II. AREA OF STUDY 



Wilmington Canyon originates near the edge 

 of the continental shelf approximately 95 nau- 

 tical miles east-southeast of the mouth of Dela- 

 ware Bay. The canyon head may be traced 

 northeastward (landward) to a minimum depth 

 of 45 fathoms, at which point it is incised into 

 the shelf for a distance of about 10 miles (Fig. 

 1). From this point the canyon trends south- 

 southwest for nearly 7 miles to an axial depth 

 of 380 fms and then makes a sharp turn to a 

 general southeasterly course. This course is 

 maintained to an axial depth of about 1000 fms, 

 near the base of the continental slope, and is in- 

 terrupted only by an abrupt turn to the east for 

 almost 3 miles at 700 to 780 fms. The canyon 

 trends almost due east across the upper part of 

 the continental rise where it gradually dimin- 

 ishes in relief. Beyond the 1300 fms isobath 

 the canyon, which would better be described as 

 a submarine valley because of its low relief, ex- 

 tends toward the east-southeast to a depth of 

 about 1800 fms. The gradient of the canyon 

 axis become steeper and the relief increases in 

 the lower rise (1800-2500 fms). The canyon 

 trend is almost due south between 1800 and 

 2000 fms, then becomes generally southeast. 



The gradient of the canyon axis is main- 

 tained at between 1 in 20 and 1 in 25 through- 

 out most of the headward portion and on the 

 upper continental slope. However steeper gra- 

 dients are encountered locally, in the vicinity 

 of the acute changes in the trend of the canyon 

 axis described above. Beyond an axial depth of 

 800 fms the gradient decreases first to 1 in 50 

 then, at about 1350 fms, to about 1 in 90. 



Followed from its head towards the regional 

 shelf-break the canyon gradually increases in 

 dimensions, attaining both its maximum width 

 (6 miles) and its greatest relief (approxi- 

 mately 500 fms) at the regional shelf edge. In 

 this headward portion, the canyon is generally 

 steep-sided with lateral slopes of 10° to 20° 

 which frequently expose bedrock. The trans- 

 verse profile of the canyon tends to be acute 

 and V-shaped in the shallower part of the head 



but becomes less acute or even flat-based be- 

 yond about 400 fms. The walls of the canyon in 

 this headward region are extensively modified 

 by many depressions and secondary ridges, in- 

 cluding several cirque-like tributary canyons 

 as much as a mile wide (Fig. 1). 



Descending the continental slope the canyon 

 diminishes both in width and depth. Near the 

 1000 fms isobath the canyon is a sharply in- 

 cised feature 0.6 n. miles wide and with a relief 

 of some 45 fms. At an axial depth of 1350 fms 

 the width of the canyon has diminished to 0.3 

 n.miles and the V-shaped depression is barely 

 30 fms deep. At greater depths the Wilmington 

 submarine valley is an inconspicuous, rather 

 broadly terraced depression which includes one 

 or more narrow, gully-like features, usually 

 less than 0.2 n.m. across and 10 to 20 fms deep. 

 An important morphological high (here 

 termed the Xyckel Ridge, after Veatch and 

 Smith, 1939) runs parallel to Wilmington Can- 

 yon from the shelf, down the continental slope 

 and across the rise to the 1400 fms isobath. It 

 is described in detail elsewhere (Stanley and 

 Kelling, 1968a, 1968b). Other subsidiary can- 

 yons and ridges, most of them originating on 

 the middle or lower regions of the slope, occur 

 both to north and south of the main Wilming- 

 ton Canyon. 



In contrast to the numerous secondary de- 

 pressions which mark the course of this fea- 

 ture in its headward region and across the con- 

 tinental slope, only one tributary canyon can 

 be linked to the Wilmington submarine canyon 

 as it crosses the upper continental rise. This 

 tributary originates on the north side of the 

 Nyckel Ridge near the 1200 fms isobath and 

 eventually merges into the Wilmington sub- 

 marine valley system at about 1500 fms (Fig. 

 1). 



A further feature of morphological interest 

 in this area is the marked contrast in bottom 

 relief between the upper and lower portions of 

 the continental slope. Except in the immediate 

 vicinity of the major canyons, the shelf-break 



