F-7 



from the regional shelf edge. The overall gradient of the 

 thalweg is 2.8 , debouching onto the continental rise at a 

 depth of about 1.5 km. The floor of the canyon is rather 

 flat and about 400-500 m wide. Where explored by this pro- 

 ject, the floor is covered by ripple-marked, well-sorted 

 sand and silty clay. 



The shelf edge strata of the Baltimore Canyon trough 

 consist of sigmoidal-shaped foreset depositional units 

 (Schlee, 1978a). These units represent a period of substan- 

 tial shelf progradation since the early Miocene (approximate- 

 ly 25 m.y.B.P.). As sampled by coring and dredging during 

 the field program (Tables Fl and F4) , these units are fine 

 grained and loosely consolidated, primarily sand or mud rich 

 in mica and quartz, with accessory clay, siliceous microfossils 

 and abundant authigenic glauconite. They drape over older 

 materials of consistently finer texture (silty mud) . 



The upper canyon walls contain several oblong-shaped 

 terraces. Kelling and Stanley (1970) postulated that two sets 

 of benches at depth ranges of 100-110 m and 128-146 m were 

 wave-cut Pleistocene shorelines. Some of these benches are 

 up to 3 70 m wide, and show a consistent depth at their outer 

 margins when traced laterally. In our high-resolution reflec- 

 tion profiles, however, these terraces appear instead to be 

 the tops of back-tilted fault blocks that have slipped down- 

 wards towards the canyon axis. 



Subbottom profiling with the camera sled in Baltimore 

 Canyon provided new data to show that many of the side tri- 



