance re- 

 quires that the data be grouped into two or 

 more sub-stations. Stations 7 and 8, for in- 

 stance, extending from the shelf margin into 

 the canyon head, display several mean vectors 

 (Fig. 8). Two transport direction are also de- 

 picted at those stations where interfering 

 groups of ripple marks differ in orientation by 

 more than 30° 



Ripple marks on the shelf and upper slope 

 tend, in general, to be asymmetrical, straight 

 to slightly sinuous and possess sharp to some- 

 what rounded crests. Two or more sets of 

 cross-cutting ripples are not infrequent at 

 shallow stations, but distinct cell-like interfer- 

 ence patterns have not been observed here. In- 

 terfering ripple-sets usually differ in dimen- 

 sions or form, and it is generally possible to 

 demonstrate that one set post-dates the others. 

 Ripples on deeper silty and mud bottoms tend 

 to be more sinuous and discontinuous with low 

 amplitudes and soft rounded crests. Many rip- 

 ples appear relatively fresh and are probably 

 of recent origin. A veneer of mud, however, 



covering crests and partially filling troughs, 

 may be detected at some deeper stations. 



Additional evidence of current transport is 

 obtained in a number of stations from the 

 alignment of shell debris or gravel, and of 

 worm tubes lying upon the bottom. Scour li- 

 neations and pockets are generally absent ex- 

 cept for Station 22 (Plate 10) in the canyon 

 axis and at Station 43 (Plate 28) at the base of 

 the slope. Similar scour lineation markings on 

 the continental slope have been reported by 

 Owen and Emery (1967, Fig. 15-4). 



Direct evidence of prevailing near-bottom 

 current activity is provided by the preferred 

 orientation of worm-tubes that appear stalk- 

 like and project obliquely from the sea-bed to a 

 maximum height of 10 cm. These structures, 

 presumably geotropic in character, locally dis- 

 play a random orientation. More frequently 

 these tubes show a preferential alignment, i.e., 

 a dominant sense of inclination, as if heeling 

 over in response to a current. It is assumed 

 that such an inclination is in a down-current 

 sense. This assumption is borne out at Station 

 29 where preferentially inclined worm tubes 

 and asymmetric ripples are associated (Plate 

 15). 



The regional current transport pattern as in- 

 ferred from photographs is evidently a com- 

 posite one. Landward of the shelf edge cur- 

 rents flow uniformly towards the west both on 

 the shelf proper and in the canyon head. In a 

 small area northwest of the canyon (Stations 3 

 and 5) currents appear to flow towards the 

 south and southwest. Observation of large sand 

 waves and dunes to depths exceeding 50 fms 

 suggest that sedimentation on this outer shelf 

 may be active, not relict, at present. 



Evidence of southerly current movement 

 down the canyon axis between 400 and 600 fms 

 is observed at Stations 22 and 30 (Plate 10). 

 Little evidence of current activity is noted on 

 the lower slope and adjacent parts of the upper 

 continental rise away from the canyon ; the 

 sea-floor in this area is one dominated by bio- 

 logical reworking of bottom sediments. A re- 

 newal of current activity on the outer sector of 

 the upper rise is noted at depths greater than 

 1400 fms; current flow at this depth tends to 

 be directed consistently towards the southwest 

 and south-southwest (Fig. 8). 



86 



